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X-123_CdTe_User_Manual

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1. AC F awer Adapter Detector H W Cooler Power Preamp Power Figure 1 2 Block diagram of the X 123 Amptek Inc Page 3 of 42 y 2 SPECIFICATIONS X 123 User Manual Rev AO Spectroscopic Performance Energy Resolution 122 keV Co Energy Range Maximum Count Rate Peaking Time usec Shaping Time usec Detector and Preamplifier Detector Type Detector Active Area Detector Thickness Be Window Thickness Thermoelectric Cooler Preamplifier Type Preamp Conversion Gain Pulse Processor Coarse Gain Fine Gain Full Scale Gain Stability Pulse Shape ADC Clock Rate Peaking Time Flat Top Baseline Restoration Fast Channel Pulse Pair Resolving Time Dead Time Per Pulse Maximum Count Rate Amptek Inc Recommended max input rate sec 9 mm2 lt 1 2 keV FWHM typical 29 mm2 lt 1 5 keV FWHM typical Efficiency gt 25 for X rays from 1 to 25 keV May be used outside this range with lower efficiency Depends on peaking time Recommended maxima are shown below 2 stage 85 AT max Combination of coarse and fine gain yields overall gain continuously adjustable from 0 84 to 127 5 Software selectable from 1 12 to 102 in 16 log steps Software selectable 0 75 to 1 25 10 bit resolution 1000 mV input pulse X1 gain lt 20 ppm C typical Trapezoidal A semi Gaussian amplifier with shaping time t has a peaking time of 2 2t and is comparable in performa
2. Check Device Communications Get Status _ READY gt 3 Upload Files Select Upload Type FPGA l uC Status Device Type DPS Seral Humber 5105 Firmware 5 2 FPGA 5 2 DPS Status Read Complete Select upload type FPGA qi DPS Upload Utility Seles Status Start 112572008 4 56 22 PM Finish 1122522008 4 57 08 PM DPS FPGA Upload Complete TTT TTT Click the Upload FPGA uC HEX File and select the FPGA programming file _dp5 fpga_v502 mcs for example All FPGA programming files have an mcs extension It will take around 40 seconds to program at 115kbaud Amptek Inc Page 25 of 42 13 Select upload type uC 14 around 4 seconds to program at 115kbaud 15 program 16 Amptek Inc Click Exit Run DP5Loader EXE again X 123 User Manual Rev AO The program says Reboot and check device Power cycle the DP5 Click Check Device Communications Get Status It should now show the version number of the FPGA you uploaded 5 3 for the example below and the old Firmware version qi DPS Upload Utility Seley 1 Select Communications Port Available Forts Double Click Selects Port COM COM Port Number Coba EE 2 Check Device Communications Check Device Communications Get Status READY 3 Upload Files Select Upload Type l FPGA l uC Status DPS Statue Read Complete 00 DP5 Upload Utility Sele 1 Select Communications Port Available Forts
3. Search for the best driver in these locations Then check the box Include this location in the search Select Browse and navigate to the USB driver Win2K_XP folder of the Amptek Installation CD Click Next gt 6 Once the driver has been installed you will see the Completing the Found New Hardware Wizard screen below Click Finish Amptek Inc Page 9 of 42 Found New Hardware Wizard Please choose your search and installation options SS gt gt e Search for the best driver in these locations Use the check boxes below to limit or expand the default search which includes local paths and removable media The best driver found will be installed C Search removable media floppy CD ROM Include this location in the search D USB_driver Wwin2k_XP y O Don t search will choose the driver to install Choose this option to select the device driver from a list Windows does not guarantee that the driver you choose will be the best match for your hardware Found New Hardware Wizard X 123 User Manual Rev AO Completing the Found New Hardware Wizard The wizard has finished installing the software for Amptek DP4 Click Finish to close the wizard 7 Now that the USB driver is installed browse to the Amptek Installation CD and copy the ADMCA directory to the local computer s Ci drive For example if the computer s CD drive is the letter D copy D
4. jack The X 123 does not draw power from the USB RS 232 Standard 2 5 mm stereo audio jack Contact signal TXD from DPS RXD to DPS GND Amptek Inc Page 22 of 42 X 123 User Manual Rev AO 7 SOFTWARE INTERFACE 7 1 INTERFACE SOFTWARE ADMCA Software The X 123 can be controlled by the Amptek ADMCA display and acquisition software This software completely controls and configures the X 123 and downloads and displays the data It and supports regions of interest ROI calibrations peak searching and so on The ADMCA software includes a seamless interface to the XRF FP quantitative X ray analysis software package Runs under Windows 98SE or later on PC compatible computers Windows XP PRO SP2 or later recommended DPP API The X 123 comes with an Application Programming Interface API in the form of a DLL library The user can use this library to easily write custom code to control the X 123 for custom applications or to interface it to a larger system Examples are provided in VB VC etc on how to use the API VB Demonstration Software The VB demonstration software runs on a personal computer and permits the user to set the X 123 parameters to start and stop data acquisition and to save data files It is provided with source code and can be modified by the user This software is intended as an example of how to manually control the X 123 through either the USB or RS 232 interface using the most basic calls with
5. Page 10 of 42 X 123 User Manual Rev AO setup button on the toolbar The dialog box shown in Figure 3 will appear The configurations can be selected through the dropdown menu labeled Read Amptek Detector Configuration 6 Once the correct configuration is selected from the dropdown menu the indented grey area above the dropdown menu should read for example Loaded CdTe 9mm2 2 Stage Cooler configuration Click Show Current Configuration to view the settings A box will appear with the settings Click OK to exit the box 7 To apply the selected configuration click the Apply button Then select the OK button to exit this dialog box 8 Now that the X 123 has loaded the appropriate configuration for that detector an acquisition can be started Place a source in front of the detector To start an acquisition press the space bar The space bar will also stop an acquisition It may take the detector a few minutes to stabilize so if the acquisition does not look correct wait a few minutes and then press the A key on the keyboard to clear the acquisition and begin a new one It can take up to 2 minutes for an Amptek detector to stabilize after a configuration has been sent Figure 4 Acquisition spectrum for an WFe source e Once the detector has stabilized adjust some of the thresholds which prevent low end noise and other unwanted counts from affecting the spectrum This can be done automatica
6. more complete information For help using the software please see the Help file in the ADMCA software e VISTA Windows 7 COMPATIBILITY All the software is compatible with the 32 bit version of Windows Vista 7 The ADMCA software will run on 64 bit versions but the USB driver that controls the device is NOT 64 bit compatible This means that control of the device is not possible but the user can use the ADMCA software to open files and perform analysis e All X 123 s now contain the DP5 digital pulse processor If you are an OEM who has used previous versions of the X 123 with the DP4 processor and has written custom software using the DPP API you will have to recompile your software with the new API and make a few minor changes to your code Please see the DP5 and DPP API documentation for instructions MAKING CONNECTIONS 1 Plug the USB cable into the X 123 mini USB connector on the back panel and the PC 2 Plug the DC power supply into a 110 220 AC outlet Connect the other end to the X 123 power supply input which is labeled BVDC and is located on the back panel The X 123 powers up whenever it is plugged in NOTE Grounding is critical to obtaining the best performance Amptek strongly recommends using a single point ground for the system To ensure this use a 3 prong to 2 prong adapter on the power supply of any notebook computer This prevents the notebook from introducing a second ground into the system Amptek Inc Page 8 o
7. 5 2 Turn on transients in the X 123 Amptek Inc Page 19 of 42 X 123 User Manual Rev A0 6 MECHANICAL INTERFACE 6 1 DIMENSIONS 0 34 8 64 1 50 OPTIONAL 38 10 0 55 EXTENDER STANDARD 13 97 EXTENDER 0 70 17 78 Optional Mo Extender Detector Height 0 34 0 64 3 15 80 00 Dimensions Inches Millimeters amp u s z J a Ree 3 7 gt 0 27 0 26 6 86 6 60 TYP 2 PLS TYP 4 PLS 2 15 54 61 Figure 6 1 Top view of the X 123 Amptek Inc Page 20 of 42 0 41 0 28 7 00 Be WINDOW Figure 6 2 Front view of the X 123 6 2 MOUNTING HARDWARE 0 50 12 70 25 40 X 123 User Manual Rev AO 2 67 WI a AUX 100 O Wes RS 232 USB lO Back View Figure 6 3 Rear view of the X 123 Figure 6 4 Left Drawing showing how the mounting hardware attaches to the X 123 Right Photograph of different extender options available with the X 123 The unit at the top has a vacuum flange 6 3 CONNECTORS Power Power Jack on X 123 Hirose MQ172 Mating Plug MQ172 3SA CV Amptek Inc 3PA 55 Page 21 of 42 X 123 User Manual Rev AO Do Not Connect Auxiliary 2x8 16 pin 2 mm spacing Samtec part number ASP 135096 01 Mates with cable assembly Samtec P N TCMD 08 S XX XX 01 Top row odd pins bottom row even pins Pin 1 Pin2 Ethernet Standard Ethernet connector RJ 45 available summer 09 USB Standard USB mini B
8. 7 and consists of a series of pulses with a fast rise 3 2 usec decay a baseline of a few hundred millivolts and maximum values of around 1V The prefilter can accommodate pulses of either polarity inverting the signals digitally In the X 123 the analog prefilter of the DP5 is configured for use with Amptek s XR100 detectors at the factory Amptek Inc Page 33 of 42 X 123 User Manual Rev AO System Gain The system conversion gain is expressed in units of channels keV it gives the MCA channel number in which a particular energy peak will occur It is the product of three terms 1 the conversion gain of the charge sensitive preamplifier in units of mV keV 2 the total gain of the voltage amplifier the product of coarse gain and fine gain and 3 the conversion gain of the MCA channels per mV For Amptek s detectors the preamp conversion gain is typically 1 mV keV The MCA s conversion gain is given by the number of channels selected for example 1024 divided by the voltage corresponding to the peak channel In Amptek s digital processors this is approximately 950 mV The DP5 gain is the product of the coarse and fine gains For example if the fine gain is 1 00 and the coarse gain is 66 3 then the system conversion gain is 1 mV keV 66 3 1 00 1025 ch 950 mV 71 5 channels keV The inverse of this is the MCA calibration factor 14 eV channel The full scale energy is 1024 channels 71 5 channels per keV or 14 3 keV Note t
9. ADMCA to C ADMCA The software will not run from CD it must be copied to the local drive 8 Browse to the C ADMCA directory and open the Admca exe file to launch the software Right click on the Admca exe file and select Create Shortcut This shortcut can then be dragged to the desktop 4 5 CONFIGURING THE UNIT 1 Connect the X 123 and PC as described in the previous section 2 Launch the ADMCA software by opening the ADMCA exe file 3 When the Starting ADMCA box appears as in figure 2 select DP5 X123 SDD and click on Connect NOTE All X 123 units now use the DP5 as the processor Older X 123 units used the DP4 as the processor Those units must select the DP4 X123 GammaRad option in the dropdown The X 123 unit should now be connected to the software To verify this confirm that the correct serial number for the X 123 is shown in the top right corner of the software The serial number can be found on the side of the X 123 The USB symbol located at the bottom right corner of the software should be green 4 When shipped from the Now that the X 123 is connected the proper configuration must be selected for the detector The ADMCA software includes configurations for most Amptek detectors These configurations are identified by the detector material dimensions and cooler type e NOTE The X 123 remembers the last configuration so when powering the system for the first time and clicking
10. Connect the factory configuration is loaded This is the same configuration that is displayed on test sheet shipped with the detector 5 To select a configuration select DPP Setup under the DPP menu in the software or by clicking the acquisition Amptek Inc Starting ADMCA Z Device Type DPSFRT2FS00 MEABDODA IDP4 4123 GammaRAD Poza DPS 24123 5DD Don t show this dialog in the future Figure 2 Starting ADMCA DPP Properties General MCA Shaping Gain amp Pole Zero Power Misc Port USB Refresh ms 1000 Loaded Si 6mm2 500um 2 Stage Cooler configuration Press Show Current Configuration to view Select New Configuration Settings DPS Boot Fl A Read Amptek Detector Configuration a ene a ei Powerup configuration Boot unconfigured vi i Boot configured normal of Recall Previous Software Configuration we PETO haga ole TE O 57 600 baud Read Current Hardware Configuration 115 200 baud normal oper FPGR Open Predefined Configuration File ape Ale 2 Configuration Options O 80MHz E i Requested H Polarity Save Current Configuration To File O Negative O Positive gt O Normal Ta Spectrum offset Startup Configuration None normal operation Use Configuration Stored In Hardware rr O Use Offset o Use Configuration Stored In Software l e Paak detect gt Figure 3 Properties dialog box
11. MCS time base is commanded to a certain value e g 0 5 sec The system records all the counts in SCA8 during the first 0 5 second writes this total into channel 1 records the counts in SCA8 during the second 0 5 second writes this total into channel 2 and so on The histogram memory can be used in either MCS or MCA mode it cannot record in both modes simultaneously 8 3 6 Electrical 8 Software Interfaces There are three main elements to the electrical interface communications power and auxiliary The communications interfaces are the primary means to control the DP5 inside of the X 123 and to acquire the data The DP5 supports USB RS232 and Ethernet interfaces With all three interfaces commands are issued to set the many configuration parameters The unit sends three classes of data packets back to the computer status packets which include the counter outputs spectral data packets which contain the MCA output array and oscilloscope packets The DP5 s software interface is very similar to that of the DP4 and PX4 and supports legacy software written for the older products with minor modification The DP5 s configuration parameters are a superset of those found in the PX4 which is a superset of those found in the DP4 To provide backward compatibility with legacy software the DP5 handles these three classes of parameters quite differently The DP4 and PX4 use the same configuration data packets the DP4 simply ignores the addition
12. except for the HV bias which switches at 50 kHz 9 APPLICATION NOTES 9 1 Do s AND DON TS DO READ THE WARNINGS AND CAUTIONS IN SECTION _ 3 THE X 123 INCLUDES MECHANICALLY DELICATE COMPONENTS AND HIGH VOLTAGES Failure to follow the instructions in Section 3 may cause personal injury or cause damage not covered by warranty o Keeping the heat sink cool is critical to obtaining the best performance O Avoid holding the X 123 in the hand Heat from the body will increase the operating temperature of the detector degrading energy resolution Keep it away from heat sources Mount the X 123 to a metal plate This will increase the surface area and allow the detector to run 4 to 6 degrees colder A colder detector will result in better energy resolution The gain and noise of the system depend on the temperature of the detector For the best stability find the maximum ambient temperature at which the system will operate go to full cooling and observe the temperature reached Then set the temperature 5 C higher o Grounding is critical to the best performance O Amptek strongly recommends using a single point ground for the system Ground currents flowing through multiple connections through a lab bench etc often induce noise We have observed several laptops in which the charger introduced ground noise In these cases better performance was found by 1 using a 3 prong to 2 prong adapter on the power supply of any notebook comp
13. gamma rays and neutrons This pulse shape discrimination can be implemented using the DP5 s RTD function Most Amptek detectors do not require or benefit from RTD but for some it is quite useful Risetime discrimination rejects from the spectrum events with a long detector current which leads to a slowly rising edge in the fast and slow shaped pulses The DP5 implements RTD by comparing the peak height in the fast channel which samples the charge integrated in the first 100 nsec to the peak height in the slow channel which samples the charge which is eventually integrated If this ratio is sufficiently high the risetime was fast and thus the pulse is accepted If this ratio is low the pulse is rejected Because the fast channel is inherently much noisier than the slower shaped channel an RID threshold is also implemented on the shaped channel Events which fall below this threshold the RTD Slow Threshold are not processed by the RTD and are thus accepted unless otherwise rejected by Pileup Rejection or some other criterion Because RTD is most often needed on interactions deep in a detector arising from high energy events low amplitude events are unlikely to benefit from RTD rejection These fall below the RTD Slow Threshold and are thus accepted Gate The gate input is used with external circuitry to determine if events should be included or excluded from the spectrum The gate can be active high or active low or disabled If disa
14. high count rates then increase the UP slew rate or decrease the DOWN slew rate If one observes occasional bursts in the system which cause the spectrum to shift to higher channels often manifesting as bursts of noise above the threshold then decrease the UP slow rate or increase the DOWN slew rate 8 3 4 Pulse Selection Thresholds The DPP uses thresholds to identify pulses Both fast and slow channels have their own independent thresholds Noise is usually higher in the fast channel and it is best to set the thresholds just above the noise so they will be different in the two channels The DPP uses the Slow Channel Threshold to identify events that should be added to the stored spectrum Events with an amplitude lower than the Slow Channel Threshold are ignored they do not contribute to the stored spectrum The slow channel threshold is the equivalent of a low level discriminator LLD The Fast Channel Threshold also functions as an LLD and is used for several functions 1 The rate of events over the fast threshold is the DPP s measurement of the incoming count rate ICR 2 Pile Up Amptek Inc Page 36 of 42 X 123 User Manual Rev AO Rejection PUR logic identifies events which overlap in the slow channel but are separated in the fast channel 3 Rise Time Discrimination RTD uses the amplitude of the fast channel signal to measure the current at the beginning of a pulse PUR and RTD are discussed in more detail belo
15. rate If problems persist there may be a communication or configuration problem Unplug the X 123 power and close the software Then open the software and plug in the X 123 power adapter In the bottom left hand corner of the software you should see a 1 Detected for the USB connection Once you see this click on Connect Then go to the DPP Properties page and reload the appropriate default configuration as discussed above and try the acquisition again Amptek Inc Page 12 of 42 fa X 123 User Manual Rev AO 5 ELECTRICAL INTERFACES 5 1 ELECTRICAL SPECIFICATIONS 5 1 1 Absolute Maximum Ratings Operating Temperature 20 C to 50 C All parts in the X 123 are rated to the industrial temperature range 40 to 85 C Power Supply Voltage 6 0 VDC NOTICE Stresses above those listed under absolute maximum ratings may cause permanent damage to the device These are stress ratings only Performance at these levels is not implied Exposure to the conditions of the maximum ratings for an extended period may degrade device reliability 5 1 2 DC Characteristic Characteristic Symboi min Typ max Unite Conditions Power Supply EXA Vm 40 50 eee AT 70 C Supply Current Initial cool down ho cooling or bias CET dd EE lt 100 usec Input Capacitance Cw 0 A o Supply current data measured at room temperature mmm o Total supply current depends very strongly on the set point for the thermoelectric
16. the right hand info panel is displayed for the selected ROI 4 5 2 Calibrating the Horizontal Axis The horizontal x axis in the plot window defaults to channels To calibrate the scale to e g energy you must know the energy of at least two peaks in your spectrum First mark two regions of interest as described above Then click on the Calibrate button on the toolbar Click the cursor into the first ROI in the plot window it becomes highlighted and then click Centroid in the Calibrate box This takes the centroid of the peak and puts it as the channel value of the first point that will be used for the calibration Enter in the value of that centroid e g the energy of that peak into the Value box Now click Add The first point will appear in the list Repeat for the second peak you highlighted There should now be two lines in the list Enter in the appropriate units in the Units box e g Energy keV and then click OK The horizontal scale will now be displayed in the calibrated units To toggle between calibrated and non calibrated units press F7 on the keyboard Amptek Inc Page 11 of 42 X 123 User Manual Rev AO 4 6 TROUBLESHOOTING By default the software accumulates the counts MCA mode During set up it may be convenient to use DELTA mode where counts are not integrated but are updated every second i e only one second s worth of data are displayed every second Click the toolbar icon marked MCA DELTA
17. which detects a very large negative going pulse and logic to lock out signal processing for some time following the reset to give time for everything to return to stable values The DPP permits the user to enable or disable reset it should be disabled for preamps with continuous feedback The user can also select the time interval during which the signal is locked out If the interval chosen is too short then there will be some distortion of the waveform and thus spectrum following reset At high count rates the reset pulses occur frequently and if the interval chosen is too long then a significant dead time is observed Amptek Inc Page 37 of 42 X 123 User Manual Rev AO Risetime Discrimination In some types of applications it is important to separate pulses based on the duration of the transient current through the detector into the preamplifier For example in some Si diodes there is an undepleted region with a weak electric field A radiation interaction in this region will generate a signal current but the charge motion is slow through the undepleted region These interactions in this region can lead to various spectral distortions background counts shadow peaks asymmetric peaks etc In CdTe diodes the lifetime of the carriers is so short that slow pulses exhibit a charge deficit due to trapping These lower amplitude pulses distort the spectrum In scintillators pulse shape discrimination is sometime used to differentiate
18. with count rate The peak of the baseline of a digital processor has some significant differences from traditional analog shaping amplifiers Because the DPP s transfer function has a finite impulse response after a pulse has passed through the processing pipeline it has no impact on the output This is fundamentally different from an analog differentiator and results in vastly enhanced baseline stability at high count rates However unlike analog shapers the DPP has to establish a DC baseline at all count rates and in practice some shifts with count rate are observed The DPP has an asymmetric baseline restorer with several different settings The DPP BLR uses the negative peaks from random noise to determine the baseline The negative going noise peaks only occur in the absence of a signal so if these are stable then the baseline is stable independent of counts The BLR generally produces an offset comparable to the rms noise value There are two independent parameters UP and DOWN each of which can be set to four values Very Slow Slow Medium and Fast These are essentially slew rates in the baseline response A setting of Very Fast for both UP and DOWN means that the BLR will respond very rapidly to any measured variation in the baseline It must be stressed that the optimum setting depends strongly on the details of a particular application the nature of the baseline drifts etc If the peaks are found to shift to lower channels at
19. 60V ch3l 10 0 V Ficha 3500mY Gate This is an INPUT by which external logic can select pulses to be accepted into the spectrum If GATE is TRUE at the time the peak is detected the falling edge of trigger the event is accepted In this figure the second pulse is accepted not the first Page 17 of 42 X 123 User Manual Rev AO 5 5 POWER INTERFACE Figure 5 1 is a schematic illustrating the circuit at the power input The PWR_IN line goes through a Polyfuse and a Schottky diode then to different switching power supplies in parallel Five of these are located on the DP5 five on the PC5 Each has a 4 7 uF input capacitor Some turn on as soon as power as applied while others are under control of the microprocessor o Reverse polarity protection The Polyfuse and diode together protect against reverse input polarity o Grounding The chassis ground of the X 123 which is tied to the box and to the other boards is connected to the return current pins in J9 J9 F1 3 3V Suppl i 3 3V Supply PC5 MQ172 3PA 55 MICROSMD150F 2 i 1 PWR_IN VIN VOUT HR 4 7UF Shut Down D9 SSA34 E3 61T GND CHASSIS GND 5 5V Suppl VIN VOUT HR 4 7UF 4 7UF E Shut Down GND More power supplies O O More power supplies DP5 PC5 Figure 5 1 Simplified chematic of power supply architecture Turn On Transients Figure 5 2 illustrates the transient currents seen as the X 123 turns on There is a complicated struct
20. DC input fast channel pulse and ICR Similar to plot above but shows ability of fast channel to identify pulses separated by 120 nsec Tek SA A A A A A A o hannah chi 5 00V IE 20 0mY CTR 00us A Ch2 f 18 OMY E 20 0mY 8 SCA uti Occurs just after the shaped pulse has begin to fall Tekstop _ ADC Input E A Trigger S00 V ch2 20 Omv M DOS rn cha F is OmV ie 20 0mY E Trigger Shows when the DPP is looking for the peak of a pulse Falling edge indicates a peak has been found Page 16 of 42 Preamp Out reset preamp TTET ici init TO ETE ch1 2 00 E 2 00 Y M 200ms A ch2 1 48 V Detector Reset Shows when the DPP detected a reset signal in the preamplifier The lockout period is the width of the reset signal Tek stop A a FEE TEARS E E A RARE EE E E EEE EEE A PAE OE AT E E E ETIENNE za 5 00 Y ch2 20 0mY M 1 00us rn Ch2 f 18 0mY AE 20 0mY E One Shot Shows when the DPP is looking for possible pile up Triggered by the fast channel Tek stop L ADC Input N TTA ici iii AT Chi 5 00 20 0mVY M 1 00jus A Ch2 f 69 6mVY ch3 20 0mY T Pile Up Shows when pile up was detected Generated at the end of the final events one shot signal Amptek Inc X 123 User Manual Rev AO Tek ae E ADC Input U sis nats Se ne oe ee re e e Shaped pr A A A IM gt gt Valid Event Chil soom 5 UNA ES OWS AL Che a 3
21. Double Click Selects Port COM COM Port Number Coba EE 2 Check Device Communications Check Device Communications Get Status READY 3 Upload Files Select Upload Type l FPGA l uC Status DPS Statue Read Complete Click the Upload FPGA uC HEX File and select the microcontroller programming file dp5 uC_v503 hex for example uC programming files have the hex extension It will take The program says Reboot and check device Power cycle the DP5 again and exit the Run DP5Loader EXE again and click Check Device Communications Get Status to confirm the Firmware amp FPGA versions in this example Firmware 5 3 amp FPGA 5 3 All done Page 26 of 42 X 123 User Manual Rev AO 8 UNDERSTANDING THE X 123 8 1 UNDERSTANDING THE COMPLETE SYSTEM Figure 8 1 is a block diagram of the X 123 The key elements include 1 the detector 2 the preamplifier 3 the digital pulse processor 4 the power supplies 5 the packaging or enclosure for the system and 6 the computer running software for instrument control data acquisition and data analysis All X ray spectroscopy systems contain these basic elements This section provides a summary of the purpose and operation of each of these elements to assist users in understanding how to optimize the system configuration for any particular application Details on the electrical interfaces and on software configuration settings are given in later sections
22. MCS _TIMEBASE etc LVCMOS 3 3V levels TTL compatible Digital Inputs Two independent inputs software selectable for MCA GATE EXTERNAL_COUNTER Two general purpose I O lines for custom application Digital Oscilloscope Displays oscilloscope traces on the computer Software selectable to show shaped output ADC input etc to assist in debugging or optimizing configurations USB 2 0 full speed 12 Mbps RS 232 at 115 2k or 57 6k baud Ethernet 10base T future release Amptek Inc Page 5 of 42 X 123 User Manual Rev AO Nominal Input 5 VDC at 500 mA 2 5 W typical Current depends strongly on detector AT Ranges from 300 to 800 mA at 5 VDC Input Range 4 V to 5 5 V at 0 4 to 0 7 A typical Initial transient 2 A for lt 100 usec High Voltage Supply Internal multiplier software control 100 1500V 500 V typ positive polarity Cooler Supply Closed loop controller with AT max 85 C Physical 7 x 10 x 2 5 cm 2 7 x 3 9 x 1 in excluding extender Extender Lengths 1 5 3 8 cm standard Options include 3 8 5 9 and vacuum flanges Weight 180 g 6 3 oz General and Environmental Operating temperature 20 C to 50 C Warranty Period 1 Year Typical Device Lifetime 5 to 10 years depending on use Storage and Shipping Long term storage 10 years in dry environment Typical Storage and Shipping 20 C to 50 C 10 to 90 humidity non condensing Customization Amptek Inc pr
23. Mode to toggle between DELTA and MCA mode If no spectrum appears check that the system is acquiring data The Status on the right hand Info Panel should read acquiring Sometimes no spectrum will appear if PUR is enabled and the Fast Threshold is set improperly in the DPP Properties Shaping tab Turn PUR off and check if the spectrum appears If it does then the Fast Threshold needs to be set correctly Remove any source from in front of the detector and click the Tune Fast Threshold button Put the source back and check if the spectrum appears If it does not then you will have to adjust it manually as described below The Fast and Slow Thresholds can be adjusted manually First turn off PUR as described above Then click the cursor to channel 1 and press F8 This will set the Slow Threshold LLD to channel 1 This will show the noise of the system Click the cursor just to the right of the noise and then press F8 Press the A key to clear There should be no counts accumulating Now put the device into Delta mode by clicking the Delta button on the toolbar Open the DPP Properties and go to the Shaping page Adjust the Fast Threshold until 5 to 15 counts per second appear in the Input Counts in the right hand Info Panel Now turn on PUR and click OK Click the Delta button to get back to normal MCA mode and put the source back in front of the detector The Input Counts should slightly exceed the Counts at low count
24. Preamp Out PCS XR 100 DPS Detector amp Preamp Power supplies A Fay Detector and Preamplifier Digital Pulse Processor F oer Adapter Detector H W Cooler Power Preamp Pobvuer Figure 8 1 Block diagram of the X 123 Amptek Inc provides a family of spectroscopy products all built around the basic elements illustrated in Figure 8 1 In brief all include a detector a preamp a DPP and power supplies There are several different detectors optimized for different applications This includes Si PIN SDD and CdTe diodes along with scintillators PMT units The components are also available in several packaging options integrated in a single package as in the X 123 or GammaRad as a separated preamp and signal processor power supply XR100 and PX4 or as printed circuit boards which users integrate into their own products The signal processor can also be used with other detectors e g proportional counters Amptek now provides two generations of the core digital processor the DP4 and DP5 packaged into the PX4 and PX5 PX5 will be available soon The discussion in this section applies to all of the products which are based on the DP5 generation of digital processor including the PX5 X 123SDD X 123 etc We will refer to the digital processing logic as the digital pulse processor or DPP which may be the DP5 circuit board itself or the same logic running in the PX5 The first generati
25. X 123 User Manual Rev AO X 123 Complete X Ray Spectrometer with CdTe Detector User Guide and Operating Instructions Amptek Inc 14 DeAngelo Dr Bedford MA 01730 PH 1 781 275 2242 FAX 1 781 275 3470 sales amptek com www amptek com Amptek Inc Page 1 of 42 fa X 123 User Manual Rev AO Table of Contents 1 TOUCH NA dd A i 3 Et Desci sastae neces oom 20s oes a sytdecieanestaanen a a a a a see 3 2 SpecCaIt ONS ernaia T eee ie eee 4 3 Cautions and WAI Si A a A oeaeeeusedstbeed stadt 7 4 Sale AAA O A 8 AA EQUINA e dl o a 8 NANOS E E In A ai a 8 4 3 Making Connections eeina niina A A A E oval 8 AA NSt SO NWT ii ii ic iia 9 4 5 GONTQUIING Ne Unicos 10 4 5 1 Regions of Interest ROI cccccccssccccesseecceeseeceeececseaseeecseueeecsegseesseaeeessageeessageeessegseeenes 11 4 5 2 Calibrating the Horizontal AXIS ccccccccseeeeeceeeeeeeaeeeeeeeeeeeeeeeeeeesaeseeeeeaeeeessaueeesaeeeeeesaaes 11 AO TOUDIESROOUNG sr A A A do 12 5 Electrical iMtemaceS retina till idas 13 Ot Electrical Speciical nS imss 13 5 1 1 Absolute Maximum Ratings sind le lodo ie 13 5 1 2 DE By gfe sore E tus dla battle dos illa oriol 13 BZ GOMMUNICAL Ossa ia adas oli ross rats 14 90 Aulay IAput and OULDULS suite e a 15 5 4 Timing of Auxiliary Inputs and Outputs c cooccccccnccccnnncccnncconnnononnnonnnnnonanonnnnnnnnnnnnnnnnnonnnnnnnnnnnnnons 16 dl HOWE Itaca aca 18 6 Mechanical Interact 20 Ot A est
26. a ray detector and preamplifier 2 the DP5 digital pulse processor and MCA and 3 the PC5 power supply The result is a complete system which can fit in your hand with no performance compromise It requires only 5 VDC power and a standard communication interface With the X 123 anyone can rapidly obtain high quality X ray spectra The X 123 uses a CdTe crystal as x ray and gamma ray detector The CdTe is mounted on a thermoelectric cooler along with the input FET and coupled to a custom charge sensitive preamplifier The thermoelectric cooler reduces the electronic noise in the detector and preamplifier but the cooling is transparent to the user it operates like a room temperature system The pulse processor is the DP5 a second generation digital pulse processor DPP which replaces both the shaping amplifier and MCA found in analog systems The digital technology improves several key parameters 1 better performance specifically better resolution and higher count rates 2 greater flexibility since more configuration options are available and selected by software and 3 improved stability and reproducibility The DPP digitizes the preamplifier output applies real time digital processing to the signal detects the peak amplitude and bins this in its histogram memory The spectrum is then transmitted to the user s computer The PC5 supplies the power to the detector including low voltages for the preamps high voltage to bias the detector and
27. a supply for the thermoelectric cooler which provides closed loop control with a maximum temperature differential of 85 C All of these are under software control The X 123 input power is unregulated 5 VDC with a current of about 500 mA The complete system is packaged in 7 x 10 x 2 5 cm aluminum box The detector is mounted on an extender with lengths from O to 9 vacuum flanges are available In its standard configuration only two connections are required power 5 VDC and communications USB RS232 or Ethernet An auxiliary connector provides several additional inputs and outputs used if the X 123 will be integrated with other equipment This includes an MCA gate timing outputs and eight SCA outputs The X 123 is supplied with data acquisition and control software It also includes an Application Programming Interface API DLL to integrate the unit with custom software Optional accessories include software for analyzing X ray spectra several collimation and mounting options and X ray tubes to complete a compact system for X ray fluorescence Co Spectrum 122 keV 14 4 keV Counts 850 ev FWHM _ 530 ev FWHM A Energy keV Figure 1 1 Photograph of complete X 123 left and a typical Co spectrum right Preamp Out PCS XR 100 DPS Computer Detector amp Digital Pulse Preamp Power 2DE Control Processor supplies Readout ray Detector and Preamplifier
28. al parameters which control options not available in the DP4 hardware For backward compatibility the DP5 recognizes the configuration packets of either the DP4 or the PX4 operating in a DP4 emulation mode or a PX4 emulation mode Since it needs all the parameters to operate properly it reads the additional parameters from nonvolatile memory These must be set via a new data packet after which legacy software may be used with minor modification Amptek s ADMCA software provides the quickest way to control and readout the DP5 It provides access to all of the configuration parameters in the DP5 lets one start and stop data acquisition reads and displays the data performs very simple analyses and saves the data in an ASCII format The files saved by ADMCA can be read by many spectral processing software packages Imprki AAT A rents Pe vow HIA Beep ishe OF ty e 0 0 Mat 2 01 MO lt ee TW A S ee A Ta SM r Da E ii de open i Fie Sh her O eet PE bop tra ii Bae EX Figure 8 13 Typical screen display for ADMCA This shows the characteristic X rays emitted by a stainless steel alloy excited by a 30 kVp X ray tube and measured by an X 123 The main window shows the spectral display The user has defined regions of interest ROIs around the main peaks shown in gray The panel on the right displays counts acquisition time key parameters and data regarding the selected ROI The toolbar along top contai
29. ating the signal processing The dark blue trace on top shows the output of the preamplifier a series of steps of a few millivolts soaced randomly in time High frequency white noise is clearly superimposed The traces on the left right were measured with 60 5 9 keV X rays The signal to noise ratio is clearly much degraded on the right The light blue traces show the output of the analog prefilter with its 3 2 usec pole The magenta trace shows the shaped output it is the peak of this which is detected and is binned in the spectrum The green trace is a logic output indicating that a valid peak has been detected Final Amp Inverts Sets offset Anit jitter low pass filter Unity Gain High Pass any wo amplifiers Buffer Filter four gain each 3 or 13pF A 3 2 usec 2 5kQ 250 o 6 8 nF Preamp ree gt ADC Output Input DNI or y 900 2 Input Offset DAC Z Figure 8 8 Block diagram of the analog prefilter in the DP5 The prefilter implements three functions 1 it applies a high pass filter with a 3 2 usec time constant so that the pulses no longer ride up on one another 2 it applies a coarse gain so that the largest pulses are approximately 1 V to maximize the ADC resolution and 3 it applies a DC offset so that the signal always falls within the range of the unipolar ADC The output of the prefilter can be seen as the cyan color trace in Figure 8
30. bled then this input is ignored and all events which meet the criteria above are counted If active high low then if the gate input is high low the event is counted in the spectrum When counts are gated off the clock accumulation time counter is also gated off so that an accurate count rate can be determined The timing of this gate input is important If the gate input is active while the fast channel threshold is triggered then the event is counted as a fast count If the gate input is active when the peak detect is triggered then the event is counted as a slow count and shows up in the spectrum Note that the fast and slow channels are triggered at different times since they have different shaping times 8 3 5 MCA MCS Counters and SCAs Multichannel Analyzer The MultiChannel Analyzer MCA operates like a conventional MCA except that the input is already digitized It detects the amplitude of the peak of the shaped pulse using a digital peak detect circuit If the selection logic indicates that the pulse is valid then it increments the value stored at a memory location corresponding to the peak amplitude The MCA supports 256 512 1024 2048 4096 or 8192 channels The DP5 uses 3 bytes per channel which allows up to 16 7M counts per channel The MCA hardware in the DP5 can be started and stopped by commands over the serial bus It can also be preset to stop after a programmed acquisition time with a minimum of 100 milliseconds o
31. cooler and on the ambient temperature The cooler draws up to 2 3 of the total power USB o The USB interface follows the USB 2 0 Full Speed 12 MBPS specifications No separate table is included here See the DP5 User manual for more information AA as as a RS A ES lt Steady state full cooling AT 70 C AT 70 C gt PDP gt gt DP gt D gt D gt gt eae II PU EA 7x vologe swing s E v EXC TT TT iL 300 10m Unpowered o TX short circuit current HO MA SS baudrate fJ 576 1152 Kbad baud rate accuracy 1 5 E o The RS232 interface uses only RXD TXD lines no hand shaking o The transceiver is a MAX3227 Please refer to the MAXIM data sheet for further specifications Amptek Inc Page 13 of 42 fa X 123 User Manual Rev AO AUX OUT Output High Voltage 3 0 Typ No load Min low 100 uA Output Low Voltage 0 1 Typ No load Min lon 100 uA F e e 5 Output Resistance Rout AUX IN a Input Voltage es E Positive going Input 2 35 Threshold Negative going Input Dulce igs e woj eo scaor AY SEA OUT High Voltage 9 Typ No load Min loy 100 uA 2 0 Min loH 12 mA Output Low Voltage 0 2 Typ No load Max lon 100 uA 1 0 Max loo 12 mA CFSE Output Resistance Rar 47 a I O q q A _ _ _ Output High Voltage Vow 33 vp o The AUX OUT lines are the output of a 74LVC2G14 Vgg 3 3V with 50 Q series resistance o The AUX IN li
32. ct performance and sensitivity Please see the Charge Transport and Efficiency Applications notes on the Amptek website http www amptek com xr100cadt html XR 100T CdTe CZT Efficiency Application Note ANCZT 1 XR 100T CdTe CZT Charge Transport Application Note ANCZT 2 Charge Transport Charge trapping which is not found in the more common silicon and germanium detectors has a major impact on the performance of CdTe detectors An understanding of trapping is important to permit users and system designers to obtain the best performance for their particular applications One important parameter to keep in mind is the HV bias The higher the HV the faster the charge is collected This results in more counts in the peak and less hole tailing Amptek recommends operating CdTe at gt 500 V Often times voltages up to 1000 V are used Efficiency An important consideration is often the detection efficiency of these detectors Due to charge transport effects defining the detection efficiency is somewhat subtle Please see the above mentioned application note for more complete information on the efficiency of CdTe Figure 8 5 shows the sensitivity of the detector as a function of energy The efficiency is 100 from approximately 10 to 60 keV At lower energies the efficiency is limited by the Be window lower energy X rays are stopped in the window At higher energies the efficiency is limited by the interaction probability in the CdTe many X ra
33. e for each pulse in the slow channel a single digital quantity is the primary output of the pulse shaper The fast channel is optimized to obtain timing information detecting pulses which overlap in the slow channel measuring the incoming count rate measuring pulse risetimes etc and to obtain Pulse Selection Logic The pulse selection logic rejects pulses for which an accurate measurement cannot be made It includes pile up rejection risetime discrimination logic for an external gating signal etc Histogram Memory The histogram memory operates as in a traditional MCA When a pulse occurs with a particular peak value a counter in a corresponding memory location is incremented The result is a histogram an array containing in each cell the number of events with the corresponding peak value This is the energy spectrum and is the primary output of the DPP The unit also includes several counters counting the total number of selected pulses but also counting input pulses rejected events etc Auxiliary outputs include eight different single channel analyzers and both a DAC output and two digital outputs showing pulse shapes selected from several points in the signal processing chain Interface The DP5 includes hardware and software to interface between these various functions and the user s computer A primary function of the interface is to transmit the spectrum to the user The interface also controls data acquisition by starting a
34. e spectrum zero is derived solely from BLR o Use Offset The Boot Option Spectrum Offset is added to BLR This shifts the spectrum left or right along the horizontal axis This permits channel zero to have zero energy Note This setting is live and will take effect immediately To change the spectrum offset set this option to Use Offset click OK then Set DP5 Boot Flags Next read the boot flags again by selecting the Get Boot Options from DPP button This will enable the DP5 Spectrum Offset box where the offset channel can be entered and set Peak Detect o Max only normal operation This is the correct setting for normal operation o Max and min This allows the peak detect and MCA to capture local minima of the shaped pulse stream in addition to local maxima This is useful for capturing the noise Gaussian for determining the true spectrum zero The slow threshold must be set very low to accomplish this Note This setting is live and will take effect immediately It is also volatile it will reset to Max only the next time the DP5 is powered on MCA Channel o Slow channel normal operation This is the correct setting for normal operation Amptek Inc Page 24 of 42 X 123 User Manual Rev AO o Fast channel This sets the source for the MCA to the fast channel rather than the slow channel The fast channel does not have BLR or a pole zero but this set
35. ectly measure it using the DP5 s fast channel The accuracy and precision of this method are much better than that obtained using livetime clocks which are traditional for analog systems under most circumstances e The ADMCA software estimates the DP5 deadtime by comparing the count rates in the fast and slow channels We recommend keeping this value below 50 The DP5 operates at higher deadtime losses and can yield very accurate results but great care is required in configuring the system and interpreting the count results Counters The DPP has several counters which are started and stopped at the same time as the spectrum This includes the fast channel counter which records all fast channel events which exceed the fast channel threshold Note that there is no upper limit and that none of the pulse selection logic applies this is gated off during reset and data transfer The slow channel counter records all events which are recorded in the spectrum Note that there is an upper limit events exceeding the maximum pulse height channel are not in the spectrum hence not in the slow counts The full pulse selection logic applies PUR RTD etc An additional counter records those events rejected by PUR and RTD This is generally not of direct use but can be a quality assurance value by which one can verify system operation The DP5 also includes an external counter an external TTL input to a counter which is started and stopped at
36. ent is not in use BERYLLIUM WINDOWS DAMAGED BY IMPROPER HANDLING WILL NOT BE COVERED BY THE WARRANTY RADIATION DAMAGE to the detector will occur if it is exposed to a high flux environment Synchrotron Radiation Beams should be modified with attenuators before they are allowed to strike the detector or the fluorescence target Damage to the detector will be permanent if the flux from an X Ray Tube a strong nuclear radiation source or an accelerator is not attenuated A RADIATION DAMAGED DETECTOR WILL NOT BE COVERED UNDER WARRANTY No operator serviceable parts inside Refer servicing to Amptek Inc To prevent electrical shock do not remove covers For the latest information about this analyzer including firmware upgrades application software upgrades application information and product information go to http www amptek com mcasoft html Warranty AMPTEK INC warrants to the original purchaser this instrument to be free from defects in materials and workmanship for a period of one year from shipment AMPTEK INC will without charge repair or replace at its option a defective instrument upon return to the factory This warranty does not apply in the event of misuse or abuse of the instrument or unauthorized alterations or repair AMPTEK INC shall not be liable for any consequential damages including without limitation damages resulting from the loss of use due to failure of this instrument All products returned under the
37. ent pulse I t just like the Si PIN The rest of the signal processing electronics is nearly identical to that used with the Si PIN diode The key difference is the small area of the anode keeps the capacitance very small and independent of detector area This is important because the dominant noise source in silicon X ray spectroscopy is voltage noise which is proportional to the total input capacitance and increases at short shaping times The SDD with its low capacitance has lower noise particularly at very short shaping times Detector Bias Incident X ray X ray Detector Bias Supply Supply Incident Cathode A electrons o 0 1 OO N ue AA V ions a C f r dt ons 7 a Cathode nN Si Pl N gt J 7 Electrodes Shaiedicd M Silicon Drift i n aoc o Diode SDD I t i I t Figure 8 3 Sketch of conventional Si PIN photodiode left and silicon drift diode SDD right Detector Reset When a preamp integrates the input current as sketched above its output will eventually saturate The X 123 uses reset circuit to periodically restore the input charge Figure 8 4 a shows voltage steps from two interactions The output is constant between steps but eventually the preamp output will saturate The reset circuit then produces a current pulse to restore the output to its initial value Figure 8 4 b shows the output of a reset preamp ov
38. er a ta aotes teen havoc eaten oes aaa ar e dtd oece amanda eaten cans 20 0 2 IMOUNtIRd HardWale sme Sa nance a nt dae seca dei 21 A o O O O thei rasta 21 T SOMWAlCINIGH ACC tasks aestaalescusy a a a e a a a a NA 23 Far Mernice SOMWaNe nui a a a a N A AN Na 23 T2 l Empedaed SONWA E iina a a a a e tn 23 137 DOOURIAGS iaa 23 Ed Upoadd Manada ia 20 8 Understanding MEX 12S 0 AS AAN 27 6 1 Understanding the Complete SYM AAA a 27 8 2 Understanding the Detector and Preamplifier ooonccccocncncoconcnnononnnnconanononnnnnnononcnnnnnanonoss 29 8 2 1 DESIGN aNd QOS all ON a tas 29 8 2 2 RerommanCer caia E 31 8 3 Understanding the Digital Processor ooccconnccconcccoccncconcncnnncnconnnncnnnnnnnnnnnnoncnnnnncnnonrnnnnnrnnnnnnnnnnass 32 8 3 1 Major ElncIoO BIC iba is 32 8 3 2 Analog Preto sarigi p n a a a a a a 33 8 3 3 P SHAPING Seea a E E EE a Adan de ewe aces eater 35 8 3 4 Pulse Seleciona e a a a a aa a 36 8 3 5 MCA MGS Counters and SCAS ui ido aaaea aia 38 8 3 6 Electrical amp Software Interfaces 1 a a ca 40 8 4 Understanding the Power SuUPpll8sS cccooocccocccococcnocoocnnccononononnononononanononanononnnnnconnnonananenanos 41 9 APPICA ON DOS aria T 42 ot DOS and DON iS a ata 42 Amptek Inc Page 2 of 42 X 123 User Manual Rev AO 1 INTRODUCTION 1 1 DESCRIPTION The X 123 combines in a single package Amptek s high performance X ray spectroscopy components 1 the XR 100T CdTe X ray and gamm
39. er a very long time many small steps of a few mV each causes the output to linearly approach the negative limit 5V in a time of several seconds The reset pulse occurs so the output goes to the initial value 5V in a few usec Reset preamplifiers provide the minimum electronic noise and so are used in Amptek s lowest noise systems including the X 123 The very large transient created during reset can affect signal processing so the DPP includes logic to lock out the effects of this reset Amptek Inc Page 29 of 42 fal X 123 User Manual Rev AO Vertical scale 2Wfdiv MO 10 0m1 M 1005 A Chl w 4 00m EN Soom MaA dus A Chi w 500m a b c Figure 8 4 Oscilloscope traces showing typical preamplifier outputs for reset preamps a and b and for continuous feedback preamps c Si PIN and SDD use reset preamps and CdTe uses continuous feedback The traditional solution is to add a slow feedback path which restores the input to a value near ground In the simplest case a feedback resistor Rp is placed in parallel with the feedback capacitor Cp on which the current is integrated After the voltage step AV due to each signal interaction the output slowly drifts back to its quiescent value with the time constant of the feedback as illustrated in Figure 8 4 b This time constant is 500 usec in this plot The long time permits accurate integration of the total charge but causes the pulses to pile up on one another The feedback re
40. f 42 X 123 User Manual Rev AO AC Adapter 5VDC Power SDD Fragile Be X Ray Spectrometer a window USB Power Computer ETHERN J3 OF 5 RS 232 USB vo 4 4 INSTALL SOFTWARE 1 Turn on the PC and make sure you are logged in as an administrator 2 The Found New Hardware Wizard should automatically appear when the X 123 is connected and powered on for the first time 3 Select No not this time and click Next gt 4 Select Install from a list or specific location Advanced and click Next gt Found New Hardware Wizard Found New Hardware Wizard Welcome to the Found New Hardware Wizard Windows will search for current and updated software by This wizard helps you install software for looking on your computer on the hardware installation CD or on the Windows Update Web site with your permission Amptek DP4 Read our privacy policy If your hardware came with an installation CD Can Windows connect to Windows Update to search for lt or floppy disk insert it now software O Yes this time only O Yes now and every time connect a device What do you want the wizard to do No not this time Install the software automatically Recommended Install from a list or specific location Advanced Click Next to continue Click Next to continue 5 Select
41. feedback but does not match the performance of the reset preamps Amptek Inc Page 34 of 42 X 123 User Manual Rev AO 8 3 3 Pulse Shaping Slow Channel The slow channel of the DPP is optimized for accurate pulse height measurements It utilizes trapezoidal pulse shaping with a typical output pulse shape shown in Figure 8 10 This shape provides a near optimum signal to noise ratio for many detectors Relative to conventional analog shapers the trapezoid provides lower electronic noise and simultaneously reduced pulse pile up top trace 5 mv 10 us bottom trace 100 mV 10 us Figure 8 10 Pulse shape produced by the DPP The user can adjust the rise fall time the rise and fall must be equal and the duration of the flat top over many steps A semi Gaussian amplifier with shaping time t has a peaking time of 2 2t and is comparable in performance with the trapezoidal shape of the same peaking time A DPP with 2 4 usec peaking time will be roughly equivalent to a semi Gaussian shaper with a 1 usec time constant Adjusting the peaking time is a very important element in optimizing the system configuration There is usually a trade off the shortest peaking times minimize dead time yielding high throughput and accommodating high count rates but the electronic noise usually increases at short peaking times The optimum setting will depend strongly on the detector and preamplifier but also on the measurement goals The electronic
42. fferential reduces electronic noise without Detector requiring cryogenics A temperature monitor is also on the substrate to FET 2 lt Temp control the temperature for stable operation Vacuum is required inside the NA n Monitor TO 8 package to achieve this AT The heat extracted by the cooler is A ON conducted to the mounting stud Pii i Y Cooler The detector is mounted behind a thin Be window 4 mil JA E Mounting 8 2 1 Design and Operation Stud Detector Operation Figure 8 3 shows sketches of a conventional Si PIN photodiode left and a silicon drift diode right The CdTe Schottky diodes have the same structure as the Si PIN In the Si PIN there are two planar contacts with a uniform electric field between them An X ray interacts at some location ionizing the Si atoms and producing electron hole pairs The electric field sweeps the carriers to their respective contacts causing a transient current pulse I t to flow through the diode The current is integrated onto the feedback capacitor Cp producing an output voltage V t I t dt The SDD uses a planar cathode but the anode is very small and surrounded by a series of electrodes The SDD is cylindrically symmetric so the anode is a small circle and the drift electrodes are annular These electrodes are biased to create an electric field which guides the electrons through the detector where they are collected at the anode producing a transient curr
43. hat these values are approximate Due to manufacturing tolerances in the feedback capacitors in resistors etc the actual gain can vary by several percent which will cause a noticeable shift in the spectrum These calculations should be used for system design and for initial configuration For any given system the gain will need tuning and the spectrum will need to be calibrated For systems other than Amptek s XR100 series the preamp conversion gain can be estimated It is the product of three terms 1 one over the energy required to create an electron hole pair in the detector W 2 any internal detector gain e g with a proportional counter or PMT and 3 the preamp s conversion gain q Cr where Cf is the feedback capacitance For example for a Xe proportional counter W is 21 5 eV Ata gain of 10 and Cf 1 pF the conversion gain is 1 21 5 eV pair 10 1 6x10 C 10 F 7 4 mV keV Reset and Continuous Preamplifiers Most spectroscopy detectors utilize a charge sensitive preamplifier which precedes the analog prefilter in the DP5 A charge sensitive preamplifier produces a voltage proportional to the time integral of the current The integrator will eventually saturate because the time integral of the current through the diode continues to increase There are two methods used to keep the preamplifier output within range resets and continuous feedback Figure 8 4 left shows the output of a reset preamp over a very long time
44. he preamp produces a voltage step with magnitude AV proportional to the deposited charge In the X 123 the conversion gain is 1 mV keV so these steps are a few millivolts in magnitude Each preamp step rides on a baseline which can be several volts and has significant random noise o The shaping amplifier converts the preamplifier output signal into a form suitable for measurements producing an output pulse with pulse height Vpeak proportional to the deposited charge Q Since deposited energy is proportional to pulse height pulse height analysis can be used to analyze the energy spectrum The shaping amplifier has three primary roles 1 separate the AV step from the larger but slowly varying baseline from the preamp 2 amplify the AV values into a range which can be digitized accurately and 3 filter out the random electronic noise In Amptek s DPP family the shaping is done digitally since digital filters provide significant performance advantages over more traditional analog shaping schemes The preamp output undergoes some analog filtering to enable accurate digitization and this is digitized at a high rate 20 to 80 MHz This waveform then passes through a digital filter which implements the shaping and peak detect functions This is implemented in an FPGA in near real time via pipeline logic o The pulse analysis electronics use the measured peak heights to produce the histogram or spectrum This component includes logic to accept
45. hing regulators for maximum efficiency All of the DP5 s supplies are located on the DP5 board itself while the detector and preamplifier supplies are located on the PC5 board The supplies on both boards are under the control of the DP5 microcontroller The DP5 turns these supplies off and on and monitors the outputs via ADCs In the HV and TEC supplies the set point is under the control of the DP5 V PC5 LVPS PWR DP5 oe Microcontroller via jumpers r A i i DAC Hv Bias HV Power YON Su l HV_SET pp y HV_MON q Polarity Flag ADC Temperature a PWR On Off 9V i TEC TEC Power 00N 2 l TEMP_SET 12C o pov CAL oca 5 5V 2 5 1 2V 43 3V TEC RET TEMP_MON Supply Supply Supply V A Enable Se y A LV m S gene Re E EE ETE a PWR P LVPS gt reamp SHDN ie LV ko Set to 8 5V or DP5 LVPS 5V via jumpers PC5 Power Supply L v USB Enable PWR Ext PWR In V PWR Figure 8 14 Block diagram of the power supplies in the X 123 Some key points of the overall architecture are as follows o The input power is nominally 5 VDC 4 V to 5 5 V acceptable In the X 123 the input connector is on the DP5 There is a fuse and reverse polarity protection and then the input 5 VDC goes to the inputs of all of the separate supplies on both boards o When the 5 VDC is plugged in the 3 3V supply in the DP5
46. in time Figure 8 12 a shows two events that are separated by less than the rise time of the shaped signal while Figure 8 12 b shows two pulses that are separated by slightly longer than the rise time In a the output is the sum of the two signals note that the signal amplitude is larger than the individual events in b and the events are said to be piled up However note that the analog prefilter outputs in a are separate For a nearly triangular shape pile up only occurs if the two events are separated by less than the peaking time in which case a single peak is observed for the two events The interval used by the DPP for both dead time and pile up rejection is the sum of risetime and the flat top duration If two events occur within this interval and pile up rejection is disabled then the single piled up value is in the spectrum If pile up rejection is enabled and two events are separated by more than the fast channel pulse pair resolution 120 nsec and less than this T i T Chi 5 00mY by M 20 045 A J 1 88Y Chi 5 00mV wt M 20 045 A J 1 88V a b Figure 8 12 Oscilloscope traces illustrating the dead time and pile up reject performance of the DPP Reset Lockout As discussed previously many preamps use pulsed reset to prevent saturation of the preamp output The reset generates a very large signal in the DPP causing its amplifiers to saturate registers to overflow etc The DPP therefore includes a reset detect circuit
47. it allows faster peaking times min 0 2us and higher throughput than 20MHz but requires a bit more power Note This setting is live and will take effect immediately HV Polarity The polarity of the HV supply on the PC5 is not under software control it is configured in hardware via jumpers set at the factory This software configuration setting tells the DP5 what polarity is required and the DP5 will not allow the PC5 to turn on if its polarity doesn t match the Boot Flag o Negative Amptek s SDD detectors require negative HV o Positive All other Amptek detectors require positive HV Note This setting requires the DP5 to be power cycled to take effect ADC Invert This setting is only used in DP4 Emulation Mode In PX4 Emulation Mode the polarity is commanded via the configuration packet o Inverting Used for SDDs and other positive pulse preamps ADC Inversion combined with the DP5 s inverting front end results in a non inverting input o Non inverting Used with negative pulse preamps all Amptek non SDD preamps Note This setting requires the DP5 to be power cycled to take effect Fast Channel Shaping o Normal The fast channel peaking time is 400nS for a 20MHz clock or 100nS at 80MHz o 4x Slower The fast channel peaking time is 1 6uS for a 20MHz clock or 400nS at 80MHZ Note This setting requires the DP5 to be power cycled to take effect Spectrum Offset o None No spectrum offset is applied th
48. ks with the range of an SCA between its LLD and ULD then a logic signal is output These output pulses are 100 nsec wide the ability to select longer pulse widths is a future enhancement RN1 U24 AT SN74LVC245APWR son HA aa SCAT 6 CS 7 SCA F 6 Sone AS 6 SCA F 5 SNS SS 5 SCA F 4 SCA4 3 eee 4 SCA F 3 PLAS APAIN 3 SCA F 2 CA2 AS 2 SCA F 1 SCA1 ZYY 3V SCA DIR 19 SCA OE Amptek Inc Page 15 of 42 5 4 TIMING OF AUXILIARY INPUTS AND OUTPUTS Tek Prevu ADC Input cite o decimated E Aan iTi ri h LF Fi OmV E 20 0mY Sich4 50 0MY 5 ro output ADC input shaped pulse Tpeax of 2 4 usec and Tra Of 0 8 usec and ICR logic pulse indicating that a fast channel pulse occurred Note that 1 the shaped pulse begins to rise after actual event due to delays in the digital pipeline and 2 ICR occurs when the shaped pulse begins to rise ABE Run jh Trig d deal SSO ON SN S O S S S S A S A S O O A O E T T 2 00 V fy M 10 0ns rn Chi f 1 00V ICR Measured by scope probe 10 MQ 15 pF and 300 MHz scope One clock 12 5 nsec wide Tekstop L i chi 5 do Y 20 Omv SM i00ns A chi F 160 V ch3 20 0mY i ADC input fast channel pulse Tpeak Of 0 1 usec and ICR Similar to plot at left but at high time resolution Amptek Inc X 123 User Manual Rev AO Tek cStop ee ams m ee Y ape Input chil 5 00 Y dE 20 omv CELIE rn ch3 Pd 77 OmV ch3 50 0mY J A
49. lly by the software by clicking the Tune Slow Fast button on the toolbar This must be done with no source in front of the detector E Tes HA Day aa DF Fl 18 0 14 mol 9 A common adjustment is to change the gain of the X 123 Changing the gain changes the full scale energy range For example a gain of 100 may correspond to a full scale energy range of 15 keV whereas a gain of 50 will have a 30 keV full scale This can be done in the Gain amp Pole Zero tab of the DPP properties dialog box or by using the gain buttons on the toolbar It is necessary to readjust the thresholds whenever the gain is changed This can be done automatically as explained in the previous step For more information on gain and calibrating the channel scale to energy please see the document How to Change the Full Scale Energy Range and Calibration located on the CD in the Documentation Application Notes and FAQs directory 4 5 1 Regions of Interest ROI To mark an ROI click the Edit RO button on the toolbar The cursor will change to a vertical arrow Click and hold the left mouse button at the left base of the peak you want to mark and drag the cursor across the peak You will see the color change as the ROI is marked Release the mouse button at the right end of the peak If you click the mouse into the highlighted region it will become a lighter color indicating that it is the selected ROI The Peak Information on
50. many small steps of a few mV each causes the output to linearly approach the negative limit 5V in a time of several seconds The reset pulse occurs so the output goes to the initial value 5V in a few usec Reset preamplifiers provide the minimum electronic noise and so are used in Amptek s lowest noise systems including the XR100 The very large transient created during reset can affect signal processing so the DPP includes logic to lock out the effects of this reset Vertical scale 2Wfdiv oh Simy 4M40 0us A Chi 1 500mV Figure 8 9 Oscilloscope traces showing typical preamplifier outputs for reset preamps a and b and for continuous feedback preamps c Another traditional solution is to add a slow feedback path which restores the input to a value near ground In the simplest case a feedback resistor Rp is placed in parallel with the feedback capacitor Cr on which the current is integrated After the voltage step AV due to each signal interaction the output slowly drifts back to its quiescent value with the time constant of the feedback as illustrated in Figure 8 4 b This time constant is 500 usec in this plot The long time permits accurate integration of the total charge but causes the pulses to pile up on one another The feedback resistor adds electronic noise so is not used in the lowest noise systems Some Amptek detectors replace the feedback resistor with a transistor This offers lower noise than resistive
51. nce with the trapezoidal shape of the same peaking time 20 or 80 MHz 12 bit ADC 30 software selectable peaking times between 0 2 and 102 Us Corresponding to semi Gaussian shaping times of 0 1 to 45 us 16 software selectable values for each peaking time depends on the peaking time gt 0 05 usec Asymmetric 16 software selectable slew rate settings 1 05 times the peaking time No conversion time 4x10 sec periodic Output count rate of 7x10 sec for a Page 4 of 42 X 123 User Manual Rev AO Trim input oF x0 6c Dead Time Correction Manual correction based on Fast Channel measurement of ICR Accurate to 1 for ICR lt 1 Mcps under typical conditions Pulse Selection Options Pile up rejection risetime discrimination gate Multichannel Analyzer 1k channels in 12 milliseconds USB or 280 milliseconds RS 232 External MCA Controls Gate input Pulses accepted only when gated on by external logic Input can be active high or active low Software controlled Counters Slow channel events accepted by MCA Incoming counts fast channel counts above threshold SCA8 counts event rejected by selection logic and external event counter Sixteen ROI counters Auxiliary Inputs Output Single Channel Analyzers 8 SCAs independent software selectable LLDs and ULDs LVCMOS 3 3V level TTL compatible Digital Outputs Two independent outputs software selectable between 8 settings including INCOMING COUNT PILEUP
52. nd stopping the processing and by clearing the histogram memory lt also controls certain aspects of the analog and digital shaping for example setting the analog gain or the pulse shaping time The DPP includes USB RS232 and Ethernet interfaces The DP5 also includes a power interface lt takes a loosely regulated 5VDC input and generates the various levels required by the circuitry 5 5V 3 3V 2 5V Amptek Inc Page 32 of 42 X 123 User Manual Rev AO 8 3 2 Analog Prefilter The DP5 was designed to process signals coming directly from a charge sensitive preamplifier used with solid state radiation detectors These signals typically have 1 a small amplitude in the range of a few mV 2 a fast rise tens of nsec to usec and 3 the small pulses ride up on one another as the signal pulses accumulate These steps can be seen in the top traces of Figure 8 7 and are not suitable to be directly digitized due to the small amplitude a few mV over the large range many volts The analog prefilter prepares the signal so it can be accurately digitized Tek Stop a Tek Stop C O Y O A O o i 7 gt e CS y ee ee 34 34 E e ar rien einem ten A 50 0mv iCh2 500mY_ M 20 0u4s A Chl 1 20 0mV A 20 0mY iCh2 500mV_ M 20 0us A Chl 1 20 4mV ch3 200mY ichg 5 00 Y 5 1 Ch3 200mVY Chg4 5 00 Y 4 1 ii 10 20 1 ii 10 20 1 Figure 8 7 Oscilloscope traces illustr
53. nes are input to a 74LVC2G14 V 3 3V with 100 kQ to ground o The I O lines are connected to a MAX7328 V 3 3V which are open drain with a weak pull up 5 2 COMMUNICATION Please refer to the DP5 User Manual and the DP5 Programmer s Guide Amptek Inc Page 14 of 42 9 3 X 123 User Manual Rev AO AUXILIARY INPUT AND OUTPUTS AUX OUT 1and 2 Each of these two lines can be configured via software to output any one of several logic signals in the FPGA These logic signals are associated with pulses processed by the FPGA The pulse timing and duration depends on which output is commanded AUX_OUT_1 is connected to the Interconnect J5 to the auxiliary connector J6 and can be jumpered to the stereo jack J10 AUX_OUT_2 is only connected to the auxiliary connector J6 R73 49 9 AUX_OUT_1 AUX OUT 1 lt lt 6 1 U27A SN74LVC2G14DBVR AUX_IN_1 and_2 Each of these two lines can be configured via software to input any one of several logic signals in the FPGA These logic signals are associated with pulses processed by the FPGA AUX_IN_1 is connected to the Interconnect J5 to the auxiliary connector J6 and can be jumpered to the stereo jack J10 AUX_IN_ 2 is only connected to the auxiliary connector J6 AUX_IN_1 SHT 2 5 AUX_IN_1 gt U22A SN74LVC2G14DBVR Single Channel Analyzers SCAs Each of the eight SCAs has an independently assignable LLD and a ULD If the shaped pulse pea
54. noise of a detector will generally have a minimum at some peaking time the noise corner At peaking times shorter or longer than this there is more noise and hence degraded resolution If this peaking time is long relative to the rate of incoming counts then pulse pile up will occur In general a detector should be operated at a peaking time at the noise corner or below the noise corner as necessary to accommodate higher count rates If the risetime from the preamp is long compared with this peaking time then the output pulses will be distorted by ballistic deficit In this case the trapezoidal flat top can be extended to improve the spectrum The specific optimum timing characteristics will vary from one type of detector to the next and on the details of a particular application e g the incoming count rate The user is encouraged to test the variation of performance on these characteristics Fast Channel The DPP s fast channel is optimized to detect pulses which overlap in the slow channel The fast channel is used for pile up reject logic rejecting pulses which are so closely spaced that they cannot be distinguished in the slow channel and for determining the true incoming count rate correcting for events lost in the dead time of the slow channel The fast channel also utilizes trapezoidal shaping but the peaking time is commendable to either 100 nsec or 400 nsec The oscilloscope traces in Figure 8 11 show the measured
55. ns a button to access the configuration parameters along with other frequently used functions Amptek Inc Page 40 of 42 X 123 User Manual Rev AO Along with ADMCA Amptek provides a DLL library of the routines used to interface to the DPP A user can incorporate these into custom software A demonstration program written in Visual Basic is provided Amptek also provides an Upload Manager permitting new releases of the DP5s firmware and FPGA code to be programmed into the DPS in the field using the RS232 interface The auxiliary interface provides logic inputs and outputs which are not needed for the normal operation of the unit but which can be used for setup and debugging or for interfacing with external hardware The DP5 includes two auxiliary outputs which can be commanded to show any of several signals These are often displayed on an oscilloscope along with the output of a DAC showing the signal processing in the FPGA for setup and debugging The SCA outputs are generally counted directly 8 4 UNDERSTANDING THE POWER SUPPLIES Figure 8 14 is a block diagram of the power supplies in the X 123 There are quite a few voltages which must be produced The DP5 itself requires several low voltages to operate the analog and digital circuitry The detector and preamplifier require low voltages for the analog circuitry plus a high voltage supply to bias the detector and supplies to operate the thermoelectric cooler All of these are switc
56. on DP4 family is very similar in overall operation although there have been many enhancements to performance and many changes to the interface details Theory of Operation When an X ray photon interacts in the detector it generates electron hole pairs The signal charge Qsig is proportional to the energy deposited in silicon one electron hole pair is formed for each 3 6 eV deposited A 5 9 keV X ray for example produces about 1 640 electron hole pairs 2 6x10 coulombs The signal processing electronics measures the charge and therefore the energy deposited by each X ray A second stage of the electronics accumulates the results of many such discrete interactions producing the energy spectrum a histogram showing how many interactions deposited energy within many energy bins The electronics also measure the total count rate Figure 8 2 shows the key components in the system the detector the preamplifier a shaping amplifier and pulse analysis electronics o The detector is a diode with a bias voltage applied to sweep the electron hole pairs into the electronics Each X ray interaction produces a pulse of current through the detector input to the charge sensitive preamplifier a k a the preamp In Amptek s XR100 family of products the detector is mounted on a thermoelectric cooler This reduces the electronic noise significantly without the need for cryogenic cooling Amptek Inc Page 27 of 42 X 123 User Manual Rev AO o T
57. or reject events using various criteria to measure count rates and to produce several auxiliary outputs Anode A electrons i incident ee as Charge Sensitive Shaping Pulse Analysis dees current Preamplifier voltage Amplifier shaped voila Electronics pulse steps pulse Detector Cathode NZ Spectrum ail E o jo J E D 5 a D Time Time Time Figure 8 2 Schematic diagram of an X ray spectroscopy system Typical outputs from each stage of the processing electronics for a single pulse are also sketched Along with these core components a complete system must include power supplies hardware and software to data acquisition data analysis and instrument control and mechanical packaging The X 123 integrates all of these functions into a compact low power complete system Amptek Inc Page 28 of 42 X 123 User Manual Rev AO 8 2 UNDERSTANDING THE DETECTOR AND PREAMPLIFIER The heart of the X 123 is the detector hybrid shown to the right The a detector is a diode In the X 123 the detector is a CdTe These diodes are A 777 Be available with areas of 9 or 25 mm and thicknesses 1 mm a yy Window The detector is mounted on a thermoelectric cooler along with key s yt preamplifier components including the input FET The cooler which can Ww achieve an 85 C temperature di
58. ounters 0 Fast Pulse gt gt Channel Selection Auxiliary Oscilloscope or i i p Signals external logic Digital Processor DPP N gt Figure 8 6 Block diagram of a Digital Pulse Processor DPP in a complete system Analog Prefilter The input to the DP5 is the output of a charge sensitive preamplifier The analog prefilter circuit prepares this signal for accurate digitization The main functions of this circuit are 1 applying appropriate gain and offset to utilize the dynamic range of the ADC and 2 carrying out some filtering and pulse shaping functions to optimize the digitization ADC The 12 bit ADC digitizes the output of the analog prefilter at a 20 or 80 MHz rate This stream of digitized values is sent in real time into the digital pulse shaper Digital Pulse Shaper The ADC output is processed continuously using a pipeline architecture to generate a real time shaped pulse This carries out pulse shaping as in any other shaping amplifier The shaped pulse is a purely digital entity lts output can be routed to a DAC for diagnostic purposes but this is not necessary There are two are two parallel signal processing paths inside the DPP the fast and slow channels optimized to obtain different data about the incoming pulse train The slow channel which has a long shaping time constant is optimized to obtain accurate pulse heights The peak valu
59. out the DPP API 7 2 EMBEDDED SOFTWARE The embedded software is responsible for controlling the pulse processing controlling the MCA carrying out some data processing and interfacing with the personal computer Firmware updates will be released by Amptek and can be uploaded in the field by the user 7 3 BOOT FLAGS y DPP Properties There are certain parameters that are not contained in the configuration of the unit These parameters are called boot flags and are stored in the hardware General MEA Shaping Gain amp Pole Zero Power Misc Port uss USB Refresh ms 1000 Loaded from2450um 2 stage Cooler SDD configuration Press Show Current Configuration to view Boot Configuration State Select New Configuration Settings DFS Boot Flags o Boot unconfigured In this mode upon power Read Amptek Detector Configuration a fay Power up configuration up the DP5 will be in an unconfigured state If Boot unconfigured present the PC5 and detector will not be Recall Previous Software Configuration ay ene powered on until the first configuration packet MA O 57 600 baud e Read Current Hardware Configuration 115 200 baud is received Also the shaper MCA etc are Sica n nienn spen not configured After power up the status _ Open Predefined Configuration Fie O 20MHz packet byte 23 bit D1 indicates whether the a a eee i i g g equeste clarity device is configured or unconfigured Save Cur
60. ovides many tailored configurations on an OEM basis and has designed the X 123 to be easily tailored and customized The DP5 digital pulse processor inside the X 123 can be customized to support various applications Please contact Amptek Inc for more details Amptek Inc Page 6 of 42 X 123 User Manual Rev AO CAUTIONS AND WARNINGS 1 A A HIGH VOLTAGES ARE PRESENT IN THE X 123 They are internal to the package so do not represent a safety hazard if the unit remains enclosed THE DETECTOR CONTAINS A THIN FRAGILE BE WINDOW If this window is damaged the detector will be destroyed and cannot be repaired Be windows damaged due to improper handling are not covered under warranty DO NOT DROP OR CAUSE MECHANICAL SHOCK TO THE X 123 Components inside the detector are mechanically fragile and may be damaged if the unit is dropped DO NOT REMOVE the red protective cap from the detector until data is to be taken The detector window is made from thin beryllium 0 004 in 100 um thick which is extremely brittle and can shatter very easily Do not have any object come in contact with the window Do not touch the window because the oil from the fingers will cause it to oxidize The window cannot be repaired If the window is damaged the detector assembly must be replaced Be windows damaged due to improper handling will not be covered under warranty Keep the red protective cover nearby at all times and cover the detector when the instrum
61. pulse shapes with a 100 nsec peaking time As seen on the right pulses which are separated by only 120 nsec are separately counted in the fast channel Amptek Inc Page 35 of 42 X 123 User Manual Rev AO Tek Stop E A TA 22 0mY IO LIGERO aaa E S00uV FO 34 0mV y i E i l l l JO 11 6mV JA 254ns di da N 128ns 4 142ns 4 a 16 0ns A AI SS A A A A Ch3 50 0mV Bf 25 Apr 2008 Ch3 50 0mY 5y 139 80 10 58 04 i 30 60 25 Apr 2008 10 56 19 Figure 8 11 Oscilloscope traces showing operation of the DPP fast channel The magenta trace at top shows the ADC input the light blue trace shows the fast channel shaped output and the dark blue trace shows the logic output which counts the fast channel events Baseline Restoration The pulse height is implicitly measured relative to a baseline Any random fluctuation or systematic variation in the baseline whether high frequency noise or a slow change will degrade the pulse height measurement The baseline is often assumed to be ground but this is a somewhat ambiguous notion since ground represents simply the reference for voltage measurements If this baseline changes with time count rate or anything else then distortions are introduced into measurements In pulse height analysis the spectrum will appear to shift while in counting systems the threshold will change In practice the most common baseline shift occurs
62. r after a programmed number of counts has been measured within the SCA8 region of interest see below Acquisition Time The DPP measures the spectrum and counts during the acquisition time which is also measured and reported The acquisition time is the real elapsed time during which data are being acquired The acquisition time clock is turned off during certain events including data transfers over the serial bus and including reset intervals If a reset preamplifier is used and the DP5 is configured for a certain reset time period then acquisition is shut down during the reset period and the acquisition clock is stopped This acquisition time is measured using a typical 50 ppm crystal oscillator so is quite accurate The true count rate should be computed using the actual acquisition time rather than the nominal data transfer time Data transfers occur based on an approximate real time clock in the host PC For example one might configure ADMCA to acquire data from the DP5 every second When the data transfer occurs the Amptek Inc Page 38 of 42 X 123 User Manual Rev AO acquisition time is shown and this will probably differ from the nominal 1 second due to the approximate clock and also due to reset losses A typical value is 1 05 second At high count rates a reset preamp resets more often and so there is less acquisition time per transfer In this case the acquisition time might become 0 85 seconds On the screen
63. rent Configuration ToFie gt Negative Positive o Use Nonvolatile Configuration Upon power Show Curent Configuration 2 Fast channel shaping up the DP5 will use the last configuration it received before it was powered off It will turn on all supplies including the PC5 HV amp TEC supplies if present and if these were previously configured to be powered on The HV amp TEC supplies will be turned on approximately 2 seconds after power is applied The DP5 will be ready to take data once the detector has cooled Copy Configuration To Clipboard Startup Configuration f Use Configuration Stored In Hardware f Use Configuration Stored In Software fresh Spectum Oris Normal O 4s Slower ia Spectrum offset 0 None normal operation O Use Offset 4 Peak detect Cancel Apply Note This setting requires the DP5 to be power cycled to take effect RS232 Baud Rate 57 600 This primarily exists for backward compatibility with DP4 PX4 RS232 applications O Amptek Inc Page 23 of 42 X 123 User Manual Rev AO o 115 200 Recommended for higher speed transfers Note This setting requires the DP5 to be power cycled to take effect FPGA Clock o 20MHz Operating the DP5 at 20MHz consumes less power than 80MHz and allows longer peaking times up to 102us but limits throughput minimum peaking time 0 8us etc o 80MHZz This is the recommended clock rate for SDD detectors
64. sistor adds electronic noise so is not used in the lowest noise systems Some Amptek detectors replace the feedback resistor with a transistor This offers lower noise than resistive feedback but does not match the performance of the reset preamps Block Diagram Shown to the right is a generic block diagram of the AXR Detector XR100 detector and preamplifier in Amptek s XR100 family All of Hybrid Preamp the detectors SIPIN SDD CdTe share the same basic circuit All of the preamps XR100 the preamp boards in the X 123 the OEM preamps also have the same circuit diagram though the pinouts differ The reset circuits bias Do Not Connect 4 Do Not Connect 5 Externally O polarity and magnitude value of Cf and other details will se Bias 1 depend on the configuration SUEN Detector Kap E 7 Notes o Pins 4 5 8 and 9 of the AXR are given as Do Not E Connect These are unused in some units but are mona i used in others T o Pin 11 of the hybrid is the ground of the AXR case and oe Temperature should ground the preamp The FET source is usually gt Low Pass Filter Blas connected to this ee ee TEC PWR Thermoelectric TEC Return Cooler S Amptek Inc Page 30 of 42 X 123 User Manual Rev AO 8 2 2 Performance CdTe detectors exhibit some complex properties that affe
65. the same time as the other counters This is useful if for example one has a second detector and the counts at the same time are of interest Single Channel Analyzers The DP5 contains eight single channel analyzers SCAs Each SCA has an upper and a lower threshold If an event occurs with a shaped output within the range defined by these thresholds and is accepted by PUR and the other pulse selection logic then a logic pulse is generated and is output to the AUX connector where it can be connected to external hardware These are commonly used when a user needs to record count rates at a much higher time resolution than the 100 millisecond minimum for spectrum acquisition and only needs the rates within a few energy bands The upper and lower limits of the 8 SCAs can be set independently in the software SCAS serves a dual purpose not only does it operate like the other SCAs but it is also used to set the Region of Interest ROI for the Preset Count mode of MCA operation That is when a Preset Count is selected the MCA will stop after the programmed number of counts occurs in the SCA8 ROI Amptek Inc Page 39 of 42 of y X 123 User Manual Rev AO Multichannel Scaler The MultiChannel Scaler MCS produces spectral packets identical to those of the MCA but they represent very different data The MCS is used to measure total counts versus time rather than amplitude Each channel in the spectrum represents a time interval The
66. this time is displayed along with the fast counts and the slow counts during the same interval The actual count rate is found by dividing the observed counts by the observed acquisition time 0 85 seconds for this example Dead Time All nuclear spectroscopy systems exhibit a dead time associated with each radiation interaction Following any interaction there will be a time period during which subsequent pulses cannot be detected and will not contribute to the output counts Because the timing of pulses is random there is always some probability that pulses will occur in these dead time intervals and therefore the output count rate Rout measured by a system is always lower than the input count rate Rn The measurement goal is to determine the incident spectrum and count rate which requires correcting for these losses The dead time characteristics of a digital processor differ considerably from those of more traditional analog systems This is discussed in some detail in an Amptek application note and a research publication Some key points are e The deadtime per pulse of a digital processor is lower than that of a comparable analog system There is no deadtime associated with acquiring the peak this is termed simply the deadtime in an analog MCA and often dominates system deadtime and the deadtime per pulse is greatly reduced due to the finite impulse response of the shaping e The best way to determine the incoming count rate is to dir
67. ting does allow some insight into the operation of the fast channel Note This setting is live and will take effect immediately It is also volatile it will reset to Slow channel the next time the DP5 is powered on 7 4 UPLOAD MANAGER One of the advantages of the DP5 inside of the X 123 is the ability to upload new FPGA and microcontroller firmware through the RS232 interface An FPGA upload takes approximately 40 seconds and a microcontroller code upload takes around 3 seconds To upload updated firmware 1 New firmware files will need to be acquired either via email from Amptek or via the Amptek com website 2 Install the DP5Loader application from the Amptek CD The installer is located at Additional DPP Software DP5 DP5 Upload Utility SWSETUP SETUP EXE on the CDROM 3 Connect the 9 pin to stereo plug RS232 cable that came with the DP5 between a PC serial port and the DP5 and apply power to the DP5 Run DP5Loader EXE which you installed in Step 2 Double click the COM port that the DP5 is connected to Click Check Device Communications Get Status This will show READY if it successfully finds the DP5 or ERROR if not For example these screen shots show updating a DP5 from FW 5 02 amp FP 5 02 to FW 5 03 amp FP 5 03 ares 2 DPS Upload Utility 1 Select Communications Port Available Ports Double Click Selects Port COM Port Number aac COM 2 Check Device Communications
68. turns on and the digital circuitry is powered When the DP5 is configured it then turns on its internal low voltage supplies and the DP5 is powered The DP5 can be configured for this to happen automatically when power is applied o In the PC5 the first step is checking the polarity of the HV bias supply This is negative for SDD and positive for Si PIN and CdTe The DP5 compares the polarity set in the PC5 hardware to that selected in the DP5 s boot flags If these do not match then the PC5 supplies will not turn on o Ifthe HV polarity in the PC5 hardware matches that of the software configuration then the DP5 turns on the PC5 supplies The set point for the HV bias is software selectable up to 1500V The set point for the TEC supply is also software selectable The temperature of the detector is measured by a diode in the detector package and is used to provide closed loop temperature control with a maximum temperature differential of 85 C The low voltage supplies for the preamp can be set to 5V or 8 5V via a jumper on the board In the X 123 it is preset at the factory to 5V Amptek Inc Page 41 of 42 X 123 User Manual Rev AO a The power dissipated will depend on many variables The most important is the AT across the cooler Reducing AT by even a small amount from its maximum will decrease power dissipation significantly The X 123 typically draws 2 5 W 500 mA at 5 V a Nominal switching frequencies are gt 1 MHz
69. ure which can be understood from Figure 5 1 1 When 5 VDC is first applied to J9 a large transient current is drawn to charge up the 50 uF of input capacitance from the input capacitors on all the supplies 2 About 400 usec later the low voltage switching supplies turn on The maximum inrush current is about 2A with a duration of lt 100 usec It is important that the external supply be able to provide this current If this current is limited some of the supplies can be destroyed 3 After the DP5 is powered up it then powers up the PC5 based on configuration settings stored in the DP5 Depending on the Boot Configuration State boot flag this either happens automatically approx 2 seconds after power is applied or upon command from the host PC The unit draws about 300 mA at 5V 4 When the cooling is turned on lin goes to its maximum drawing approximately 700 mA 5 In Figure 5 2 the set point was 230K the ambient 295K and a Si PIN on a two stage cooler was used After about 50 seconds the temperature approached the set point and so began regulating The current decreased to its steady state value 400 mA Amptek Inc Page 18 of 42 X 123 User Manual Rev AO se Cha Supplies e l re E SI A i dE Turn On MAS ANYIN WOT ITA ugha bi ERA olla dilo 1 A div E A Cooler J E Regulating i a ee nd See ee PEE HO E er TE SEE E E SE E E LR CRENTE ESETE E rr J TEE Figure
70. uter and 2 making a separate ground connection from the chassis of the X 123 Note that the X 123 s AC DC supply is isolated Place the X 123 away from computer terminals CRT monitors and magnetic fields It is susceptible to radiated magnetic interference o Other setup suggestions O The system is somewhat susceptible to acoustic pickup especially at higher frequencies Minimize high frequency vibrations either at the source or by mounting of the unit o Configuration suggestions O Amptek Inc The fast and slow thresholds have a significant impact on performance After setting other configuration options reset the thresholds either using the Autotune button or manually The baseline restoration setting can have a significant impact on performance lt stabilizes the spectrum over count rate but also suppresses low frequency noise and interference Tuning BLR parameters can often improve or degrade resolution and spectral artifacts Page 42 of 42
71. w Properly setting these thresholds is very important for getting the best performance from the DPP Under most circumstances the thresholds should be set just above the noise and the ADMCA software includes an AutoTune function to set these Improperly set thresholds are responsible for a large number of problems reported by customers If the fast channel threshold is too low for example and PUR is enabled then every event will be rejected and so there appears to be no signal If the slow channel threshold is too high then it is also possible to reject all events Pile Up Rejection The goal of the pile up reject PUR logic is to determine if two interactions occurred so close together in time that they appear as a single output pulse with a distorted amplitude The DPP PUR uses a fast slow system in which the pulses are processed by a fast shaping channel in parallel with the slower main channel both channels are purely digital Though similar in principle to the techniques of an analog shaper the pile up reject circuitry and the dead time of the DPP differ in significant ways resulting in much better performance at high count rates First the symmetry of the shaped pulse permits the dead time and pile up interval to be much shorter Second there is no dead time associated with peak acquisition and digitization only that due to the pulse shaping Figure 8 12 illustrates the operation of the DPP for pulses that occur close
72. warranty must be shipped prepaid to the factory with documentation describing the problem and the circumstances under which it was observed The factory MUST be notified prior to return shipment The instrument will be evaluated repaired or replaced and promptly returned if the warranty claims are substantiated A nominal fee will be charged for unsubstantiated claims Please include the model and serial number in all correspondence with the factory Amptek Inc Page 7 of 42 4 X 123 User Manual Rev AO GETTING STARTED High voltages are present in the X 123 They are internal to the package so do not represent a safety hazard if the unit remains enclosed destroyed and cannot be repaired Do not touch the window e The detector contains a thin fragile Be window If this window is damaged the detector will be 4 1 4 2 4 3 The components inside the detector hybrid are mechanically fragile and may be damaged if the unit is dropped EQUIPMENT LIST o X 123 X Ray Spectrometer o Mini USB cable o 5 VDC power supply o Amptek Installation CD o APC supplied by the user with Windows XP PRO SP2 or higher recommended NOTES e The Amptek X 123 is a combination of other Amptek products The x ray detector and preamplifier are the same as the XR100T CdTe The digital pulse processor is the DP5 and the power supply board is the PC5 Please refer to the user manuals and specifications of those products included on the CD for
73. ys pass through without interacting 1mm Thick CdTe Detection Efficiency 1mm Thick CdTe Detection Efficiency 4d r 4 10 mit Ba 4 HH HHH K A HEN IA 4 mil Be N Total Interaction it Photoelectric aN t L AN UN BERN 7 E J A 7 tit TE TEG p We HAD Efficiency bh ERME HAT 0 100 1000 10 40 70 100 130 160 19 250 Energy keV Energy keV Figure 8 5 Plots showing the efficiency as a function of energy for the CdTe E a Amptek Inc Page 31 of 42 X 123 User Manual Rev AO 8 3 UNDERSTANDING THE DIGITAL PROCESSOR 8 3 1 Major Function Blocks Figure 8 6 shows how a Digital Pulse Processor DPP is used in the complete signal processing chain of a nuclear instrumentation system and its main function blocks The DPP digitizes the preamplifier output applies real time digital processing to the signal detects the peak amplitude digitally and bins this value in its histogramming memory generating an energy spectrum Pulse selection logic can reject pulses from the spectrum using a variety of criteria The spectrum is then transmitted over the DPP s interface to the user s computer Digital Pulse Shaping Peak Detect Detector and Analog Slow E uC and eo E E gt gt gt gt Preamplifier Prefilter ADE a Channel i ig ole Interface computer C

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