Model 570 Spectroscopy Amplifier Operating and Service Manual
Contents
1. 4 2 3 INPUT nis SEE Ib LER bU SR UTERE UR AE UR AER ARUBA BAM IR 4 2 4 OUTPUTS uiri bd usos tud ee a a Ta LR LR a A ooa 5 2 5 ELECTRICAL AND MECHANICAL 5 3 INSTAELATION Sehen Renee LAS LAE LA ene e nde e Se 5 3 1 GENERAL iub REEL LARA LECCE Res 5 3 2 CONNECTION TO POWER 0 5 3 3 CONNECTION TO 1 4 5 3 4 CONNECTION OF TEST PULSE GENERATOR 6 3 5 SHAPING CONSIDERATIONS 0 6 3 6 LINEAR OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS 6 3 7 SHORTING OR OVERLOADING THE AMPLIFIER OUTPUT 7 3 8 BUSY OUTPUT CONNECTION 4 4 2 4 7 4 7 4 1 INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS 2 4 4 7 4 3 FRONT PANEL CONNECTORS 1 4 8 4 4 REAR PANEL CONNECTORS Em 8 4 5 STANDARD SETUP PROCEDURE 2 8 4 6 POLE ZERO ADJUSTMENT iia t UR e DR a a 9 4 7 BLR THRESHOLD ADJUSTMENT 72. 11 4 8 OPERATION WITH SEMICONDUCTOR DETECTORS 12 4 9 OPERATION IN SPECTROSCOPY SYSTEMS 14 4 10 OTHER EXPERIMENTS odium c a C Us T tis 15 5 MAINTENANCE 253224 44 84 08 ABB ABBA BARBARA m d eno 17 5 1 TEST EQUIPMENT REQUIRED 17 5 2 PULSER TESTS iid a db db d bud b bid bud dd ee 17 5 3 SUGGESTIONS FOR TROUBLESHOOTING 19 5 4 FACTORY REPAIR 2 19 5 5 TABULATED TEST POINT VOLTAGES 19 ji Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig ILLUSTRATIONS Differentiation in Amplifier Without Pole Zero 2 Differentiation in a Pole Zero Canceled 2 Pulse Shapes for Good Signal to Noise Ratios 3 Typical Effects of Shaping Time Selection on Output Waveforms 8 Typical Waveforms Illustrating Pole Zero Adjustment 9 A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope Input 10 Pole Zero Adjustment Using a Square Wave Input to the Preamplifer 10 Thr
3. Emp 200410 Fig 1 2 DiflerenBalian in a Pola Zero Can elled Amplifier Pole zero cancellation is accomplished bv the network shown in Fig 1 2 The pole s 1 T due to the preamplifier pulse decay time is canceled by the zero of the network s k R C In effect the dc path across the differentiation capacitor adds an attenuated replica of the preamplifier pulse to just cancel the negative undershoot of the differentiating network Total preamplifier amplifier pole zero cancellation requires that the preamplifier output pulse decay time be a single exponential decay and matched to the pole zero cancellation network The variable pole zero cancellation network allows accurate cancellation for all preamplifiers having 40 Us or greater decay times Improper matching of the pole zero network will degrade the overload per formance and cause excessive pileup distortion at medium counting rates Improper matching causes either an undercompensation undershoot is not eliminated or an overcompensation output after the main pulse does not return to the baseline but decays to the baseline with the preamplifier time constant The pole zero adjust is accessible on the front panel of the 570 and can easily be adjusted by observing the baseline on an oscilloscope with a monoenergetic source or pulser having the same decay time as the preamplifier under overload conditions The adjustment should be made so that the pulse returns to the ba
4. OVERLOADING THE AMPLIFIER OUTPUT The 570 output is dc coupled with an output impedance of about 0 1Q If the output is shorted with a direct short circuit the output stage will limit the peak current of the output so that the amplifier will not be harmed When the amplifier is terminated with 100Q the maximum rate allowed to maintain the linear output is 200 000 cps 10 3 8 BUSY OUTPUT CONNECTION The signal through the rear panel Busy output connector rises from 0 to about 5 V at the onset of each linear input pulse Its width is equal to the time the input pulse amplitude exceeds the BLR discriminator level It can be used to provide MCA dead time correction to control the generation of input pulses to observe normal operation with an oscilloscope or for any of a variety of other ap plications Its use is optional and no termination is required if the output is not being used 4 OPERATION 4 1 INITIAL TESTING AND OBSERVATION OF PULSE WAVEFORMS Refer to Section 6 for information on testing performance and observing waveforms at front panel test points Figure 4 1 shows some typical unipolar output waveforms 4 2 FRONT PANEL CONTROLS GAIN A Coarse Gain switch and a Gain 10 turn locking precision potentiometer select and precisely adjust the gain factor for the amplification in the 570 Switch settings are X20 50 100 200 500 and 1000 Continuous fine gain range is from X0 5 to X1 5 using markings of 500 through 1500
5. a 5 47 MeV alpha particle energy e Turn on the pulser and use its Normalize control and attenuators to set the output due to the pulser for the same pulse height as the pulse obtained in step c Lock the Normalize control and do not move it again until recalibration is required The pulser is now calibrated the Pulse Height dial reads directly in MeV if the number of dial divisions is divided by 100 AMPLIFIER NOISE AND RESOLUTION MEASUREMENTS As shown in Fig 4 6 a preamplifier amplifier pulse generator oscilloscope and wide band rms voltmeter such as the Hewlett Packard 3400A are required for this measurement Connect a suitable capacitor to the input to simulate the detector capacitance desired To obtain the resolution spread due to amplifier noise a Measure the rms noise voltage Ems at the amplifier output b Turn on the 419 Precision Pulse Generator and adjust the pulser output to any convenient readable voltage E as determined by the oscilloscope The full width at half maximum FWHM resolution spread due to amplifier noise is then 12 Ao Z1 PLP Da apt PULEE TER aint Fig 4 6 Sysblem for Measuring Amplifier and Detector Moise Resolution 2 35 N FWHM where E is the pulser dial reading in MeV and 2 35 is the factor for rms to FWHM For average responding voltmeters such as the Hewlett Packard 400
6. dial divisions An internal jumper setting provides one additional gain factor selection of either X1 0 or X0 1 Collectively the range of gain can be set at any level from X1 0 through X1500 using all three of these controls POS NEG A locking toggle switch selects an input circuit that accepts either polarity of pulses from the preamplifier PZ ADJ A screwdriver control to set the pole zero cancellation to match the preamplifier pulse decay characteristics The range is from 40 Us to 77 DC ADJ A screwdriver control adjusts the dc baseline level of the unipolar output in the range of 0 1 V to 0 1 V SHAPING 6 position switch selects equal integrate and differentiate time constants to shape the input pulses Settings are 0 5 1 2 3 6 and 10 Us BLR A 3 position locking toggle switch controls the operation of the internal baseline restorer BLR circuit The center setting of the switch is effectivelv Off and this permits adjustment of the PZ ADJ control without interference from the BLR circuit The Auto setting of the switch selects a circuit that regulates the threshold of the BLR gate according to the output noise level The Threshold setting permits manual control of the BLR gate threshold using the screwdriver control immediatelv below the toggle switch 4 3 FRONT PANEL CONNECTORS INPUT Accepts input pulses to be shaped and or amplified bv the 570 Compatible characteristics positive or negative with rise t
7. need to be moved to another bin to achieve operation 3 3 CONNECTION TO PREAMPLIFIER The preamplifier output signal is connected to the 570 through the Input BNC connector on the front panel The input impedance is about 1000Q and is dc coupled to ground therefore the preamplifier output must be either ac coupled or have approximately zero dc voltage under no signal conditions The 570 incorporates pole zero cancellation in order to enhance the overload and count rate characteristics of the amplifier This technique requires matching the network to the preamplifier decay time constant in order to achieve perfect compensation The pole zero adjustment should be set each time the preamplifier or the shaping time constant of the amplifier is changed For details of the pole zero adjustment see Section 4 6 An alternate method is accomplished easily by using a monoenergetic source and observing the amplifier baseline with an oscilloscope after each pulse under approximately X2 overload conditions Adjustment should be made so that the pulse returns to the baseline in a minimum amount of time with no undershoot Preamplifier power at 24 V 24 V 12 V and 12 V is available through the Preamp Power connector on the rear panel When the preamplifier is connected its power requirements are obtained from the same bin and power supply as is used for the amplifier and this increases the dc loading on each voltage level over and above the r
8. D the measured noise must be multiplied by 1 13 to calculate the rms noise The resolution spread will depend on the total input capacitance since the capacitance degrades the signal to noise ratio much faster than the noise DETECTOR NOISE RESOLUTION MEASUREMENTS The measurement just described can be made with a biased detector instead of the external capacitor that would be used to simulate detector capacitance The resolution spread will be larger because the detector contributes both noise and capacitance to the input The detector noise resolution spread can be isolated from the amplifier noise spread if the detector capacity is known since Nampo where Nota is the total resolution spread and Nimp S the amplifier resolution spread when the detector is replaced by its equivalent capacitance The detector noise tends to increase with bias voltage but the detector capacitance decreases thus reducing the resolution spread The overall resolution spread will depend upon which effect is dominant Figure 4 7 shows curves of typical noise resolution spread versus bias voltage using data from several ORTEC silicon surface barrier semiconductor radiation detectors EA DO B A Dum ed ARE Fig 4 7 Molse as a Function of Bias Voltage AMPLIFIER NOISE RESOLUTION MEASUREMENTS USING MCA Probabiv the most convenient method of making resolution measurements i
9. ER REQUIRED not including any load on the Preamp Power connector 24 V 80 mA 24 V 85 mA 12 V 60 mA 12 V 30 mA FRONT PANEL DIMENSIONS _ NIM standard single width module 1 35 by 8 714 in per TID 20893 Rev 3 INSTALLATION 3 1 GENERAL The 570 operates on power that must be furnished from a NIM standard bin and power supply such as the ORTEC 401 402 Series The bin and power supply is designed for relay rack mounting If the equipment is to be rack mounted be sure that there is adequate ventilation to prevent any localized heating of the components that are used in the 570 The temperature of equipment mounted in racks can easily exceed the maximum limit of 50 C unless precautions are taken 3 2 CONNECTION TO POWER The 570 contains no internal power supply and must obtain the necessary dc operating power from the bin and power supply in which it is installed for operation Always turn off power for the power supply before inserting or removing any modules After all modules have been installed in the bin and any preamplifiers have also been connected to the Preamp Power connectors on the amplifiers check the dc voltage levels from the power supply to see that they are not overloaded The ORTEC 401 402 Series Bins and Power Supplies have convenient test points on the power supply control panel to permit monitoring these dc levels If any one or more of the dc levels indicates an overload some of the modules will
10. ION COUNTER GAMMA SPECTROSCOPY SYSTEMS The ORTEC 570 can be used in scintillation counter spectroscopy systems as shown in Fig 4 13 The amplifier shaping time constants should be selected in the region of 0 5 to 1 Us for Nal or plastic scintillators 15 Te Cari Foe m Drame and Trep SEGLI CHANNEL ORTEC LIMEAK AMPLIFIER FARD OH TIDAL COUNTER FEE LMP IFES RAL TZER PROPOR THOMAL oun TEA PULSI GERERATOR Fig 4 14 High Resolution X Ray Energy Analysis System Using a Proportional Counter For scintillators having longer decay times longer time constants should be selected X RAY SPECTROSCOPY USING PROPORTIONAL COUNTERS Space charge effects in proportional counters operated at high gas amplification tend to degrade the resolution capabilities drastically at x ray energies even at relatively low counting rates By using a high gain low noise amplifying system and lower gas amplification these effects can be reduced and a considerable improvement in resolution can be obtained The block diagram in Fig 4 14 shows a system of this type Analysis can be accomplished by simultaneous acquisition of all data on a multichannel analyzer or counting a region of interest in a single channel analyzer window with a counter and timer or counting ratemeter 4 10 OTHER EXPERIMENTS Block diagrams illustrating how the 570 and other OR
11. Model 570 Spectroscopv Amplifier Operating and Service Manual Printed in U S A ORTEC Part Number 733480 1202 Manual Revision E Advanced Measurement Technology Inc ORTEC a subsidiary of AMETEK Inc WARRANTY ORTEC warrants that the items will be delivered free from defects in material or workmanship ORTEC makes no other warranties express or implied and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ORTEC s exclusive liability is limited to repairing or replacing at ORTEC s option items found by ORTEC to be defective in workmanship or materials within one year from the date of delivery ORTEC s liability on any claim of any kind including negligence loss or damages arising out of connected with or from the performance or breach thereof or from the manufacture sale delivery resale repair or use of any item or services covered by this agreement or purchase order shall in no case exceed the price allocable to the item or service furnished or any part thereof that gives rise to the claim In the event ORTEC fails to manufacture or deliver items called for in this agreement or purchase order ORTEC s exclusive liability and buyer s exclusive remedy shall be release of the buyer from the obligation to pay the purchase price In no event shall ORTEC be liable for special or consequential damages Quality Control Before being approved for shipment each ORTEC instrument must p
12. NEAR ABNTPLIFIER DELAY AMPLIFFEH Fig 417 Gamma Gamma Coincidence Experiment 5 MAINTENANCE 5 1 TEST EQUIPMENT REQUIRED The following test equipment should be utilized to adequately test the specifications of the 570 Spectroscopy Amplifier 1 ORTEC 419 Precision Pulse Generator or 448 Research Pulser 2 Tektronix 547 Series Oscilloscope with a type 1A1 plug in or equivalent 3 Hewlett Packard 3400A rms Voltmeter 17 5 2 PULSER TEST FUNCTIONAL CHECKS Set the 570 controls as follows Coarse Gain 1K Gain 1 5 Input Polarity Positive Shaping Time Constant 1 us BLR PZ ADJ Variable control Fully CW for 300 mV a Connect a positive pulser output to the 570 Input and adjust the pulser to obtain 410 V at the 570 output This should require an input pulse of 6 6 mV using a 100Q terminator at the input b Change the Input polarity switch to Neg and then back to Pos while monitoring the output for a polarity inversion c Varv the DC ADJ control on the front panel while monitoring the Unipolar output Ensure that the baseline can be adjusted through a range of 0 1 to 0 1 V Readjust the control for zero d Recheck the output pulse amplitude and adjust if necessary to set it at 10 V with maximum gain Decrease the Coarse Gain switch stepwise from 1K to 20 and ensure that the output amplitude changes by the appropriate amount for each step Return the Coarse Gain switch to 1K e Decrease the Gain contr
13. TEC modules can be used for experimental setups for various other applications are shown in Figs 4 15 4 16 and 4 17 ORTEC LIME AR mese ap REIR ORTEC MTEC FAST GATED EURF ACE E INCIDENCE NA SEE Lever Cugat BARRIER IHE TECTA UNIT Pa lo B Arnal ee DETECTOR ORTEC QATEL DELAY DISTA NAi TENER AT GR HATOR TATEC TIMING FILTER AMPLIFIER DATEC j LIME A AMPLIFIER MPL OF FE Fig 4 15 Gamma Ray Charged Particle Coincidence Experiment ORTEC ZEIMTIL LINEAR AMPLIFIER AMF DRTEC iis ATER TEES CPL BA Fatt GATE DELA ATOR GENERATOR a DETECTOR DATEC FILTER DATEC AMPLIFIER ORTEC GATES LINEAR DELAY GATED AMPLIFIER AMPLIFIER Lira Qumuri Palrichanesel Sina yer ORTEC ORTEC SCANTIL LINEAR Latin FREAMF AMPLITIER Fig 4 16 Gamma Ray Pair Spectrometry 16 ATEC LINEAR AMPLINER LATOA AP HATHA Gf RPA AUS LUE DETECTOR QATEC T SHINE AMPLIFFER ORTEC FREA KE COL NCETRE ICE DETEC TCA DATEL ORTEC Fast ATED oo marro AMPLIFIER Chutpsat is Hunde rat QUE WE A TOR DATEC LI
14. Z Adj The BLR threshold is determined by the threshold potentiometer The BLR time constant is greatly increased to facilitate PZ adjustment This position may give the lowest noise for conditions of 5000 counts per second and or longer shaping times Threshold The BLR threshold is set manually by the threshold potentiometer Range is 0 to 300 mV referred to the positive output signal The BLR time constant is the same as for the Auto switch setting DC ADJ Screwdriver potentiometer adjusts the unipolar output baseline dc level range 100 mV to 100 mV 2 3 INPUT INPUT Type BNC front panel connector accepts either positive or negative pulses with rise times in the range from 10 to 650 ns and decay times from 40 to 2000 us 2 10000 dc coupled linear maximum 1 V 10 V with attenuator jumper set at X0 1 absolute maximum 20 V 2 4 OUTPUTS UNI Unipolar front panel BNC with Z lt 10 Short circuit proof prompt full scale linear range 0 to 10 V active filter shaped and dc restored dc level adjustable to 100 mV BUSY Rear panel BNC with Z 100 provides a 5 V logic pulse for the duration that the input pulse exceeds the baseline restorer discriminator level Connect to the ORTEC MCA Busy input for dead time correction PREAMP POWER Rear panel standard ORTEC power connector Amphenol 17 10090 mates with captive and non captive power cords on all standard ORTEC preamplifiers 2 5 ELECTRICAL AND MECHANICAL POW
15. as extremely low noise a wide gain range and excellent overload response for universal application in high resolution spectroscopy It accepts input pulses of either polarity that originate in germanium or silicon semiconductor detectors in scintillation counters with either fast or slow scintillators in proportional counters in pulsed ionization chambers in electron multipliers etc The 570 has an input impedance of approximately 1000Q and accepts either positive or negative input pulses with rise times lt 650 ns and fall times gt 40 Us Six integrate and differentiate time constants are switch selectable to provide optimum shaping for resolution and count rate The differentiation network has variable pole zero cancellation that can be adjusted to match preamplifiers with decay times gt 40 Us The pole zero cancellation drastically reduces the undershoot after the differentiator and greatly improves overload and count rate characteristics In addition the amplifier contains an active filter shaping network that optimizes the signal to noise ratio and minimizes the overall resolving time The output is unipolar and is used for spectroscopy in systems where dc coupling can be maintained from the 570 to the analyzer A BLR baseline restorer circuit is included in the 570 for improved performance at all count rates Baseline correction is applied during intervals between input pulses only and a front panel switch selects a discri
16. ass a stringent set of quality control tests designed to expose any flaws in materials or workmanship Permanent records of these tests are maintained for use in warranty repair and as a source of statistical information for design improvements Repair Service If it becomes necessary to return this instrument for repair it is essential that Customer Services be contacted in advance of its return so that a Return Authorization Number can be assigned to the unit Also ORTEC must be informed either in writing by telephone 865 482 4411 or by facsimile transmission 865 483 2133 of the nature of the fault of the instrument being returned and of the model serial and revision Rev on rear panel numbers Failure to do so may cause unnecessary delays in getting the unit repaired The ORTEC standard procedure requires that instruments returned for repair pass the same quality control tests that are used for new production instruments Instruments that are returned should be packed so that they will withstand normal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the designated ORTEC repair center The address label and the package should include the Return Authorization Number assigned Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the sender s expense and it will be the sender s responsibility to make claim with the shipper Instruments not in warrant
17. by using digital suppression on the MCA in many cases Alphaparticle resolution is obtained in the following manner Some guidelines for obtaining optimum resolution are a Keep interconnection capacities between the de tector and preamplifier to an absolute minimum no a Use appropriate amplifier gain and minimum long cables biased amplifier gain and bias level Accumulate the alpha peak in the MCA b Keep humidity low near the detector preamplifier junction ORTEC zi CHANNEL FALSE HEIGHT a cetecton AMAL YZER SCHL Lo Peru DETECTOR SCOPE g IPL Y a vacuum CHAMBER ORTEC PULSE GENERATOR Fig 4 11 System for High Resolution Alpha Particle Spectroscopy 14 DRTEC LINE AMPLIFIER E PULSE HEIGHT 5 BMA GERMAN LUMI and CRYOSTAT FULSI ENERAT A Fig 4 12 System for High Resolution Gamma Spectroscopy HIGH VOLTAGE PORE RSUPPL PULSE HEIGHT ANALYZER ORTEC SCINTIL COUNTER PRE AMPLIFIED LiMERR ELMPLIFILR SCINTILLATION Cul TER DATEC FULBE GENI RA TOR Fig 4 13 Scintillatlon Counter Gamma Spectroscopy System c Operate the amplifier with the shaping time that provides the best signal to noise ratio d Operate at the highest allowable detector bias to keep the input capacity low SCINTILLAT
18. ce for Nal a 1 Us shaping time constant is about optimum For gas proportional counters the collection time is normally in the 0 5 to 5 Us range and a 2 Us or greater time constant selection will generally give optimum resolution For surface barrier semiconductor detectors 0 5 to 2 Us resolving time will generally provide optimum resolution Shaping time for Ge Li detectors will vary from 1 to 6 Us depending on the size configuration and collection time of the specific detector and preamplifier When a charge sensitive preamplifier is used the optimum shaping time constant to minimize the noise of a system can be determined by measuring the output noise of the system and dividing it by the system gain Since the 570 has almost constant gain for all shaping modes the optimum shaping can be determined by measuring the output noise of the 570 with a voltmeter as each shaping time constant is selected 3 6 LINEAR OUTPUT CONNECTIONS AND TERMINATING CONSIDERATIONS Since the 570 unipolar output is normally used for spectroscopy the 570 is designed with a great amount of flexibility in order for the pulse to be interfaced with an analyzer A gated baseline restorer BLR circuit is included in this output for improved performance at all count rates A switch on the front panel permits the threshold for the restorer gate to be determined automatically according to the input noise level or manually with a screwdriver adjustment T
19. channel using DM the pulser and the known energy of the alpha peak OATES DATEC DHS WHN see Calibration of Test Pulser or two D ATEC DANII known energy alpha peaks 11 GRTEC 245 150 100 Calculate the resolution bv measuring the number of channels at the FWHM level in the peak and converting this to keV Deck Current HIGH RESOLUTION GAMMA SPECTROSCOPV Vel SVSTEM A high resolution gamma spectroscopv svstem block diagram is shown in Fig 4 12 Fig 4 70 Silicon Detector Back Current Bias Voltage Although a biased amplifier is not shown an analyzer with more channels being preferred it can be used if the only analyzer available has 4 9 OPERATION IN SPECTROSCOPY fewer channels and only higher energies are of SYSTEMS interest HIGH RESOLUTION ALPHA PARTICLE When germanium detectors that are cooled by a liquid nitrogen cryostat are used it is possible to obtain resolutions from about 1 keV FWHM up depending on the energy of the incident radiation and the size and quality of the detector Reasonable care is required to obtain such results SPECTROSCOPY SYSTEM The block diagram of a high resolution spectroscopy system for measuring natural alpha particle radiation is shown in Fig 4 11 Since natural alpha radiation occurs only above several MeV an ORTEC 444 Biased Amplifier is used to suppress the unused portion of the spectrum the same result can be obtained
20. control fully clockwise for 300 mV c Observe the unipolar output on the 100 mV cm scale of the oscilloscope using 5 Us cm horizontal deflection Trigger the oscilloscope with the Busy output from the 570 d Reduce the control setting until the baseline discriminator begins to trigger on noise this corresponds to about 200 counts s from the Busy output Adjust the trigger level according to the information in Fig 4 5 If a ratemeter or counter timer is available it can be connected to the Busy output and the threshold level can then be adjusted for about 200 counts s 11 4 5 Sel Too Low ELA Threshold Variable Control Sckings 4 8 OPERATION WITH SEMICONDUCTOR DETECTORS CALIBRATION OF TEST PULSER An ORTEC 419 Precision Pulse Generator or equivalent is easily calibrated so that the maximum pulse height dial reading 1000 divisions is equivalent to 10 MeV loss in a silicon radiation detector The procedure is as follows a Connect the detector to be used to the spectrometer system i e preamplifier main amplifier and biased amplifier b Allow excitation from a source of known energy for example alpha particles to fall on the detector c Adjust the amplifier gain and the bias level of the biased amplifier to give a suitable output pulse d Set the pulser Pulse Height control at the energy of the alpha particles striking the detector for example set the dial at 547 divisions for
21. d external pileup rejection The amplifier will hold the baseline reference up to count rates in excess of 150 000 counts s OVERLOAD RECOVERY Recovers to within 296 of rated output from X300 overload 2 5 nonoverloaded unipolar pulse widths using maximum gain same recovery from X1000 overload for bipolar pulses 2 2 CONTROLS GAIN Ten turn precision potentiometer for continu ously variable direct reading gain factor of X0 5 to X1 5 COARSE GAIN Six position selector switch selects feedback resistors for gain factors of 20 50 100 200 500 and 1 K INPUT ATTENUATOR Jumper on printed circuit board selects an input attenuation factor of 1 or 10 gain factor of X1 or XO 1 POS NEG Locking toggle switch selects input circuit for either polarity of input pulses from the preamplifier SHAPING TIME Six position switch selects time constant for active filter network pulse shaping selections are 0 5 1 2 3 6 and 10 s PZ ADJ Potentiometer to adjust pole zero cancellation for decay times from 40 s to e Factory preset at 50 5 to match normal characteristics of ORTEC preamplifiers BLR Locking toggle switch selects a source for the gated baseline restorer discriminator threshold level from one of three positions Auto The BLR threshold is automatically set to an optimum level as a function of the signal noise level by an internal circuit This allows easy setup and very good performance under most conditions P
22. e quirements for the 570 at the module position in the bin When the 570 is used with a remotelv located preamplifier i e preamplifier to amplifier connection through 25 ft or more of coaxial cable be careful to ensure that the characteristic impedance of the transmission line from the preamplifier output to the 570 input is matched Since the input impedance of the 570 is about 1000 2 sending end termination will normally be preferred the transmission line should be series terminated at the preamplifier output All ORTEC preamplifiers contain series terminations that are either 930 or variable coaxial cable type RG 62 U or RG 71 U is recommended 3 4 CONNECTION OF TEST PULSE GENERATOR THROUGH A PREAMPLIFIER The satisfactory connection of a test pulse generator such as the ORTEC 419 Precision Pulse Generator or equivalent depends primarily on two considerations the preamplifier must be properly connected to the 570 as discussed in Section 3 3 and the proper input signal simulation must be applied to the preamplifier To ensure proper input signal simu lation refer to the instruction manual for the particular preamplifier being used DIRECTLY INTO THE 570 Since the input of the 570 has 1000Q of input impedance the test pulse generator will normally have to be terminated at the amplifier input with an additional shunt resistor In addition if the test pulse generator has a dc offset a large series isolating capacitor is a
23. e zero adjustment inthe 570 can be obtained by using a square wave signal as the input to the preamplifier Many oscilloscopes include a calibration output on the front panel and this is a good source of square wave signals at a frequency of about 1 kHz The amplifier differentiates the signal from the preamplifier so that it generates output signals of alternate polarities on the leading and trailing edges of the square wave input signal and these can be Fig 42 Typical Waveforma IHiuslraling Pale Zera Adjustment EHects Oscilloscope Trigger 570 Busy Cuiput Ca Source with 1 33 Peak Adjusted 9 V Coumi Rabe 3 kHz haping Time Constant 2 us FRON AMPLIFIER TO CGCILEDSCOPE QUTPUT ik INPUT 2800 SLHOTTK T MODES OR FAST Ge DIODES Fig 4 3 A Clamp Circuit that can be used to Prevent Overloading the Oscilloscope Input compared as shown in Fig 4 4 to achieve excellent pole zero cancellation Use the following procedure a Remove all radioactive sources from the vicinity of the detector Set up the system as for normal operation including detector bias A Properly Adjusted Slow Trigger lo Separate Pulses C Properly Adjusted Pulses Superimposed b Set the 570 controls as for normal operation this includes gain shaping and input polarity c Connect the source of 1 2 square waves through an attenuator to the Test input of the preamplifier Adjust the attenuator so that the 570
24. es an external control source for the pulser The amplifier gain and the pulser attenuator must be adjusted to measure 0 V at the null point when the pulser output is 10 V The variation in the null point as the pulser is reduced gradually from 10 V to0 V is a measure of the nonlinearity Since the subtraction network also acts as a voltage divider this variation must be less than 10 V full scale x 0 05 maximum nonlinearity x 1 2 for divider network 2 5 V for the maximum null point variation OUTPUT LOADING Use the test setup of Fig 5 1 Adjust the amplifier output to 10 V and observe the null point when the front panel output is terminated in 100Q The change should be less than 5 Mv NOISE Measure the noise at the amplifier Unipolar output with maximum amplifier gain and 2 Us shaping time Using a true rms voltmeter the noise should be less than 5 UV x 1500 gain or 7 5 mV For an average responding voltmeter the noise reading would have to be multiplied by 1 13 to calculate the rms noise The input must be terminated in 100 during the noise measurements 5 3 SUGGESTIONS FOR TROUBLESHOOTING In situations where the 570 is suspected of a malfunction it is essential to verifv such malfunction in terms of simple pulse generator impulses at the input The 570 must be disconnected from its position in anv svstem and routine diagnostic analvsis performed with a test pulse generator and an oscilloscope It is imperative t
25. eshold Variable Control Settings 11 System for Measuring Amplifier and Detector Noise Resolution 12 Noise as a Function of Bias Voltage 13 System for Measuring Resolution with a Pulse Height Analyzer 13 System for Detector Current and Voltage Measurements 13 Silicon Detector Back Current vs Bias Voltage 14 System for High Resolution Alpha Particle Spectroscopy 14 System for High Resolution Gamma 15 Scintillation Counter Gamma Spectroscopy System 15 High Resolution X Ray Energy Analysis System Using a Proportional Counter 15 Gamma Ray Charged Particle Coincidence 16 Gamma Ray Pair Spectrometry nnna annnak 16 Gamma Gamma Coincidence Experiment 17 Amplifier Block Diagram 18 Circuit Used to Measure Nonlinearity 20 ill 570 AMPLIFIER GA PREAP UNIPOLAR OUTPUT iv 1 DESCRIPTION 1 1 GENERAL The ORTEC 570 Spectroscopy Amplifier is singlewidth NIM module that features a versatile combination of switch selectable pulse shaping characteristics The amplifier h
26. fferentiating network In an amplifier not using pole zero cancellation Fig 1 1 the exponential tail on the preamplifier output signal usually 50 to 500 Us causes an undershoot whose peak amplitude is roughly determined from undershoot amplitude differentiation time differentiated pulse amplitude preamplifier pulse decay time For a 1 45 differentiation time and 50 45 pulse decay time the maximum undershoot is 2 and this decays with a 50 45 time constant Under overload conditions this undershoot is often sufficiently large to saturate the amplifier during a considerable portion of the undershoot causing excessive dead time This effect can be reduced by increasing the preamplifier pulse decay time which generally reduces the counting rate capabilities of the preamplifier or compensating for the undershoot by causing pole zero cancellation Differentiated Emag ello x Gil seit 1 1 max fsi Laplace Ta E E 206409 IF heh aT t where Ty Fig 1 1 Differentiation in an Jmplilier Without Pole Zero Cancellation eft egit ett Pm ee eeu Pole era cancel by betting meheak uredershoot E U il oF FLUIT Git aa t Emax Emax A Ri PEL UM m POR R A A C L ox RU u E t Laplace tranicere i A Ay a l C EL n hh
27. h no input signal with the input terminated in 100 Q and all controls set fully clockwise at maximum Location TP1 TP2 TP3 4 5 6 TP7 Q15E 16 IC13 2 Voltage 10 mV 30 m V 20 mV 20 mV 30 mV 0 to 3 3 V 6mV 15 V 0 8 V 15 V 20 8 V 5 V 40 3 V Table 5 1 Typical dc Voltages Pin ON OAR 16 17 18 19 20 21 22 BIN MODULE CONNECTOR ASSIGNMENTS FOR STANDARD NUCLEAR INSTRUMENT MODULES PER DOE ER 0457T Function 3 volts 3 volts Spare Bus Reserved Bus Coaxial Coaxial Coaxial 200 volts dc Spare 6 volts 6 volts Reserved Bus Spare Spare Reserved 12 volts 12 volts Spare Bus Reserved Bus Spare Spare Reserved Pin 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Function Reserved Reserved Reserved Spare Spare 24 volts 24 volts Spare Bus Spare Spare 117 volts ac Hot Power Return Ground Reset Scaler Gate Reset Auxiliary Coaxial Coaxial Coaxial 117 volts ac Neut High Quality Ground Ground Guide Pin Pins marked are installed and wired in ORTEC s 4001A and 4001C Modular System Bins 20
28. hat testing not be performed with a source and detector until the amplifier performs satisfactorilv with the test pulse generator The testing instructions in Section 5 2 should provide assistance in locating the region of trouble and repairing the malfunction The two side plates can be completelv removed from the module to enable oscilloscope and voltmeter observations 5 4 FACTORY REPAIR This instrument can be returned to the ORTEC factory for service and repair at a nominal cost Our standard procedure for repair ensures the same quality control and checkout that are used for a new instrument Always contact Customer Services at ORTEC 865 482 4411 before sending in an instrument for repair to obtain shipping instructions and so that the required Return Authorization Number can be assigned to the unit This number should be marked on the address label and on the package to ensure prompt attention when the unit reaches the factory 5 5 TABULATED TEST POINT VOLTAGES The voltages given in Table 5 1 are intended to indicate typical dc levels that can be measured on the printed circuit board In some cases the circuit will perform satisfactorily even though due to component tolerances there may be some voltage measurements that differ slightly from the listed values Therefore the tabulated values should not be interpreted as absolute voltages but are intended to serve as an aid in troubleshooting Note All voltages measured wit
29. he switch also has a center PZ ADJ setting that can be used to eliminate the BLR effect when making pole zero adjustments The unipolar output dc level can be adjusted from 0 1 to 0 1 V to set the zero intercept on the analyzer when direct coupling is used Three general methods of termination are used The simplest of these is shunt termination at the receiving end of the cable A second method is series termination at the sending end The third is a combination of series and shunt termination where the cable impedance is matched both in series at the sending end and in shunt at the receiving end The combination is most effective but this reduces the amount of signal strength at the receiving end to 50 of that which is available in the sending in strument To use shunt termination at the receiving end of the cable connect the output on the 570 front panel through 930 cable to the input of the receiving instrument Then use a BNC tee connector to attach both the interconnecting cable and a 100Q terminator at the input connector of the receiving instrument Since the input impedance of the receiving instrument is normally 1000Q or more the effective instrument input impedance with the 1000 terminator will be of the order of 930 and this will match the cable impedance correctly For customer convenience ORTEC stocks the proper terminators and BNC tees or they can be ordered from a variety of commercial sources 3 7 SHORTING OR
30. ime from 10 to 650 ns decay time greater than 40 Us for proper pole zero cancellation input linear amplitude range 0 to 10 V with a maximum limit of 20 V Input impedance is approximately 1000Q UNIPOLAR OUTPUT Provides a unipolar positive output with characteristics that are related to input peak amplitude gain shaping time constants pole zero cancellation and baseline stabilization The dc baseline level is adjustable for offset to 0 1 V Output impedance through this connector is about 0 10 dc coupled Linear range 0 to 10 V 4 4 REAR PANEL CONNECTORS BUSY Provides a signal that rises to approximately 5 V for the time that the input pulse amplitude exceeds the BLR discriminator level which can be controlled manually or automatically The output can be used to correct for dead time in the ORTEC MCA by connecting it to the MCA Busy input PREAMP Provides power connections from the bin and power supply to the ORTEC preamplifier The dc levels include 24 V 24 V 12 V and 12 V 4 5 STANDARD SETUP PROCEDURE a Connect the detector preamplifier high voltage power supply and amplifier into a basic system and connect the amplifier output to an oscilloscope Connect the preamplifier power cable to the Preamp connector on the 570 rear panel Turn on power in the bin and power supply and allow the electronics of the system to warm up and stabilize Fig 4 1 Typical ElTects of Shaping Time Selection on Oulpul Wavelo
31. lso required since the 570 input is dc coupled The ORTEC test pulse generators are designed for direct connection When any one of these units is used it should be terminated with a 100Q terminator at the amplifier input or be used with at least one of the output attenuators set at In The small error due to the finite input impedance of the amplifier can normally be neglected SPECIAL CONSIDERATIONS FOR POLE ZERO CANCELLATION When a tail pulser is connected directly to the amplifier input the PZ ADJ should be adjusted if overload tests are to be made other tests are not affected See Section 4 6 for the pole zero adjustment If a preamplifier is used and a tail pulser is connected to the preamplifier test input similar precautions are necessary In this case the effect of the pulser decay must be re moved i e a step input should be simulated 3 5 SHAPING CONSIDERATIONS The shaping time constant on the 570 is switch selectable in steps of 0 5 1 2 3 6 and 10 Us The choice of the proper shaping time constant is generally a compromise between operating at a shorter time constant for accom modation of high counting rates and operating with a longer time constant for a better signal to noise ratio For scintillation counters the energy resolution depends largely on the scintillator and photomultiplier and therefore a shaping time constant of about four times the decay time constant of the scintillator is a reasonable choi
32. minator level to identify input pulses The unipolar output dc level can be adjusted in the range from 100 mV to 100 mV This output permits the use of the direct coupled input of the analyzer with a minimum amount of interface problems The 570 can be used for constant fraction timing when operated in conjunction with an ORTEC 551 552 or 553 Timing Single Channel Analyzer The ORTEC Timing Single Channel Analyzers feature a minimum of walk as a function of pulse amplitude and incorporate a variable delay time on the output pulse to enable the timing pick off output to be placed in time coincidence with other signals The 570 has complete provisions including power distribution for operating any ORTEC solid state preamplifier Normally the preamplifier pulses should have a rise time of 0 25 Us or less to properly match the amplifier filter network and a decay time greater than 40 Us for proper pole zero cancellation The 570 input impedance is 10000 When long preamplifier cables are used the cables can be terminated in series at the preamplifier end or in shunt at the amplifier end with the proper resistors The output impedance is about 0 10 and the output can be connected to other equipment by a single cable going to all equipment and shunt terminated at the far end of the cabling See Section 3 for further information 1 2 POLE ZERO CANCELLATION Pole zero cancellation is a method for eliminating pulse undershoot after the di
33. ol from 1 5 to 0 5 and check to see that the output amplitude decreases by a factor of 3 Return the Gain control to maximum at 1 5 ATTENUATED eur T IGGEA 2901 0 q Al H TURE VERTICAL INPUT Fig 5 1 Circuit Used Measure Nonlinearity 18 f With the Shaping switch set for 1 Us measure the time to the peak on the unipolar output pulse this should be 2 2 Us for 2 27 Measure the time to baseline crossover of the bipolar output this should be 2 8 Us for 2 8 7 g Change the Shaping switch to 0 5 through 10 Us in turn At each setting check to see that the time to the unipolar peak is 2 2 7 Return the switch to 1 Us OVERLOAD TESTS Start with maximum gain 2 us and a 10 V output amplitude Increase the pulser output amplitude by X200 and observe that the unipolar output returns to within 200 mV of the baseline within 24 Us after the application of a single pulse from the pulser It will probably be necessary to vary the PZ ADJ control on the front panel in order to cancel the pulser pole and minimize the time required for return to the baseline LINEARITY The integral nonlinearity of the 570 can be measured by the technique shown in Fig 5 1 In effect the negative pulser output is subtracted from the positive amplifier output to cause a null point that can be measured with excellent sensitivity The pulser output must be varied between 0 and 10 V which usually requir
34. ons of integration the waveform identified as a Gaussian approximation can be obtained and this deteriorates the signal to noise ratio by about 22 The ORTEC active filter network in the 570 provides a fourth waveform in Fig 1 3 this waveform has characteristics superior to the Gaussian approximation yet obtains them with four complex poles By this method the output pulse shape has a good signal to noise ratio is easy to measure and yet requires only a practical amount of electronic circuitry to achieve the desired results 2 SPECIFICATIONS 2 1 PERFORMANCE GAIN RANGE Continuously adjustable from X1 through X1500 PULSE SHAPING Gaussian on all ranges with peaking time equal to 2 27 and pulse width at 0 1 level equal to 2 9 times the peaking time INTEGRAL NONLINEARITY lt 0 05 0 025 typical using 2 Us shaping NOISE lt 8 UV referred to the input 5 UV typical using 2 Us shaping and gain gt 100 TEMPERATURE INSTABILITY Gain lt 0 0075 C 0 to 50 C DC Level lt 50 UV SC 0 to 50 C WALK lt 3 ns for 50 1 dynamic range including contribution of ORTEC 551 or 552 Constant Fraction Timing Single Channel Analyzer using 50 fraction and 0 5 Us shaping COUNT RATE STABILITY The 1 33 MeV gamma peak from a source positioned at 85 of analyzer range typically shifts 0 02496 and its FWHM broadens lt 16 when its incoming count rate changes from 0 to 100 000 counts s using 2 Us shaping an
35. output amplitude is about 9 V d Observe the Unipolar output of the 570 with an oscilloscope triggered from the 570 Busy output Adjust the PZ ADJ control for proper response according to Fig 4 4 Use the clamp circuit or Fig 4 3 to prevent overloading the oscilloscope input Figure 4 4A shows the amplifier output as a series of alternate positive and negative Gaussian pulses In the other three pictures of this figure the oscilloscope was triggered to show both positive and negative pulses simultaneously These pictures show more detail to aid in proper adjustment D Lindercormgpensebmrd Pulses Superimposed Fig 44 Pole Zero Adjusiment Using a Square Wave Input io the Preamplifier 4 7 BLR THRESHOLD ADJUSTMENT After the amplifier gain and shaping have been selected and the PZ ADJ control has been set to operate properlv for the particular shaping time the BLR Thresh control can be used to establish the correct discriminator threshold for the baseline restorer circuit Normallv the toggle switch can be set at Auto and the threshold level will be set automaticallv just above the noise level If desired the switch can be set at Threshold and the manual control just below the switch can then be used to select the level manuallv as follows a Remove all radioactive sources from the vicinitv of the detector Set up the svstem as for normal operation including detector bias b Set the BLR switch at Threshold and turn the
36. rma b Set the 570 controls initiallv as follows Shaping 2 us Coarse Gain 50 Gain 1 000 Internal Jumper 1 0 factorv installed position BLR PZ ADJ Thresh Fully clockwise Pos Neg Match input pulse polarity c Use a CO calibration source place it about 25 cm from the active face of the detector The unipolar output pulse from the 570 should be about 8 to 10 V using a preamplifier with a conversion gain of 170 mV MeV d Readjust the Gain control so that the higher peak from the CO source 1 33 MeV provides an amplifier output at about 9 V 4 6 POLE ZERO ADJUSTMENT The pole zero adjustment is extremely critical for good performance at high count rates This adjustment should be checked carefully for the best possible results USING A GERMANIUM SYSTEM AND CO a Adjust the radiation source count rate between 2 kHz and 10 kHz b Observe the unipolar output with an oscilloscope Adjust the PZ ADJ control so that the trailing edge of the pulses returns to the baseline without overshoot or undershoot see Fig 4 2 The oscilloscope used must be dc coupled and must not contribute distortion in the observed waveforms Oscilloscopes such as Tektronix 453 454 465 and 475 will overload for a 10 V signal when the vertical sensitivity is less than 100 mV cm To prevent overloading the oscillbscope use the clamp circuit shown in Fig 4 3 USING SQUARE WAVE THROUGH PREAMPLIFIER TEST INPUT Amore precise pol
37. s with a pulse height analyzer as shown by the setup illustrated in Fig 4 8 DETEC FLL Rast UH mi STMETGHEM rec BAL TH Ara L mundi AMAL Y TER Fig 4 6 Syelem Measuring wilh Pulas Height Analyzer The amplifier noise resolution spread can be measured directly with a pulse height analyzer and the mercury pulser as follows a Select the energy of interest with an ORTEC 419 Precision Pulse Generator Set the amplifier and biased amplifier gain and bias level controls so that the energy is in a convenient channel of the analyzer b Calibrate the analyzer in keV per channel using the pulser full scale on the pulser dial is 10 MeV when calibrated as described above 13 c Obtain the amplifier noise resolution spread by measuring the FWHM of the pulser peak in the spectrum The detector noise resolution spread for a given detector bias can be determined in the same manner by connecting a detector to the preamplifier input The amplifier noise resolution spread must be subtracted as described in Detector Noise Resolution Measurements The detector noise will vary with detector size and bias conditions and possibly with ambient conditions CURRENT VOLTAGE MEASUREMENTS FOR Si AND Ge DETECTORS The amplifier system is not directly involved in semiconductor detector current voltage measurements but the amplifier ser
38. seline in the minimum time with no undershoot 1 3 ACTIVE FILTER When only FET gate current and drain thermal noise are considered the best signal to noise ratio occurs when the two noise contributions are equal for a given input pulse shape The Gaussian pulse shape Fig 1 3 for this condition requires an amplifier with a single RC differentiate and n equal RC integrates where n approaches infinity The Laplace transform of this transfer function is G s S 1 1 RC s 1 RC where the first factor is the single differentiate and the second factor is the n integrates The 570 active filter approximates this transfer function Figure 1 3 illustrates the results of pulse shaping in an amplifier Of the four pulse shapes shown the cusp would produce minimum noise but is impractical to achieve with normal electronic and circuitry would be difficult to measure with an ADC The true Gaussian shape deteriorates the signal to noise ratio by only about 12 from that of 1 00 i 1 12 i y i ALES ARAN A mm iz X x a iad b ICH ACTIVE FILTER 74 17 L EXIIT 1 s HACI 1 a 8 e hey EA ke na Do Hl Fig 1 3 Pulse Shapes lor Good Signal to Naise Ratios the cusp and produces a signal that is easy to measure but requires many sections of integration n 9 with two secti
39. ves to permit noise monitoring during the setup The detector noise measurement is a more sensitive method than a current measurement of determining the maximum detector voltage that should be used because the noise increases more rapidly than the reverse current at the onset of detector breakdown Make this measurement in the absence of a source Figure 4 9 shows the setup required for current voltage measurements An ORTEC 428 Bias Supply is used as the voltage source Bias voltage should be applied slowly and reduced when noise increases rapidly as a function of applied bias Figure 4 10 shows several typical current voltage curves for ORTEC silicon surface barrier detectors When it is possible to float the microammeter at the detector bias voltage the method of detector current measurement shown by the dashed lines in l awwETER OATEC VOL TMETER FRLABIF AMIFLIFSER DETEETDH Fig 4 9 System for Detector Current and Voltage Measurements am Caras BARS CAFAEITDR Fig 4 9 is preferable The detector is grounded as b Slowly increase the bias level and biased in normal operation and the microammeter is amplifier gain until the alpha peak is spread over 5 connected to the current monitoring jack on the 428 to 10 channels and the minimum to Detector Bias Supplv maximum energv range desired corresponds to the first and last channels of the MCA c Calibrate the analyzer in keV per
40. y should follow the same procedure and ORTEC will provide a quotation Damage in Transit Shipments should be examined immediately upon receipt for evidence of external or concealed damage The carrier making delivery should be notified immediately of any such damage since the carrier is normally liable for damage in shipment Packing materials waybills and other such documentation should be preserved in order to establish claims After such notification to the carrier please notify ORTEC of the circumstances so that assistance can be provided in making damage claims and in providing replacement equipment if necessary Copyright 2002 Advanced Measurement Technology Inc All rights reserved ORTEC is a registered trademark of Advanced Measurement Technology Inc All other trademarks used herein are the property of their respective owners TABLE OF CONTENTS a SOD RU l PN TA i T DESCRIPTION 322222 252 5 c2 24 1 1 1 GENERAL i2 du tA A bbb bled lb ndn 1 1 2 POLE ZERO 2 2 1 1 3 AGTIVE FILTER sexi ii Abd obw b dene e 3 2 SPECIFICATIONS ts 4 2 1 PERFORMANCE 5 25 5 16 i bike RE aa a a 4 2 2 GONTROLS ases ARJA aU Sa UR CR ECT RR
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