PIXIE-4 Online Help
Contents
1. If event dead time is a concern the trace length should be set as short as possible In particular if only energies and time stamps are of interest the trace length can be set to zero The PSA Start and PSA End specify the trace range for Pulse Shape Analysis PSA Currently Pixie 4 supports two types of PSA XIA_PSA and USER_PSA XIA_PSA reports the signal arrival time by measuring the time when the trace reaches a preset percentage level constant fraction of its magnitude The preset percentage threshold can be set defined in the CCSRAEditPanel The arrival time is relative to the starting time of the trace So for XIA_PSA the PSA Start and PSA End should be set to include the rising edge of the trace USER_PSA is a user defined PSA value calculated by customized user code linked to the general software 4 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved Action Buttons Edit Channel Register CCSRAEditPanel Edit Module Register HitEditPanel Copy Copy settings CopyPanel Extract Extract settings ExtractPanel Files Path Files and path AllFilesPanel Load Load settings Save Save settings CCSRAEditPanel Settings gt Channel Register Edit Each channel has its own channel control status register CCSRA Click a check box to set or clear particular bits We give a brief description of all relevant bits here In the CCSRAeditPanel they appear in top to bottom order Bit 0 Group trigger2. In a larger experiment you may want to exercise control over which events to accept and which to reject based on external logic A logic signal inhibiting event triggers can be distributed on the PXI backplane When bit 6 is set a logic high on the GFLT Veto backplane line will inhibit latching data and issuing triggers for this channel Bit 7 Histogram energies Switch on incrementing an energy histogram in the DSP s MCA memory with this bit You can choose to have histogramming in list mode runs The histograms will continue to be updated over multiple runs started with the resume run command Bit 10 Compute constant fraction time The DSP can use pulse shape analysis to compute a precise signal arrival time using the digital equivalent of a constant fraction discriminator For this to work correctly the rising part of the signal should be fully contained in the recorded trace The time computed is the arrival time after the start of the acquired waveform in units of 1 256th of an ADC sampling interval This information can be used to replace the recorded channel time which is derived from a digital leading edge discriminator cf the User s Manual The DSP code shipped with the Pixie 4 has some pulse shape analysis capabilities already built in One of these functions the digital constant fraction discriminator takes an input parameter the threshold percentage The default value is 25 since it is a commonly used threshold fraction for t
3. Since available memory limits the number of events that each module can store in its buffer the Pixie 4 Viewer computes the maximum number of events When the maximum is reached the run is stopped and the buffer is read out For a longer run in list mode you can request several spills or buffer fills For example if you request a run with 10 spills you will get 10 list mode buffers worth of data At start of the first run all previous run history is cleared For instance MCA memory and run and live time information are cleared The next nine sub runs are started with a Resume Run command which leaves previous run information intact Run times and live times and spectra in MCA memory are incremented 10 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved You can also manually adjust the maximum number of events stored before the run is stopped Some data acquisition systems which are geared towards event by event readout and are not able to handle large buffers may benefit from the capability to reduce the maximum number of events per spill Fast List Mode Fast list mode is an event by event data acquisition run without waveforms Since no traces are read out the data acquisition is faster than a regular list mode however no pulse shape analysis PSA values are available There will also be no run statistics and no checks if the event buffer is filled faster than the event processing rate So the average trigger rate must be kept
4. in the HitEditPanel i e accept any hit pattern Coincidence Window A delay time set in the Pulse Shape Analysis section or a difference in peaking times between channels increases the overall event time Consequently the width of the coincidence window in ns has to be adjusted to accommodate the full event Usually this is done automatically by the Pixie Viewer and there is no need to edit the coincidence window manually On the other hand if the delay time is decreased a smaller coincidence window is possible This would reduce data processing time and allow for a higher event rate However to avoid overwriting a large coincidence window intentionally set by the user the value is not adjusted automatically Instead the HitEditPanel displays both the minimum coincidence window and the actual coincidence window The user can set the actual coincidence window but it should not be smaller than the minimum coincidence window Backplane Options If group trigger operation is requested in the CCSRAEditPanel each channel will respond to distributed triggers rather than own local trigger Triggers are always distributed within a module Any channel with trigger enabled will issue a trigger for distribution and any channel set to group trigger will respond to the distributed trigger including those issued by itself In addition triggers can be distributed over the PXI backplane between modules If the checkbox Share triggers with ot
5. Control Tab The readout deadtime will be higher in this mode 12 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved e Analyze On the top left part of the Analyze tab shows the run time and the measured event rate for the selected module On the right part shows for each channel the fractional live time and the input count rate Note that the run time is the sum of time spent in sub runs called spills but ignoring the time it took the host to read out the data from Pixie 4 modules Similarly the live time was measured only while one of the sub runs was ongoing MCA Spectrum Pulse height spectra accumulated in the internal Pixie 4 memory can be displayed after pressing the MCA Spectrum button Pulse heights are computed to 16 bits precision i e correspond to 64k spectra As the memory allows for only 32k words per channel bins have to be combined according to the Binning factor for each channel in the Histogram Control You can select the module you want to inspect and you can add or remove individual channel displays by clicking the MCA check boxes The Fit menu allows you to make Gaussian fits to peaks in the histograms The fit range can be set channel by channel in the Min and Max fields or by placing cursors on the spectrum with the mouse The Fit menu starts a fitting routing for one or all channels The routine does take a constant background term into account though its value is not displayed The fit results
6. amplitude vs frequency The plot is calibrated such that a sine wave with 100 ADC units amplitude 200 units peak to peak will show up with an amplitude of 100 To convert a noise floor measurement into ADC units sqrt Hz use the variable FFTbin displayed at the top of the chart which tells the width of each frequency bin in the Fourier spectrum The conversion from amplitudes to rms ADC units sqrt Hz is accomplished by multiplying with 1 sqrt 2 FFTbin Now observe that an ADC unit corresponds to 61yV Using the known gain of the Pixie 4 you can convert the noise into an input noise voltage density measured in V sqrt Hz Or given a particular energy calibration the noise density can be expressed as eV sqrt Hz If you click on the Apply Filter button you can see the effect of the energy filter simulated on the noise spectrum Run If not all described controls are visible click on the More button at the bottom of the panel Run Type This popup menu is used to set the run type to one of the following modes List Mode List mode is the general data acquisition run Waveforms energies and time stamps are collected on an event by event basis The data is stored in various formats see section 3 6 of the user manual for details 0x100 full event data 9 words plus waveforms 0x101 full event data 9 words no waveforms 0x102 compressed event data 4 words no waveforms 0x103 compressed event data 2 words no waveforms
7. cables supplied by XIA Then Switch on power of the chassis 4 After the controller booted find Pixie4 pxp in the installed folder and double click it to open the Pixie 4 Viewer Initial Startup When the Pixie 4 Viewer has been loaded the Pixie Start Up Panel should be prominently displayed in the middle of the desktop It will prompt you to do the following Specify the Pixie 4 modules First select the number of Pixie 4 modules in the system Then specify the PXI slot number in which each module resides Then click Start Up System In the IGOR history window a message will show if the modules have been initialized successfully You will now see the main Pixie Control Panel from which all work is conducted The tabs in the Control Panel are arranged in logical order from left to right For most of the actions the Pixie 4 Viewer interacts with one Pixie 4 module at a time The number of that module is displayed at the top right corner of the Control Panel inside the Module control Next to the Module control is the Channel control which specifies the current channel the Pixie 4 viewer is interacting with The Module and the Channel are the target for all actions executed from the Viewer Proceed with the steps below to configure your system 1 Inthe Calibrate tab click on the Oscilloscope button This opens a graph that shows the untriggered signal input Click Refresh to update the display The pulses sh
8. each Pixie 4 module will be read out and saved into a file If more than one spill is requested the run will resume in all modules For MCA runs when the Run time time out control counts down to 0 the Pixie 4 Viewer will issue a run stop command to stop the runs in all modules Then the MCA histogram of each module will be read out and saved into a file Stop Run If you want to stop a run before it finishes by itself you can click on this button to manually stop it This will end runs in all modules and read out and save the data Data Record Options This panel gives you three options for automating tasks after each run They are all checked by default to ensure all data are saved for each data run In addition you can choose to automatically update the MCA spectrum every 5 seconds during MCA runs or every 5 spills during List mode runs The last option changes the data readout for list mode runs If checked the module stores 32 data buffers in external memory which then are read out in a fast block read Each readout counts as one spill The total number of events will be 32 times the Maximum no of events times the Number of spills shown in the Run Control Tab External memory readout is not supported for Rev B modules If not checked buffers are read one by one from internal memory Each readout counts as one spill The total number of events will be the Maximum no of events times the Number of spills shown in the Run
9. for each channel The time between samples can be set using the dT variable The display is updated through its Refresh button The DC offset of the preamplifier signal has to be compensated for in order to bring the DC coupled input into the ADC range The exact DC value has no bearing on the acquired spectrum and its origin which is always at zero The DC adjustment is used only to ensure that the signals to be 9 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved measured fall comfortably into the ADC range When clicking the Adjust Offsets button the Pixie 4 Viewer will set the DC offset to a percentage of the full ADC range specified in the Baseline control The offset calibration must be performed with the preamplifiers connected to the Pixie 4 inputs and with both the preamplifier power and detector HV switched on One should also repeat the offset calibration each time measurement conditions change in any major way e g when the count rate changes greatly All such changes may influence the DC offset value of the preamplifier signal To analyze the noise spectrum of the acquired trace click on the FFT Display button which opens the FFTDisplay FFTdisplay You can analyze the noise spectrum in the trace captured in the Oscilloscope by observing the Fourier transform of the signal For best results remove any source from the detector and only regard traces without actual events The chart shows a plot of
10. variable indicates the maximum number of list mode events the Pixie 4 module can store in its buffer for each run It should be zero indicating unlimited events for MCA runs Synchronization The first check box asks if all modules should start and stop simultaneously In almost all multi module systems this will be the case and the box should be checked Synchronization signals are distributed over a PXI backplane line If a Pixie 4 module is present in the crate but not part of the current data acquisition setup it might inhibit the synchronization setup If you also want all timers in all modules to be reset with the start of the next data acquisition run click the box Synchronize clocks For this feature to be useful all Pixie 4 modules should be operating from the same master clock as described in the user s manual Output File You can choose a base name and a run number in order to form an output file name The run data will be written to a file whose name is composed of both The run number is automatically incremented at the end of each run if you select Auto update run number on the Data Record Options panel but you 11 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved can set it manually as well Data are stored in files in either the MCA folder if the run is a MCA run or the PulseShape folder if the run is a List Mode run These files have the same name as the output file name but different extension as descr
11. well below the processing rate Otherwise the data from the remainder of the run will be corrupted The data is stored in various formats see section 3 6 of the user manual for details 0x200 full event data 9 words no waveforms 0x201 full event data 9 words no waveforms 0x202 compressed event data 4 words no waveforms 0x203 compressed event data 2 words no waveforms MCA Mode MCA mode puts all modules into a typical spectrum only acquisition mode in which there are no list mode data required The event data is not stored in the output buffer but only used to calculate the energy for incrementing the spectrum Runs end after the time specified in the RunTime TimeOut control counts down to zero The Maximum no of Events control is set to zero for MCA runs since it is not used to end the run Any Minimum Energy entered in the Histogram Control is ignored for MCA runs Polling Time The polling time indicates the time interval at which the Pixie 4 Viewer checks if the run in the selected modules has ended If so runs are stopped in all modules if they have not stopped already and the data are read out Run Time Time Out This variable is used to indicate the total run time for MCA runs or the timeout limit for list mode runs Number of Spills The variable indicates the number of repeated runs It is only used in list mode runs Even if set to zero there will be at least one spill Maximum no of Events This
12. PIXIE 4 Online Help Version 1 20 August 2004 X Ray Instrumentation Associates 8450 Central Ave Newark CA 94560 USA Phone 510 494 9020 Fax 510 494 9040 http www xia com Disclaimer Information furnished by XIA is believed to be accurate and reliable However XIA assumes no responsibility for its use or for any infringement of patents or other rights of third parties which may result from its use No license is granted by implication or otherwise under the patent rights of XIA XIA reserves the right to change the DGF product its documentation and the supporting software without prior notice e Getting Help for the Pixie 4 There are several ways to get help for the Pixie 4 You can use IGOR s built in help browser to access the Pixie 4 specific help file by selecting Help gt Help Topics from the top menu bar Choose Pixie4 Help in the popup menu on the left and select the appropriate help topic from the list on the right Each Pixie 4 Run Control Panel also has a Help button which directly displays the help topic for that panel In the help topics click on blue underlined links to jump to cross references e Getting Started Preparations 1 Install Wavemetrics IGOR Pro 2 Install the Pixie 4 software from XIA see file readme txt on CD ROM 3 Install the Pixie 4 modules and system controller in the PXl CompactPCl crate with power switched off Connect detector signals to the Pixie 4 modules using the
13. a run at any time List Mode Traces After a list mode run has finished the pulse shape can be displayed on an event by event basis in the List Mode Traces panel The most recently acquired data file will be searched for the event required in the Event number field The display will show the ADC traces from the selected module and the associated energy for those channels that reported a hit in this event Traces and energies are scaled 13 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved as 16 bit numbers Note that the ADC traces shown in the Oscilloscope are raw 14 bit numbers i e ADC traces have values divided by 4 In order to display traces from an earlier experimental run one needs to change the Data File name by entering it directly in the Data File control or clicking the Find button If you want to see the response of the energy and trigger filters for the current event click on the Digital Filter button which opens the Filter Display tab This window is mainly intended for diagnostic purposes For information how to use the Pixie 4 for more detailed pulse shape analysis please contact XIA Filter Display This graph is used to see the simulated response of the energy and trigger filters in an event You can browse the leading edge trigger filter response and the energy filter response of individual events The latter requires a trace length of at least twice the peaking time plus the gap time to be displ
14. adjusted automatically through clicking on Adjust Offsets on the Oscilloscope The gain and offset settings are given in units of V V and V respectively The voltage gain computed is the ratio between the pulse height at the module input to the pulse height at the ADC input Note that the ADC has a 2 2V input range Histogram Control This section shows the parameters controlling the operation of the multichannel analyzer built into the DSP memory Energy values are calculated to 16 bit fixed point numbers This would correspond to a 64k spectrum To map the full energy range into the available 32k spectrum one has to combine bins At minimum 2 bins have to be combined into one so the Binning Factor has to be set to 1 combining 2 1 bins Higher binning factors can be useful for low count rate or low resolution applications 8 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved If you want to see a certain range of the spectrum at higher resolution you can enter a Minimum Energy This will discard all energies below the minimum and start binning the spectrum from the minimum energy Bin 0 Emin The minimum energy is not applied in MCA runs Decay Time The Decay Time is the exponential RC time constant of the preamplifier It is required in order to properly calculate corrections to measured energy values To set and measure the decay time enter an estimated value then click on the Auto Find button You can als
15. ation of Energy Filter panel should be fulfilled first This is to ensure that valid MCA spectra will be produced during the optimization and Gauss Fit of energy peaks on the MCA spectra will generate meaningful results The four channels of a Pixie 4 module can be used to optimize four different Auto Scanning Limits at the same time when the same detector signal is split and input into the four channels This would speed up the scanning of a large range of energy filter rise time and flat top You could change the Auto Scanning Limits of each channel by changing the Channel control on the left upper corner of the Pixie 4 Run Control panel At any time the Pixie 4 module used to carry out this optimization is the current module i e the module indicated by the Module control on the left upper corner of the Pixie 4 Run Control panel So if you want to use a different module change the Module number before you set the Auto Scanning Limits for each channel Pulse Shape Analysis The trace length and delay values to be entered here both in units of us govern the waveform acquisition Especially if you request pulse shape analysis these two parameters have to be set correctly You can use the delay parameter to move the trace Delay measures the trigger time with respect to the beginning of the recorded trace For ordinary data taking the trace lengths are up to 13 6us for each channel The waveforms will be read in 13 3ns increments from FIFO memory
16. ayed The trace is shown in red The trigger filter is shown in blue FF is for fast filter and the energy filter is shown in green SF is for slow filter List Mode Spectrum Pulse height spectra can be reconstructed from list mode data stored on the disk The file shown in the Data File field will be processed and the resulting histograms will be displayed for the selected Pixie 4 module Use Read after changing the data file to process the new data and Histo to update the displayed spectrum The full spectrum length is equal to 64k channels Use No of bins and Delta E settings to compress the spectrum such that it fits the display Hint use 8000 and 4 to see the full range of data and then adjust these numbers to zoom into the range of interest The number of bins and the deltaE variables are kept in memory for each channel individually Be sure to select the channel of interest prior to changing these variables Use the mouse to zoom in on peaks of interest In the max and min fields you can select a fit range Gauss fit will produce a Gaussian fit with constant background Displayed results are the area under the peak and the energy resolution Again the min and max variables are stored for each channel 14 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved
17. clock cycle before the end of the flat top plus the signal arrival may jitter by up to one decimated clock cycle with respect to the decimated clock You should therefore make the flat top two notches longer than the signal rise time The sum of energy filter rise time and flat top cannot exceed 127 decimated clock periods If you type in a rise time or flat top value that violates this bound the Pixie 4 Viewer will adjust it accordingly The trigger threshold can be set in units of ADC steps You can get an idea of what the noise in your system is by looking at the trace acquired in the Oscilloscope located on the Calibrate Tab Use the mouse to zoom in on parts of the displayed trace s and estimate the noise Optimize Energy Filter An optimization of energy filter settings is carried out by scanning all possible combinations of energy filter rise and flat top within their respective limits specified by the user examining the energy resolution at each combination and picking the optimal combination which gives the best energy resolution Results of this optimization including energy filter rise time flat top and energy resolution are stored in an output file whose name is specified by the user in the beginning of the run Another file which has the same name as the output file but with a different extension tmp is used to store step by step intermediate results Before starting the optimization all conditions listed on the Auto Optimiz
18. her modules is checked the module issues and responds to triggers from other modules in the system If not the module is disconnected from the backplane group triggers are only distributed between the 4 channels of the module If no channel is set to respond to group triggers this checkbox should be cleared Rev B modules are always connected to the backplane CopyPanel Settings gt Copy This panel can be used to copy parameter settings from one module to another The source module and channel are selected at the top of the panel The parameters to be copied are organized into list box in the left hand column The right hand column shows the destination channels and modules for the copy operation The Items to copy shown on the Copy Panel and the actual variables to be copied are listed below Items Actual variables to be copied Gain Gain V V Offset Offset V Filter Energy Filter Rise Time and Flat Top Baseline Cut Trigger Trigger Filter Rise Time and Flat Top Trigger Threshold FIFO Trace Length Delay dT us PSA Start PSA End CFD Threshold CSR Channel CSRA Channel CSRB Module CSRB Coinc Coincidence Pattern Coincidence Window 7 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved MCA Cut Off Energy Binning Factor TAU Tau ys INTEGRATOR Integrator After selecting source destination and parameters click on the Copy button to execute the copy operation ExtractPanel Settings gt Extract T
19. his type of discriminator The result of the computation is the time of signal arrival measured with respect to the start of the acquired waveform The result is written into the channel header in the linear output data buffer cf the User s Manual for details Integrator This variable controls the event energy reconstruction 0 Normal code 1 Use energy filter gap sum only This is equivalent to simply integrating over the pulse It is useful for scintillator applications where event energies can be derived by setting the energy filter flat top long enough to cover the whole scintillation pulses 2 Ignore energy filter gap sum when reconstructing event energy This is useful for step pulses whose amplitude is the difference between the high and low steps HitEditPanel Settings gt Module Register Edit The coincidence pattern mask is useful for Pixie 4 channels operating independently from each other though they may be sharing clocks and triggers With this mask you may require that an event as witnessed by an individual channel match any of the preset hit patterns to be accepted by the DSP An example shall illustrate this feature Assume a single module connected to 4 detectors which observe a Na 22 source emitting back to back 511keV gamma rays from positron annihilation Channels 0 and 1 are connected to one pair of back to back detectors and channels 2 and 3 are connected to a second pair of back to back detectors You are interes
20. his panel can be used to extract parameter settings from a file to selected modules and channels The source file is specified at the top of the panel Clicking on the Find button to locate the source file Parameters to be extracted and destination modules or channels are selected in the same manner as in the copy panel Click the Extract button to execute the operation AllFilesPanel Settings gt Files Paths This panel gives you access to the underlying files of the Pixie 4 software Usually these files are already loaded in the memory of the Pixie 4 Viewer You only have to change these files when you receive updates from XIA The directory locations are specified as complete not relative search paths the DSP Path for the DSP code and the FPGA Path for the trigger filter FPGA configuration Use a colon as the separator between drive name directory and subdirectories Do not use backslashes For example use D XIA data rather than D XIA data File and Path names should not exceed 80 characters Calibrate If not all described controls are visible click on the More button at the bottom of the panel Analog Signal Conditioning In the Analog Signal Conditioning section you can set the gain and DC offset for the selected channel and module Note that the ADCs are dc coupled to the Pixie 4 inputs and thus compensation for any DC offset is necessary You will rarely have to set this manually as the DC offsets can be
21. ibed below bin For list mode runs buffer data are stored in a file with name extension bin This is a binary file consisting of 16bit unsigned integers dat For list mode runs a Summary of event data is stored in a file with name extension dat This is an ASCII file mca For both list mode runs and MCA runs MCA spectrum data are stored in a file with name extension mca if you select Auto store spectrum data on the Data Record Options panel This is a binary file consisting of 32bit unsigned integers It includes MCA data for all modules ordered from channel 0 of module 0 to channel 3 of the last module set Module settings are stored in a file with name extension set after each run if you select Auto store settings on the Data Record Options panel This is a binary file consisting of 16bit unsigned integers It is equivalent to the itx files saved from the Settings tab Start Run After you have set all parameters you can start a run to take data During the run the Run time time out control shows the remaining time for MCA runs or time out count down for list mode runs If you select multiple spills for list mode runs the number of spills will also count down during the run For list mode runs when the first module reaching the preset maximum number of events stops its run it will also stop the runs in all other modules if Module Synchronization is enabled Then the data buffer of
22. mode This bit controls waveform acquisition To stop the FIFO and store a waveform two conditions must be fulfilled A fast trigger primes the FIFO to stop after a programmed delay but only if by that time a valid trigger is recorded When bit 0 is cleared the source for that valid trigger is the locally generated event trigger of this channel When bit 0 is set the trigger source will be a signal on the distributed DSP trigger line This allows for master slave operation as outlined in the User s Manual Note that a module control determines how trigger signals are distributed within and between modules If the checkbox Share triggers with other modules in the HitEditPanel is checked the module issues and responds to triggers from other modules in the system through the backplane If not the module is disconnected from the backplane group triggers are only distributed between the 4 channels of the module This is a module wide parameter If no channel is set to respond to group triggers this checkbox should be cleared Rev B modules are always connected to the backplane Bit 1 Measure individual live time This bit will in almost all applications be opposite to bit 0 Its setting decides who asserts the live time control When cleared the DSP ensures that during the event interrupt no channel can generate another trigger and latch new event data at least not after the coincidence time window see HitEditPanel below This setting is useful i
23. n master slave operation and almost in all cases where list mode data are required On the other hand when channels are operating independently and only MCA information is needed MCA mode but not list mode data then this bit should be set to achieve the highest throughput Bit 2 Good channel Only channels flagged as good will be read out This setting has no bearing on the channel s capability to issue a trigger There can be a triggering channel whose data are discarded Channels not marked as good will not be included in the automatic offset adjustment Bit 3 Read always Set this bit if you want a good channel to be read out even if it did not report a hit It cannot report valid energy or timing data in that case but if operated in group trigger mode you will get a valid waveform This way you can collect waveforms not biased by trigger requirements Bit 4 Enable trigger You can switch on any channel s ability to contribute to the event trigger with this bit Bit 5 Trigger positive For channels with triggering enabled this causes triggering on the rising edge of the input signal when the bit is set and triggering on the falling edge when the bit is not set The core of the trigger filter 5 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved FPGA can only trigger on a rising edge So if the bit is not set the FPGA will invert the signal before storing it in the FIFO and sending it to the core Bit 6 GFLT required
24. o enter a known good value directly in the control The RC calibration needs to be performed only once for a given preamplifier The result is then stored in the parameter database and can be saved in the settings file by clicking on the Save button in the Settings tab Manual Fit Manual Fit is done on a channel by channel basis First choose the channel on which you want to do the manual fit by changing the Channel control on the left upper corner of the Pixie 4 Run Control panel Then set proper dT on the TauDisplay panel and click the Run button to read an untriggered trace for the chosen channel The exponential fit range can be set either by putting the Cursors A and B on the trace or changing the Fitting start and Fitting _end controls on the TauDisplay panel Clicking the Do exponential fit button will perform the exponential fit on the portion of the trace specified by the fitting range If possible some of the baseline after the pulse should be included in the fit region The fitted tau is going to be reported in the Fitted tau control and the deviation between the fitting curve and original ADC trace is shown in the Deviation control Click the Tau Ok control to download the Tau value to the Pixie 4 module Optimize Tau The Tau optimization is carried out by scanning all Tau values within the scanning limit specified by the user examining the energy resolution at each Tau and picking the optimal Tau value which give
25. ole The Settings Tab also contains controls used to load save copy and extract settings If not all described controls are visible click on the More button at the bottom of the panel Energy and Trigger Filter In this section you can set the rise and flat top times for the energy and trigger filter of each channel The units of time are us The energy filter uses averaging of the ADC data and then operates the same filter core at a decimated i e reduced clock rate As a result there are several filter ranges with a granularity of 0 027 us for filter range 1 1 bit decimation 0 053us for filter range 2 2 bit decimation and so on You can select the filter range in the corresponding control The trigger filter is always operated at the ADC sampling rate Its rise time can be varied between 27ns and 413ns Its flat top however is valid between Ons and 387ns The trigger filter will most often use a flat top comparable 3 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved with the average signal rise time In applications with very short rise times a flat top of zero will give the best pileup rejection performance Employing a trapezoidal filter avoids the kind of ballistic deficit that occurs when a finite rise time signal is used in conjunction with a Gaussian shaper The energy filter flat top time should thus be a little larger than the longest rise time expected The output of the energy filter is sampled one decimated
26. other channels while working on only one channel You can do a Gauss fit on a peak by entering values in the Min and Max fields as the limits for a Gauss fit You can also use the mouse to drag the Cursor A and B in the MCA spectrum to the limits of the fit Enter the true energy value in the Peak field to calibrate the energy scale If you are not getting a nice looking spectrum you may need to adjust some settings such as filter rise time and flat top etc Refer to the User s Manual for details Pixie 4 Control Panel The Main Control Panel is displayed on the desktop after starting the IGOR experiment file Pixie4 pxp Using the four control tabs arranged in logical order from left to right you can set up the system set run parameters take data and view the results Control Tabs Settings Calibrate Run Analyze It also has four buttons on the bottom of the panel Start System More Help and About Start System can be used to re initialize the modules More will show additional controls on the control panel Help will open this help file at the entry corresponding to the currently active tab About will show software and hardware version information Settings The Settings Tab of the Pixie 4 Control Panel contains parameters that control the operation of the Pixie 4 Most settings are changed on a channel by channel basis The only exceptions is the coincidence pattern which affect the module as a wh
27. ould fall between about 1600 and 15000 on the left axis If no pulses are visible or if they are cut off above 16384 or below 0 click Adjust Offsets to automatically set the DC offset There is a control called Baseline on the Oscilloscope which can be used to adjust the DC offset for each channel If the pulse amplitude is too large to fall in the display range decrease the Gain in the Calibrate tab of the Pixie 4 Control Panel Since the offsets might drift for example after changes in input count rate it is useful to leave the display open and check the offsets once in a while 2 In the Calibrate tab input an estimated preamplifier RC decay time for Tau in us then click on Auto 2 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved Find to determine the actual Tau value for the current channel of the current module Repeat this for other channels if necessary The Tau finder works best for a Tau value from 20 us to 200 us 3 In the Settings tab click on Save to save the system parameters found so far You can save the settings into either an existing settings file or a new file 4 Click on the Run tab set Run Type to 0x301 MCA Mode Polling time to 1 second and Run time time out to 30 seconds or so then click Start Run After the run is complete select the Analyze tab and click on the MCA Spectrum button The MCA spectrum shows the MCA histograms for all four channels You can deselect
28. s the best energy resolution Results of this optimization including the Tau value and energy resolution are stored in an output file whose name is specified by the user in the beginning of the run Another file which has the same name as the output file but with a different extension tmp is used to store step by step intermediate results Before starting the optimization all conditions listed on the Auto Optimization of Decay Time panel should be fulfilled first This is to ensure that valid MCA spectra will be produced during the optimization and Gauss Fit of energy peaks on the MCA spectra will generate meaningful results The four channels of a Pixie 4 module can be used to optimize four different Decay Time Limits at the same time when the same detector signal is split and input into the four channels This would speed up the scanning of a large range of Tau values You could change the DecayTime Limits of each channel by changing the Channel control on the left upper corner of the Pixie 4 Run Control panel At any time the Pixie 4 module used to carry out this optimization is the current module i e the module indicated by the Module control on the left upper corner of the Pixie 4 Run Control panel So if you want to use a different module change the Module number before you set the DecayTime Limits for each channel Oscilloscope Calibrate gt Oscilloscope The Oscilloscope shows 8192 untriggered ADC samples from the input
29. ted only in gammas from positron annihilation Thus a coincidence in channel 0 and 1 or a coincidence in channel 2 and 3 is required If all 4 channels were in coincidence that would be fine too So the acceptable hit patterns would be 0 0 1 1 1 1 0 0 and 1 1 1 1 where the right most digit indicates channel 0 and the left most is for channel 3 To achieve the desired behavior you have to select the three acceptable hit patterns in the HitEditPanel by checking the appropriate boxes and deselect all other hit patterns by not checking their boxes 6 PIXIE 4 Online Help V1 20 XIA 2004 All rights reserved Note the difference between hit and trigger A hit occurs if a pulse goes over threshold and passes pileup inspection Hits can not be disabled A trigger means there is a hit plus a request for event processing is sent to the module s DSP unit Triggers can be disabled on a channel by channel basis in the CCSRAEditPanel Event processing is still subject to the four channels showing an acceptable hit pattern Furthermore each channel is only processed if it shows a hit or is marked as read always in the CCSRAEditPanel Only hit channels will have valid energy and timing information but all channels will have waveforms In general with 4 channels there are 16 distinct possible hit patterns and you can select any combination of these to be a valid event If you want to disable this feature you should check all boxes
30. that are displayed include the peak position the number of counts in the peak and its relative and absolute full width at half maximum FWHM calculated from the Gaussian fit For best results be sure to extend the fit range to cover some of the constant background To calibrate your energy scale you can after the fit type the true energy value into the field Peak and the scale will automatically be adjusted The Sum menu gives you three options of summing the spectrum You can either sum the range defined by the Min and Max fields without any corrections sum the range and subtract the background or sum the entire MCA Summing is performed on all four channels at the same time The calculated Sum is displayed in the Peak Area field and the MCA maximum of the sum range is displayed in the Peak field The Files popup menu allow to store individual spectra and read back stored spectra from disk There are three operations Save MCA to Igor text file will save the current MCA 4 channels as a scaled wave with some added comments in a text file This can be useful to import data into other applications Read MCA from Igor text file will read back a Igor text file saved as above Extract MCA from binary file will read MCA data for the current module from a binary file such as the mca file automatically saved at the end of the run The file is assumed to be in 32bit unsigned integer format You can Update the MCA during
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