Main Page/PHYS 4210/Gamma Ray Spectroscopy - Revision history

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Gloria at 21:07, 12 December 2018

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Gloria at 19:15, 7 March 2018

2018-03-07T19:15:17Z

Gloria at 19:12, 7 March 2018

2018-03-07T19:12:09Z

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 <ol>
 <li>Preston and Dietz,[https://www.library.yorku.ca/find/Record/1038893 ''The Art of Experimental Physics''], Wiley.</li>
-<li>G.F. Knoll, ''Radiation Detection and Measurement, 3rd or 4th ed.'', Wiley. </li>
+<li>G.F. Knoll, [https://ocul-yor.primo.exlibrisgroup.com/permalink/01OCUL_YOR/mc13rm/alma991008455689705164 ''Radiation Detection and Measurement''], Wiley. </li>
 <li>J.L. Duggan, ''Laboratory Investigations in Nuclear Science'', Tennelec.</li>
 <li>A.C. Melissinos, [https://www.library.yorku.ca/find/Record/1641963 ''Experiments in Modern Physics''], Academic Press.</li>

@@ Line 138: / Line 138: @@
 <p>Besides sum peaks another complication can occur for high-energy gamma rays. When pair creation is an important energy deposition mechanism, so-called escape peaks are observed. These correspond to events where one or more of the created electrons/positrons escape the crystal without giving up their energy. Such peaks occur at ''E<sub>g</sub>'' - ''j'' (0.511 MeV), where ''j'' is the number of escaped electrons/positrons. Since we do not use sources with ''E<sub>g</sub>'' > 2 MeV in this experiment, we do not find this complication in our spectra.</p>
-<h1>Experimental Procedure</h1>
+<h2>Experimental Procedure</h2>
 <p>While conducting the experiment, make sure that only the source whose spectrum you are observing is near the apparatus otherwise your calibration results will be skewed. Take only one source out at a time, and keep the others in the box away from the detector. Be careful while handling sources. Become familiar with the documentation and all the apparatus before starting. </p>
@@ Line 144: / Line 144: @@
 <p>In our setup, we have mounted the PMT vertically, allowing you to place the source on a tray at several different distances from the source. Once you have found an optimal distance for all three sources (i.e. you do not get ‘pile up’ effects (see Leo)), it is best to use this distance for calibration and determination of the peak energies. However, in the last part of the experiment you will be asked to draw qualitative conclusions by placing a source at varying distances. </p>
-<h2>Settings</h2>
+<h1>Settings</h1>
 <p>Please ensure the following running parameters</p>
 <ul>
@@ Line 162: / Line 162: @@
 <ol>
 <h3>Calibration Curve</h3>
-<li><p>Use Experiment 2.1 as a guide for gamma ray calibration from Duggan in the red binder in the lab. The eMorpho software will only be used for data collection and observing the spectra. All data analysis, including energy calibration, can be conducted using software like Excel or Mathematica. Use the 5 known sources Cs-137 (0.662 MeV), Co-60 (1.173 MeV, 1.332 MeV), Mn-54 (0.835 MeV), Na-22 (0.511 MeV) and Zn-65 (1.115 MeV) provided in the RSS 8 radiation source kit (Spectrum Techniques). Centre each source (label down) about 5 cm from the face of the detector and collect a spectrum for at least 5 minutes with each source. Longer collection times correspond to smaller statistical errors, why? <b>Stop collection prior to saving and record the dead time, live time and real time for each spectrum.</b> Save the spectrum. (The .csv file generated contains a single column with MCA parameters in the first 74 entries followed by the spectrum data (number of events) in each channel from 0 to 4096. Prior to data analysis delete the first 74 entries. Create a calibration curve using all five sources i.e. for each spectrum locate the channel number corresponding to the gamma ray energy peaks and create a plot of the energy of each peak and the peak channel number. What is the error of a straight line fit to this curve?  If the fit is poor, you have made a mistake in assigning peak-channel values, and may have to repeat the analysis. Discuss sources of error. </p>
+<li><p>Use Experiment 2.1 as a guide for gamma ray calibration from Duggan in the red binder in the lab. The UCS 30 software will only be used for data collection and observing the spectra. All data analysis, including energy calibration, can be conducted using software like Excel or Mathematica. Use the 4 known sources Cs-137 (0.662 MeV), Co-60 (1.173 MeV, 1.332 MeV), Mn-54 (0.835 MeV) and Na-22 (0.511 MeV) provided in the RSS 8 radiation source kit (Spectrum Techniques). Centre each source (label down) about 5 cm from the face of the detector and collect a spectrum for at least 5 minutes with each source. Longer collection times correspond to smaller statistical errors, why? <b>Stop collection prior to saving and record the dead time, live time and real time for each spectrum.</b> Save the spectrum. (The .csv file generated contains a single column with the UCS 30 parameters in the first 18 rows followed by the spectrum data (number of events) in each channel from 0 to 1023. Create a calibration curve using all five sources i.e. for each spectrum locate the channel number corresponding to the gamma ray energy peaks and create a plot of the energy of each peak and the peak channel number. What is the error of a straight line fit to this curve?  If the fit is poor, you have made a mistake in assigning peak-channel values, and may have to repeat the analysis. Discuss sources of error. </p>
 <p>Using your calibration fit plot the calibrated Cs-137 spectrum, Co-60 spectrum and Na-22 spectrum separately(i.e. events as a function of energy). Explain all the peaks on the spectra. Do you see any 'sum peaks’? (Plot your data on a logarithmic scale for a better view!) Explain why this peak occurs. Does it occur at the value you expect? What is the source of the 511 keV peak in the Na-22 spectrum? The Na-22 has a gamma ray energy at 1275 keV. What value of the maximum position do you find based on your calibration curve?  Is this consistent with the resolution ''dE/E''? What is the present activity of these three sources (note the date marked on the source)? Present the calibrated spectra in your report and explain all the interesting details.</p> </li>
 <li><p> Put a sheet of lead on the shelf and then place the Co-60 source above. How does the spectrum change?  Now place the sheet of lead on top of the source. What, if anything, has changed in the spectrum?  You may have to move the source closer or farther from the detector to observe the backscattering signals. Collect a spectrum for each case for a sufficient collection time and save. <b> Caution: Always wear gloves when handling the lead sheets.</b></p> </li>
@@ Line 171: / Line 172: @@
 <li> Place the Cs-137 source at varying distances from the detector and explain qualitatively the rates that you observe. Put the source at slot 2 below the detector, and place first one, then two, and then three sheets of lead on top of the source. Comment on the rates, and the reason for the observed behaviour. Repeat for sheets of aluminum.</li>
 <li> A spectrum of the unknown source (the background in the room) will be collected by the Lab Technologist. The data will be saved and the file can be found in the "data" folder located on the desktop.  Using this data, create a calibrated spectrum using your calibration fit. Use your now-calibrated gamma-ray spectrum to identify the radioisotope(s) found in the background.</li>
 </ol>

@@ Line 111: / Line 111: @@
   </p>
-<p> Turn the power on the spectrum analyzer (UCS 30) and run the program "USX" located on the desktop. </p>
+<p> Turn the power on the spectrum analyzer (UCS 30) and run the program "USX" located on the desktop. (The UCS 30 manual is located on the desktop and should be referred to for additional information.)  Hover over the toolbar icons and note the descriptions.  Click on each icon and note the options available.  For example, you can toggle between a linear and logarithmic y-axis scale by clicking on the "y-log" icon on the toolbar.  Additionally, during data collection you can adjust the scale of the y-axis by scrolling up and down when the mouse is in the graph region.  Review the operation section (pg 16-25) of the UCS30 lab manual. </p>
 <!-- <p> There are two programs required for the computer to be able to get data from the eMorpho MCA. First, ''MDS.exe'' on the desktop needs to be run in order to start the data server. Second, the software to control the settings and acquire data is ''EMorpho Client v1.0.exe'' and is on the desktop. Run this program and become familiar with its control for monitoring in the pulse height and taking a histogram. </p> -->
-<p>The signal from the PMT is directly input to a multichannel analyser which is a device that sorts incoming pulses according to pulse height and keeps count of the number at each height in a multichannel memory. The contents of each channel is displayed on a screen to give a pulse height spectrum, which is then analysed. The amplitude of the incoming pulse is digitized with an Analogue to Digital Converter (ADC), and sorting is done based on how many pulses had a particular value of the digitized amplitude. The total number of channels into which the voltage range is digitized determines the resolution of the MCA. Read the Bridgeport eMorpho manual to understand the characteristics of the electronics you are supplied with, and to learn more about the ADC range and resolution that can be achieved. Read ref. 1, 2, 4 to understand the functions of a MCA. Review what is meant by ‘dead time’ and ‘live time’. Do not operate with a dead time of more than 30%, since too high count rates can cause the electronics to misbehave.</p>
+<p>The signal from the PMT is directly input to a multichannel analyser which is a device that sorts incoming pulses according to pulse height and keeps count of the number at each height in a multichannel memory. The contents of each channel is displayed on a screen to give a pulse height spectrum, which is then analysed. The amplitude of the incoming pulse is digitized with an Analogue to Digital Converter (ADC), and sorting is done based on how many pulses had a particular value of the digitized amplitude. The total number of channels into which the voltage range is digitized determines the resolution of the MCA. Refer ref. 1, 2 and 4 to understand the characteristics of the electronics you are supplied with, and to learn more about the ADC range and resolution that can be achieved. Also, use ref. 1, 2, 4 to understand the functions of a MCA. Review what is meant by ‘dead time’ and ‘live time’. Do not operate with a dead time of more than 30%, since too high count rates can cause the electronics to misbehave.</p>
-<p>To understand this experiment it is crucial to observe the pulses fed from the scintillator/PMT to the MCA. This can be done using the Bridgeport eMorpho Client v1.0 on the desktop. This is the software which controls the parameters of the MCA and displays the acquired data. By selecting the "Pulse" icon along the top, you can observe the shape of pulses coming from the MCA. You will observe high-amplitude pulses (high energy was recorded since many visible photons were produced), as well as lower-amplitude pulses occurring randomly in rapid succession. The MCA records the pulse heights and the software assembles them into a histogram according to channel number. One can then calibrate the channels using known gamma sources.</p>
+<!--<p>To understand this experiment it is crucial to observe the pulses fed from the scintillator/PMT to the MCA. This can be done using the Bridgeport eMorpho Client v1.0 on the desktop. This is the software which controls the parameters of the MCA and displays the acquired data. By selecting the "Pulse" icon along the top, you can observe the shape of pulses coming from the MCA. You will observe high-amplitude pulses (high energy was recorded since many visible photons were produced), as well as lower-amplitude pulses occurring randomly in rapid succession. The MCA records the pulse heights and the software assembles them into a histogram according to channel number. One can then calibrate the channels using known gamma sources.</p>-->
 <p>The natural linewidth of the gamma rays is extremely narrow (a few eV compared to the MeV range of the energies themselves!). The broadening observed in the recorded spectra is a result of the detection method (a cooled Germanium detector would show these lines being much narrower, but again at a resolution that depends on the detector itself). It is important to realize on the example of the Cs137 spectrum, for which a single energy at 0.662 MeV is expected that several effects occur in ‘real life’:</p>
 <ol>
@@ Line 141: / Line 140: @@
 <h1>Experimental Procedure</h1>
 <p>While conducting the experiment, make sure that only the source whose spectrum you are observing is near the apparatus otherwise your calibration results will be skewed. Take only one source out at a time, and keep the others in the box away from the detector. Be careful while handling sources. Become familiar with the documentation and all the apparatus before starting. </p>
 <h2>Settings</h2>
 <p>Please ensure the following running parameters</p>
 <ul>
-<li>High-Voltage to PMT: +1000V (set on the actual power supply)</li>
+<li>High-Voltage to PMT: +1000V (Click on the "Amp/HV/ADC" icon on the toolbar to set and turn on the voltage.)</li>
-<li>Electronic Gain: 2</li>
+<li>Amplifier Gain: Use the course gain and fine gain controls to set the gain in the range of 16 - 18. </li>
-<li>Digital Gain: 4096</li>
+<li>Conversion Gain: 1024</li>
-<li>Integration Time: 0.625</li>
+<li>Peak Time: 1 micro sec</li>
 </ul>
-<p> <b>Note:</b> The <b>trigger threshold</b> located under the Settings tab should be set to 14. </p>
+<!--<p> <b>Note:</b> The <b>trigger threshold</b> located under the Settings tab should be set to 14. </p>-->
 <table width=500 align=center><td>
 <p align=justify>[[File:Gam-fig4.png|700px|border|center]]

@@ Line 96: / Line 96: @@
 <h2>The Multichannel Analyser (MCA)</h2>
 <p> The electrons collected at the anode of the PMT pass directly into the Spectrum Techniques MCA (UCS 30). This pulse of electrons enters the internal pre-amplifier, followed by the internal amplifier. The voltage across the internal amplifier resistance is digitized into one of 1024 bins according to its maximum value (peak height)- this process of converting an analog voltage into a digital value is called analog-to-digital conversion (ADC). The MCA performs this task for all pulses and creates a histogram of counts in each ADC bin.</p>
-<p>There are several important parameters which affect the performance of the MCA.
+<p>There are several important parameters which affect the performance of the MCA.  For a detailed explanation of the pulse processing details refer to the book by Knoll, "Radiation Detection and Measurements" listed in the references section below.
 <ul>
 <!-- <li><b>Electronic Gain: </b> As mentioned above, setting this parameter changes the value of the resistance that the PMT current is being passed through. The allowed values are 0-100 Ohm, 1-430 Ohm, 2- 1100 Ohm, 4- 3400 Ohm. These values are with the eMorpho. </li>
 <li><b>Digital Gain: </b> Once passing through the ADC, the resulting value can then be further scaled by this amount. This is useful if one is trying to match up bin number to a calibrated energy in eV.</li>-->
 <li><b>Lower Level Discriminator (LLD) :</b> The amount above the average background which is required for the MCA to accept a particular pulse and record its statistics in the histogram.</li>
 <li><b>Run Time: </b> The actual length of time for which to acquire data.</li>
@@ Line 106: / Line 107: @@
 <li><b>Dead Time:</b> The time during collection when the detector is unable to process additional events.   Look up live time and dead time and discuss in your report.</li>
 <li><b>High Voltage: </b> The parameter "high voltage" in the MCA client software does nothing. Bridgeport makes an HV supply for PMTs which connect directly to the eMorpho. We are using a separate power supply, hence adjusting this parameter in the software does nothing. However, changing the 1000V supplied to the PMT from the power supply will mean that more electrons are collected per pulse. If this dc voltage is set too high and and too many photons are present, there could be a buildup of charge inside the PMT and catastrophic damage could occur.<i>Please do not change the setting of the voltage to the PMT from 1000V.</i></li>
-<li><b>Hold off time: </b>This is the time after detection of a pulse for which the MCA will not register the detection of another pulse. In practice, this should be set to a few times the 1/e decay time of a pulse to avoid another trigger event occurring from the decay of the pulse which was just recorded.</li>
+<!--<li><b>Hold off time: </b>This is the time after detection of a pulse for which the MCA will not register the detection of another pulse. In practice, this should be set to a few times the 1/e decay time of a pulse to avoid another trigger event occurring from the decay of the pulse which was just recorded.</li>-->
 </ul>
   </p>

@@ Line 63: / Line 63: @@
 <h2>The Radioactive Sources</h2>
-<p>You will be working with five radioactive sources: Mn-54, Zn-65, Na-22, Cs-137, and Co-60. You should note the radiation dosage and date marked on the source, and read about radiation safety and how to handle radiation sources from ref. 1, pg 326-328. Calculate the number of disintegrations per second for each of the sources based on the quoted dosage.</p>
+<p>You will be working with five radioactive sources: Mn-54, Na-22, Cs-137, and Co-60. You should note the radiation dosage and date marked on the source, and read about radiation safety and how to handle radiation sources from ref. 1, pg 326-328. Calculate the number of disintegrations per second for each of the sources based on the quoted dosage.</p>
 <h2>The Detector</h2>
@@ Line 95: / Line 95: @@
 <h2>The Multichannel Analyser (MCA)</h2>
-<p> The electrons collected at the anode of the PMT pass directly into the Spectrum Techniques MCA (UCS 30). This pulse of electrons is passed across a resistor whose value is set by the user (using the "electronic gain" parameter). The voltage across this resistor is digitized into one of 1024 bins according to its maximum value (peak height)- this process of converting an analog voltage into a digital value is called analog-to-digital conversion (ADC). The MCA performs this task for all pulses and creates a histogram of counts in each ADC bin.</p>
+<p> The electrons collected at the anode of the PMT pass directly into the Spectrum Techniques MCA (UCS 30). This pulse of electrons enters the internal pre-amplifier, followed by the internal amplifier. The voltage across the internal amplifier resistance is digitized into one of 1024 bins according to its maximum value (peak height)- this process of converting an analog voltage into a digital value is called analog-to-digital conversion (ADC). The MCA performs this task for all pulses and creates a histogram of counts in each ADC bin.</p>
 <p>There are several important parameters which affect the performance of the MCA.
 <ul>
-<li><b>Electronic Gain: </b> As mentioned above, setting this parameter changes the value of the resistance that the PMT current is being passed through. <!--The allowed values are 0-100 Ohm, 1-430 Ohm, 2- 1100 Ohm, 4- 3400 Ohm. These values are with the eMorpho. --></li>
+<!-- <li><b>Electronic Gain: </b> As mentioned above, setting this parameter changes the value of the resistance that the PMT current is being passed through. The allowed values are 0-100 Ohm, 1-430 Ohm, 2- 1100 Ohm, 4- 3400 Ohm. These values are with the eMorpho. </li>
-<li><b>Digital Gain: </b> Once passing through the ADC, the resulting value can then be further scaled by this amount. This is useful if one is trying to match up bin number to a calibrated energy in eV.</li>
+<li><b>Digital Gain: </b> Once passing through the ADC, the resulting value can then be further scaled by this amount. This is useful if one is trying to match up bin number to a calibrated energy in eV.</li>-->
 <li><b>Lower Level Discriminator (LLD) :</b> The amount above the average background which is required for the MCA to accept a particular pulse and record its statistics in the histogram.</li>
 <li><b>Run Time: </b> The actual length of time for which to acquire data.</li>

@@ Line 163: / Line 163: @@
 <li> Obtain the energy resolution for the photopeak for Cs-137 and for one of the Co-60 peaks (See Knoll, chapter 4). Does this agree with what you have learned about scintillator devices? </li>
 <li> Place the Cs-137 source at varying distances from the detector and explain qualitatively the rates that you observe. Put the source at slot 2 below the detector, and place first one, then two, and then three sheets of lead on top of the source. Comment on the rates, and the reason for the observed behaviour. Repeat for sheets of aluminum.</li>
-<li> Attain an unknown source from the Lab Technologist. Collect a spectrum and calibrated using you calibration fit. Use your now-calibrated gamma-ray spectrometer to identify the radio isotope(s) in the unknown source.</li>
+<li> A spectrum of the unknown source (the background in the room) will be collected by the Lab Technologist. The data will be saved and the file can be found in the "data" folder located on the desktop.  Using this data, create a calibrated spectrum using your calibration fit. Use your now-calibrated gamma-ray spectrum to identify the radioisotope(s) found in the background.</li>
 </ol>