Difference between revisions of "KJM-FYS 5920 Lab Exercise 2 - Student Report"

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(Undo revision 81 by Ingerru@uio.no (Talk))
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University of Oslo 1<sup>st</sup> October 2010  
 
University of Oslo 1<sup>st</sup> October 2010  
  
<br>
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<br>  
  
 
==== Introduction  ====
 
==== Introduction  ====
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(Written by:&nbsp;Jon Petter Omtvedt)  
 
(Written by:&nbsp;Jon Petter Omtvedt)  
  
<br>
+
<br>  
  
<br>
+
<br>  
  
 
==== Detector and Preamplifier Signals  ====
 
==== Detector and Preamplifier Signals  ====
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(Written by: Pejman)  
 
(Written by: Pejman)  
  
<br>
+
<br>  
  
 
==== Spectroscopy Amplifier Setup &amp;&nbsp;Signals  ====
 
==== Spectroscopy Amplifier Setup &amp;&nbsp;Signals  ====
  
 
(Written by: Martin)  
 
(Written by: Martin)  
 
<br>
 
 
==== ADC&nbsp;and MCA Setup  ====
 
 
ADC (or A/D) means analog to digital converter. The ADC is a fundamental link between analog and digital electronics as it converts information in an analog signal to an equivalent digital form. This happens by the ADC accepting input pulses of 0-10V and converting these to digital numbers ranging from 0-8195. (The ranges here are from the device used in the experiment, the voltage- and digital number range may differ from model to model.) E.g for this device an input pulse of 2.0V would be converted to the digital number 1639.
 
 
MCA means multi-channel analyzer. Together with the ADC it forms a unit which sorts out and keeps count of the different pulses, and stores the count of each pulse in a multi-channel memory. The memory channel adress corresponds to the digitized value of the signal. In this way the pulses received from the detector system are sorted out and counted according to pulse height (voltage), which is proportional to the gamma energy. The total number of channels into which the voltage range is digitized is known as the conversion gain, and it determines the resolution of the MCA. <br>It can be connected to a computer, or another output device, in order to view the acquired spectre (Counts per channel).<br>
 
 
[[Image:Basic mca.jpg|frame|center|Basic architecture of a MCA]]
 
 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br>
 
 
The SA is connected to the ADC/MCA for conversion of the enhanced pulses. The next step is to adjust the gain, we want 0.5keV per channel. <sup>137</sup>Cs has a gamma peak at 662keV, this energy then corresponds to channel number 1324. What voltage should the incoming pulses have? The answer is channel number divided by total channel number times the maximum voltage in the range of the ADC, here (1324/8195)*10V=1.62V. <br>With 137-Cs in front of the detector, we adjust the gain until we see pulses about 1.62V on the oscilloscope. The gain is then 10.348 and the MCA should now have a resolution of 0.5keV per channel. <br>Now the ADC/MCA unit is ready for connection to a computer to view the acquired spectre, and for further calibration.<br>
 
 
[[Image:Pulse to spectre.jpg|frame|center|Analog to digital conversion. The channel number given by the ADC is proportional to the amplitude of the incoming pulse.]]
 
  
 
<br>  
 
<br>  
 
[[Image:SpecAmp and ADC-MCA 01Oct2010.jpg|thumb|center|221x205px|ADC/MCA and SA units.]]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 
 
(Written by: Tomas)
 
 
KJM-FYS&nbsp;5920 Lab&nbsp;Exercise 2 report (Autumn 2010):
 
 
== Setting up a HPGe gamma-spectroscopy system  ==
 
 
Participating students (authors): '''Tomas''' Kvalheim Eriksen, '''Alexander'''&nbsp;Mauring,&nbsp;'''Therese''' Renstrøm, '''Inger Eli''' Ruud, '''Pejman''' Mansouri Samani,&nbsp;'''Martin''' Ytre-Eide, '''Sindre''' Øvergaard.
 
 
Teachers:&nbsp;Prof. '''Jon Petter''' Omtvedt&nbsp;and '''Hilde-Therese''' Nyhus (lab assistant)&nbsp;
 
 
University of Oslo 1<sup>st</sup> October 2010
 
 
<br>
 
 
==== Introduction  ====
 
 
(Written by:&nbsp;Jon Petter Omtvedt)
 
 
<br>
 
 
<br>
 
 
==== Detector and Preamplifier Signals  ====
 
 
(Written by: Pejman)
 
 
<br>
 
 
==== Spectroscopy Amplifier Setup &amp;&nbsp;Signals  ====
 
 
(Written by: Martin)
 
 
<br>
 
  
 
==== ADC&nbsp;and MCA Setup  ====
 
==== ADC&nbsp;and MCA Setup  ====
Line 101: Line 49:
 
[[Image:SpecAmp and ADC-MCA 01Oct2010.jpg|thumb|center|221x205px|ADC/MCA and SA units.]]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
 
[[Image:SpecAmp and ADC-MCA 01Oct2010.jpg|thumb|center|221x205px|ADC/MCA and SA units.]]&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  
  
(Written by: Tomas)
+
(Written by: Tomas)  
  
 
==== Calibration  ====
 
==== Calibration  ====
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The signals from the main amplifier are analysed by the ADC/MCA unit. Information from the MCA is received by the lab-computer in the form of a histogram; number of counts pr energy bin. We use the spectrum analysis program MAESTRO to look at the resulting spectra. Since the detector has an approximately linear response, we have that:  
 
The signals from the main amplifier are analysed by the ADC/MCA unit. Information from the MCA is received by the lab-computer in the form of a histogram; number of counts pr energy bin. We use the spectrum analysis program MAESTRO to look at the resulting spectra. Since the detector has an approximately linear response, we have that:  
  
E_gamma = a * ch + b, &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(1)  
+
E_gamma = a * ch + b, &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;(1) where we ignore higher order terms. To determine the two unknowns, a and b, in (1) we need two equations. So we need two known gamma energies and their corresponding channel number. Co-60 has two prominent peaks, one at 1173 keV and one at 1332 keV. This radioactive isotope provides excellent calibration for energies in this region. In the spectrum we observed three strong peaks. The unknown peak appeared to come from the considerable concentration of K-40 in the concrete walls of the lab. Table of Isotopes gives one gamma energy for K-40, E_gamma = 1460 keV. This peak would correspond to the highest of the three detected peaks. We also tested this theory by removing the Co-60 source. The two peaks with the lower energy disappeared as expected. The reason why the background line was so strong, was that we did not shield the source with lead blocks. A rough calibration was performed with Co-60. We need an additonal calibration-point at lower energy to get a more accurate calibration for low gamma energies. Co-57 has clear, separable peak ( KLADD: bad at low E. one peak from Co-57(122keV). good sep in E. zero in zero. adjust energy pr channel. )  
where we ignore higher order terms.  
 
To determine the two unknowns, a and b, in (1) we need two equations. So we need two known gamma energies and their corresponding channel number. Co-60 has two prominent peaks, one at 1173 keV and one at 1332 keV. This radioactive isotope provides excellent calibration for energies in this region. In the spectrum we observed three strong peaks. The unknown peak appeared to come from the considerable concentration of K-40 in the concrete walls of the lab. Table of Isotopes gives one gamma energy for K-40, E_gamma = 1460 keV. This peak would correspond to the highest of the three detected peaks. We also tested this theory by removing the Co-60 source. The two peaks with the lower energy disappeared as expected. The reason why the background line was so strong, was that we did not shield the source with lead blocks. A rough calibration was performed with Co-60. We need an additonal calibration-point at lower energy to get a more accurate calibration for low gamma energies. Co-57 has clear, separable peak ( KLADD: bad at low E. one peak from Co-57(122keV). good sep in E. zero in zero. adjust energy pr channel. )  
 
  
 
<br>  
 
<br>  
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<br> (Written by: Therese and Inger Eli )  
 
<br> (Written by: Therese and Inger Eli )  
  
<br>
+
<br>  
  
 
==== Detector Performance  ====
 
==== Detector Performance  ====
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(Written by: Alexander and Sindre)  
 
(Written by: Alexander and Sindre)  
  
<br>
+
<br>  
  
 
==== Conclusion  ====
 
==== Conclusion  ====
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(Written by: )  
 
(Written by: )  
  
<br>
+
<br>  
  
<br>
+
<br>  
  
 
==== Teachers Remarks  ====
 
==== Teachers Remarks  ====
  
 
+
[[Category:Gamma_spectroscopy]] [[Category:Laboratory_exercise]] [[Category:Electronics]] [[Category:Germanium_detector]] [[Category:HPGe_detector]]
 
 
[[Category:Gamma spectroscopy]][[Category:Laboratory exercise]][[Category:Electronics]][[Category:Germanium detector]][[Category:HPGe detector]]
 
 
 
==== Detector Performance  ====
 
 
 
(Written by: Alexander and Sindre)
 
 
 
<br>
 
 
 
==== Conclusion  ====
 
 
 
(Written by: )
 
 
 
<br>
 
 
 
<br>
 
 
 
==== Teachers Remarks  ====
 
 
 
 
 
 
 
[[Category:Gamma spectroscopy]][[Category:Laboratory exercise]][[Category:Electronics]][[Category:Germanium detector]][[Category:HPGe detector]]
 

Revision as of 13:35, 11 October 2010

KJM-FYS 5920 Lab Exercise 2 report (Autumn 2010):

Setting up a HPGe gamma-spectroscopy system

Participating students (authors): Tomas Kvalheim Eriksen, Alexander Mauring, Therese Renstrøm, Inger Eli Ruud, Pejman Mansouri Samani, Martin Ytre-Eide, Sindre Øvergaard.

Teachers: Prof. Jon Petter Omtvedt and Hilde-Therese Nyhus (lab assistant) 

University of Oslo 1st October 2010


Introduction

(Written by: Jon Petter Omtvedt)



Detector and Preamplifier Signals

(Written by: Pejman)


Spectroscopy Amplifier Setup & Signals

(Written by: Martin)


ADC and MCA Setup

ADC (or A/D) means analog to digital converter. The ADC is a fundamental link between analog and digital electronics as it converts information in an analog signal to an equivalent digital form. This happens by the ADC accepting input pulses of 0-10V and converting these to digital numbers ranging from 0-8195. (The ranges here are from the device used in the experiment, the voltage- and digital number range may differ from model to model.) E.g for this device an input pulse of 2.0V would be converted to the digital number 1639.

MCA means multi-channel analyzer. Together with the ADC it forms a unit which sorts out and keeps count of the different pulses, and stores the count of each pulse in a multi-channel memory. The memory channel adress corresponds to the digitized value of the signal. In this way the pulses received from the detector system are sorted out and counted according to pulse height (voltage), which is proportional to the gamma energy. The total number of channels into which the voltage range is digitized is known as the conversion gain, and it determines the resolution of the MCA.
It can be connected to a computer, or another output device, in order to view the acquired spectre (Counts per channel).

Basic architecture of a MCA

                                            

The SA is connected to the ADC/MCA for conversion of the enhanced pulses. The next step is to adjust the gain, we want 0.5keV per channel. 137Cs has a gamma peak at 662keV, this energy then corresponds to channel number 1324. What voltage should the incoming pulses have? The answer is channel number divided by total channel number times the maximum voltage in the range of the ADC, here (1324/8195)*10V=1.62V.
With 137-Cs in front of the detector, we adjust the gain until we see pulses about 1.62V on the oscilloscope. The gain is then 10.348 and the MCA should now have a resolution of 0.5keV per channel.
Now the ADC/MCA unit is ready for connection to a computer to view the acquired spectre, and for further calibration.

Analog to digital conversion. The channel number given by the ADC is proportional to the amplitude of the incoming pulse.


ADC/MCA and SA units.
                                                    

(Written by: Tomas)

Calibration

Bilde av 2 energitopper til Co-60 

The electrical signal from the Ge-detector has now propagated through many components that has both shaped and enhanced the pulse. The energy of interest is of course that deposited by the gamma in the detector. The Gaussian-like pulse produced in the main amplifier will have an amplitude proportional to the gamma-energy.

The signals from the main amplifier are analysed by the ADC/MCA unit. Information from the MCA is received by the lab-computer in the form of a histogram; number of counts pr energy bin. We use the spectrum analysis program MAESTRO to look at the resulting spectra. Since the detector has an approximately linear response, we have that:

E_gamma = a * ch + b,                                    (1) where we ignore higher order terms. To determine the two unknowns, a and b, in (1) we need two equations. So we need two known gamma energies and their corresponding channel number. Co-60 has two prominent peaks, one at 1173 keV and one at 1332 keV. This radioactive isotope provides excellent calibration for energies in this region. In the spectrum we observed three strong peaks. The unknown peak appeared to come from the considerable concentration of K-40 in the concrete walls of the lab. Table of Isotopes gives one gamma energy for K-40, E_gamma = 1460 keV. This peak would correspond to the highest of the three detected peaks. We also tested this theory by removing the Co-60 source. The two peaks with the lower energy disappeared as expected. The reason why the background line was so strong, was that we did not shield the source with lead blocks. A rough calibration was performed with Co-60. We need an additonal calibration-point at lower energy to get a more accurate calibration for low gamma energies. Co-57 has clear, separable peak ( KLADD: bad at low E. one peak from Co-57(122keV). good sep in E. zero in zero. adjust energy pr channel. )




(Written by: Therese and Inger Eli )


Detector Performance

(Written by: Alexander and Sindre)


Conclusion

(Written by: )



Teachers Remarks