Difference between revisions of "CH HPGe Efficiency"

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The conversion from ADC Channel to KeV is as follows:
 
The conversion from ADC Channel to KeV is as follows:
  
<small><math> Photon\ Energy\ (KeV)=0.398344*(Channel\ Number)-28.5131 </math></small>
+
<center><small><math> Photon\ Energy\ (KeV)=0.398344*(Channel\ Number)-28.5131 </math></small></center>
  
 
==='''Background Spectrum'''===
 
==='''Background Spectrum'''===

Revision as of 00:04, 28 July 2022

Efficiency Measurements Summer 2022

Electronics Chain

Click here to view the electronics chain used for these efficiency measurements.

Experimental Setup

Measurements

Energy Calibration

A linear regression was performed on the ADC Channel Number - Peak Energy data set. The data set is included in the table below.

Peak Number ADC Channel Number Eu152 Peak Energy (KeV)
1 689 244.70
2 937 344.28
3 1105 411.12
4 1187 443.96
5 2025 778.90
6 2247 867.37
7 2490 964.08
8 2796 1085.9
9 2862 1112.1
10 3607 1408.0

The conversion from ADC Channel to KeV is as follows:

[math] Photon\ Energy\ (KeV)=0.398344*(Channel\ Number)-28.5131 [/math]

Background Spectrum

On Axis

90 Degrees Off Axis

Past Work

Most likely incorrect

Eu152 Calibration

  • HPGe calibrated using Eu152 source
CH Eu152 Calibration Spectrum.png

As of 9/28/21

The calibration used to map from ADC channel number to KeV is:

[math]Photon\ Energy\ =\ -36.2928\ +\ 0.449519\ x\ -\ 0.000000861277\ x^2[/math]

Where x = channel 9 of the ADC and is input as PADC.PADC785N[9].

Total Efficiency

This is total efficiency using the Gadolinium foil as the source.

[math] (line\ intensity)\ (incident\ thermal\ neutrons\ per\ second)\ (\sigma_{total})\ (MCNP\ fudge\ factor\ from\ Paul\ approx\ 4)\ =\ Theoretical\ Rate [/math]

For the ease of calculation, I will use the outgoing photon rate from the Gd foil as tabulated by MCNP, thanks to Paul Stonaha. The number given was into 2pi, towards the HPGe detector, multiplying by 2 should give the rate into 4pi.

The 897 KeV peak found in the Gd in/out measurements can be attributed to two different lines created by neutron capture on Gd157. The high purity germanium detector used in this experiment would not be able to resolve the two distinct lines as the resolution is not fine enough. However, adding the intensities together should yield the theoretical rate for the peak measured at that energy.

The first peak is 897.506 KeV with a relative intensity of 17.846%, according the capgam nndc data repository.

The second peak is 897.62 KeV with a relative intensity of 16%, according the capgam nndc data repository.

(0.17846 + 0.16) (2*1374Hz) (234000) = Rate

234000 is the total thermal neutron capture cross section for 157Gd

Note: the fudge factor comes from the nucleus being excited and then de-exciting from the neutron absorption and emits on average, 4 photons per neutron capture

Then find detected rate using HPGe

Divide (detected rate) by (theoretical rate) for total detector efficiency

An easier way to calculate the detector efficiency is

[math]Det.\ Eff.\ =\ \frac{Detected\ Rate}{(Normalized\ Line\ Intensity)(Theoretical\ Total\ Rate)}[/math]

Theoretical total rate = 2748 Hz from simulations

Line Energy Line Weighting Detected Rate Detector Efficiency
897 KeV (2 lines) 0.03967382135 0.357 Hz 0.33% [math]\pm[/math] 0.03
1107 KeV 0.02885336857 0.264 Hz 0.33% [math]\pm[/math] 0.03
~1186 KeV (2 lines) 0.05145546699 0.511 Hz 0.36% [math]\pm[/math] 0.03

Previous Page

CaGaS Phase II

PAS_Experiment

PAS HPGe Detector