Difference between revisions of "Fast neutron damage to HPGe Detector"

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An observable decrease in the energy resolution of large HPGe detectors was first seen after the irradiation of 5*10^7 n/cm^2<ref>P. H. Stelson, J. K. Dickens, S. Raman, and R. C. Trammell, “Deterioration of Large Ge(Li) Diodes Caused by Fast Neutrons,” Nuclear Instruments and Methods 98,481 (1972).</ref>. I choose a factor of ten below that value to be the maximum allowable neutron irradiation.  
 
An observable decrease in the energy resolution of large HPGe detectors was first seen after the irradiation of 5*10^7 n/cm^2<ref>P. H. Stelson, J. K. Dickens, S. Raman, and R. C. Trammell, “Deterioration of Large Ge(Li) Diodes Caused by Fast Neutrons,” Nuclear Instruments and Methods 98,481 (1972).</ref>. I choose a factor of ten below that value to be the maximum allowable neutron irradiation.  
  
The maximum neutron flux from a point source will occur exactly at the center of the detector face, where the expression for integral flux over a period <math>\Delta t</math>is simply: <math>\Delta t\times  n_{rate}\frac{1}{4\pi d^2}</math>, where <math>n_{rate}</math> is the neutron rate of the source.   
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The maximum neutron flux from a point source will occur exactly at the center of the detector face, where the expression for integral flux over a period <math>\Delta t</math> is simply: <math>\Delta t\times  n_{rate}\frac{1}{4\pi d^2}</math>, where <math>n_{rate}</math> is the neutron rate of the source.   
  
 
The number of days it would take to reach an integral flux of 5*10^6 n/cm^2, as a function of the distance from source to HPGe face is shown below. The calculation uses a neutron rate of 19,066 <math>\pm</math> 300 n/s, which was the neutron rate of the CF-252 source on 01/2017 (see [[Cf-252 FTC-CFZ-431| here]] for discussion of source rates).
 
The number of days it would take to reach an integral flux of 5*10^6 n/cm^2, as a function of the distance from source to HPGe face is shown below. The calculation uses a neutron rate of 19,066 <math>\pm</math> 300 n/s, which was the neutron rate of the CF-252 source on 01/2017 (see [[Cf-252 FTC-CFZ-431| here]] for discussion of source rates).

Revision as of 09:10, 29 December 2016

An observable decrease in the energy resolution of large HPGe detectors was first seen after the irradiation of 5*10^7 n/cm^2<ref>P. H. Stelson, J. K. Dickens, S. Raman, and R. C. Trammell, “Deterioration of Large Ge(Li) Diodes Caused by Fast Neutrons,” Nuclear Instruments and Methods 98,481 (1972).</ref>. I choose a factor of ten below that value to be the maximum allowable neutron irradiation.

The maximum neutron flux from a point source will occur exactly at the center of the detector face, where the expression for integral flux over a period [math]\Delta t[/math] is simply: [math]\Delta t\times n_{rate}\frac{1}{4\pi d^2}[/math], where [math]n_{rate}[/math] is the neutron rate of the source.

The number of days it would take to reach an integral flux of 5*10^6 n/cm^2, as a function of the distance from source to HPGe face is shown below. The calculation uses a neutron rate of 19,066 [math]\pm[/math] 300 n/s, which was the neutron rate of the CF-252 source on 01/2017 (see here for discussion of source rates).


MaxHPGeCF252Time.png

  • The formula used in the graph above is,

[math]y=\frac{5\times 10^6}{(19066 * 60^2 * 24 * \frac{1}{(4*\pi * x^2)})}[/math]


References

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