How to Calculate Detection Probability of Alpha Particles from a 241Am Source?

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Discussion Overview

The discussion revolves around calculating the detection probability of alpha particles emitted from a 241Am source using a silicon detector. Participants explore the geometric factors affecting detection, the impact of distance, and the conditions under which alpha particles can be detected.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks to calculate the number of alpha particles detectable from a 241Am source with a given activity and distance to the detector.
  • Another participant suggests considering the fraction of the surface area of a sphere that the detector covers, raising the importance of geometry in the calculation.
  • A participant asserts that with a vacuum between the source and detector, energy loss of alpha particles is minimal, which may enhance detection probability.
  • There is a proposed formula for calculating the fraction of radiation that the detector can capture, but the correctness of the calculation is questioned.
  • One participant states that if the detector is perfect, the geometric ratio can represent the probability of detection, but acknowledges that imperfections in the detector require additional data for accurate probability assessment.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the detector's geometry and the conditions affecting alpha particle detection. There is no consensus on the correctness of the proposed calculations or the assumptions made regarding the detector's performance.

Contextual Notes

Limitations include assumptions about the detector's efficiency and the isotropic emission of radiation from the source. The discussion does not resolve the mathematical steps involved in calculating the detection probability.

india
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Probability for detection !

I have to calculate the probability of alpha particle or photon being detected by Si detector from the 241Am source. How to know no of alpha that can be detected from the 241Am source ?? source have acticity of 3.7kBq and distance between source and detector is 35mm. as well the area of square detector is 8*8mm2.
 
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Consider a sphere with a radius of 35mm - which fraction of the surface area does your detector cover?
If you have air or some other material between source and detector, alpha particles might lose their energy before they reach the detector.
 


So there will be the vacuum inbetween source and detector. So there will be very less chance for energy loss of alpha, That can be detected at 35mm distance. Also there is no material in between.
Area of detector is 64mm^2, and distance is 35mm. So i think fraction of surface are covers detector (or fraction of total radiation) can be given by, A/(4pi*R^2)=64/4*pi*34*35 = 0.0042
Am I right ?
and If so, then How to get the probability out of it ?

mfb said:
Consider a sphere with a radius of 35mm - which fraction of the surface area does your detector cover?
If you have air or some other material between source and detector, alpha particles might lose their energy before they reach the detector.
 


So there will be the vacuum inbetween source and detector. So there will be very less chance for energy loss of alpha, That can be detected at 35mm distance. Also there is no material in between.
Area of detector is 64mm^2, and distance is 35mm. So i think fraction of surface are covers detector (or fraction of total radiation) can be given by, A/(4pi*R^2)=64/4*pi*34*35 = 0.0042
Am I right ?
and If so, then How to get the probability out of it ?
 


If your detector is perfect, that ratio is the probability simply by geometry (and assuming your source emits radiation in all directions with the same intensity, e.g. there is no shielding in the source itself). If it is not perfect, you need additional data about the detector.
 

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