Source radioactivity estimate from a radiation detector

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If I have a source of radioactivity that is concentrated instead of evenly spread out, like a "tablet" source instead of a evenly distributed aerosol/dust on ground for example then is it possible to even estimate the total number of disintegrations (Becquerels per second) by measuring the activity some distance away from the "tablet" point source? Or is this type of measurement mainly used for approximate personal dose estimate.

Let's say I have a decent gain and sensitivity GM tube type detector some distance away from my point source. Let's say I don't know the type of isotope giving off the radiation , all I get are certain amount of "clicks" that represent the amount of radiation hitting my tube minus the ones that don't get counted due to the limited efficiency of the tube.
So would I then knowing the efficiency of my detector could estimate the total radioactivity of the source by then measuring the distance from the source and using that distance as radius and then integrating over an imaginary sphere around the source where the distance from the source to my detector is the radius. I guess I would also need to know the size of my tube in order to know the size of the surface "patches" that I have to integrate over the sphere surface.
Is this the only method to approximate the total count rate per second of the source in my described situation?
Could I in any way also know the isotope I'm looking at solely based on this information (distance to source, integrated total surface activity) ? It seems I couldn't.
 

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  • #2
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Also could I estimate the isotope if I used a scintillation detector?
I know these types of detectors can determine the incoming energy and are used to do radiation spectroscopy but can that only be done in a controlled environment where the sample is brought in and fixed at a certain know distance from the detector preferably in a closed barrel that shields the detector from outside radiation sources (background) or can it also be used "out in field" applications but then how does one know the total count rate of a point source , does one have to follow the same integration that I said above?

PS. I wonder is the same integration used to get the total count rate even in a lab scintillation setting as the detector usually is of a limited size and the radiation from a sample goes out in all directions?
 
  • #3
gleem
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If you do not know the isotope then you can only estimate the exposure rate assuming gamma/xrays. Each isotope has a unique half-life that determines the activity. The isotope can be identified by its gamma ray/x-ray spectrum.

To determine the activity of a source you must know the position of the source relative to the detector, know the efficiency of the detector for the radiation it detects, know the area of the aperture that the radiation to reach the detector, know the characteristics of the scattered radiation that reaches the detector if any.

Activity is often measured with a detector that is able to intercept most or all of the radiation such as a "well counter", a liquid scintillation detector or a gas flow counter which has the source placed within the detector.

The best way to measure the activity of a source is to identify the isotope and then calibrate the detector with a standard source of that isotope leaving only an inverse law correction unless it is a beta emitter where you must account for the absorption of the beta particles in the air or even in the source.
 

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