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MWoot
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Homework Statement
The issue I have is that I am asked to estimate the activity of a small source of gamma radiation; the question is written below:
'A small source of gamma radiation is placed at a distance of 160mm from a detector of area 18mm^2. The count recorded on the detector after 30 minutes was 15804. Estimate the activity of the source.
2. The attempt at a solution
As I understand it, activity in Becquerels is just the rate of decay of a given nucleus, i.e. 1Bq is one nucleus decay per second. I have calculated the 'counts-per-minute' of the source, simply as (15804/30)=526.8CPM, or 8.78 Counts per second. I have read in various places that the CPM can be converted into Becquerels 'if one applies a number of significant conversions that take into account the radiation background, the detector efficiency, the counting geometry, the sample size, and the self-absorption of the radiation by the sample.' The only relevant information to take into account in this example if the sample size/counting geometry, since the area of the detector and the distance of the source from the detector is given. The total volume of the area between the detector and the γ source is (160*18)=2880mm^3, or 2.88*10^-6m^3 as I understand it.
The answer given is 1.57*10^5 Bq.
Help would be massively appreciated, as I am completely stumped