### 38B57 quantitative (food) measurents

Posted:

**13 Nov 2018, 08:22**Hi folks,

my initial goal when stepping into gamma spectrometry was to make quantitative measurents of Cs137 in food samples (mushrooms).

Actually, it was harder than expected. I got a 38B57 tube and a GS-1100 Pro together with theremino MCA.

At the end I think I did it and would like to share the results to anyone interested:

Steps solved:

- estimate efficiency function over keV from sources with known ratio of different peaks (actually only Ra226, Cs137 and Th232 are halfways useful?!, I do not have other sources)

- measure efficiency from a point source around max 10cm of the probe (currently only in front of it at arbitrary radius from the middle) => making a regression of the 2D field =>now I can calculate the geometric influence of an arbitrary probe dimension with any distance from the scintillator

- making a food sample from mushroom (ash) and have it tested by a lab => now the total efficiency can be calibrated against the professional measurement. Together with the information above any other size of sample can be used and measured.

Now I am x2 away from efficiencies given in the literature (for a 3" only) and could be happy so far, but it is only one comparison.

Did anyone of you also try to do quantitative measurements (at least for Cs137)? I'd be happy to share some experience and provide my results if somebody is interested.

Greetings from Nuremberg,

Martin

PS: If you have some idea where to get nice sources from (e.g. from Europe) please let me know. I do not need and like hot sources or sources that produce radioactive dust. Best is something less than 500Bq. Best would be a calibrated source, but it is almost impossible to get one over here for private usage as well as only weak sources....

my initial goal when stepping into gamma spectrometry was to make quantitative measurents of Cs137 in food samples (mushrooms).

Actually, it was harder than expected. I got a 38B57 tube and a GS-1100 Pro together with theremino MCA.

At the end I think I did it and would like to share the results to anyone interested:

Steps solved:

- estimate efficiency function over keV from sources with known ratio of different peaks (actually only Ra226, Cs137 and Th232 are halfways useful?!, I do not have other sources)

- measure efficiency from a point source around max 10cm of the probe (currently only in front of it at arbitrary radius from the middle) => making a regression of the 2D field =>now I can calculate the geometric influence of an arbitrary probe dimension with any distance from the scintillator

- making a food sample from mushroom (ash) and have it tested by a lab => now the total efficiency can be calibrated against the professional measurement. Together with the information above any other size of sample can be used and measured.

Now I am x2 away from efficiencies given in the literature (for a 3" only) and could be happy so far, but it is only one comparison.

Did anyone of you also try to do quantitative measurements (at least for Cs137)? I'd be happy to share some experience and provide my results if somebody is interested.

Greetings from Nuremberg,

Martin

PS: If you have some idea where to get nice sources from (e.g. from Europe) please let me know. I do not need and like hot sources or sources that produce radioactive dust. Best is something less than 500Bq. Best would be a calibrated source, but it is almost impossible to get one over here for private usage as well as only weak sources....