Trinitite @ 1945

[Peter-1]

hello,
I make an attempt to calculate the activity of Trinitite at the time it was created in 1945. As a starting point i measured a sample of trinitite with 4 grams. My geiger counter showed 0.13 µSv/h as the background and an activity of 0.3 µSv/h at a distance of 3cm with trinitite. 0.3 µSv/h - 0.13 µSv/h = 0.17 µSv/h. With the dose rate constant for Cs 137, a value of approx. 1.6 kBq can then be calculated. Cesium 137 has a half-life of 30.2 years and the 1945 event was 75 years ago. Thus 17.9% of the activity is still preserved. That means the activity was 5.58 times higher in 1945. 1.6 kBq * 5.58 = 9 kBq (at 1945).
Extrapolated from my 4 grams to 1 kg, it is 2.2 MBq /kg. By comparison, 1 kg nat. Uranium ~ 12 MBq /kg. Now my question: can this calculation be correct? I think that the part of Am241 is too small to have a strong influence on the calculation.

Peter

[cicastol]

It is not so simple, you need to consider branch ratio , for example 661keV gamma decay happens only 85% , remaining is B- , so you need also to consider the beta efficiency of the detector at given energy and then take account of the geometry error because it is not a point source and neither a uniform field radiation......
Calculating the real total activity in a specimen ,especially with multiple isotopes ,is not an easy task.