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Dear all,
My name is Oscar Merino. I have been using by the first time a Gamma ray detector for measuring Gamma Ray in a carbonate succession. It is a Ludlum Model 3 Survey Meter with a Model 44-2 Gamma Scintillator. Measurements are taken in μSv/h and I would like to convert them into API units for representing gamma-ray logs. Which is the equivalence or the conversion factor?
Thank you very much

Dear Oscar,

You may want to try the following linear conversion from uSv/h to API units.
However, I am not sure it will be the exact conversion for your particular scintillation counter.

GR(API units) = [200/(C2 -C1)] x GR(uSv/h)

You need to measure two different count rates C1 and C2 at two different carbonate sections, which have appreciable difference in count rates, so that you will have a better estimation of the slope.
Here, it is assumed that your counter does not have an offset at zero radiation. which is equivalent to 0 API units.

Dear kokokyi,
Thank you very much for your help.
In the section in which we measured the gamma ray log there are different litologies including: a) light grey crinoidal grainstones with very low gamma ray, shales with an intermediate-high values and several ash layers with the highest gamma ray. Could we use the gamma ray value of the ash layers as C2 and the value of the light grey crinoidal grainstone as C1?
Cheers

Yes, you can use the GR in the ash layer as C2 and the GR in the light grey grainstones as C1. As long as you have enough difference between the two count rates to give you a good gradient, it should be alright. Once again, it is assumed that there is NO offset in your scintillation counter at ZERO radiation, meaning to say the counter reads zero at zero background radiation.