Natural Gamma radiation is found in different environments. However when it comes to detecting these radiation many of modern devices assign only the number of radiation particles as count per unit time such as per second, per minutes (Cps/Cpm) as count rates, emitted from those radioelements. This post will assist you and give a basic idea on how you can convert these count rates into their elements contents. Keep enjoying the post!
Energy Spectrum of Natural radiation
From the figure spectrum energy has energy peaks at 1.46Mev, 1.76Mev and 2.62 Mev. Through these peaks one can distinguish gamma rays from K, U, and Th.
Energy Windows
Channel 1: Total Count 0.4 - 3.00 Mev
Channel 2: Potassium 1.36 - 1.56 Mev
Channel 3: Uranium 1.66 - 1.86 Mev
Channel 4: Thorium 2.42 - 2.82 Mev
Converting Counts rates into Elements Contents
Gamma Ray Spectrometer (GRS) measures radiation in the form of Count rates (Count Per unit time).
How is the conversion done?
First before conversion the GRS is calibrated, then gamma counts are converted into element contents such as Potassium ( in K%), Uranium (U) and Thorium (Th) in ppm.
Then the following formula are adapted to get element Contents from such counts
Thorium : All gamma rays from Thorium channel originating only from Thorium.
Th (ppm) = K1 × Tc
Uranium : Uranium channel records gamma rays from Thorium and Uranium
U (ppm) : K2(Uc - S1Tc)
Where
K1 - Constant for Thorium Channel
K2 - Constant for Uranium Channel
S1 - Stripping Ratio
Potassium (K%): Potassium channel records gamma rays from both Thorium and Uranium channels
K% = K3 (Kc - S2 [Uc - S1Tc] - S3Tc)
Where
K3 - Constant for Potassium Channel
S2 and S3 - Stripping Ratio for Uranium and Thorium gamma rays recorded in K.
Then If six (6) constants are known then one can convert gamma Ray counts into elements contents.
Converting Concentration of radioelements K, U & Th into equivalent Dose rate
If you want to do monitoring of hazardous radiation, at a given site after having Concentration of the radioelements you can use the equation here down to have the dose rate,
D = 0.0833 × E [Grasty et al.,1991]
But E = 1.505(K%) + 0.653 [U(ppm)] + 0.287 [Th(ppm)] (IAEA,1991)
Where D - Dose rate (mSvy-1)
E - Exposure rate (μRh-1)
IAEA - International Atomic Energy Agency.
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