GammaVision
®
v7 (A66-BW) 783620H / 1013
6.10.6.1. External Absorption
The external absorption is used when the source is separate from the absorber, as in a source in a metal can. All of the gamma rays from the source must pass through all of the absorber before reaching the detector. The corrected peak areas are the spectrum peak areas multiplied by the correction as:
(88)
where:
A = the peak area at energy E
μ = the table value at energy E; normally the mass attenuation coefficient
x = the absorption factor; a function of the sample weight, density, or thickness such that it is in inverse units of
μ (Length, entered on the Corrections tab)
For values between the table values, the
μ are linearly interpolated between the table values using the natural logarithms of the
μ values and their associated energies when using the coefficient table. If the spectrum is being used to calculate the
μ values, linear interpolation is used on the
μ values and their associated energeis to obtain μ between energies. The correction value is always 1 or greater.
6.10.6.2. Internal Absorption
The internal absorption is used when the source and the absorber are mixed together, such as soil or sand samples. Some of the gamma rays pass through no part of the absorber and some pass through the entire sample. The following formula for the corrected areas assumes that the absorbing matrix is homogeneous and that the source is uniformly distributed in the matrix.
(89)
where:
A = the peak area at energy E
μ = the table value at energy E; normally the mass attenuation coefficient
x = the absorption factor; a function of the sample weight, density or thickness such that it is in inverse units of
μ (Length, entered on the Corrections tab)
Internal Absorption Correction
For other absorbing conditions, these approximations might not apply. The corrections should be checked against a known situation to ensure that these conditions are met for the current analysis situation.
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