In situ gamma-ray spectrometry models in fresh fallout and monitoring situations- An overview of current radionuclide monitoring capacity in the field
Publish date: 2020-08-10
Report number: FOI-R--4917--SE
Pages: 23
Written in: Swedish
Keywords:
- gamma-ray spectrometry
- in-situ
- depth distribution
- preparedness model
- radioactive fallout
- environmental radiology
Abstract
For in situ gamma-ray spectrometry, the calibration factor used for calculating ground deposition levels depends on the geometric distribution of radionuclides in, or on, the ground. Models describing these distributions have through the years been developed at FOI. The multiple slab model can give a good description of the total calibration factor despite some geometrical simplifications and assumptions. Here, the soil profile is discretised in an appropriate number of slabs, each with a soil density, thickness and relative activity contents and their uncertainties. A software (developed at FOI) making this correction is synoptically described herein. Relation wise efficiency calculations are presented for different detectors and hypothetical deposition models. Calculations indicate over- and underestimations of ground deposition of no more than tens of percent by choosing an unrealistic model. However, a larger variation in the detector field-of-view is observed between models. An investigation of the importance of slab thickness on the efficiency calibration for two activity depth profiles is presented and discussed. Recommendations on appropriate choices of terms in the function fitting step preceding correction is presented.