In situ gamma-ray spectrometry for environmental monitoring: a semi empirical calibration method

Abstract

In situ gamma spectrometry using high-purity germanium (HPGe) detectors is a frequently used method for the determination of radionuclide ground deposition levels. Such measurements do, however, require an efficiency calibration based on detector sensitivity and parameters such as soil density and vertical activity distribution. In this work, a novel expression is used for the detector efficiency, incorporating both the influence of photon energy and incidence angle. Detector-specific efficiency data are determined empirically. For the theoretical calculation of the photon fluence at the detector, a three-layer model of finite thickness is developed for the description of soil density and vertical activity distribution. In order to facilitate the calibration of in situ measurements, a PC program has been developed to enable rapid, on-site calculations of radionuclide ground deposition levels. The semi empirical calibration method was tested on in situ measurements with two different detectors, and the results show good agreement with results obtained from traditional soil sampling.

Evaluation of Monte Carlo-based calibrations of HPGe detectors for in situ gamma-ray spectrometry

“…Results from site 1 have been previously reported by Boson et al (2006). The sites chosen display a fairly wide range of activity levels and also represent a variety of different soil and vegetation types.…”

“…Two different soil corers were used, with radii 2.4 and 2.15 cm, respectively. The sampling and sample preparation procedures were previously described in detail (Boson et al, 2006). At site 4, one of the samples was excluded, as the second and third layers were mistakenly put into the same plastic bag.…”

“…Calibration factors for the in situ measurements were calculated using both a previously described semi-empirical method (Boson et al, 2006) and Monte Carlo simulations. For both methods, a three-layer model previously described by Boson et al (2006), was used for the description of soil density and activity depth distributions.…”

“…For both methods, a three-layer model previously described by Boson et al (2006), was used for the description of soil density and activity depth distributions. Source matrix data (i.e.…”

Monte Carlo simulation by GEANT 4 and GESPECOR of in situ gamma-ray spectrometry measurements

“…In the present version several distributions S(z) are included: (a) the model of several uniform slabs (Boson et al, 2006); (b) a numerical profile of the distribution; (c) exponential or linear distributions, defined by the characteristic parameters. In the case of the numerical profile of the distribution, a linear interpolation is used between the tabulated values.…”