Analysis of HPGe spectra by spectrum matching--experimental verification.

A new approach to spectrum analysis in gamma-ray spectrometry has recently been proposed, based on channel-by-channel matching of the measured spectrum with calculated synthetic spectra. In this paper, verification of the new method against experimental data and a comparison with the standard approach to the analysis of HPGe spectra is presented.

Twenty-year follow-up study of radiocesium migration in soil.

The profile of (137)Cs present in undisturbed soil due to the Chernobyl accident was measured repeatedly for approximately 20 y. The vertical migration of (137)Cs in soil is a very slow process. The mean vertical migration velocity is estimated at approximately 0.1-0.2 cm y(-1). A method based on in situ gamma spectrometry measurements and Monte Carlo computations, aimed at estimating the profile of (137)Cs without performing any soil sampling, is investigated.

Monte Carlo calculation of entire in situ gamma-ray spectra.

We present a method for the synthesis of entire in situ gamma-ray spectra based on Monte Carlo calculations and measured data that characterize the detector properties. The method can serve for the determination of the effective depth of 137Cs in soil based on the information contained in the low-energy part of an in situ spectrum. Effective depth is defined as the depth of a plane distribution of 137Cs beneath the surface that reproduces the fluence energy and angular distribution at 1 m above the ground of gamma rays belonging to the real 137Cs distributions. We managed to reproduce the measured in situ spectra with our method and to demonstrate that the method allows the determination of the effective depth of 137Cs with a precision of 10(-2) m. The method requires minimal experimental characterization of the detector and is not sensitive to the details of the detector model and the soil composition and density employed in the Monte Carlo calculations.

Analysis of gamma-ray spectra from HPGe detectors in field conditions without explicit energy calibration.

A novel approach to the analysis of high-resolution gamma-ray spectra from HPGe detectors is presented. Identification of the nuclides contributing to the spectrum is performed in an energy-calibration-free manner by a correlation technique. The performance of the system proves to be robust with a possibility of integrating a high degree of expertise. This is most suitable for in-field emergency applications, where intelligent software is of essential importance. The approach is also suitable for laboratory analysis in less experienced laboratories, where HPGe detectors are used sporadically.

Automated construction of detector models for efficiency interpolation in gamma-ray spectrometry.

A method was developed for automated construction of detector models in gamma-ray spectrometry, which can be used in Monte Carlo calculations of efficiency calibration curves. Full-energy peak efficiencies were first measured for different gamma-ray energies and for a given sample-detector arrangement and then calculated by the Monte Carlo method. For these calculations a detector model was employed along with a computer algorithm, which seeks agreement between the experimental efficiencies and the calculated ones by automatically determining the parameters of the model. The resulting agreement of the calculated data with the experimental one was within the relative uncertainty of the latter (3-4%) and the parameters of the detector models obtained were close to the values specified by the manufacturers. The detector models thus constructed can then be used for interpolation of calibration curves.

A theoretical description of diffusion and migration of 137Cs in soil.

Careful measurements of activity concentrations of 137Cs in soil samples taken layer by layer in autumn of 1999 in Slovenia are confronted with a prediction based on the diffusion-convection equation with a boundary condition which--unlike the boundary conditions applied in the literature so far--conserves the deposited activity over time, except for the natural decay. It is shown that it is essential to consider the deposits from atmospheric nuclear weapons tests and the Chernobyl accident to arrive at a good fit to the measured data. The corresponding Green's function as well as the diffusion constant and migration speed based on the analysis are given.

Monte Carlo determination of gamma-ray dose rate with the GEANT system.

Conversion factors for the dose rate 1 m above the ground level from the measured activities for different gamma-ray emitters in soil are calculated using the Monte Carlo method. The calculations are based on the GEANT system developed at CERN, Geneva. Results for the uniform and surface distribution of the emitters in the soil are given for gamma-ray energies in the interval between 20 keV and 3 MeV. They are similar to those of the recent report of ICRU that indicates that GEANT system is suitable for application in health physics problems. For 137Cs the dose rates for plane sources at different depths are given, which allow for the calculation of the dose rate for any depth distribution of the activity in the soil.