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Semi-empirical method for self-absorption correction of photons with energies as low as 10 keV in environmental samples
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics.
2002 In: Nuclear Instruments and Methods in Physics Research A, Vol. 484, 625-641 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2002. Vol. 484, 625-641 p.
Identifiers
URN: urn:nbn:se:uu:diva-90005OAI: oai:DiVA.org:uu-90005DiVA: diva2:162009
Available from: 2002-10-04 Created: 2002-10-04Bibliographically approved
In thesis
1. Optimisation of environmental gamma spectrometry using Monte Carlo methods
Open this publication in new window or tab >>Optimisation of environmental gamma spectrometry using Monte Carlo methods
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dissertation in Environmental Physics to be publicly examined in Häggsalen (Ångström Laboratory), Uppsala University, on Friday, November 8, 2002 at 10:00 am for the degree of doctor of philosophy in Physics. The examination will be conducted in English.

Gamma spectrometry is one of the tools commonly used for the measurement of various environmental radionuclides. Simultaneous determination of the absolute activity of gamma emitting radiotracers in a wide range of environmental matrices and fractions necessitates proper and accurate evaluation of the sample-to-detector efficiency. Several radiotracers require, in addition, the use of sub-routines for self-absorption corrections.

Gamma spectrometry is an important and elegant tool for assessing environmental changes. Optimisation of ultra low-level gamma spectrometry for reliable assessment of such changes requires harmonisation of laboratory needs with sampling and site conditions.

Different aspects of the calculation of sample-to-detector efficiencies using empirical and Monte Carlo approaches are discussed here, including the uncertainties related to the simulation of the performance of different HPGe detectors and the effects of the incomplete collection of charges in Ge-crystals. Various simulation codes for the computation of peak efficiencies in planar and well Ge-detectors have been developed from scratch. The results of the simulations have been tested against experimental data and compared to other simulation results obtained with the Monte Carlo N-Particle code (MCNP). The construction of calibration sources with improved absorption and collimation characteristics have been, also, described in this work. These sources have been especially designed for the efficiency calibration of Ge-detectors at energies below 100 keV.

Flexible, fully tested and prototype approaches for the evaluation of self-absorption corrections, based on Monte Carlo simulations, are described. Special consideration is given to the problems related to the sample's variability in size, density and composition. Several examples of the absolute and simultaneous determination of environmental multitracers which benefited from self-absorption corrections and the optimised efficiency calibration algorithms are, also, presented and discussed. These examples include, among other things, a comprehensive analysis of the gamma spectrometry of 234Th in a wide range of matrices and the speciation of several radionuclides in sediments from a hard-water lake.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2002. 64 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 751
Keyword
Physics, Gamma spectrometry, Environmental multitracers, Monte Carlo simulations, HPGe detectors, Efficiency calibration, Self-absorption corrections., Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-2672 (URN)91-554-5399-6 (ISBN)
Public defence
2002-11-08, Häggsalen (Ångström Laboratory), Uppsala, 10:00
Opponent
Available from: 2002-10-04 Created: 2002-10-04 Last updated: 2014-01-21Bibliographically approved

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