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In situ measurements of radionuclide concentration in soil: An investigation into detector properties and methods
Stockholm University, Faculty of Science, Department of Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In case of a release of radioactive nuclides into the environment it is necessary to  have reliable methods to estimate the potential effect on people and the ecosystem. In this context the total activity deposited, the elemental composition and the depth distribution are of importance.

An efficient in situ method to estimate the average contamination over larger areas using high purity germanium (HPGe) detectors has been developed. The method combines simulation of photon transport with measured detector properties. The total activity of 137Cs determined from gamma-ray spectra recorded in situ are compared to results from soil sampling.

Another in situ method has been developed to determine the depth distribution of a radionuclide contamination, using an array of small detectors inserted into the ground, as an alternative to the standard procedure of soil sampling. The possibility to use cadmium telluride (CdTe) detectors as well as lanthanum bromide (LaBr3) detectors has been investigated. As a demonstration of the developed method the small-scale variation of the activity distributions in an area covering 350 m2 have been measured and is compared to results obtained by other methods.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2010. , 80 p.
Keyword [en]
In situ gamma-ray spectrometry, LaBr3, CdTe, Cs-137, soil samples
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-47398ISBN: 978-91-7447-192-2 (print)OAI: oai:DiVA.org:su-47398DiVA: diva2:373882
Public defence
2011-01-28, sal FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted. Available from: 2011-01-03 Created: 2010-12-01 Last updated: 2010-12-02Bibliographically approved
List of papers
1. Development of methods to use CdTe detectors in field measurements
Open this publication in new window or tab >>Development of methods to use CdTe detectors in field measurements
2006 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 41, 523-526 p.Article in journal (Refereed) Published
Abstract [en]

We are currently investigating the possibility to use CdTe detectors for in situ determinations of radionuclide concentration in soil. Buried activity can be reliably determined by a comparison of the count rate in the photo peak and the region between the photo peak and Compton edge. However, the pulse-height spectrum from CdTe detectors is severely deteriorated, due to poor charge collection, in particular for high gamma-ray energies. Our efforts have, therefore, been concentrated on improving the peak to valley ratio for such detectors. A simple, non-discriminating, algorithm for the analysis of output from two amplifiers with different shaping times is described. By means of this algorithm the peak-tovalley ratio for a small planar CdTe detector is improved by more than a factor of six compared to the uncorrected ratio without loss of efficiency.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-12515 (URN)10.1088/1742-6596/41/1/060 (DOI)
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2010-12-02Bibliographically approved
2. Efficient in situ method to determine radionuclide concentration in soil
Open this publication in new window or tab >>Efficient in situ method to determine radionuclide concentration in soil
2005 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 547, no 2-3, 400-410 p.Article in journal (Refereed) Published
Abstract [en]

A simple realisation of the so-called peak-to-valley method is described combining simulations of photon transport in soil with measured detector properties. Comparisons regarding the total activity of Cs-137 determined from gamma spectra recorded in situ to results from soil sampling show excellent agreement for six different sites in Sweden with different surface properties and activities ranging from 15 to 1000 kBq/m(2). These results are quite insensitive to assumptions regarding soil composition. Our results for the burial depth are more sensitive to assumptions regarding soil composition, however, still in general agreement with the results from the soil samples.

Keyword
in situ gamma-ray spectrometry; peak-to-valley methods; measured detector response
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-12474 (URN)10.1016/j.nima.2005.03.143 (DOI)
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2010-12-02Bibliographically approved
3. Investigation into the properties of CdTe detectors for in-situ measurements
Open this publication in new window or tab >>Investigation into the properties of CdTe detectors for in-situ measurements
2008 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 596, no 3, 409-416 p.Article in journal (Refereed) Published
Abstract [en]

As part of a program investigating means to improve gamma-ray spectra obtained with CdTe detectors, we report results obtained with two 10×10×5 mm^3 CdTe detectors, one planar the other of quasi-hemispheric geometry. Applying a combination of cooling and pulse rise-time discrimination with the quasi-hemispheric detector, we obtain a resolution of 4 percent at 662 keV and a peak-to-valley ratio of 92 at a loss of approximately 25 percent of the counts in the full-energy region.

Keyword
CdTe, Gamma-ray spectra, Rise-time discrimination
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-14868 (URN)doi:10.1016/j.nima.2008.08.132 (DOI)000261369000020 ()
Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2010-12-02Bibliographically approved
4. In-situ method to determine depth distribution of buried activity
Open this publication in new window or tab >>In-situ method to determine depth distribution of buried activity
2011 (English)In: Applied Radiation and Isotopes, ISSN 0969-8043, E-ISSN 1872-9800, Vol. 69, no 5, 773-779 p.Article in journal (Refereed) Published
Abstract [en]

A method is described to determine the depth distribution of buried activity offering an alternative to conventional soil sampling and laboratory analysis by in-situ measurements with small detectors inserted into the ground. As ad demonstration of the method small-scale variations in the distribution of Cs-137 in a riparian marsh in central-eastern Sweden are determined using lanthanum bromide detectors (LaBr3). The results show variations of the activity ranging between 400 and 2200 kBq/m^2 over an area not exceeding 350 m^2. The decrease of the average activity since 2003 coincides with the physical decay indicating that no net redistribution of activity into this part of the marsh has occurred during the inter weening years.

Keyword
In-situ gamma-ray spectroscopy, LaBr3, soil samples, caesium-137
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-47397 (URN)10.1016/j.apradiso.2011.01.012 (DOI)000288876700009 ()
Available from: 2010-12-01 Created: 2010-12-01 Last updated: 2012-01-18Bibliographically approved

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