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Photon and neutron dose discrimination using low pressure proportional counters with graphite and A150 walls
Stockholm University, Faculty of Science, Medical Radiation Physics (together with KI).
2007 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, Vol. 125, no 1-4, 314-317 p.Article in journal (Refereed) Published
Abstract [en]

A graphite-walled proportional counter with low neutron sensitivity was used in combination with a tissue-equivalent proportional counter (TEPC) to separate the photon and neutron components in mixed radiation fields. Monte Carlo (MCNP4C) simulations of the photon and neutron responses of the two detectors were done to obtain correction factors for the sensitivity differences. In an alternative method the radiation components were determined using constant-yD-values for typical photon and neutron energy distributions. The results show no significant difference between the two methods and the measured neutron dose-equivalent agrees within ±50% with Bonner sphere determined values. The experimental data were obtained in measurement campaigns organised within the EVIDOS-project.

Place, publisher, year, edition, pages
Oxford University Press , 2007. Vol. 125, no 1-4, 314-317 p.
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:su:diva-24147DOI: 10.1093/rpd/ncm162OAI: oai:DiVA.org:su-24147DiVA: diva2:196870
Note
Part of urn:nbn:se:su:diva-6687Available from: 2007-03-01 Created: 2007-02-26 Last updated: 2011-01-18Bibliographically approved
In thesis
1. The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy
Open this publication in new window or tab >>The microdosimetric variance-covariance method used for beam quality characterization in radiation protection and radiation therapy
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radiation quality is described by the RBE (relative biological effectiveness) that varies with the ionizing ability of the radiation. Microdosimetric quantities describe distributions of energy imparted to small volumes and can be related to RBE. This has made microdosimetry a powerful tool for radiation quality determinations in both radiation protection and radiation therapy. The variance-covariance method determines the dose-average of the distributions and has traditionally been used with two detectors to correct for beam intensity variations. Methods to separate dose components in mixed radiation fields and to correct for beam variations using only one detector have been developed in this thesis. Quality factor relations have been optimized for different neutron energies, and a new algorithm that takes single energy deposition events from densely ionizing radiation into account has been formulated. The variance-covariance technique and the new methodology have been shown to work well in the cosmic radiation field onboard aircraft, in the mixed photon and neutron fields in the nuclear industry and in pulsed fields around accelerators.

The method has also been used for radiation quality characterization in therapy beams. The biological damage is related to track-structure and ionization clusters and requires descriptions of the energy depositions in nanometre sized volumes. It was shown that both measurements and Monte Carlo simulation (condensed history and track-structure) are needed for a reliable nanodosimetric beam characterization. The combined experimental and simulated results indicate that the dose-mean of the energy imparted to an object in the nanometre region is related to the clinical RBE in neutron, proton and photon beams. The results suggest that the variance-covariance technique and the dose-average of the microdosimetric quantities could be well suited for describing radiation quality also in therapy beams.

Place, publisher, year, edition, pages
Stockholm: Medicinsk strålningsfysik (tills m KI), 2007. 146 p.
Keyword
ionizing radiation, radiation quality, radiation protection, radiation therapy, microdosimetry, nanodosimetry, variance-covariance method
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-6687 (URN)91-7155-391-6 (ISBN)
Public defence
2007-03-23, föreläsningssalen, Radiumhemmet, Karolinska universitetssjukhuset, Solna, 10:00
Opponent
Supervisors
Available from: 2007-03-01 Created: 2007-02-26Bibliographically approved

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