Dosimetry in mixed fields (neutrons, photons) using electron spin resonance (ESR) spectrometry.
Marie-Laure HERVE, doctorate thesis of the University of Paris XI speciality Radiological and medical Physics, 198p., defended on the 23rd March 2006.
In a radiological accident, the assessment of the dose received by the victim is relevant
information for the therapeutic strategy. Two complementary dosimetric techniques based
on physical means are used in routine practice in the laboratory: EPR spectroscopy
performed on materials removed from the victim or gathered from the vicinity of the
victim and Monte Carlo calculations. EPR dosimetry, has been used successfully several
times in cases of photon or electron overexposures. Accidental exposure may also occur
with a neutron component.
The aim of this work is to investigate the potentiality of EPR dosimetry for mixed photon
and neutron field exposure with different organic materials (ascorbic acid, sorbitol,
glucose, galactose, fructose, mannose, lactose and sucrose). The influence of irradiation
parameters (dose, dose rate, photon energy) and of environmental parameters
(temperature of heating, light exposure) on the EPR signal amplitude was studied. To
assess the neutron sensitivity, the materials were exposed to a mixed radiation field of
experimental reactors with different neutron to photon ratios. The relative neutron
sensitivity was found to range from 10% to 43% according to the materials.
Prior knowledge of the ratio between the dose in samples measured by EPR spectrometry and organ or whole body dose obtained by calculations previously performed for these different configurations, makes it possible to give a first estimation of the dose received by the victim in a short delay. The second aim of this work is to provide data relevant for a quick assessment of the dose distribution in case of accidental overexposure based on EPR measurements performed on
one or several points of the body. The study consists in determining by calculation the relation between the dose to the organs and whole body and the dose to specific points of
the body, like teeth, bones or samples located in the pockets of victim clothes, for different external exposures corresponding to most representative configurations.