18 research outputs found
Study of suitability of Fricke-gel-layer dosimeters for in-air measurements to characterize epithermal/thermal neutron beams for NCT
The reliability of Fricke gel dosimeters in form of layers for measurements aimed at the characterization
of epithermal neutron beams has been studied. By means of dosimeters of different isotopic composition
(standard, containing 10B or prepared with heavy water) placed against the collimator exit, the spatial
distribution of gamma and fast neutron doses and of thermal neutron fluence are attained. In order to
investigate the accuracy of the results obtained with in-air measurements, suitable MC simulations have
been developed and experimental measurements have been performed utilizing Fricke gel dosimeters,
thermoluminescence detectors and activation foils. The studies were related to the epithermal beam
designed for BNCT irradiations at the research reactor LVR-15 (Řež). The results of calculation and
measurements have revealed good consistency of gamma dose and fast neutron 2D distributions obtained
with gel dosimeters in form of layers. In contrast, noticeable modification of thermal neutron
fluence is caused by the neutron moderation produced by the dosimeter material. Fricke gel dosimeters
in thin cylinders, with diameter not greater than 3 mm, have proved to give good results for thermal
neutron profiling. For greater accuracy of all results, a better knowledge of the dependence of gel dosimeter
sensitivity on radiation LET is needed
dosimetry methods in boron neutron capture therapy
Dosimetry studies have been carried out at thermal and epithermal columns of LVR-
15 research reactor for investigating the spatial distribution of gamma dose, fast
neutron dose and thermal neutron fluence. Two different dosimetry methods, both
based on solid state detectors, have been studied and applied and the accuracy and
consistency of the results have been inspected. One method is based on Fricke gel
dosimeters that are dilute water solutions and have good tissue equivalence for
neutrons and also for all the secondary radiations produced by neutron interactions in
tissue or water phantoms. Fricke gel dosimeters give the possibility of separating the
various dose contributions, i.e. the gamma dose, the fast neutron dose and the dose due
to charged particles generated during thermal neutron reactions by isotopes having
high cross section, like 10B. From this last dose, thermal neutron fluence can be
obtained by means of the kerma factor. The second method is based on
thermoluminescence dosimeters. In particular, the developed method draw advantage
from the different heights of the peaks of the glow curve of such phosphors when
irradiated with photons or with thermal neutrons. The results show that satisfactory
results can be obtained with simple methods, in spite of the complexity of the subject.
However, the more suitable dosimeters and principally their utilization and analysis
modalities are different for the various neutron beams, mainly depending on the
relative intensities of the three components of the neutron field, in particular are
different for thermal and epithermal columns