E. Artuso

Study of Fricke-gel dosimeter calibration for attaining precise measurements of the absorbed dose

A calibration method has been studied for attaining, with good precision, absolute measurements of the spatial distribution of the absorbed dose by means of the Fricke gelatin xylenol orange dosimetric system. With this aim, the dose response to subsequent irradiations was analyzed. In fact, the studied modality is based on a pre-irradiation of each single dosimeter in a uniform field with a known dose, in order to extrapolate a calibration image for a subsequent non-uniform irradiation with an unknown dose to be measured.

Study of suitability of Fricke-gel-layer dosimeters for in-air measurements to characterise 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 (10)B 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 3mm, 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.

Dose measurements at epithermal beams of research reactors with fricke gel and thermoluminescence detectors

Suitable dosimeter methods have to be developed to measure the different dose contributions in phantoms exposed to epithermal/thermal neutron beams of a research reactor. The method based on Fricke xylenol orange gel dosimeter in form of layers has shown to be very effective for achieving images of the various dose components in air or in phantoms exposed to epithermal/thermal neutron beams with very high fluence rate. Another useful method is based on the use of TLD-700 chips, from whose response the gamma dose and the thermal neutron fluence can be obtained by means of appropriate parameters of the glow curve.

Study of the absorption spectra of Fricke xylenol orange gel dosimeters

A systematic study of the absorption spectra of Fricke xylenol orange gel dosimeters has been performed, in the wavelength range from 300 nm to 700 nm. The spectrum of xylenol orange (without ferrous sulphate solution) has been achieved, in order to subtract its contribution from the absorption spectra of the irradiated Fricke xylenol orange gel dosimeters. The absorbance due to ferric ions chelated by xylenol orange has been studied for various irradiation doses. Two absorbance peaks are visible, mainly at low doses: the first peak increases with the dose more slowly than the second one. This effect can explain the apparent threshold dose that was frequently evidenced.

Gel dosimeters for dose imaging in high fluences of epithermal neutrons: Potentiality and limitations

Gel dosimeters with planar geometry (3 mm in thickness, many centimeters in diameter) have shown noticeable potentiality for dosimetry in phantoms exposed to the epithermal neutron beams of research reactors. In fact, it is possible to achieve images of the spatial distribution of the gamma dose, the neutron dose and the dose due to the charged particles generated by thermal neutron reactions. Such a dose separation is attained by means of measurements with gel dosimeters having suitable isotopic composition, and thanks to the planar geometry, the neutron transport in the phantom is not sensibly affected by the change in the gel matrix isotopic content. Moreover, the reliability of the results obtained utilizing these dosimeters with planar geometry for in-air measurements aimed at neutron beam characterization has been investigated. The obtained results show that gel dosimeters with suitable design can be a valid support for epithermal neutron beam dosimetry.