Monte Carlo based voxel phantoms for in vivo internal dosimetry

The purpose of this communication is to describe briefly the computer programs developed to generate the MCNP input file corresponding to any segmented tomographic data and its application to the calibration procedures for in vivo internal dosimetry. The method has been applied to the determination of 241Am in bone by measurement in skull and knee using MCNP voxel models of a real human head and knee based on the tomographic Voxelman and Arms Down phantoms developed by Zubal et al. at Yale University.

On the use of LiF TLD-600 in neutron-gamma mixed fields

A new procedure allowing the separate estimation of neutron and gamma dose in mixed radiation fields has been developed in our laboratory. In this communication, a description of the main features of the discrimination procedure and some preliminary results obtained by its use are presented. The procedure is based on the significantly different structure of the glow curve of LiF TLD-600 produced by neutron and gamma radiation. The use of peak resolving numerical methods, sometimes called deconvolution, for the analysis of the glow curves from controlled irradiations at absorbed doses in the range 10-300 mGy with different neutron and gamma proportions, permits to quantify the differences peak by peak, also characterising the well-known neutron quasi-exclusive contribution to the high temperature region, above peak 5. From this study, it was possible to propose a n/gamma TL factor by which the respective doses can be estimated through a simplified analysis, not peak resolving, of the particular features of the glow curves obtained in field measurements. A first set of rather satisfactory results have been obtained by irradiating TLD-600 together with TLD-700 chips using Am-Be sources with different degree of moderation and using lead absorbers to change the gamma component. This component is directly measured by the TLD-700 detectors, allowing the testing of the gamma estimation reached by the discrimination procedure applied to the TLD-600 glow curve.

Pilot study on the application of computerised glow curve analysis in TL based personal dosimetry services

Preliminary results of an inter-laboratory collaborative work on the application of computerised glow curve analysis to TL personal dosimetry are presented. Very simple analysis methods have proved to be useful for the evaluation of glow curves similar to those encountered in the dosimetric control of radiation workers. A first result obtained in the study has been the possibility of simplifying the TL working procedures by eliminating pre-annealing or pre-heating steps employed in conventional systems to avoid low temperature peaks. The presence of these unwanted peaks can be detected by the computerised evaluation methods, discriminating their contribution to the dosimetric TL data.

Computerised glow curve deconvolution using general and mixed order kinetics

Some accurate glow curve fitting functions for general and mixed order kinetics glow peaks are proposed and discussed. These mathematical expressions are used together with peak search and non-linear minimisation algorithms in order to provide a fast glow curve deconvolution for those materials which cannot be well fitted using first order kinetics. To test the accuracy of the proposed method. the result of the fitting of synthetic glow curves is compared with the original data giving negligible errors for values of parameters currently found in TL materials.

Computerised glow curve analysis: a tool for routine thermoluminescence dosimetry

The basic features of computerised glow curve analysis methods are presented, together with the advantages derived from their use for dosimetry. The rapid development of personal computers with progressively greater computation capability has permitted the application of different analysis methods for practical dosimetry. A very simple glow curve analysis method, specifically developed for the measurement of low or very low doses usually measured in personal and environmental dosimetry, is also discussed.

Application of glow curve analysis methods to radiotherapy mailed dosimetry with LiF TLD-100

This paper presents the results obtained in a study of LiF TLD-100 performance for mailed dosimetry in radiotherapy, using glow curve analysis of TL evaluation and reusable chips. An excellent reusability is assured by a simple thermal treatment of 1 h at 400 degrees C followed by a controlled and reproducible cooling to room temperature that accurately reproduces the sensitivity of the detectors. Particular attention was devoted to studying sensitivity changes during room temperature storage of TLD-100 detectors. These changes can be one of the major sources of uncertainty in mailed dosimetry, where long intervals can occur between detector preparation, irradiation and readout. Based on the features of the individual peak evolution during storage a rather simple method to correct for these sensitivity modifications is proposed. The analysis of the different influential factors permitted us to estimate a combined uncertainty for the measurement of absorbed doses within the 0.5-4 Gy range of 1.0%.