Study of the improvement of TLD cards for personal neutron dosimetry

In this work, personal thermoluminescence dosimeter (TLD) cards type of GN-6770 (holder type 8806) from Harshaw were used for personal neutron dosimetry. The response of the dosimeters has been determined in terms of the personal absorbed dose and personal dose equivalent for different neutron energy components, based on the recommendations of ICRP-60 and ICRU-49. Neutron irradiation was performed using a 5 mCi Am–Be neutron source. The TLD reader, type Harshaw 6600, was installed and calibrated for accurate neutron doses equivalent to gamma-ray doses. It was found that fast neutron doses measured by TLD (badges or cards) are in agreement with those measured by neutron TE (tissue equivalent gas) ionization chambers and neutron monitors. Thermal neutron doses measured by TLD cards were overestimated when compared with those measured by neutron monitors. Additional Cd was used to reduce thermal neutron doses to be in agreement with actual thermal doses. Other configurations for TLD crystals are also suggested for accurate thermal neutron dose measurements.     

Dosimetry and fast neutron energies characterization of photoneutrons produced in some medical linear accelerators

This work focusses on the estimation of induced photoneutrons energy, fluence, and strength using nuclear track detector (NTD) (CR-39). Photoneutron energy was estimated for three different linear accelerators, LINACs as an example for the commonly used accelerators. For high-energy linear accelerators, neutrons are produced as a consequence of photonuclear reactions in the target nuclei, accelerator head, field-flattening filters and beam collimators, and other irradiated objects. NTD (CR-39) is used to evaluate energy and fluence of the fast neutron. Track length is used to estimate fast photoneutrons energy for linear accelerators (Elekta 10 MV, Elekta 15 MV, and Varian 15 MV). Results show that the estimated neutron energies for the three chosen examples of LINACs reveals neutron energies in the range of 1–2 MeV for 10 and 15 MV X-ray beams. The fluence of neutrons at the isocenter (Φ_total) is found to be (4×10⁶ n cm² Gy^?1) for Elekta machine 10 MV. The neutron source strengths Q are calculated. It was found to be 0.2×10¹² n Gy^?1 X-ray at the isocenter. This work represents simple, low cost, and accurate methods of measuring fast neutrons dose and energies.     

Thermoluminescence sensitivity of daily-use materials

The thermoluminescence (TL) response of silicon-rich daily-use materials, namely charoite (silicate gemstone), Spanish dental crown, phone chip and Spanish glass has been investigated. All the samples previously characterised by means of X-ray diffraction, electron microscopy associated with energy-dispersion and wavelength-dispersive spectrometry and X-ray fluorescence exhibit a reasonable sensitivity to ionising radiation. The preliminary results, based on their TL properties, allow us to speculate that these materials could be potentially of interest in situations where conventional dosimetric systems are not available. The dose dependence of the 400 nm TL emission of the studied samples displays a very good linearity in the range of 0.1–10 Gy.     

The potential of luminescence signals from electronic components for accident dosimetry

This study investigated the optically stimulated luminescence of a large number of electronic components extracted from both old and new generation mobile phones and chip modules of phone cards. Most resistors and all chip modules studied present a linear dose response (R > 0.99) in the dose range investigated (200 mGy up to 6 Gy, respectively 10 Gy), while capacitors, inductors and integrated circuits generally have a non-linear growth (exponential or cubic). For our experimental setup, an average specific luminescence of ∼20,000 cts in 2 s/Gy (n = 10) and ∼6000 cts in 2 s/Gy (n = 14) was obtained for two types of chip modules with a relatively high degree of homogeneity (relative standard deviation of 23% and 31%) and a minimum detectable dose of 7 mGy for immediate measurement. The investigated signals show small sensitivity changes (generally <10%) after repeated cycles of irradiation and readout. Preliminary fading measurements are presented. It can be concluded that most mobile phones and phone card components have a significant potential as retrospective luminescence dosimeters.     

Synthesis of silver nanoparticles using dl-alanine for ESR dosimetry applications

The potential use of alanine for the production of nanoparticles is presented here for the first time. Silver nanoparticles were synthesized using a simple green method, namely the thermal treatment of silver nitrate aqueous solutions with dl-alanine. The latter compound was employed both as a reducing and a capping agent. Particles with average size equal to 7.5 nm, face-centered cubic crystalline structure, narrow size distribution, and spherical shape were obtained. Interaction between the silver ions present on the surface of the nanoparticles and the amine group of the dl-alanine molecule seems to be responsible for reduction of the silver ions and for the stability of the colloid. The bio-hybrid nano-composite was used as an ESR dosimeter. The amount of silver nanoparticles in the nanocomposite was not sufficient to cause considerable loss of tissue equivalency. Moreover, the samples containing nanoparticles presented increased sensitivity and reduced energetic dependence as compared with pure dl-alanine, contributing to the construction of small-sized dosimeters.     

Determination of Radiation Dose Distribution by Magnetic Resonance Imaging in the New Tissue Equivalent Gel

Abstract

A new tissue-equivalent substance for the MR dosimetry has been developed. It is composed of water, bovine serum albumin, acrylamide with N,N′-methylene-bis-acrylamide, ammonium ferrous sulphate and sulphuric acid. The elemental composition, mass density, and electron density of the PIRA gel are closer to real tissue than those of dosimeter gels previously investigated. Irradiation causes the changes in the NMR properties of the gel. The dose dependence of NMR longitudinal relaxation rate, R1, is reproducible (less than 2% variation) and is linear up to about 30 Gy, with a slope of 0.023 s^?1Gy^?1 at 0.48 T. The gel, referred to as PIRA, can be used to obtain accurate radiation dose distribution with conventional magnetic resonance imaging devices.     

Synchrotron X‐ray microbeam dosimetry with a 20 micrometre resolution scintillator fibre‐optic dosimeter

Cancer is one of the leading causes of death worldwide. External beam radiation therapy is one of the most important modalities for the treatment of cancers. Synchrotron microbeam radiation therapy (MRT) is a novel pre‐clinical therapy that uses highly spatially fractionated X‐ray beams to target tumours, allowing doses much higher than conventional radiotherapies to be delivered. A dosimeter with a high spatial resolution is required to provide the appropriate quality assurance for MRT. This work presents a plastic scintillator fibre optic dosimeter with a one‐dimensional spatial resolution of 20 µm, an improvement on the dosimeter with a resolution of 50 µm that was demonstrated in previous work. The ability of this probe to resolve microbeams of width 50 µm has been demonstrated. The major limitations of this method were identified, most notably the low‐light signal resulting from the small sensitive volume, which made valley dose measurements very challenging. A titanium‐based reflective paint was used as a coating on the probe to improve the light collection, but a possible effect of the high‐Z material on the probes water‐equivalence has been identified. The effect of the reflective paint was a 28.5 ± 4.6% increase in the total light collected; it did not affect the shape of the depth‐dose profile, nor did it explain an over‐response observed when used to probe at low depths, when compared with an ionization chamber. With improvements to the data acquisition, this probe design has the potential to provide a water‐equivalent, inexpensive dosimetry tool for MRT.     

Evaluation of the dose received in the tissues of the neck during quantification of iodine in the thyroid by X-ray fluorescence spectrometry

The determination of the iodine content in the thyroid is of great interest for many investigations of this gland. The conventional scintigraphic method, using radionuclides, is efficient but delivers a significant dose to the patient. The X-ray fluorescence spectrometry could give information about the iodine content in the thyroid. The measured signal is obtained after stimulation of the stable iodine contained in the gland by X-rays. The advantage of this technique is the complete absence of radioactive isotope injected into the patient body. By applying this, a decrease in effective dose to the patient should be obtained. In this work, the study of the dose received by a thyroid phantom (surrounded by the different tissues of the neck) was performed. The phantom is made of PLA. The dose is measured in optimised conditions defined for the analytical technique. A total head-neck phantom was also used in order to consider the absorbed dose in each different tissues and organs as spinal cord or eyes. Thermo-luminescence dosimeters were chosen for their small size, their sensitivity and the easy positioning on the surface of the phantom but also inside of it to evaluate dose to internal organs. Those LiF 100 dosimeters have been calibrated within the X-ray beam also used for the analysis of iodine. The repeatability and reproducibility of the method has been evaluated. The influence of parameters as concentration of iodine in the thyroid, distance between the X-ray generator and the neck, thickness of the tissues surrounding the thyroid, has been investigated in terms of modifying parameters of the dose received by different tissues situated in the neck and the head.