Measurements of Neutrons In A Mixed GammaNeutron Field Using Three Different Types of Detectors

A linear electron accelerator for medical use is a device for the treatment of tumors by collimated beams of electrons and/or photons. These accelerators are devices that employ electromagnetic waves of high frequency, to accelerate electrons that are used directly in the treatment of superficial tumors, or, if they are made to hit them on an appropriate target, they can produce photons of high energy destined to the treatment of deeptumors.Depending on the energy of the electrons and photons and the materials that make up the head of the accelerator and the target, this equipment will produce in addition to the aforementioned radiation, neutron fields of regular intensity. It is necessary to estimate the equivalent dose due to the neutrons themselves, the doses due to the gamma field of neutron capture, produced by the capture of thermal neutrons in the concrete of the bunker, and the gamma doses due to phenomena of neutron activation of elements of the own accelerator. It is therefore important to be able to measure (detect, quantify, dose, etc.) both photons and neutrons in these cases and others more. In this work we use three different detectors, namely a scintillator-photomultiplier system, a fast reading dosimeter and bubble detector. The idea is to measure the radiation separately and compare their results. The results obtained were the mixed gamma-neutron field spectrum, the dose due only to neutrons obtained by the bubble detectors, which is compared to the dose obtained by the second fast reading dosimeters (model 884), plus the dose obtained by the first dosimeters (model 609) and finally the dose obtained by the Victoreen dosimeter

Measurements of the optical density and the thermoluminescent response of LiF : Mg,Ti exposed to high doses of Co-60 gamma rays

The absorption spectra and glow curves of LiF:Mg,Ti exposed to high doses of Co-60 gamma rays as well as the optical density curves and thermoluminescent (TL) response as a function of dose were measured. Absorption peaks around 442 nm (2.8 eV), 307 nm (4.0 eV) and 248 nm (5.0 eV) were observed. The optical density is a linear function of dose up to 2500 Gy and then sublinear for the 5.0 eV band, and for the 4.0 eV band it is sublinear with a filling constant of 2.1 x 10(-4) and 6.2 x 10(-4) Gy(-1). The dose response of the 2.8 eV band is linear from 2500 Gy to 10 kGy with a slope of 1.0 x 10(-5) Gy(-1). Once the absorption spectra were obtained, the glow curves and the TL response were obtained. In the dose range, 290-10,000 Gy, the TL response of peaks 5 and 7 was supralinear-sublinear

Supralinear response and efficiency of LiF : Mg,Ti to 0.7, 1.5 and 3 MeV protons

The thermoluminescent (TL) response, supralinearity function, and relative efficiency with respect to Co-60 gamma -rays, of TLD-100 exposed to 0.7. 1.5 and 3 MeV protons have been measured. The TL response of the glow curve peaks using two different deconvolutions, separating in either 7 (3-9) or 9 peaks (3-10 and peaks 6a and 6b). was investigated. Results for the supralinearity function of peaks 5 and 7-9 and the relative response of peaks 5 and 7 are insensitive to the chosen deconvolution scheme. At all energies we observe that peak 5 is slightly supralinear and that supralinearity increases as a function of the peak temperature. The relative efficiencies, measured for the total TL signal (area under the glow curve) and peaks 5 and 7, decrease with the proton energy having values of 0.33, 0.46 and 0.70 (total TL signal), 0.22, 0.32 and 0.53 (peak 5) and 1.4, 2.6 and 3.6 (peak 7) at 0.7. 1.5 and 3 MeV, respectively. These data agree with the systematics reported in the literature. The measurements of the supralinearity function are compared with Monte Carlo track interaction model calculations. The analysis suggests that the model ion track effective radius and the saturation radius are independent of the incident ion energy. (C) 2001 Elsevier Science B.V. All rights reserved

Thermoluminescent response of TLD-100 exposed to low energy protons

The fluence response curve of LiF:Mg,Ti (TLD-100) exposed to 0.7, 1.5 and 3 MeV proton beams has been measured. In all cases, the total TL signal and glow curve peaks 5 to 9 show a linear-supralinear response for fluences between 10(7) and 10(12) protons/cm(2). The supralinearity increases with the energy of the incident beam. The measured relative efficiencies for protons with respect to Co-60 gamma-rays, for the total TL signal and peaks 5 and 7 indicate that the efficiency increases with energy, that is, decreases with the linear energy transfer. The efficiencies are lower than unity for the total TL signal and peak 5 and greater than unity for peak 7

Thermoluminescent response of TLD-100 to low energy protons

The fluence-response curve of LiF:Mg,Ti (TLD-100) exposed to 0.7, 1.5 and 3 MeV protons has been measured in the 10(7)-10(12) protons.cm(-2) fluence range. The total TL signal and glow curve peaks show in all cases a linear-supralinear response and the degree of supralinearity increases with the energy of the incident beam and the temperature of the TL peak. The possible effect on the results of alternative glow curve deconvolutions has been studied, finding only minor differences in the supralinearity functions for individual peaks. Measurements for peaks 5 and 8 have been compared with track interaction model (TIM and UNIM) predictions, and it is concluded that the assumption that Omega scales with LET fails to describe the observed energy dependence of the supralinearity

TLD-100 thermoluminescent efficiencies for low-energy ions: correlation of efficiency with ion incident energy

A systematic investigation of heavy charged particle-to-gamma thermoluminescent (TL) efficiencies has been performed for the total signal and peak 5 of LiF : Mg, Ti (TLD-100) dosemeters. Experimental and theoretical efficiencies are presented for protons as well as helium, carbon, nitrogen and oxygen ions. Proton, helium and carbon irradiations were performed at incident energies between 0.7 and 11 MeV. For nitrogen and oxygen, two energies, corresponding to 'mirror' values below and above the Bragg peak energy, were used to measure TL efficiencies for the same linear energy transfer (LET) entrance value. The energies chosen were 4.83 and 9.95 MeV for nitrogen ions and 6.02 and 12.95 MeV for oxygen ions. Distinct curves are found for each ion species. Data for energies higher than the Bragg peak energy follow the well-known tendency, efficiency values decrease with increasing LET. Efficiencies measured below the Bragg peak display the opposite effect, efficiency increases with increasing LET. Presenting results as a function of incident energy shows a monotonic and single valued behaviour, efficiency decreases with decreasing energy. The measured efficiencies of the higher-energy data (above the Bragg peak) were found to be 1.45 times greater than their low-energy counterparts. Modified track structure theory efficiency calculations were performed for all the ions investigated using radial dose distributions obtained via Monte Carlo simulations in solid-state LiF and 8.1 keV x-rays as test radiation. The theoretical values show agreement with data within 40% for both peak 5 and the total signal. The calculations predict the observed behaviour, higher efficiency for higher ion energy

Sublinear response of peak 5 in LiF : Mg,Ti to low energy protons and carbon ions

This work analyses experimentally and mathematically the heavy charged particle (HCP) thermoluminescence (TL) fluence response of sensitised LiF:Mg,Ti (TLD-100) peak 5 to 0.91, 2.95 and 4.32 MeV protons and 10.3 and 11.8 MeV carbon ions. Supralinearity was suppressed by sensitising the TLD-100 chips following a pre-exposure/annealing treatment. HCP irradiations took place using a Pelletron accelerator at fluences that ranged from about 6 x 10(8) to 3 x 10(11) cm(-2) and from 3 x 10(7) to 1 x 10(11) cm(-2) for protons and carbons, respectively. Results were compared to a Monte Carlo simulation of the Extended Track Interaction Model (ETIM) performed for each particle-energy combination. Experimental data show that the onset and behaviour of the HCP-TL fluence response function is weakly energy dependent for each ion type, in agreement with previously reported data of sensitised TLD-100 irradiated with low energy helium ions. ETIM fails to predict this behaviour showing instead a strong energy dependence of the simulated HCP-TL fluence response function. (C) 2004 Elsevier B.V. All rights reserved

On the correct measurement of relative heavy charged particles to gamma thermoluminescent efficiencies

In order to better understand the most important experimental aspects for performing correct measurements of relative thermoluminescent (TL) efficiencies, an investigation has been carried out to quantify the effect of using different experimental procedures in the evaluation of 3 MeV proton-to-gamma relative efficiency (eta(p,gamma)) of LiF:Mg,Ti. Variations in batch, presentation, annealing and reader have been studied. When the same protocol is used to measure proton and gamma TL response, efficiency values obtained range from 0.36 to 0.59 for peak 5 and from 0.44 to 0.79 for the total signal. The use of different annealings and different batches leads to 20% and 10% differences in eta(p,gamma), respectively. Large differences (40%) are found between efficiency values measured with TLD-100 chips and those obtained using TLD-100 microcubes. When 'mixed' procedures are used to measure the proton and the gamma response, differences in eta(p,gamma), may increase even more. The main conclusion of this work is to stress the importance of measuring an entire series of experiments in the same laboratory with a carefully defined protocol and using dosemeters from the same batch to obtain heavy charged particle TL response and gamma TL response with identical annealing and readout procedures

Response of radiochromic dye films to low energy heavy charged particles

We have studied the possible use of radiochromic dye films (RCF) as heavy charged particle dosemeters. We present the results of irradiating two commercial RCF (GafChromic HD-810 and MD-55-1) with 1.5, 2.9 and 4.4 MeV protons, 1.4, 2.8, 4.7, 5.9, 6.8 MeV He-4 ions and 8.5 and 12.4 MeV C-12 ions, at proton doses from about 1 Gy up to 3 kGy, helium ions doses from 3 Gy to 5 kGy and carbon ion doses from 30 Gy to 20 kGy. The films were scanned and digitized using commercial equipment. For a given particle, the response per unit dose at different energies indicates an energy dependence of the sensitivity, which is discussed. Comparison was made for the use of a standard spectrophotometer to obtain optical density readings versus a white light scanner. (C) 2002 Elsevier Science B.V. All rights reserved