Description: Publication date: Available online 19 June 2018 Source: Radiation Measurements Author(s): A.M. Sadek, G. Kitis The analysis of complex thermoluminescence (TL) glow curves in its individual peaks is achieved by a computerized glow curve deconvolution (CGCD). The correct application of the CGCD requires the fulfillment of the superposition principle (SP), which postulates that the TL peaks have to be independent of each other. In the present work we simulate the application of the CGCD using interactive phenomenological models in which the SP is not fulfilled. The thermoluminescence (TL) processes of four active traps and one thermally disconnected deep trap (TDDT) was simulated over a wide range of doses and under different competition cases. The TL glow-curves were analyzed by the CGCD algorithm and the accuracy of the kinetic parameters and the dose dependence of each trap were investigated over the doses. In most of the simulated cases, the non-fulfillment of the superposition principles has no significant effect on the accuracy of the computed kinetics parameters. Different behaviors of dose response curve were discussed including sub-linear and supra-linear dose dependence. It has been also found that in the case of presence of competitions among the active traps, an almost linear dose response curve can be observed for the last glow-peak in a series of overlapping glow-peaks.

Description: Publication date: Available online 19 June 2018 Source: Radiation Measurements Author(s): Jintang Qin, Jie Chen, Yuetian Li, Liping Zhou The poor dose recovery ratios reported for the infrared (IR) stimulated luminescence and post-IR IR stimulated luminescence (pIRIR) measurements of potassium feldspar (K-feldspar) have been attributed to the initial sensitivity changes. The change in electron trapping probability was inferred as a possible cause of the initial sensitivity change. However, there is still a lack of experimental evidence. In this study, the electron trapping probability changes were traced by recording the radiofluorescence (RF) emitted in the IR band (IR-RF) during the irradiation steps of the “single regenerative point” dose-recovery-like experiments. The IR-RF data shows that both high temperature heating and the preceding received dose during the laboratory measurements lead to a decrease in electron trapping probability for the sample employed in this study. For the pIRIR 290 signal, a 20% sharp decrease in the trapping probability is induced by the high temperature preheat, irrespective of the dose administered. For the pIRIR 225 and pIRIR 170 signals, the trapping probability decreases more gradually during the measurements for small doses and a 20% sharp decrease is only observed after the aliquot was irradiated with a large dose. The decrease of trapping probability does not always lead to initial sensitivity change. We infer that the heating and dosing may induce an increase in recombination probability, which serves as a compensation mechanism to balance out the trapping probability decrease. The amplitude of recombination probability increase may decrease with the increase of dose, and therefore, the occurrence of initial sensitivity change shows dependence on the type of pIRIR signal and the size of given and test doses.

Description: Publication date: Available online 14 June 2018 Source: Radiation Measurements Author(s): Linh T. Tran, Lachlan Chartier, David Bolst, Jeremy Davis, Dale A. Prokopovich, Alex Pogossov, Susanna Guatelli, Mark I. Reinhard, Marco Petasecca, Michael L.F. Lerch, Naruhiro Matsufuji, Marco Povoli, Anand Summanwar, Angela Kok, Michael Jackson, Anatoly B. Rosenfeld This paper presents recent development of Silicon on Insulator (SOI) detectors for microdosimetry at the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong. A new CMRP SOI microdosimeter design, the 3D mushroom microdosimeter is presented. Modification of SOI design and changes to the fabrication processes have led to improved definition of the microscopic sensitive volumes (SV), and thus to better modelling of the deposition of ionizing energy in a biological cell. The electrical and charge collection properties of the devices have been presented in previous works. In this study, the response of the microdosimeters in monoenergetic and spread out Bragg peak therapeutic 12 C ion beam at Heavy Ion Medical Accelerator in Chiba (HIMAC, Japan) are presented. Derived relative biological effectiveness (RBE) in 12 C ion radiation therapy matches the tissue equivalent proportional counter (TEPC) well, along with outstanding spatial resolution. The use of SOI technology in experimental microdosimetry offers simplicity (no gas system or HV supply), high spatial resolution, low cost, high count rates capabilities for beam characterisation and quality assurance (QA) in charged particle therapy.

Description: Publication date: Available online 11 June 2018 Source: Radiation Measurements Author(s): Derek Bingham, George Etherington This article summarises the information provided by two sources on applying internal dosimetry in an occupational setting. It describes the current ISO standards in internal dosimetry, which provide a basis for delivering monitoring and dose assessment for radiation workers under conditions where it can be judged that dose limits have not been exceeded. It also outlines the contents of the report on the Technical Recommendations for Monitoring Individuals for Occupational Intakes of Radionuclides, which builds on ICRP publications, the ISO standards, the EURADOS IDEAS Guidelines and other published documents to present a comprehensive account of the principles and practice of individual monitoring and internal dosimetry.

Description: Publication date: Available online 11 June 2018 Source: Radiation Measurements Author(s): Bastian Breustedt, Augusto Giussani, Dietmar Noßke In contrast to external dosimetry, which can be based on measurement of operational quantities directly related to the effective dose (mSv), the assessment of doses due to intakes of radionuclides relies on the measurement of activities (Bq) and subsequent modelling. The methodology and the models are published by the International Commission on Radiological Protection (ICRP) and are later implemented in national regulations. This paper describes the general concepts for assessment of internal occupational exposure and diagnostic nuclear medicine applications using biokinetic and dosimetric models. The current changes in the models which are presented in the OIR series (Occupational Intakes of Radionucldes) of ICRP are outlined and information on the uncertainties in internal dose assessment are presented.

Description: Publication date: Available online 9 June 2018 Source: Radiation Measurements Author(s): Seiichi Yamamoto, Kuniyasu Okudaira, Fumitaka Kawabata, Takayoshi Nakaya, Hiroshi Oguchi Measurements of dose distribution in water are important for high-energy electron beams from medical linear accelerators (LINAC). Although ionization chambers are commonly used for this purpose, measurements take a relatively long time, especially to obtain data for two- or three-dimensional dose distributions. To solve the problem, we tried imaging of produced light in water during irradiations of high energy electron-beams from LINAC. We placed a water phantom on a table of a LINAC system, and images of produced light in water were measured with a high-sensitivity cooled charge coupled device (CCD) camera during electron-beam irradiations of the water phantom. Measurements were made for different energies and doses of electron beams. We also measured the light spectra of the images by changing optical filters, to observe the difference of the images with respect to the wavelengths and to confirm the source of the optical light. In all irradiations of different energies and doses of electron-beams, we could obtain clear images of produced light in water. From the optical images, although the depth profiles were significantly smaller in shallow part of water, the ranges of the beams could be estimated within 1.7 mm difference with those calculated by the planning system. The lateral profiles and widths derived from the images of produced light were almost identical to those calculated by the planning system; the difference of the width was less than 2.3 mm. The light spectra of the images of produced light of water showed similar distribution to that of the Cerenkov-light although the distribution was slightly steeper. There was not a significant difference observed in the depth profiles between different wave lengths of light. The imaging of produced light in water during electron-beam irradiations has potential to be used for lateral profiles measurements, range and width estimations.

Description: Publication date: Available online 9 June 2018 Source: Radiation Measurements Author(s): F. Therriault-Proulx, Z. Wen, G. Ibbott, S. Beddar Purpose To characterize the response of plastic scintillation detectors (PSDs) to high-energy photon radiation as a function of magnetic field strength. Materials and methods PSDs were placed inside a plastic phantom held at the center point between 2 magnets and irradiated using a 6-MV photon beam from a linear accelerator. The magnetic field was varied from 0 T to 1.5 T by 0.3-T increments. The light emission and stem-effect-corrected response as a function of magnetic field strength were obtained for both a commercial PSD (Exradin W1, Standard Imaging) and an in-house hyperspectral PSD. Spectral signatures were obtained for the in-house PSD, and light emission from a bare fiber was also measured. Results Light emission increased as magnetic field strength increased for all detectors tested. The tested PSDs exhibited an increase in light intensity of 10%–20%, mostly owing to the increase in Cerenkov light produced within and transmitted along the optical fiber. When corrected for stem effects, the increase in PSD response went down to 2.4% for both detectors. This most likely represents the change in the inherent dose deposition within the phantom. Conclusion PSDs with a suitable stem-effect removal approach were less dependent on magnetic field strength and had better water equivalence than did ion chambers tested in previous studies. PSDs therefore show great promise for use in both quality assurance and in-vivo dosimetry applications in a magnetic field environment.

Description: Publication date: Available online 7 June 2018 Source: Radiation Measurements Author(s): Alex Miller, Rachid Machrafi, Abuzar Fariad Lanthanum Halide scintillators such as lanthanum bromide (LaBr 3 :Ce) and lanthanum chloride (LaCl 3 :Ce) have been studied extensively in gamma radiation fields and have shown to be excellent gamma ray detectors. Measurements with these detectors in complex radiation fields that include neutrons, protons and heavy ions may produce some information about the radiation field. For example fast neutron (n,γ), (n,p), and (n,α) reactions produce scintillations in the crystal from the energy deposited by the resulting secondary particles. Also high energy radiation environments such as those encountered in spacecraft and high energy charged particle facilities contain protons and heavy ions with enough energy to penetrate typical scintillation detectors. The light produced in the crystal by these heavy ions is proportional to the energy deposited along the ion track. To investigate the response of LaBr 3 detectors to heavy ions, a series of experiments have been carried out at the Heavy Ion Medical Accelerator in Chiba, Japan (HIMAC). Measurements with He and Si ions with various incident energies have been performed and the light output of the scintillator has been measured. The experimentally measured spectra have been compared to simulations using the particle and heavy ion transport system (PHITS) code and quenching effects have been observed in the measured spectra. The quenching of the Si ion experiments is greater than the quenching observed in the He ion experiments. The results from both simulation and experiment are presented and discussed.

Description: Publication date: Available online 5 June 2018 Source: Radiation Measurements Author(s): V. Anechitei-Deacu, A. Timar-Gabor, K.J. Thomsen, J.-P. Buylaert, M. Jain, M. Bailey, A. Murray There is evidence that optically stimulated luminescence (OSL) dating of quartz using the single-aliquot regenerative-dose (SAR) protocol underestimates the equivalent dose (D e ) for paleodoses above 100–200 Gy. Additionally, ‘infinitely’ old samples found not to be in laboratory saturation were reported. We present single and multi-grain SAR-OSL investigations for a coarse-grained (180–250 μm) quartz sample extracted from loess collected below the Brunhes/Matuyama transition at the Roksolany site (Ukraine). The sample was dated to more than 1000 ka by electron spin resonance using a multi center approach (Al and Ti signals), confirming that the D e (∼2000 Gy) falls beyond the limit of standard OSL D e measurement techniques. However, the natural signal measured using multi-grain aliquots of quartz was found to be below the laboratory saturation level. A comparison was made between synthetic dose response curves (DRCs) generated from single-grain and multi-grain aliquot data, respectively; the natural signal was found to be closer to the latoratory saturation level (92%) in the case of the single-grain synthetic DRC than for the multi-grain synthetic DRC where the signal was 86% of the saturation level. This difference could not be attributed to stimulation with different wavelengths, i.e. blue and green light stimulation for multi and single-grain measurements, respectively. By analysing synthetic data obtained by grouping grains according to their brightness, it was observed that brighter grains give a natural signal closer to the laboratory saturation level. This trend was confirmed for multi-grain aliquot data. Based on these findings we infer that variability in the contribution from populations of grains with different levels of brightness may represent a controlling factor in the closeness of the natural signal to laboratory saturation level for infinitely old samples.

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): Elizabeth L. Chamberlain, Jakob Wallinga, Zhixiong Shen Optically stimulated luminescence (OSL) dating of heterogeneously-bleached sediment by means of a minimum age model requires the input of a 'sigma_b' ( σ b ) value describing the overdispersion of the single-aliquot D e distribution expected for a well-bleached sample. We propose that σ b and associated uncertainty can be accurately determined if a large dataset of D e distributions is available and includes well-bleached samples. Our approach applies the bootstrapped Minimum Age Model (bootMAM) to a dataset of overdispersions in D e distributions, to obtain quantitative estimates of σ b . Corrections are made for constant-diameter aliquots of different grain sizes, based on the published dependency of overdispersion on the number of grains per aliquot. These adapted σ b values are then input to bootMAM to obtain robust paleodoses for the samples. We test the sensitivity of paleodose to σ b and we demonstrate that with correct σ b , identical paleodoses are obtained using bootMAM and the central age model on samples judged to be well-bleached. We conclude that for large datasets consisting of well- and heterogeneously-bleached samples, appropriate σ b values can be obtained from the data, and that bootMAM can be applied to all samples within this dataset.