Description: Publication date: Available online 2 December 2014 Source: Radiation Measurements Author(s): I. Bikit , D. Mrdja , K. Bikit , S. Grujic , D. Knezevic , S. Forkapic , U. Kozmidis-Luburic Due to well defined three dimensional nano- and micro-porous structure, one of the most important properties of zeolite is its surface adsorption capacity. Nevertheless, a natural zeolite adsorption capability of 222 Rn has not been thoroughly investigated. The objective of this paper is to review the research concerning the application of natural zeolite in 222 Rn adsorption. To achieve this goal the investigation based on measurements of radon adsorption by various zeolite granulation was done. Ball mill is used to achieve different granulations of zeolite in the range of μ m-mm, whereas the particle size distributions are determined by particle size analyzer, Master Sizer 2000. The zeolite samples were exposed to elevated radon concentrations up to 1800 Bq/m 3 inside a closed chamber (volume ≈ 5.4 x 10 -3 m 3 ). The absorbed radon quantity was measured by high resolution gamma spectroscopy. The influence of particle size was measured and discussed. We found that the adsorption coefficients that were obtained in our experiment for natural zeolite samples for different granulations are similar to adsorbing coefficients for silica gel, but they are an order of magnitude lower than radon adsorbing coefficient for synthetic zeolite. The adsorption coefficient for activated charcoal derived in our experiment ( ≈ 3 m 3 /kg) is in average 50 times higher comparing to the adsorption coefficients obtained for zeolite samples (0.038 m 3 /kg - 0.11 m 3 /kg). All adsorbing coefficients are determined for very low relative humidity of air of about 7%, since our simple experimental setup did not allow possibility to change the relative humidity, or temperature. In addition, we explored the perturbation of radon concentration inside small-volume radon chamber caused by the presence of adsorbing sample and influence of this perturbation on obtained values of adsorbing coefficients.

Description: Publication date: Available online 29 November 2014 Source: Radiation Measurements Author(s): Daniela Ekendahl , Boris Bulánek , Libor Judas Because retrospective dosimetry utilises commonly occurring materials and objects, it is particularly useful in cases of large-scale radiation accidents or malevolent acts with radioactive materials where casualties are inflicted on the general public and first emergency responders. The aim of this study was to investigate whether retrospective dosemeters can provide dose estimates with comparable accuracy like conventional personal dosemeters. Using an external source of radiation 137 Cs and an anthropomorphic phantom, we simulated serious irradiation of a human body in anterior-posterior and rotational geometries. Retrospective luminescence dosimetry objects, such as mobile phones, dental ceramic and household salt, and conventional personal dosemeters (thermoluminescent and electronic) were fixed to the anthropomorphic phantom. The doses obtained were compared with specific reference values. In most cases, relative deviations between the measured doses and the reference values did not exceed 20%. As the retrospective and conventional dosemeters show no significant differences in laboratory conditions, the retrospective luminescence dosimetry objects represent a very promising tool if handled properly.

Description: Publication date: Available online 29 November 2014 Source: Radiation Measurements Author(s): P. Urbanova , D. Hourcade , C. Ney , P. Guibert Archaeological mortars are more convenient and much more representative for the chronology of buildings than brick or wood constructions that can be re-used from older buildings. Before dating unknown samples of mortars, further investigation of OSL from mortars is required and the most efficient methodology needs to be established. In this study we compared the ages obtained by OSL dating of quartz extracted from mortars of the Roman amphitheatre Palais-Gallien in Bordeaux with independent age information. Resetting of the OSL signal occurred during the preparation of mortar when grains of sand (quartz) were extracted and mixed with lime and water. The mortar was subsequently hidden from light by embedding within the structure which is the event to be dated. Various factors contribute to uncertainties in the age determination. The frequency of measured equivalent doses reveals a large scattering. Optical bleaching of certain grains can be partial due to the short duration of the exposure to light. We worked with the single grain technique in order to find and select the grains that were sufficiently exposed to daylight. To determine the average equivalent dose, we tried three different approaches: a calculation of an arithmetic mean and one following either the central age model or the 3-parameter minimum age model, the latter turned out to be the only relevant way to evaluate the experimental data. The proportion of grains included in the calculation of the average equivalent dose represents 2.7-4.7 % of the overall analyzed grains. The results obtained for the three out of four samples are approaching the expected age, however, the minimum doses and the corresponding ages are significantly over-estimated in case of two samples. The studied material is very coarse, which causes heterogeneity of irradiation at the single grain scale, and contributes to a dispersion of equivalent doses. Different analytical methods (scanning electron microscopy with energy dispersive X-ray spectroscopy cartography, Beta-radiography imaging, inductively coupled plasma mass spectrometry) were employed to demonstrate the presence of this phenomenon. Despite the extremely large proportion of high equivalent doses in equivalent dose distributions, there is an apparent presence of well-bleached grains at the beginning of equivalent dose distributions. The study shows the potential of dating mortars by single grain OSL.

Description: Publication date: Available online 28 November 2014 Source: Radiation Measurements Author(s): M.K. Kievets , I.V. Zhuk , A.N. Sosnin

Description: Publication date: Available online 28 November 2014 Source: Radiation Measurements Author(s): Patrik Sibolt , Rickard O. Cronholm , Anders R. Beierholm , Claus F. Behrens Conversion to absolute dose in Monte Carlo (MC) simulations of MV radiotherapy beams needs correct modeling of backscatter (BS) to the linear accelerator (linac) monitor chamber. For some linacs the BS depends largely on jaw settings. The backscattered fraction (BSF) of radiation can be determined experimentally by measuring ratios of target charge for a given number of monitor units as a function of jaw settings. This was done using the in-house developed ME40 dosimetry system, which is able to determine the target charge for each radiation pulse from the linac. The BSF measurements were performed for different linac models at five Danish radiotherapy clinics. The investigated linacs were four Varian TrueBeams (TB), one Varian iX (iX) and one Elekta Synergy (ES). BSF measurements were performed for square field side lengths ranging from 1 to 40 cm, using the 10 × 10 cm 2 field as reference. The impact of the flattening filter on the BSF was investigated through measurements in flattened as well as flattening filter free (FFF) beams. Furthermore, to investigate the contribution from the upper and lower jaws separately, measurements at one of the clinics also included asymmetric fields. For the iX, the obtained BSF measurements were compared with MC simulations performed using the BEAMnrc user code. For flattened beams on the Varian linacs, the measured BSF exhibited a clear linear correlation with square jaw settings (correlation coefficient r > 0.9 with p 〈 0.001 in all cases). For the ES, however, no correlation between BSF and jaw settings was found (r=0.04, p=0.92). The change in BSF with jaw settings was also found to be negligible for FFF beams on the TB linacs, indicating that the flattening filter has a substantial influence on the BSF. Furthermore, the backscatter effect was found to be more pronounced (up to a factor of 7) for the iX compared to the TB. MC simulations on the iX agreed within 0.4 % with BSF measurements, indicating that the target charge measurement method used for determination of BSF is accurate. Furthermore, the similar BSF observed for the four TB linacs included in the study also indicates that the method used for target charge measurements is reproducible. The reproducibility lies mainly in the fact that the method basically has no set-up errors and therefore is user independent.

Description: Publication date: January 2015 Source: Radiation Measurements, Volume 72 Author(s): Bhaskar Mukherjee The ratio of thermoluminescence light outputs (TLO) of Beryllium Oxide (BeO) and Lithium Fluoride (LiF) dosimeters increases with increasing LET (Linear Energy Transfer) of the impinging particles on the dosimeter chips. This unique phenomenon was utilized to develop a microdosimeter using the common LiF (TLD-700) and BeO (American Beryllia-CF5427-000) dosimeter chips. The dosimeter pairs were exposed to complex mixed radiation fields produced by bombarding a polystyrene plate phantom with therapeutic proton beams of energies from 81 to 231 MeV at the West German Proton Therapy Centre Essen (WPE), Germany. The linear energy transfer (LET) and quality factor ( Q ) of the secondary radiation fields were simultaneously estimated using a REM 500B tissue equivalent proportional counter (TEPC). The TLD chips were evaluated and the corresponding LET and Q values were plotted as linear functions of the ratio of the TL-glow curve areas within 100–250 °C of TLD-700 and BeO chips. The TLD pairs embody a passive, solid-state, tissue-equivalent, microdosimeter that enable the delivery of dose equivalent (DE), dose-average LET and Q within a broad dynamic range for a given mixed-radiation field relevant to particle therapy, long haul aviation dose monitoring and human space exploration.

Description: Publication date: Available online 30 October 2014 Source: Radiation Measurements Author(s): X.Y. Zhang , L. Chen , P. Luo , Y.Q. Ju , H.B. Zhang , F. Ma , H.L. Ge , Y.B. Zhang , B. Wan , Y.Y. Li , X.W. Xu , W. Mao The characteristics of nat .,7 LiF:Mg,Cu,P thermoluminescent detectors exposed to high-energy 12 C (165 MeV/nucleon) ions and 60 Co γ -rays have been investigated. Through a careful analysis of the glow curves by the GlowFit program, it is found that the relative amplitude of satellite peaks 3, 5, 6 and 7 to peak 4, measured after irradiated with high-energy 12 C ions, is higher than that with 60 Co γ -rays for both types of TL detectors. It is observed that nat .,7 LiF:Mg,Cu,P thermoluminescent detectors would also exhibit a good linear dose response when the delivered dose of high-energy 12 C ions is in the range from 100 mGy to 1600 mGy. Furthermore, the relative efficiency of the nat .,7 LiF:Mg,Cu,P thermoluminescent detectors is independent of the absorbed dose in the linear dose response range. Compared to previously published data, the relative efficiency of the 7 LiF:Mg,Cu,P TL detectors decreases with increasing LET values.

Description: Publication date: Available online 8 November 2014 Source: Radiation Measurements Author(s): Therése Geber-Bergstrand , Christian Bernhardsson , Maria Christiansson , Sören Mattsson , Christopher L. Rääf Optically stimulated luminescence (OSL) was used to test different kinds of desiccants for their potential use in retrospective dosimetry. Desiccants are used for the purpose of absorbing liquids and can be found in a number of items which may be found in the immediate environment of a person, including hand bags, drug packages, and the vehicles of rescue service teams. Any material exhibiting OSL properties suitable for retrospective dosimetry is a useful addition to the existing dosimetry system available in emergency preparedness. Eleven kinds of desiccants were investigated in order to obtain an overview of the fundamental OSL properties necessary for retrospective dosimetry. Measurements were made using a Risø TL/OSL reader and irradiations were achieved with the 90 Sr/ 90 Y source incorporated in the reader. Several of the desiccants exhibited promising properties as retrospective dosemeters. Some of the materials exhibited a strong as-received signal, i.e. without any laboratory irradiation, but the origin of this signal has not yet been established. The minimum detectable dose ranged from 8 to 450 mGy for ten of the materials and for one material (consisting of natural clay) the minimum detectable dose was 1.8 Gy.

Description: Publication date: January 2015 Source: Radiation Measurements, Volume 72 Author(s): L. Baly , G. Martín , I. Quesada , F. Padilla , R. Arteche A new approach based on the Monte Carlo simulation is used to calculate the infinite matrix dose rate correction factors of gamma, beta and internal conversion radiations for 250 μm diameter grains of quartz and TLD500 chips. Here, the dependence of the correction factor on the radiation energy is initially calculated for each type of emitted particle and with this result the correction factors for the 232 Th and 238 U series and 40 K are determined. This analysis is made for dry soil and also for different levels of water content in it. The obtained beta correction factors for quartz are in good agreement with those previously reported. For the TLD500 chip certain differences with previously reported data are found. The analysis of the gamma water correction factor for quartz based on Zimmerman equation shows the correspondence with the similar correction factor for electrons. In the case of TLD500 chip a gamma water correction factor value of 1.0 was found.

Description: Publication date: Available online 22 November 2014 Source: Radiation Measurements Author(s): Zaiwei Fu , Shangke Pan , Fan Yang , Shenjie Gu , Xiangcui Lei , Yuekun Heng , Guohao Ren , Ming Qi Li 6 Y(BO 3 ) 3 :Ce crystal is a promising type of scintillator for neutron detection. In this study, the properties of Li 6 Y(BO 3 ) 3 :3at%Ce are studied, including its γ sensitivity, neutron efficiency, α/γ ratio, relative light yield, neutron pulse-height spectrum and decay time. Geant4 simulations indicate that its capture efficiency for thermal neutrons is as high as 78% for the natural abundances of the boron and lithium elements. The α/γ ratio of Li 6 Y(BO 3 ) 3 :Ce is measured to be 0.03, which is 10 times lower than that of lithium glass. If the per-MeV light yield of lithium glass is defined to be 100, then the light yields generated by Li 6 Y(BO 3 ) 3 :Ce for γ rays and α particles are 253.3 and 24.8, respectively. Under γ-ray irradiation, the light yield of Li 6 Y(BO 3 ) 3 :Ce is approximately 6 times lower than that of NaI:Tl. In neutron detection, the neutron signal can be clearly distinguished from the backgrounds caused by the 252 Cf source itself. Li 6 Y(BO 3 ) 3 :Ce is also a fast scintillator, with decay times of 48.6±14.4 ns, 24.6±13.3 ns and 37.8±17.8 ns under irradiation with γ rays, α particles and thermal neutrons, respectively. This study offers a systematic study of useful parameters of Li 6 Y(BO 3 ) 3 :3at%Ce crystal for application in and the improvement of neutron detection.