Description: Publication year: 2011 Source: Radiation Measurements, Available online 18 November 2011 X.L. Wang, A.G. Wintle When using a single-aliquot regenerative dose (SAR) protocol for luminescence dating of sedimentary quartz grains, the fundamental assumption is that the sensitivity of the optically stimulated luminescence (OSL) produced by the regenerative doses can be monitored by their following test dose OSL response. Using well-bleached coarse quartz grains, OSL production in a SAR protocol was studied in detail when dose response curves were constructed using both single and multiple aliquot regenerative dose procedures. During application of the SAR protocol, two preheats are applied, each ahead of an OSL measurement that is produced by the regenerative dose and test dose, respectively. It is shown that sensitivity changes caused by heating were well corrected for using the OSL response to the test dose. However, these preheats are shown to result in thermally stimulated OSL signals that contribute both to the OSL response from the regenerative doses used to construct the dose response curve and to the OSL response from the test dose used to monitor OSL sensitivity changes as the quartz grains are repeatedly measured. A simple test is proposed to identify the contribution of the latter signal. Highlights ► Measurement of OSL during construction of MAR and SAR dose response curves. ► TT-OSL affects both L and T in SAR protocol causing lack of direct proportionality. ► Test dose response affected by size of regenerative dose in same cycle. ► Test proposed to detect TT-OSL contribution to test dose response.

Description: Publication year: 2011 Source: Radiation Measurements, Available online 20 November 2011 M Zehtabian, R Faghihi, M H Zahmatkesh, A S Meigooni, M A Mosleh-Shirazi, ... PurposeNowadays, medical physicists need dosimeters like Gel dosimeters capable of determining three-dimensional dose distributions with a high spatial resolution. To date, in combination with magnetic resonance imaging (MRI), polyacrylamide gel (PAG) polymers are the most promising gel dosimetry systems. The purpose of this work was to investigate the dose rate dependency of the PAGAT gel dosimeter at low dose rates. Methods: The gel dosimeter was used for measurement of the dose distribution around a Cs-137 source from a brachytherapy LDR source to have a range of dose rates from 0.97 Gy/hr to 0.06 Gy/hr. After irradiation of the PAGAT gel, it was observed that the dose measured by gel dosimetry were almost the same for different distances (different dose rates) from the source although the points nearer the source had been expected to receive greater doses. Therefore, it was suspected that the PAGAT gel is dose rate dependent at low dose rates. To test this further, three other sets of measurements were performed by placing vials containing gel at different distances from a Cs-137 source. In the first two measurements, several plastic vials were exposed to equal doses at different dose rates. An ionization chamber was used to measure the dose rate at each distance. In addition, three TLD chips were simultaneously irradiated in order to verify the dose to each vial. In the third measurement, to test the oxygen diffusion through plastic vials, the experiment was repeated again using plastic vials in Nitrogen box and glass vials. Results and conclusions: The study indicates that oxygen diffusion through plastic vials for dose rates lower than 2 Gy/hr, would affect the gel dosimeter response. Therefore, it is suggested that the plastic vials or (phantoms) in an oxygen free environment or glass vials should be used in dosimetry of low dose rate sources using PAGAT gel, to avoid oxygen diffusion through the vials. Highlights ► Oxygen diffusion through plastic vials for dose rates lower than 2 Gy/hr, would affect the gel dosimeter response. ► It is suggested that plastic vials or phantoms be used in an oxygen free environment, for LDR sources dosimetry by PAGAT gel. ► To avoid oxygen diffusion, it is better to use glass vials in dosimetry of low dose rate sources by PAGAT gel.

Description: Publication year: 2011 Source: Radiation Measurements, Available online 20 November 2011 Anuj Soni, D.R. Mishra, B.C. Bhatt, S.K. Gupta, N.S. Rawat, ... Commercially available α-Al2O3:C powder was studied for deep energy level defects by a newly suggested method using thermally assisted optically stimulated luminescence(TA-OSL) phenomenon. The method involves simultaneous application of continuous wave optically stimulated luminescence (CW-OSL) as well as thermal stimulation up to 400C, using a linear heating rate of 4K/s. By using this method, two well defined peaks at 121C and 232C were observed. These TA-OSL peaks have been correlated to two different types of deeper defects which can be bleached at 650C and 900C respectively on thermal treatment. These deeper defects, having larger thermal trap depth and relatively lower photoionization cross-section at room temperature for stimulation with blue LED (470nm), are stable up to 500C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or temperature. As only a fraction of signal is bleached during TA-OSL readout, multiple readouts could be performed on an exposed sample using this technique. The dose vs TA-OSL response from deep traps of α-Al2O3:C was found to be linear up to 10kGy, thus extending its application for high dose dosimetry. The value of thermally assisted energy (EA) associated with these traps in α-Al2O3:C has been determined to be 0.268eV and 0.485eV respectively and the corresponding values of photoionization cross-section at room temperature (25C), for optical stimulation with blue light (470nm), are 5.82×10and 3.70×10cm, respectively. The process of thermally assisted OSL has been formulated analytically as well as theoretically for describing the temperature dependence of optical cross-section and evaluation of thermally assisted energy associated with deep traps. Highlights ► A noval method of measuring the signal from deeper traps in Al 2 O 3 :C for its use in high dose dosimetry. ► Mathmatical formulation of TA-OSL phenomenon. ► Extended dose linearity of Al 2 O 3 :C phosphor up to 10kGy using TA-OSL of deeper traps, with gives choice of multiple readout. ► Discusses about the nature of deep traps in Al 2 O 3 :C. ► Determination of thermally assisted energy associated with the deeper traps and corresponding photoionization cross section.

Description: Publication year: 2011 Source: Radiation Measurements, Available online 15 November 2011 T.K. Maity, S.L. Sharma, G. Chourasiya A detailed study of the effect of gamma radiation on the current-voltage characteristics of the TeO2thin films of different thicknesses, prepared by thermal evaporation in a vacuum, has been carried out for a much wider range of the gamma radiation doses than made here-to-fore. Subsequently, for the thin films of different thicknesses at different applied voltages, the variations of the current density with dose have been obtained. The current density increases near linearly with the gamma radiation dose up to a critical radiation dose, a dose value higher for the thicker films and decreases thereafter. The sensitivities of these TeO2thin films at different applied voltages have been found to be in the range 1.2 - 37.0nA/cm/μGy. Correspondingly, the detection limits have also been estimated and have been found to be in the range 0.22 - 2.16 mGy. Clearly, the TeO2thin films have high potential for their use as real-time gamma radiation dosimeters in monitoring the gamma radiation doses under a variety of practical situations involving low level to high level of the doses. Highlights ► Current density increases linearly up to a critical gamma radiation dose. ► The critical dose is higher for the thicker films. ► Thin films of different thicknesses have sensitivities 1.2 - 37.0 nA/cm/μGy. ► The corresponding dose detection limits range from 0.22 to 2.16 mGy. ► Linear variation of current density has a high potential for real-time dosimetry.

Description: Publication year: 2011 Source: Radiation Measurements, Available online 28 December 2011 K. Tang, H. Cui, H. Zhu, Z. Liu, H. Fan The preparation method and some dosimetric properties of the new LiF:Mg,Cu,Si discs are presented. The effect of heat treatments on LiF:Mg,Cu,Si was investigated. The shape of the glow curve for LiF:Mg,Cu,Si is similar to that for standard LiF:Mg,Cu,P (GR-200A), and shows minimal differences when annealed in the range from 260oC to 290oC for 10 min. The TL sensitivity for LiF:Mg,Cu,Si is much lower than that for GR-200A, but is 35 times larger than that for TLD-100 and is slightly higher than that for HMCP. The height of the high-temperature peaks for LiF:Mg,Cu,Si is not only lower than that for GR-200A, but also lower than that for HMCP. The glow curve shape of LiF:Mg,Cu,Si annealed at 260oC for different times shows minimal differences and TL response remains stable. These results indicate that the new LiF:Mg,Cu,Si disc has a good stability to thermal treatments and a lower residual TL signal. Highlights ► The TL sensitivity for LiF:Mg,Cu,Si is 35 times larger than that for TLD-100. ► Glow curve shows minimal differences in the range from 260C to 290C. ► The temperature between 260C and 290C can be used to treat LiF:Mg,Cu,Si. ► LiF:Mg,Cu,Si has a good stability to thermal treatments and a lower residual TL signal.

Description: Publication year: 2011 Source: Radiation Measurements, Available online 3 December 2011 Kaixuan Tan, Zehua Liu, Liangshu Xia, Junwen Lv, Hanqiao Hu Tailings produced during mining and milling of uranium ores represent potentially large volumes of low level radioactive materials. A typical environmental problem associated with mill tailings is radon emanation. Covering tailings is widely applied to reduce radon exhalation rate. In this paper, the fractal theories and field covering tests are used to study the fractal characters of size distribution of six types of covering materials, including waste rock, sand, laterite，kaolin, mixture of sand and laterite,and mixture of waste rock and laterite, and their influences on radon exhalation. The size distributions of uranium tailings and the six aforementioned covering materials all exhibit a good fractal structure. The contents of fine grain increase with the increasing value of fractal dimension. The results of field radon measurement show that the radon emanation rate of tailings without covers is 14.7-18.6 Bq/m•s. Covering tests were carried out of the six abovementioned covering materials with thickness of 0.4m, 0.8m, 1.2m, 1.6m and 2.0 m. The results indicate that the application of these materials for cover layers can decrease the radon exhalation rate markedly. The effectiveness of a cover layer in reducing radon exhalation is related to its fractal texture of size distribution. Under the same thickness conditions, the attenuation coefficient of radon exhalation rate increases with the increasing fractal dimension of size distribution of covers. The empirical expressions of the attenuation coefficients in relation to fractal dimension D of size distribution and thickness x of covers is obtained for evaluating the effectiveness of final covers for uranium tailings impoundments. Highlights ► In this study, the fractal theories and field covering experiments were used to study the fractal characters of size distribution of uranium tailings and six types of covering materials, including waste rock, sand, laterite, kaolin, mixture of sand and laterite, and mixture of waste rock and laterite, and their influences on the radon exhalation. The empirical expressions of the attenuation coefficients in relation to fractal dimension D of size distribution and thickness x of covers is obtained for evaluating the effectiveness of final covers for uranium tailings impoundments.

Description: Publication year: 2012 Source: Radiation Measurements, Available online 12 January 2012 A. Tomal, I. Mazarro, E.M. Kakuno, M.E. Poletti

Description: Publication year: 2012 Source: Radiation Measurements Toshio Kurobori, Shoichi Nakamura We report a novel two- and three-dimensional (2-D, 3-D) imaging detector based on the radiophotoluminescence (RPL) phenomenon in silver-activated phosphate glass (PG:Ag) and evaluate its dosimetric characteristics. A compact disk-type PG:Ag detector with a diameter of 80 mm was rotated at a rate of 400 rpm to read out the accumulated dose information and then remove the images for reuse. After X-ray exposure, three RPL dosimeter processes, i.e., preheating, reading, and erasing, were carried out with only a UV laser at 375 nm by adjusting the stepwise output levels. The 3-D images and dose distributions were rapidly reconstructed with a high spatial resolution of 1 μm and a sensitivity of 1 mGy. Highlights ► Proposal and evaluation of a novel area imaging detector using Ag-doped glass. ► Construction of a compact disk-type glass detector. ► Preheating, reading, and erasing processes with only a UV laser. ► Reconstruction of 2-D images with a high spatial resolution of 1 μm and a sensitivity of 1 mGy

Description: Publication year: 2012 Source: Radiation Measurements F. Castillo, G. Espinosa, J.I. Golzarri, D. Osorio, J. Rangel, P.G. Reyes, J.J.E. Herrera The chemical etching parameters (etching time, temperature, normality of etchant, etc.) for the use of CR-39 (allyl diglycol carbonate - Lantrack ® ) as a fast neutron dosimeter have been optimized. The CR-39 chips, placed under a 1.5 mm polyethylene radiator, were exposed for calibration to an 241 Am-Be source at different time intervals for a given neutron fluence. After several chemical etching processes of the detectors with different conditions, the optimum characteristics for the chemical etching were found at 6N KOH solution, 60±1°C, for 12 hrs. An accurate relationship between the dose and fluence calculations was obtained as a function of the track density. Highlights ► Optimum etching time for fast neutron irradiated CR-39 track detectors is found. ► Relationship between dose and fluence obtained as a function of the track density. ► Results are consistent with those reported elsewhere, and extend the dose range.

Description: Publication year: 2012 Source: Radiation Measurements G. Espinosa, J.I. Golzarri, A. Chavarria, V.M. Castaño Indoor radon concentration represents an important public health challenge, for simple and inexpensive measurement devices and methods, suitable for large-scale indoors radon measurements, are required. Nuclear Track Methodology, by using a closed-end cup device as a radon chamber is an attractive option for such large-scale indoor radon measurements. A comparative analysis of the detection efficiency of four different (one commercial and 3 specially designed) passive closed-end cup devices for the measurement of indoor radon concentrations is presented. CR-39 (Lantrack®) polycarbonate was the detector material. The four devices were simultaneously exposed to a mean radon concentration of 860 ± 60 Bq m −3 inside a closed room for periods of one, two and three months. An AlphaGUARD ® radon monitoring system was used to continuously monitor the radon concentration within the room. The chemical etching and reading procedures were carried out following a well-established protocol for indoor radon surveys. The detection efficiency and the exposure-time-response relationship of each of the devices were determined. Highlights ► Low cost Nuclear Track detectors systems. ► Reliable indoor radon measurements. ► Long term assessment of home radiation levels. ► Large scale indoor radon measurements.