Description: Publication date: Available online 30 December 2016 Source: Radiation Measurements Author(s): Chen Xiang, Han He-Tong, L.I. Gang The linear response is the key property for a radiation detector to obtain accurate intensity of the radiation field. In this experiment, a high-intensity pulsed X-ray source, named “QiangGuang-I” is utilized to test the linear response of cadmium zinc telluride (CZT) detector. The total dose per pulse 20 cm from the pulse source is 200–3000 Gy. The full width at half maximum of each pulse is 20–30 ns, and the average energy of X-ray is approximately 1 MeV. Two detectors are placed in different intensities, and their responding curves are used to draw the Lissajous figure, analyzing the maximum energy dose rate of the CZT detector. The total dose of the pulsed X-ray into the experimental detectors is simultaneously measured by thermoluminescent dosimeter (TLD) chips. The result shows that the output of CZT detectors remains linear when the energy fluence rate is lower than 10 17 MeV/(cm 2 ·s).

Description: Publication date: January 2017 Source: Radiation Measurements, Volume 96

Description: Publication date: Available online 29 December 2016 Source: Radiation Measurements Author(s): P. Bilski, B. Marczewska, Ya Zhydachevskii Radiophotoluminescence emission (RPL) and excitation (RPL-E) spectra of LiF:Mg,Cu,P and LiF:Mg,Ti sintered pellets, normally used as thermoluminescent (TLD) MCP-N and MTS-N detectors, were investigated following irradiations with various beta and alpha doses. The RPL spectra consist of two peaks: at 520 nm and at 670 nm, similarly as for undoped LiF single crystals. The radiation dose has however a significant influence on RPL spectra, as with the increasing dose a relative growth of the peak at 670 nm is observed. Alpha particle irradiation produces a relative increase of the peak at 520 nm, as compared with beta irradiation. Characteristics of LiF:Mg,Cu,P and LiF:Mg,Ti are similar but not identical. Especially dose response of 520 nm and 670 nm peaks for both materials is different. These differences should be taken into account if LiF TLDs are planned to be used as photoluminescence dosimeters. Excitation spectra for emission at 670 nm remains basically unchanged disregarding detector type, radiation type and dose. In case of emission at 520 nm the situation is different: increase of radiation dose results in broadening of the RPL-E spectrum or even in splitting of the main peak into two separate ones. The effect is observed for both LiF:Mg,Ti and LiF:Mg,Cu,P, while no such effects occur for undoped LiF single crystals.

Description: Publication date: Available online 28 December 2016 Source: Radiation Measurements Author(s): George Polymeris, Vasilis Pagonis, George Kitis Thermoluminescence (TL) glow curves from feldspar samples have been studied extensively in luminescence dating and dosimetry applications. However, the mechanism responsible for their unusual shape and behavior in preheated samples is not well understood. This paper presents new experimental TL glow curves for four types of preheated feldspar samples; an orthoclase, a sanidine and two microclines. Both the preheat temperature and the duration of the preheat are varied, before measurement of the remnant TL glow curve. Kinetic analysis of the experimental results is carried out using a recently proposed physical kinetic model which describes localized electronic recombination in a random distribution of donor-acceptor pairs, with nearest-neighbor interaction. The experimental data are analyzed using two different methods within the model. In the first method one follows the development of the distribution of nearest neighbor distances for each of the four stages of the experiment, namely irradiation followed by heating to a temperature and holding the sample at this temperature for certain time, and finally measurement of the TL glow curve. In the second method the TL glow curves are analyzed by using a single adjustable parameter in the model, which characterizes the thermal history of the sample. Good agreement is found between the two methods. However, the second method is much simpler to use in practical situations, and in principle it can be applied for any thermally or optically pretreated feldspar sample.

Description: Publication date: Available online 25 December 2016 Source: Radiation Measurements Author(s): A. Bresolin, F. Bonfantini, C.G. Stucchi, V. Mongioj, M. Carrara, E. Pignoli The commissioning of up-to-date linacs, designed to deliver flattening-filter-free (FFF) photon beams, is performed by measurements using air-vented ionization chambers which are often employed for traditional beams. The aim is to select the ionization chambers which are able to minimize the ion recombination effect, critical for these high intensity beams. In order to provide operators with information about the response to FFF beams of widely used chambers, the recombination correction factor k s and the dose-per-pulse (DPP) were determined in different irradiation conditions. The study, performed by using devices available in most radiotherapy departments, confirmed the reliability of the Boag model for FFF beams as well as with-flattening-filter (WFF) beams. The results showed that k s factor largely depends on the spacing between the collecting electrodes ( d el )in the ionization chamber and on the DPP of the linac output, which in turn depends on beam energy but is independent of monitor unit rate (MU/min). For plane-parallel and pin-point chambers, whose d el is minimal, the k s factor is negligible, whereas for Farmer type chambers the recombination could be important and hence the correction is to be applied (also at voltages higher than the recommended one).

Description: Publication date: Available online 22 December 2016 Source: Radiation Measurements Author(s): Anna A. Romanyukha, Mauro Carrara, Chiara Tenconi, Davide Mazzeo, Giulio Rossi, Marta Borroni, Emanuele Pignoli, Annamaria Cerrotta, Dean Cutajar, Marco Petasecca, Michael Lerch, Joseph Bucci, Anatoly B. Rosenfeld In vivo dosimetry (IVD) is an excellent mode of treatment verification and detection of possible overexposures. A feasibility study was conducted to evaluate a proposed IVD procedure for gynecological HDR brachytherapy procedure quality assurance. MO Skin dosimeters were selected due to their small size and capability of measuring steep dose gradients, such as those relevant in HDR brachytherapy procedures. Two in-phantom experiments measuring dose with MO Skin s at the position simulating the rectal wall were conducted employing a cylindrical single channel applicator and a multichannel applicator. Three MO Skin s were incorporated onto a rectal catheter, which was then attached to the applicator, separated by a small wooden plaque, simulating the vaginal to rectal wall distance and fixing catheter position. This setup was inserted into a water phantom and three treatment plans prescribing 300 cGy to 3 different targets were assigned with various dose distributions. Each treatment was administered three times, and doses measured by the MO Skin s were recorded. Doses measured by the MO Skin s were within 5% of the dose determined by the treatment planning system (TPS), ranging between 208 and 332 cGy, depending on dosimeter position on the rectal catheter. The overall average dose difference between measured and TPS values was 2.09% ± 1.15% (ranging between 0.83 and 4.27%, with measured values always higher than TPS dose), subdivided in 1.40 ± 0.37% and 2.79 ± 1.27% for single and multichannel applicator experiments, respectively. An overall dose agreement between the TPS and measured values, detector reproducibility, and practicality of the rectal catheter demonstrated the suitability of the proposed method for in vivo real time QA purposes in gynecological HDR brachytherapy.

Description: Publication date: Available online 22 December 2016 Source: Radiation Measurements Author(s): M.L. Chithambo, A.H. Wako, A.A. Finch The kinetic analysis of thermoluminescence of beta-irradiated SrAl 2 O 4 :Eu 2+ ,Dy 3+ is reported. The glow-curve is dominated by an apparently-single peak. It has been demonstrated using a number of tests including partial dynamic-heating, isothermal heating, phosphorescence and, the effect of fading, that the peak and the glow-curve consists of a set of closely-spaced peaks. In view of the peak being complex, its first few components were abstracted and analysed and for comparison, the peak was also analysed assuming it is genuinely single. In the latter, the order of kinetics is calculated to be intermediate between first and second-order and not first-order as predicted by qualitative tests such as the T m − T s t o p or T m − d o s e procedures. A model based on density of energy states has been used to account for and reconcile the qualitative and quantitative results. The activation energy is found as ∼1 eV, consistent with the value expected of Dy 2+ , the presumed electron trapping state of the Dy 3+ electron trap. The thermoluminescence is subject to thermal quenching with an activation energy of 0.520 ± 0.002 eV. The luminescence is ascribed to 5d→4f 7 Eu 2+ transitions whereas the thermal quenching is presumed to occur from an alternative level of the degenerate 5d energy level of the Eu 2+ cation.

Description: Publication date: Available online 21 December 2016 Source: Radiation Measurements Author(s): G.M. Orchard, T. Hatakeyama, A.J. Waker A nested neutron spectrometer (NNS) and a tissue equivalent proportional counter (TEPC) were used to measure the spatial dose equivalent and energy neutron fluence distribution of a P 385 D-D Thermo Fisher Scientific Neutron Generator located in the mixed field dosimetry facility at the University of Ontario Institute of Technology. The P 385 Neutron Generator uses the D-D nuclear reaction to generate neutrons with an expected average energy of 2.5 MeV. The NNS uses a He-3 proportional counter to measure the neutron capture count rate as a function of nested cylindrical moderator thickness. Using the NNS and associated unfolding software, the energy neutron fluence distribution at various locations from the P 385 neutron generator were determined along with other radiation protection quantities of interest. Measurements of the dose equivalent rate were also conducted at the same locations using a 5-inch spherical TEPC and compared to the NNS results. The TEPC was further used to measure the dose equivalent as a function of radial distance from the neutron generator target and also for different P 385 operating conditions.

Description: Publication date: Available online 15 December 2016 Source: Radiation Measurements Author(s): J. Farah, M. De Saint-Hubert, N. Mojżeszek, S. Chiriotti, M. Gryzinski, O. Ploc, F. Trompier, K. Turek, F. Vanhavere, P. Olko This paper compares the performance of four different Tissue-Equivalent proportional counters (TEPC) first in standard radiation fields, with gamma and neutron sources, then in the mixed and complex/intense neutron and photon stray radiation field of a scanning proton therapy facility. The paper focuses on the dead time correction and introduces a new spectra processing methodology to enable the comparison of the four TEPCs while accounting for their different gas filling and gain, lineal energy range of the spectrum and the analysis methodology. Measurements with 137 Cs and/or 60 Co gamma sources demonstrate variable low-LET threshold for each TEPC while data acquired with a 252 Cf neutron source show comparable response of the four TEPCs for high-LET particles. Meanwhile, in the scattered field of proton therapy, microdosimetric spectra measured at different positions and orientations around the patient show a majority of high-LET events at the smallest angle with respect to the beam axis while low-LET particles were mainly dominant at 90° from the beam axis. The introduced processing methodology led to good overlapping of microdosimetric spectra for the four systems.

Description: Publication date: Available online 15 December 2016 Source: Radiation Measurements Author(s): Kei Watanabe, Masanori Koshimizu, Yutaka Fujimoto, Yamato Hayashi, Hirotsugu Takizawa, Takayuki Yanagida, Keisuke Asai We synthesized ZnO ceramics scintillators without or with dopants using a high-pressure synthesis method. The dense ceramics were successfully obtained, and the densified structure was confirmed by SEM observation. Doping with Ga is proven to be effective for suppressing the deep level (DL) emission as well as the long decay component in the scintillation temporal profile. Based on the pulse height spectra, the light yield is estimated to be 1500 photons/5.5-MeV alpha-ray for the undoped ceramics, and the doped ceramics exhibit similar light yields. These results indicate that the high-pressure synthesis method is effective for the synthesis of dense ZnO ceramics scintillators with a fast response.