Prevezanou, K.Kioselaki, G.Tsoutsoumanos, E.Konstantinidis, P. G....
9页
查看更多>>摘要：In Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL), the study of complex experimental TL glow curves and OSL signal processing, also known as deconvolution, was revolutionized by using a single, analytic master equation described by Lambert W function. This latter equation has been also adopted for the case of dose response fitting. The present study exploits the utilization of Lambert W function in Python programming environment. These analytic expressions are based on One Trap-One Recombination center (OTOR) and Two Traps-One Recombination center (TTOR) models. Python scripts, with corresponding software flowchart being described in general, are created to deconvolve TL, LM-OSL, CW-OSL as well as to fit dose response experimental data. The calculated results are in agreement with those of the existing literature. Also, all scripts are free and available in GitHub to the research community for downloading.
查看更多>>摘要：Gamma-ray spectrometry is a well-established technique which enables to perform qualitative and quantitative analyses of gamma-ray emitting radionuclides. In trapped charge dating, portable spectrometers can be used to acquire spectra in the field, allowing for the assessment of radionuclide concentrations and hence the determination of dose rates at the exact location where samples are collected for dating. Accurate assessment of concentrations and dose rates demands proper energy, width, and efficiency calibration of the instrument by comparison against one or several radioactive standards. The 'Oxford blocks' which consist of four concrete cubes doped with known concentrations of potassium [K-block], thorium [Th-block], and uranium [U-block], as well as a background [BG-block], were constructed for this purpose and have become widely adopted by researchers for calibrating their instruments. For inexperienced users, the calibration of detectors and the analysis of field spectra for determining the concentration of radionuclides can be a challenging and laborious task that often involves multiple steps (e.g., downloading and converting data files, peak identification and selection, energy calibration, true full-peak area calculation, efficiency calculation, etc.). The processing of calibration spectra from the Oxford blocks is further complicated by the fact that the K-block contains only similar to 72% concrete and the Th-block contains a small amount of uranium. These factors must be accounted for in order to obtain accurate radionuclide concentrations and dose rates. Here, we present a practical and user-friendly MATLAB based application (OxGamma), available as a free download for both Windows OS and macOS, intended to facilitate the calibration process of portable gamma-ray detectors and to provide a quick and efficient means for determining the concentration of radionuclides (K, U and Th) and dose rates. The software has been tested and checked against results obtained independently and provides output using both the windows and threshold approaches. Crucially, it does not require users to possess in-depth experience in programming or gamma-spectrometry.
查看更多>>摘要：This study proposes a technique for alanine dosimetry using a superconducting quantum interference device (SQUID) magnetometer. Conventional measurements performed using an electron spin resonance spectrometer typically detect the relative amount of stable radicals generated in irradiated alanine using a magnetic field and microwaves. The SQUID magnetometer uses a magnetic field and a pickup coil to measure the total magnetic moment of stable alanine radicals. In this study, we demonstrate the principle of the alanine/SQUID measurement system. SQUID successfully detected the alanine radical at 4.2 K, and the reproducibility test showed that the relative standard deviation were 0.13 % and 0.10 % at the minimum value and averaged value in the measurement with different angles after 11 repetitions. This study shows that calibration curves can be constructed between 0.3 and 101 kGy and that the magnetic moment of alanine radicals can be measured in that dose range. The magnetic moments corresponding to the dose range of the calibration curve were 6.7 x 10(-3) to 1.1 x 10(- 1) mu A.m(2).mg(- 1). The number of radicals in alanine pellet induced by 101 kGy irradiation was 1.91 x 10(22) kg( -1), which was determined by measuring the magnetic moment in the range of 80 K-300 K. Radiation chemical yield (G-value) of the alanine derived from the measured radical number was 0.31 mu mol.J(-1).
Williams, Owen M.Smith, Barnaby W.Spooner, Nigel A.
8页
查看更多>>摘要：The role that oxygen vacancies can play in the emission of quartz ultraviolet luminescence is investigated. Within a defect pair model approach we highlight the significance of aluminium, titanium and germanium point defects. By comparing known trace element estimates with estimates of the number of luminescent photons that are emitted globally from our bright quartz samples, we confirm that the available impurity defects outnumber the emitted photons by several orders of magnitude. Our conclusion is that another defect species must play a significant role in the observed luminescence sensitivity of quartz. By reviewing the literature on oxygen vacancies, we develop a hypothesis that the well-known oxygen vacancy E'1 centers act as a barrier to migration of holes along the quartz c-channel wall structure, preventing the emission of luminescence. We proceed to examine the processes via which E'1 centers migrate historically under ambient temperature conditions from their source location. By applying known potential barrier information, we contend that a thermally-assisted solar UV exposure mechanism can explain the migration process. In particular, we argue that during such migration the E'1 centers can be trapped at other centers which neutralise them, allowing free passage for subsequent holes enroute to the luminescence centers . Such a mechanism predicts that bright luminescence should be observed from quartz extracted from hot sunny locations, compared with lower levels of luminescence in the case of quartz from cool overcast locations. This is consistent with known observations that quartz sensitivity increases with cumulative sunlight exposure.
查看更多>>摘要：This study aimed to characterize CaF2:Dy (TLD-200) thermoluminescence dosimeter (TLD) in mammography, and to determine entrance surface dose (ESD), relative depth dose (RDD), and mean glandular dose (MGD) values. The angular and energy dependencies, dose-response, and TL intensity reproducibility characteristics of dosimeters were investigated. The dosimeters showed a linear dose-response behavior corresponding to air kerma values ranging between 2.11 and 21.98 mGy and a reproducibility of +/- 5%. The response of the dosimeters showed by ~48% over response when the tube potential increased from 22 to 32 kVp, indicating that they have a substantial energy dependence. On the other hand, the TL intensity at 90? decreased by 70% compared with that at 0?, when the angular dependence of dosimeters was investigated. The ESD and MGD values obtained for both polymethyl methacrylate (PMMA) and BR-12 phantoms were compatible with existing literature, and the MGD values were also agreed with the European Federation of Organisations for Medical Physics (EFOMP). The RDD value decreased by nearly 90% at 6 cm depth. These dosimetric quantities did not change considerably for PMMA and BR-12 phantoms. The results showed that TLD-200 could be used as an alternative dosimeter in mammography to determine dosimetric quantities.
Presilla, StefanoPiliero, Maria A.Pupillo, Francesco
8页
查看更多>>摘要：In this work, we performed the characterization of the Konica Minolta CM-700d spectrophotometer as a portable device for radiation dosimetry based on EBT3 GAFchromic films. The measurements were carried out in the CIE XYZ colour space. In this colour space, colour is described as a triplet of numbers representing the values at each coordinate (X, Y or Z coordinate). High stability and reproducibility of colour measurements was observed, with variations of coordinate values below 0.04% and 0.2% respectively. Dose calibration was carried out by irradiating film pieces with a 6 MV photon beam with a dose between 0.1 and 8 Gy. For dose measurements up to 2 Gy, 2% accuracy was achieved. This is comparable to what achieved with flatbed scanners, although the Konica Minolta spectrophotometer can be used for point dose measurements only. However it allows for a faster readout procedure thanks to its stable response from the first measurement (it does not need any warm up period). Moreover, no image processing is required.
查看更多>>摘要：Beta Dose Rate heterogeneity is a recognized source of uncertainty when applying luminescence dating to heterogeneous samples, such as coarse crystalline rocks and clast-rich sediments. Simulations have shown that a combination of a heterogeneous distribution of minerals and radioactive elements can lead to complex dose distributions, overdispersion and potentially to bias in equivalent dose determinations. However setting realistic conditions for such simulations remains difficult, and there are at present only a few experimental validation cases for such simulated systems. Project ADDEM is investigating means of linking Monte Carlo simulations of dose rate to specific minerals with direct observations using high sensitivity phosphor plates and laser scanning imaging systems in combination with phase mapping. To overcome some of the limitations of autoradiographic imaging of low level beta dose distributions work has been undertaken using Landauer alumina OSL phosphor screens in combination with a laser scanning system developed at the Scottish Universities Environmental Research Centre (SUERC). Preliminary excitation spectra, emission band characterization and time resolved measurements were undertaken, confirming the potential to recording low doses using asynchronous stimulation at 635 nm coupled with blue band detection. Taking advantage of the slow decay of the luminescence signal the scanning equipment has been configured for pulsed stimulation and asynchronous detection to maximise signal to background ratios. Exploratory work was calibrated using a Co-60 facility capable of calibrating doses in the mu Gy to mGy range. A series of powdered granulite/basalt mixtures of known mean activity and dose rate (Dr) have also been used to calibrate the phosphor screens. To reduce background levels during autoradiographic signal accumulation rock slices are being exposed in the Zeplin shield of the STFC Boulby Underground Laboratory, in an environment which is essentially free from cosmic ray muon background. Simulations have been conducted providing preliminary deconvolution parameters in order to either reconstruct the beta dose rate (beta Dr) distribution received by the grains in the sample, or retrieve the radioactive element distributions in the minerals of the sample, providing the data required for representative simulations of beta Dr. This paper outlines the spectroscopy and sensitivity verification of the autoradiography system, confirming its prospects for measuring spatially resolved beta Dr distributions with single pixel lower detection limit of 130 mu Gy and spatial resolution of 150 mu m. Prospects are outlined.
查看更多>>摘要：Objectives: Interventional professionals tend to receive extended radiation exposure given the complexity and machine settings of procedures in interventional cardiology departments, resulting in a high eye lens dose. This study developed a method for estimating the occupational radiation dose to the eye lens based on the personal dose equivalent to the skin at 0.07-mm depth [H-p(0.07)] obtained using an over-apron dose badge, investigated whether glasses with lateral shielding but a thin Pb-equivalent material could adequately protect the eye lens from radiation in clinical situations, and identified factors affecting the occupational radiation dose to the eye lens. Methods: The occupational radiation dose was prospectively measured using dosimeters near the eye and over the lead apron at the collar level in 26 interventional professionals performing 444 procedures in interventional cardiology departments. Type A (0.07-mm front and lateral Pb equivalence) and type B (0.5-mm front Pb equivalence and 0.25-mm lateral Pb equivalence) glasses were worn by the operators during operation to protect the eye lens. Results: The median personal dose equivalent to the eye lens at 3-mm depth [H-p(3)/dose area product (DAP)] of the primary operator was the highest (7.6 mu Sv/Gycm(2)) for upper limb percutaneous transluminal angioplasty among all examined procedures. The secondary operator's median H-p(3)/DAP values ranged from 17% to 41% of that of the primary operator. The median H-p(3)/DAP values did not significantly differ between the primary operators wearing type A glasses and those wearing type B glasses for percutaneous coronary intervention or diagnostic cardiology studies (all p > 0.05). The Pearson correlation test results revealed significant positive correlations between the H-p(3) and H-p(0.07). The estimated annual H-p(3) values ranged from 3.3 +/- 0.6 to 62.4 +/- 8.3 mSv and from 6.0 to 8.0 +/- 4.6 mSv for the cardiologists and radiographers, respectively. Conclusions: The H-p(3) value can be estimated from the H-p(0.07) value obtained using an over-apron dose badge at the collar level. Glasses with 0.07-mm front and lateral Pb equivalence provide satisfactory radiation protection to the eye lens. Regularly using appropriate radiation-protective lead glasses, adopting small angles for left anterior oblique projections, and undertaking moderate workloads are highly recommended to prevent cardiologists from receiving excessive radiation doses to the eye lens.
Klavsen, M. F.Ankjaergaard, C.Behrens, C. P.Vogelius, I. R....
11页
查看更多>>摘要：One of the newest developments within radiotherapy is the integration of Magnetic Resonance (MR) scanners and Megavoltage X-rays from linear accelerators into the new MR-Linacs. Some MR-Linacs are able to perform gated treatments based on continuously acquired 2D MR images taken during dose delivery, which has the potential to reduce margins required for tumor coverage. We have developed a dosimetry system that can provide time-resolved, dose-per-pulse, dosimetry without distorting the MR images in order to characterize this technology. The system is based on a plastic BCF-60 scintillation detector (PSD) coupled to an optical PMMA fiber cable. The detector was placed in a plastic tube filled with water and inserted into the piston of a dynamic MRI compatible phantom to be treated on a ViewRay MRIdian 0.35 T MR-Linac. The piston performed a sinusoidal movement to simulate a breathing cycle of either 4 or 8 s. We demonstrate that the detector system is able to provide real-time dose-per-pulse measurements without causing distortions in the MR images. The time-resolved dosimetry system revealed systematic dose rate transients during gated treatments that lasted about 1 s in every gating sequence where the beam turned on and off. Detection of such effects require real time dosimetry which does not interfere with the MRI based gating.
查看更多>>摘要：Advances in neutron-based radiation therapies such as Boron Neutron Capture Therapy (BNCT) pushes towards the development of new neutron spectrometers, whose key features are to be their practicability, reliability, energy resolution and detection range. The ACSpect is a novel neutron spectrometer based on a two-stages monolithic silicon telescope detector coupled to an organic scintillator working as an active neutron converter. This paper reports the latest developments of the ACSpect and the results of the measurements of an accelerator-based neutron beam moderated by AlF3. The AlF3 is a moderator material optimised to obtain an epithermal neutron beam for accelerator-based BNCT of deep seated tumours. The experiments carried out are the first neutron spectrometry of a neutron beam moderated by AlF3. The performances of the ACSpect have been compared against Monte Carlo simulations, literature data and the gold-standard neutron spectrometer DIAMON. While the agreement between experiments and simulations allowed to validate the Monte Carlo model used to simulate the new moderator material, the agreement between literature data, ACSpect and DIAMON results confirmed the ACSpect as a compact and relatively easy-to-use high-resolution neutron spectrometer, capable of reliably operating in the energy range 250 keV - 4 MeV.
NSTL
Elsevier