In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co⁶⁰ gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co⁶⁰ neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy^?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.     

Further investigations of tunneling recombination processes in random distributions of defects

The shape of infrared stimulated luminescence signals (IRSL) from feldspars has been the subject of numerous studies in the field of luminescence dating. Specifically linearly modulated IRSL signals (LM-IRSL) are commonly assumed to consist of several first order components corresponding to distinct optical stimulation cross sections. This paper models the shape of LM-IRSL signals using a recently proposed kinetic model, which describes localized electronic recombination in donor–acceptor pairs of luminescent materials. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. The model has been used previously successfully to describe both thermally and optically stimulated luminescence (TL, OSL). This paper shows that it is possible to obtain approximate solutions for the distribution of donors in the ground state as a function of two variables, time and the distance between donors and acceptors. Approximate expressions are derived for several possible modes of optical and thermal stimulation, namely TL, OSL, linearly modulated OSL (LM-OSL), LM-IRSL and isothermal TL (ITL). Numerical integration of these expressions over the distance variable yields the distribution of remaining donors at any time t during these experimental situations. Examples are given for the derived distributions of donors in each experimental case, and similarities and differences are pointed out. The paper also demonstrates how LM-IRSL signals in feldspars can be analyzed using the model, and what physical information can be extracted from such experimental data. The equations developed in this paper are tested by fitting successfully a series of experimental LM-IRSL data for Na- and K-feldspar samples available in the literature. Finally, it is shown that the equations derived in this paper are a direct generalization of an equation previously derived for the case of ground state tunneling.     

Advantages and challenges of high-dose thermoluminescent detectors

The current status of high-dose luminescent detector investigations is discussed. The examples of successful applications of various materials for medium and high-dose luminescent detector creation are presented. High-dose irradiation effect on luminescence of TLD-500 (α-Al₂O₃:C) detectors has been described. The challenges of detector properties restoration after high-dose irradiation are considered.     

On the relationship between the lightning electromagnetic field and the channel-base current based on the TL model

A set of approximation expressions relating the lightning channel-base current and the lightning electric and magnetic fields on earth surface are proposed respectively in the near-zone and far-zone, by employing the transmission line (TL) model. The derived expressions show that, the electric and magnetic fields waveforms can be expressed approximately by the channel-base current waveform with different factors at a certain distances, whether in the near-zone or far-zone. The factors can be expressed in terms of the return stroke wavefront speed v, the speed of light c, and the horizontal distance r between the return-stroke channel and the observation point.     

Role of fluorescent lamp phosphors in accidental radiation monitoring

The present paper reports studies on the applicability of fluorescent lamp phosphors in accidental radiation dosimetry. Strontium orthophosphate, which is used as one of the components in the fluorescent lamps, has been studied for its thermo-luminescence (TL) characteristics on exposure to different doses of beta irradiation. The analysis of the TL glow curve of the phosphor, with a well-defined glow peak at 553 K, and other experiments carried out have proved the utility of strontium orthophosphate as dosimetric material in the range of 10–200 Gy. It has been observed that the material satisfies most of the fundamental criteria for a good TLD-material. A fluorescent lamp developed with this material as TLD grade lamp phosphor is thus expected to serve twin purposes of providing illumination and monitoring the radiation released during a nuclear accident.     

TL法和UL法对刚架弹性大位移分析的适用性

本文分别基于Total Lagrange(TL)和Updated Lagrange(UL)描述分别导出了适用于刚架问题几何非线性分析的有限元公式系统，并研制了相应的计算程序，文中从量化的角度讨论了上述两种列式方法在通常情况下的适用性，并研究了诸如有限单元划分、杆件中轴向力的大小以及采用通常积分方法或积分平均化方法时等多种因素对于有限单元TL法和UL法适用性方面的影响，本文得出了一些相对量化的结论，对于非线性有限元方法的实际工程应用具有一定的指导意义。     

Influence of sintering temperatures on LiF:Mg,Cu,P with various magnesium concentrations

The dependence of LiF:Mg,Cu,P samples with various concentrations of Mg on sintering temperatures was investigated to find a new dosimeter. The influence of high sintering temperatures on LiF:Mg,Cu,P chips depends strongly on Mg concentrations. The height of the main peak versus the sintering temperatures exhibits a maximum, the position of which varies between 690 °C and 750 °C, depending on the Mg concentration in the range studied. The high temperature peaks of LiF:Mg,Cu,P for various Mg concentrations reduce basically when the sintering temperature is increased. LiF:Mg,Cu,P is much less sensitive than LiF:Mg,Cu,Si to sintering temperature. LiF:Mg,Cu,P with 0.6 mol% of Mg can be re-used at annealing temperature of 260 °C, regardless of the sintering temperature. It was found that the optimum concentration is Mg: 0.6 mol%, the optimum sintering temperature is 750 °C, considering that LiF:Mg,Cu,P with a low residual signal and good sensitivity can be re-used at annealing temperature of 260 °C and produced in a large scale. The new optimum LiF:Mg,Cu,P formation has 52 times higher than that of the TLD-100, and an extremely low residual signal of 0.07% without an initialization readout procedure.     

Retrospective and emergency dosimetry in response to radiological incidents and nuclear mass-casualty events: A review

This paper reviews recent research on the application of the physical dosimetry techniques of electron paramagnetic resonance (EPR) and luminescence (optically stimulated luminescence, OSL, and thermoluminescence, TL) to determine radiation dose following catastrophic, large-scale radiological events. Such data are used in dose reconstruction to obtain estimates of dose due to the exposure to external sources of radiation, primarily gamma radiation, by individual members of the public and by populations. The EPR and luminescence techniques have been applied to a wide range of radiological studies, including nuclear bomb detonation (e.g., Hiroshima and Nagasaki), nuclear power plant accidents (e.g., Chernobyl), radioactive pollution (e.g., Mayak plutonium facility), and in the future could include terrorist events involving the dispersal of radioactive materials. In this review we examine the application of these techniques in ‘emergency’ and ‘retrospective’ modes of operation that are conducted on two distinct timescales. For emergency dosimetry immediate action to evaluate dose to individuals following radiation exposure is required to assess deterministic biological effects and to enable rapid medical triage. Retrospective dosimetry, on the other hand, contributes to the reconstruction of doses to populations and individuals following external exposure, and contributes to the long-term study of stochastic processes and the consequential epidemiological effects. Although internal exposure, via ingestion of radionuclides for example, can be a potentially significant contributor to dose, this review is confined to those dose components arising from exposure to external radiation, which in most studies is gamma radiation.The nascent emergency dosimetry measurement techniques aim to perform direct dose evaluations for individuals who, as members of the public, are most unlikely to be carrying a dosimeter issued for radiation monitoring purposes in the event of a radiation incident. Hence attention has focused on biological or physical materials they may have in their possession that could be used as surrogate dosimeters. For EPR measurements, in particular, this includes material within the body (such as bone or tooth biopsy) requiring invasive procedures, but also materials collected non-invasively (such as clippings taken from finger- or toenails) and artefacts within their personal belongings (such as electronic devices of which smart phones are the most common). For luminescence measurements, attention has also focused on components within electronic devices, including smartphones, and a wide range of other personal belongings such as paper and other polymer-based materials (including currency, clothing, bank cards, etc.). The paper reviews progress made using both EPR and luminescence techniques, along with their current limitations.For the longer-established approach of retrospective dosimetry, luminescence has been the most extensively applied method and, by employing minerals found in construction materials, it consequently is employed in dosimetry using structures within the environment. Recent developments in its application to large-scale radiation releases are discussed, including the atomic bomb detonations at Hiroshima and Nagasaki, fallout from the Chernobyl reactor and atmospheric nuclear bomb tests within the Semipalatinsk Nuclear Test Site and fluvially transported pollution within the Techa River basin due to releases from the Mayak facility. The developments made in applying OSL and TL techniques are discussed in the context of these applications. EPR measurements with teeth have also provided benchmark values to test the dosimetry models used for Chernobyl liquidators (clean-up workers), residents of Semipalatinsk Nuclear Tests Sites and inhabitants of the Techa River basin.For both emergency and retrospective dosimetry applications, computational techniques employing radiation transport simulations based on Monte Carlo code form an essential component in the application of dose determinations by EPR and OSL to dose reconstruction problems. We include in the review examples where the translation from the physical quantity of cumulative dose determined in the sampled medium to a dose quantity that can be applied in the reconstruction of dose to individuals and/or populations; these take into account the source terms, release patterns and the movements of people in the affected areas. One role for retrospective luminescence dosimetry has been to provide benchmark dose determinations for testing the models employed in dose reconstruction for exposed populations, notably at Hiroshima and Nagasaki. The discussion is framed within the context of the well-known radiation incidents mentioned above.     

Effects of high-temperature annealing on ESR properties of solid solutions of garnet minerals

A garnet (G7) silicate mineral belonging to pyralspite subgroup was studied using the technique of electron spin resonance (ESR). This study shows that iron is present in G7 as isolated species as well as species coupled by dipolar interactions. The ESR data shows a gradual increase of cluster of Fe³⁺ ions accompanied by decrease of dipolar interactions and increase of possible exchange interactions at high temperature. The Fe²⁺→Fe³⁺ oxidation process occurs in the garnets as a function of annealing temperature. Thermoluminescence (TL) peaks at approximately 190 and 340 °C are observed in the irradiated G7 garnet. Investigations using the technique of ESR were carried out to identify the centers involved in the TL process.     

Beta-delayed neutron spectra for application in reactor technology,nuclear physics and astrophysics

Recent developments in ß-delayed neutron (DN) spectroscopy are reviewed, and the importance of DN energy spectra for various problems in reactor physics, nuclear physics and astrophysics is discussed.