A CR-39 based thermal neutron dosimeter

Both chemically and electrochemically etched CR-39 detectors are used for the detection of fast neutrons. In practical situations, fast neutrons are always accompanied by thermal neutrons. Therefore, the response of the CR-39 based dosimeter has to be extended to thermal neutrons. To do so, a radiator/converter like LiF is introduced in front of the CR-39 detector and an optimum thickness of the LiF film is determined so that a response similar to that of the fast neutrons is achieved. Thin films of natural LiF were prepared and the response of the CR-39 detector was studied as a function of the film thickness.     

面向个人剂量计校准的小尺度伽玛参考辐射模拟研究

针对伽玛射线个人剂量计基于标准伽玛参考辐射进行校准时检定效率低、校准工作复杂和需要远程送检的关键技术问题,建构了1 Ci ¹³⁷Cs放射源小尺度参考辐射场物理模型,采用蒙特卡罗方法,研究了小尺度参考辐射场内的剂量分布、装置结构和待检剂量计变化导致散射射线对剂量场的影响,获得了待检剂量计形状、数量、类型和装置结构产生的散射伽玛射线对小尺度参考辐射量值定度的影响结果。研究结果表明,1 Ci ¹³⁷Cs可以为小尺度参考辐射辐射场检验点提供1.5 mSv/h的伽玛遂行剂量率,辐照个人剂量计载台直径30 cm束斑上的剂量率相对标准偏差约为0.48%。当载台厚度为20 mm时,散射射线对小尺度参考辐射检验点处剂量率值的影响率为3.27%,高于剂量计尺寸（1.62%）和剂量计数量（0.56%）的影响。     

A new ESR dosimeter based on bioglass material

Bioglass (Bio-G) samples were irradiated with 60Co gamma-rays to study radicals for dosimetric materials with electron spin resonance (ESR). The ESR spectrum of Bio-G is characterized by two main signals. The first signal at g approximately = 4.3 corresponds to Fe3+ impurities and the second signal at g approximately = 2.0130 with line-width 10.85 G is ascribed as a hole center. The gamma-ray dose response and thermal stability were studied to establish the suitability of bioglass as an ESR dosimeter. A radical formation efficiency, G-value, of 0.53 +/- 0.11 was obtained. The lifetime of radicals and the activation energy were estimated from Arrhenius plots to be approximately 255 +/- 46 days and 0.71 eV, respectively.     

Sensitivity optimization in amplitude-modulated CW-EPR experiment

A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR) is studied depending on the parameters of the modulation field. The case of the significant saturation and high modulation frequency is addressed. It is found, that the rapid resonance passage effect is essential for AM-CW-EPR. However, its manifestation is different comparing to the conventional CW-EPR experiment. Both experimental data and numerical simulations support the enhancement of the AM-CW-EPR sensitivity under the rapid passage conditions for the modulating magnetic field, which is important for practical use of the method.     

A comparison of the dosimetric characteristics of a glass rod dosimeter and a thermoluminescent dosimeter for mailed dosimeter

A radiophotoluminescent glass rod dosimeter (RPL-GRD) system has recently become commercially available. The purpose of this study was to investigate the dosimetric characteristics (reproducibility, linearity, fading, energy dependence and angular dependence) of the RPL-GRD for a mailed dosimeter and to compare it with LiF-TLD powder. In this study, the model GD-301 GRD and TLD-700 were powder type used. All measurements with the exception of angular dependence were performed in a water phantom using a holder stand. The RPL-GRD has better reproducibility than the TLD for the Co-60 beam as well as for the clinical photon beam. The RPL-GRD signal was linear as a function of applied dose in the range of 0.5–3 Gy for the Co-60 gamma rays. The fading of the RPL-GRD after a received dose of 2 Gy was initially found to be within 1.7% for five months. The energy dependence of both dosimeters was found to be less than 1.6% for photon beams, but was less than 5.0% for electron beams, which was in agreement with published data. The angular dependence of the RPL-GRD was measured to be approximately 1.4% for angles ranging ±90° from the beam axis using a spherical polystyrene phantom. The measurements comparing RPL-GRD and TLD dosimetric characteristics demonstrated that the RPL-GRD is suitable for mailed dosimetry in a quality assurance (QA) audit program.     

钙钛矿铁电体原子势参数的灵敏度分析及优化

原子相互作用势参数在分子动力学模拟中非常关键.本文针对钙钛矿铁电体原子势参数较多的特点,提出了一种高效的优化参数的方法:首先应用灵敏度分析方法从众多参数中找到对结构和性能影响最为明显的主要参数,忽略影响很小的次要参数,大大降低优化问题的维数;然后应用遗传算法对主要参数进行优化.优化结果表明,用本文得到的势参数模拟BaTiO₃ 和SrTiO₃,其结构和物理性能更接近实验值.     

Development of a micro-size dosimeter using an optical fiber probe based on photostimulable phosphorescence

We have developed a novel micro-size dosimeter using an optical fiber probe coupled with a photostimulable storage phosphor, such as BaFBr:Eu²⁺. Our micro-size dosimeter is based on the concept in which the radiation dose response is temporally compressed by using integrating-type dosimeter elements, such as a photostimulable storage phosphor, and the signal-to-noise ratio is improved to downsize the dosimeter probe. We fabricate the prototype dosimeter probe which has the detectable volume of 100 μm thick and 400 μm diameter and the outer diameter of 900 μm. The lower limit of detectable dose, which is defined as three times the noise level, is evaluated to be 0.9 mGy. This value is much smaller than the typical irradiation dose (a few Gy per treatment) in the radiotherapy. We, therefore, conclude that the proposed micro-size dosimeter can be a promising candidate of in-vivo and on-line dose monitor in the radiotherapy.     

Sensitivity and optimization in the determination of deformations by holographic interferometry

The use of a fringe-counting holographic interferometric technique for measuring small superficial displacements can present difficulties in determining the measurement inaccuracy. A useful general method is given here for the analysis of errors in displacement measurements. The optimum number and type of observation directions are determined and correspond to counting in the four semi-diagonals of the holographic plate. The technique, as applied to skull experiments, makes it possible to measure directly displacements of up to 20 μm, in the object plane parallel to the holographic plate. The associated errors range from 0.1–0.3 μm, for a counting inaccuracy of of a fringe and increments of traction of 100 g to 1 kg of force.     

Sensitivity analysis and optimization of nodal point placement for vibration reduction

A method is developed for sensitivity analysis and optimization of nodal point locations in connection with vibration reduction. A straightforward derivation of the expression for the derivative of nodal locations is given, and the role of the derivative in assessing design trends is demonstrated. An optimization process is developed in which added lumped masses on the structure are used as design variables to move the node to a preselected location—for example to where a low response amplitude is required or to a point which makes the mode shape nearly orthogonal to the force distribution, thereby minimizing the generalized force. The optimization formulation leads to values for added masses that adjust a nodal location while minimizing the total amount of added mass required to do so. As an example, the node of the second mode of a cantilever box beam model of a rotor blade is relocated to coincide with the centroid of a prescribed force distribution, thereby reducing the generalized force substantially without adding excessive mass. A comparison with an optimization formulation that directly minimizes the generalized force indicates that nodal placement gives essentially a minimum generalized force when the node is appropriately placed.     

EPR of gamma-irradiated polycrystalline alanine-in-glass dosimeter

This study attempts to overcome some of the reported discrepancies in alanine-EPR reproducibility that may be related to alanine dosimeter preparation and/or EPR spectrometer settings. The dosimeters were prepared by packing pure polycrystalline $\text{<mi mathsize="small" is="true">L</mi>}\text{-}\alpha \text{-}\mathrm{alanine}$ directly as supplied by the manufacturer in glass tubes. This dosimeter production scheme avoids any possible contribution to the EPR signal from a binding material. The dosimeters were irradiated with gamma ray to low-dose ranges typical for medical therapy (0–20 Gy). Special attention has been paid to the study of minimum detectable dose, measurement repeatability and reproducibility, and post-irradiation stability. The dosimeter exhibited a linear dose response in the dose range from 0.1 to 20 Gy. These positive properties favor the polycrystalline alanine-in-glass tube as a radiation dosimeter.     

Design of a direction-dependent neutron dosimeter

A theoretical design for a neutron dosimeter has been investigated to determine whether it is capable of estimating effective dose. The design is essentially simple: a 10.16 cm radius sphere of borated scintillator that is interrogated by a tetrahedral arrangement of photomultipliers. A sigmoid artificial neural network was used to analyse MCNP calculations of the neutron capture distribution within the sphere for energies from thermal to 16 MeV, incident from 26 separate directions. Results to date are sufficiently encouraging that a prototype device is now under consideration.     

Modeling and validation of polyurethane based passive underwater acoustic absorber

The acoustic behavior of an acoustically transparent polyurethane and an interpenetrating polymer network of polyurethane with polydimethyl siloxane were studied using dynamic mechanical analysis, finite element modeling, and experimental evaluation of acoustic properties in a water-filled pulse tube setup. Dynamic mechanical measurements in the temperature range -50?°C to +70?°C were carried out, and the data were used for time temperature superposition to generate material behavior at high frequencies. These inputs were used for modeling the acoustic behavior of these materials using ATILA, which is a commercial finite element code, capable of computing transmission and reflection characteristics of materials. From this data, absorption characteristics were computed. The results were compared with the experimental results obtained using a water-filled pulse tube facility.     

A passive radon dosimeter based on the combination of a track etch detector and activated charcoal

The aim of this work is to test a combination of a Makrofol track detector with a new type of charcoal (Carboxen-564) to design a personal radon dosimeter. The intention is to use this dosimeter as a personal radon dosimeter to measure the monthly radon exposure in workplaces, especially when the occupancy is not ecactly known. The proposed combination was exposed to low and high concentrations of radon in a large range of relative humidity (RH). For the optimal layer thickness, a charcoal bed of 2.2 mm, a specific track density of 5.1 tracks cm⁻²/kBq h m⁻³ was obtained. For a monthly working exposure (170 h) at an average radon concentration of 100 Bq/m³, this means 87 tracks/cm² or 10 times the background of the Makrofol detector, with a statistical uncertainty of 15%.     

Sensitivity of a LR-115 based radon dosemeter

The first results of a study on the sensitivity of a LR-115 based radon dosemeter as a function of the absorber thickness are presented. The theoretical sensitivity was analytically calculated considering a constant detector response to alpha particles within a given energy range and up to a critical angle of incidence. The results are presented in two extreme situations: i) both radon and its decay products uniformly distributed in the chamber volume; ii) radon decay products uniformly deposited on the chamber walls. The agreement with the experimental curve shape appears better in the former case, suggesting that either the parameter values of the model could be different from the chosen values, or the model was too simplified.     

基于渐进结构优化的结构-声拓扑优化研究

研究了连续结构在外力作用下的声辐射拓扑优化问题。运用有限元法(FEM)分析结构响应,运用边界元法(BEM)处理外场的声辐射问题,采用渐进结构优化(ESO)来进行声拓扑优化分析。以一平板为例分析了在外谐力作用下的结构-声辐射拓扑优化。结果表明用渐进结构优化(ESO)来进行结构-声拓扑优化是可行的、有效的。     

Prediction of polyurethane hard segment structures based on diphenylmethane-urethane model compounds

The hard segments in MDI/diol-based polyurethanes form crystalline domains, and these have been found to exist in different polymorphic structures depending on processing history. Structures of the crystal structures of low molecular weight urethane model compounds possess a number of common features that can be used to predict models for the polymers. Specifically, information is derived concerning the conformation of the diphenylmethane, phenyl-urethane, and chain extender region of the chain. This information has been used to predict the possible conformation of poly (MDI/diol) chains in which the diol region is fully extended (all trans). Less information is available that is relevant to the structures that have a more contracted conformation, but the options to be considered are discussed.     

Structural-acoustic topology optimization analysis based on evolutionary structural optimization approach

The continuum structural-acoustic topology optimization with external loading is investigated herein. Finite element method （FEM） is used to obtain the structural frequency response and boundary element method （BEM） is adopted to perform exterior acoustic radiation analysis. The evolutionary structural optimization （ESO） is served as an optimization method in structural-acoustic radiation topology analysis. The acoustic radiation optimization of a plate under harmonic excitation is given for example. The numerical results show that using ESO solution to analyze structural-acoustic topology optimization is feasible and effective.     

UV dosimeter based on polyamide woven fabric and nitro blue tetrazolium chloride as an active compound

This paper reports on the preparation and features of a UV light dosimeter composed of nitro blue tetrazolium chloride (NBT) and polyamide woven fabric. This textile dosimeter is based on the conversion reaction of NBT into formazan, which was initially examined in aerated aqueous solutions through steady state UV irradiation. Irradiated solutions change their colour as a consequence of the formation of polydisperse NBT formazan particles. This was analysed in relation to the absorbed dose of UV light through UV–VIS spectrophotometry and dynamic laser light scattering measurements. When NBT substrate molecules are embedded in polyamide textile, UV irradiation leads to similar effects as in solution. However, the tinge intensity changes at much lower absorbed doses. The dependence of the tinge intensity on the absorbed dose was followed by measurements of the remission of light from the NBT-polyamide samples. Consequently, the calibration parameters were calculated such as the dose sensitivity, dose range, and quasi-linear dose range. An improvement of the NBT-polyamide samples by application of a colour levelling agent and improvement of their resistance to humidity is presented. Finally, the samples were used for estimation of absorbed UV energy distribution showing their capability as new dosimeters for in-plane high resolution radiation dose measurements.     

EPR dosimeter material properties of potassium tartrate hemihydrate

The ability of potassium tartrate hemihydrate as a radiation sensitive material for electron paramagnetic resonance (EPR) dosimetry was investigated. The samples were subjected to different doses, in the range of 1–9 Gy of ⁶⁰Co gamma rays at room temperature. The EPR spectra were investigated through variation of signal intensity with respect to absorbed dose, magnetic field modulation amplitude, microwave power and time stability. The results indicate that the sensitivity of potassium tartrate hemihydrate is about 30% higher than that of alanine. However, the EPR signal is timely less stable within the first two weeks after irradiation.