Effect of γ-dose rate on crystallinity and morphological changes of γ-sterilized biomedical polypropylene

The present work is aimed to study the changes in crystallinity and morphology of biomedical polyolefins after γ-sterilization. The isotactic polypropylene (iPP) films were sterilized by γ-radiation and the changes were characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and atomic force microscopy (AFM) techniques. The effect of dose rate on crystallinity changes also was focused. It was found that crystallinity and morphology significantly changed with γ-irradiation. There was an increase in crystallinity up to 10 kGy accompanied with decrease in viscosity and mechanical properties. The changes in crystallinity mainly depend on γ-irradiation dose and dose rate. The rise in crystallinity was attributed to chain scission and forming new perfect lamellae. However, the reduction was accompanied by occurrence of γ- and β-phases and crosslinking. Possible explanations for transitions in phases are also discussed based on our results.     

Optimal Threshold for the k-Out-Of-n Monitor with Dual Failure Modes

A monitor consists of n identical sensors working independently. Each sensor measures a variate of output or environment of a system, and is activated if a variate is over a threshold specified in advance for each sensor. The monitor alarms if at least k out of n sensors are activated. The performance of the monitor, the probabilities of failure to alarm and false alarming, depends on the number k, the threshold values and the probability distributions of the variate at normal and abnormal states of the system. In this paper, a sufficient condition on the pair of the distributions is given under which the same threshold values for all the sensors are optimal. The condition motivates new orders between probability distributions. Solving an optimization problem an explicit condition is obtained for maximizing or minimizing a symmetric function with the constraint of another symmetric function.     

THE EFFECT OF IRRADIATION ON THE POLYETHERKETONE WITH CARDO GROUP

The effects of irradiation on the polyetherketone with cardo group (PEK-C) were studied. It was found that PEK-C can be crosslinked by irradiation under vacuum, while degradation reaction occurred in PEK-C at room temperature in the presence of air. Moreover. it was also found that Ts value of the crosslinked PEK-C at high temperature is higher than that at room temperature in the case of the same gel content, whose value is about 8℃higher than that of unirradiated PEK-C. The gelation dose of PEK-C at 300℃under vacuum is 1.5×10~4 Gy, which is about hundred times smaller than that at room temperature.     

Comparative study of effect of low and medium dose rate of γ irradiation on microporous polysulfone membrane using spectroscopic and imaging techniques

The effect of low (LDR) and medium dose rate (MDR) of γ irradiation at low doses (0-100 kGy) on the structural and chemical changes of microporous polysulfone (PSf) membrane has been studied using UV-vis, FTIR, SEM and dead-end filtration techniques. PSf membrane was cast by phase inversion method. Irradiation was done at room temperature in air media. The doses chosen were 0-100 kGy for LDR and 0-50 kGy for MDR; they were below and above sterilization dose. Analysis of UV-vis and IR spectra and SEM images obtained suggested that chain scissions and crosslink had occurred simultaneously in the irradiated membranes in both cases. This radio-oxidation effects observed start at a very low dose i.e. 1.66 kGy and increase with increase in dose. It is supported by the flux values obtained; it is increased with increase in dose. The results indicate that a very low dose γ irradiation was able to change the physicochemical characteristics of microporous PSf membrane which depend on dose rate of exposure.     

3-D Confocal microscopy track analysis: a promising tool for determining CR-39 response function

A new method based on the use of the confocal microscope is described in order to evaluate the CR-39 response function for Li-7 ions with an incident energy of 10.77 MeV. This method uses the formulations developed by Fromm et al. and considers two etching velocities: V_B represents the bulk etch rate and remains constant, and V_T the track etch rate, which varies along the particle's path. The confocal microscope seems to bring big improvements for track analysis. The first results of V_T versus the particle range are presented and compared with the curves obtained by the sequential etching method. The obtained V_T are plotted and compared to LET, REL₃₅₀ and the cumulative radial dose.     

Underestimation of equivalent dose in single-aliquot optical dating of feldspars caused by preheating

The ability of single-aliquot techniques to recover a known laboratory dose in coarse-grain potassium-rich feldspar separates is tested. It is shown that, for the samples under study, single-aliquot methods underestimate the known dose. It is deduced that this phenomenon is caused by an increase in electron trapping probability as a consequence of heating. The same phenomenon would lead to an underestimation in the equivalent dose in a natural sample. Multiple-aliquot techniques for equivalent dose determination may not suffer from this problem, but are not suitable for samples that might not have been completely bleached at the time of deposition. It is argued that testing for changes in electron trapping probability should become routine practice in the single-aliquot dating of feldspar.     

X射线闪光照相杆箍缩二极管技术最新进展

 综合介绍了杆箍缩二极管的应用背景、工作原理和目前的研究概况,并阐述了目前较为典型的两种二极管,即真空杆箍缩二极管和等离子体填充杆箍缩二极管的性能。详细介绍了已经用于地下实验的Cygnus装置的运行参数和实验结果。最后分析了杆箍缩二极管在X射线闪光照相领域的发展前景。     

利用拉曼光谱研究60CO γ射线对EC9706细胞的辐射损伤

将EC9706细胞经不同剂量^60Coγ射线辐照后继续培养24 h。利用激光拉曼光谱分析EC9706细胞内部蛋白质、核酸、脂类等生物大分子的构象和含量变化。分析结果发现,各剂量组拉曼谱的峰强和频移与空白对照组之间存在较大的差异,主要表现是蛋白质酰胺Ⅲ带1 244 cm^-1谱带在中等剂量组（4、5Gy）β折叠结构向无规卷曲转化;色氨酸残基的吲哚环振动谱带1 341 cm^-1在各剂量组中出现不同程度的红移;782 cm^-1谱带在大剂量组（7、8Gy）红移2～3 cm^-1,说明大剂量γ射线辐照导致DNA中的磷酸二酯（O—P—O）基团的非氢键化程度增强。脂类的CH2和CH3弯曲振动谱带1 446 cm^-1在2、4Gy组蓝移4 cm^-1,其他剂量组频移不大,这与60Coγ射线对EC9706细胞的生物膜造成一定损伤有关。拉曼特征峰在不同剂量组中的变化,为进一步研究60Coγ射线辐照损伤EC9706细胞的最佳剂量提供了一定实验依据。     

TL response of a natural fluorite

A batch of a naturally occurring fluorite (CaF₂) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224°C at a heating rate of 10°C s⁻¹. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224°C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal in low temperature glow peaks and a corresponding enhancement at higher temperature, is suggested.     

Benchmark measurements and simulations of dose perturbations due to metallic spheres in proton beams

Monte Carlo simulations are increasingly used for dose calculations in proton therapy due to its inherent accuracy. However, dosimetric deviations have been found using Monte Carlo code when high density materials are present in the proton beamline. The purpose of this work was to quantify the magnitude of dose perturbation caused by metal objects. We did this by comparing measurements and Monte Carlo predictions of dose perturbations caused by the presence of small metal spheres in several clinical proton therapy beams as functions of proton beam range and drift space. Monte Carlo codes MCNPX, GEANT4 and Fast Dose Calculator (FDC) were used. Generally good agreement was found between measurements and Monte Carlo predictions, with the average difference within 5% and maximum difference within 17%. The modification of multiple Coulomb scattering model in MCNPX code yielded improvement in accuracy and provided the best overall agreement with measurements. Our results confirmed that Monte Carlo codes are well suited for predicting multiple Coulomb scattering in proton therapy beams when short drift spaces are involved.