Protocol for TL dating with zircon: Computer simulation of temperature and dose rate effects

Natural zircon is irradiated internally by U and Th impurities. After exposure to ionizing irradiation zircon exhibits thermoluminescence (TL), which can be used to calculate the irradiation dose and the sample age. A kinetic model for TL of zircon developed earlier is used to model the processes relevant for dating. The response of zircon to irradiation at different dose rates is simulated for different temperatures. Several scenarios for the dating procedure are considered, including laboratory added irradiation, fading and preheat. It is shown that by irradiating the sample at elevated temperatures one can imitate natural irradiation, i.e. it is possible to reproduce the structural state of the trap system (distribution functions of filled electron and hole traps), which is responsible for the TL behavior. This implies that the dose dependence of the TL signal from samples, which had been irradiated under natural conditions, can be produced by irradiation at an elevated temperature.     

Effect of gamma irradiation on the thermal,mechanical and structural properties of chlorinated polyvinyl chloride

Non isothermal studies were carried out using thermogravimetry (TG) and differential thermogravimetry (DTG) to obtain the activation energy of decomposition for chlorinated polyvinyl chloride (CPVC) before and after exposure to gamma doses at levels between 5.0 and 50.0 KGy. Thermal gravitational analysis (TGA) indicated that the CPVC polymer decomposes in one main breakdown stage and a decrease in activation energies was observed followed by an increase on increasing the gamma dose. The variation of melting temperatures with the gamma dose has been determined using differential thermal analysis (DTA). Also, mechanical and structural property studies were performed on all irradiated and non-irradiated CPVC samples using stress-strain relations and X-ray diffraction. The results indicated that the exposure to gamma doses at levels between 27.5 and 50 KGy leads to further enhancement of the thermal stability, tensile strength and isotropic character of the polymer samples due to the crosslinking phenomenon. This suggests that gamma radiation could be a suitable technique for producing a plastic material with enhanced properties that can be suitable for high temperature applications and might be a suitable candidate for dosimetric applications.     

Comparison of dose measurements in CT using a photodiode and a small ion chamber

Owing to the advance of multislice computed tomography (CT), the dosimetric protocol currently used in CT has become inadequate. Instead of dosimetry based on the measurement of the Computed Tomography Dosimetry Index (CTDI) using a pencil ion chamber (IC) 100 mm in length, the use of a short IC and the calculation of the dose equilibrium (D_eq) at the location of the chamber are proposed. The objective of this work was to compare the performance of a short IC and a commercial photodiode (BPW34FS) to measure the accumulated dose at the center of the scan length L, D_L(0), and to obtain the equilibrium dose D_eq using the two detectors. The result for L = 100 mm was compared with the result of the pencil chamber. The results indicate that the commercial photodiode is suitable to measure the accumulated dose at the center of the scan length L as compared with the ICs. This methodology allows measurements of the accumulated dose for any desired scan length, allowing measurement of the equilibrium dose D_eq if the phantom is long enough to allow it.     

鲜红斑痣光动力治疗的荧光光谱监测

应用荧光光谱技术监测了鲜红斑痣(PWS)光动力治疗(PDT)中的光敏剂血药浓度与光产物生成。以532 nm倍频Nd∶YAG激光器作为PDT照射光源与荧光激发光源,以光谱仪与ICCD采集荧光光谱。在系统验证实验中,构建含有血卟啉单甲醚(HMME)的小鼠正常皮肤的荧光基本光谱,通过最小二乘光谱拟合区分HMME荧光(624 nm)与光产物荧光(652 nm)。含有PSD-007的病人患区荧光光谱拟合采用相同基本光谱,获得不同病人个体具有显著差异的光敏剂血药浓度曲线与光产物生成漂白曲线。所建立的荧光光谱监测系统与光谱拟合方法可为PDT精确量化剂量学方法的建立提供技术手段,所得结果有利于制定个性化的PDT治疗方案。     

Dose control in electron beam processing: Comparison of results from a graphite charge collector, routine dosimeters and the ISS alanine-based dosimeter

A 12 MeV linear accelerator is currently used for electron beam processing of power semiconductor devices for lifetime control and, on an experimental basis, for food irradiation, sludge treatment etc. In order to control the irradiation process a simple, quick and reliable method for a direct evaluation of dose and fluence in a broad electron beam has been developed. This paper presents the results obtained using a “charge collector” which measures the charge absorbed in a graphite target exposed in air. Calibration of the system with super-Fricke dosimeter and comparison of absorbed dose results obtained with plastic dosimeters and alanine pellets are discussed.     

The use of ESR spectroscopy for the investigation of dosimetric properties of egg shells

Electron spin resonance (ESR) spectroscopy was used to investigate the dosimetric properties of chicken egg shells. The ESR spectra of the irradiated egg shell were found to have an asymmetric absorption characterized by a major resonance at g=2.0019 and a minor resonance at g_||=1.9980. The study was carried out on g=2.0019 signal because of the accuracy of measurements and the possibility of using it as ESR dosimeter. The activation energy (E), frequency factor (k₀) and mean-life (τ) were calculated to be 1.50±0.10 eV, 2×10¹³ s⁻¹ and (4.4±0.4)×10⁴ year respectively. Dose–response was investigated between dose ranges of 1 Gy and 10 kGy for ⁶⁰Co γ-rays. Dose–response was found to be appropriate for dosimetry in the range 3 Gy to 10 kGy. The lower limit of observable doses for egg shell sample was about 3 Gy. The other ESR dosimetric parameters of egg shell samples, fading characteristic, light effect, dose-rate dependence and energy dependence, have also been studied in detail. Apart from its non-tissue equivalence, egg shell has very good dosimetric properties with insignificant fading, light independence, linearity in dose–response (3 Gy–10 kGy), dose-rate independence and independence from energy above 500 keV. It suggests that egg shell may be used as a retrospective γ radiation dosimetry after nuclear accidents or other short accidental radiation events.     

Dependence of thermoluminescence response of calcium sulphate activated by dysprosium on the temperature irradiation

Radiation dosimetry is a very important issue in space research and in experiments that try to simulate chemical processes that may occur in cometary nucleus, interstellar grains, and other extraterrestrial environments, due to their irradiation by cosmic rays. The temperature effect is an important factor that has not been considered in many of these experiments. In this work, this effect was studied in TLD dosimeters exposed to gamma rays. The irradiations were done from 77 to 298 K in a Gamma cell unit with a dose rate of 1.0 Gy/s. Results obtained for CaSO₄:Dy show that there is a considerable effect in the evaluation of the dose as function of the irradiation temperature.     

Retrospective dosimetry with ceramics

This paper reviews recent progress that has been made in the application of luminescence techniques with ceramic materials to the problem of dose reconstruction at: Hiroshima and Nagasaki; areas downwind of the Nevada Test Site; regions of Belarus, the Russian Federation and the Ukraine contaminated by fallout from Chernobyl; settlements along the Techa River affected by releases from the Mayak facility at Chelyabinsk; Kiisa, Estonia where a stolen ¹³⁷Cs irradiator source was discovered. Luminescence has an increasingly important role in radiological health studies at such sites because of the ability of the method to measure dose retrospectively in areas where radiation monitoring was lacking or sporadic following the incident. Commonly produced ceramics such as brick, tile and porcelain fittings and artefacts have been used to determine the integrated external gamma radiation dose (the transient dose). Evaluation of the reliability and accuracy with which the transient dose can be estimated when it approaches and drops below the level of the integrated natural background dose (<50 mGy for ceramic samples of age 20–30 y) is the subject of current research. In addition to various improvements in the performance of the experimental techniques and understanding of the luminescence properties of the minerals, other developments include improved integration with the requirements of dose reconstruction by the combined use of luminescence and computational modelling.     

Concepts and methods of ESR dating

Electron spin resonance (ESR) dating is an absolute dating method suitable for the Quaternary which can be applied to a wide range of materials. It is based on determining the natural radiation dose to which a sample has been exposed during its burial period. This paper outlines the basic concepts, and reviews recent studies on the methods and models of ESR dating.

Scope of this paper. This review paper is one of two in this volume providing an overview of recent developments in the field of electron spin resonance (ESR) dating. The paper focuses on studies investigating the fundamental concepts and methods employed in ESR dating, while the companion paper by Rink (this issue) focuses on applications of the method. Previous review articles have been published by Ikeya (1978) and Ikeya (1985), Hennig and Grün (1983), Nambi (1985) and Grün (1989b). Subsequently, papers by Grün (1991), Schwarcz (1994) and Ikeya (1994a); Ikeya (1994b) and Ikeya (1994c) have reviewed specific aspects of the field. There are three books on ESR dating by Ikeya (1986), in Japanese), Grün (1989a)Grün (1989b), in German) and Ikeya (1993), in English) respectively. In view of the coverage of previous reviews of the field, this paper concentrates on research undertaken since 1990.

The first part introduces and outlines the basic ideas of ESR and its application to dating. This is followed by an overview of recent studies concerned with the basic concepts of the field, its methods and models, as independently of specific materials as possible.     

OSL signal of lithium fluoride and its relationship with TL glow-curves

The widely known LiF TL detectors: LiF:Mg,Ti (MTS-N) and LiF:Mg,Cu,P (MCP-N), were investigated with respect to their OSL properties. It was found that both materials exhibit quite substantial OSL sensitivity. In particular, in the case of LiF:Mg,Cu,P this sensitivity was very high, significantly exceeding that of BeO, the standard OSL dosimetric material. LiF:Mg,Cu,P could be a very promising candidate for application in dosimetry, if not for the fading, which was found to be quite high, reaching nearly 80% loss of the signal within 60 h. The OSL signal intensity shows a correlation with the peak 2 of the TL glow curves indicating that the same trapping sites are responsible for both processes. Peak 2 of LiF:Mg,Ti shows a peculiar property, that blue light stimulation removes only about half of its initial intensity, disregarding the duration of stimulation. This suggests, that this peak may have a composite structure and originates from both light-sensitive and light-insensitive trapping centres.