[en] This thesis summarises research and development of optically stimulated luminescence (OSL) and its applications by the author at Risoe National Laboratory, up to 1999. These developments have been directed primarily at retrospective accident dosimetry and luminescence dating. Experimental investigations include the studies of OSL properties of the natural minerals quartz and feldspars and the artificial materials porcelain and aluminium oxide (Al₂O₃). Blue light emitting diodes and infrared laser diodes are shown to provide simple and practical alternatives to broad-band light and visible laser stimulation. The development of OSL apparatus designed for the rapid measurement of single grains of phosphors also opens up a new area of luminescence measurement, allowing the detailed examination of dose distributions within a multiple-grain sample. This is of particular importance to the studies of incompletely reset geological sediments, and to accident dosimetry measurements using unheated materials. Al₂O₃:C single crystals are tested as environmental OSL dosemeters for assessing both the natural background photon radiation dose rates in the field and the natural dose rates inside bricks collected for accident dose evaluation. Environmental doses of the order of few μGy are measured with high precision. UV photo-stimulated luminescence spectra obtained from porcelain samples are used to confirm that the main component responsible for the OSL signal from porcelain is Al₂O₃. OSL single-aliquot regenerative-dose (SAR) techniques are used with quartz extracted from Chernobyl bricks to determine the accrued dose after the accident. This has improved the measurement precision significantly, from about 5-6 % using traditional methods to now less than 2 %. Depth-dose profiles measured in Chernobyl bricks are compared with those obtained in the laboratory using different gamma sources and these comparisons show that the average energy of the accident radiation was lower than that of ¹³⁷Cs photons. It is further demonstrated that doses lower than 50 μGy can be measured using the SAR method with a precision in the order of 2 %. This thesis was submitted to the University of Copenhagen in September 1999. (au)

[en] A Nordic meeting sponsored by the Nordic Liaison Committee for Atomic Energy, was held at Risoe 2-4 June 1980 with the aim of intercomparing detector systems for background radiation monitoring. Several Nordic Laboratories participated in the intercalibration programme with different types of instruments and detectors. Ionization chambers appeared to yield the most reliable results but in general large variations of detector responses were found when the instruments were exposed identically. This demonstrates the need for intercomparison programmes and for establishing standardized calibration procedures. The present paper gives a description of the programme and presents the results for the assessment of background radiation monitoring with different sensitive doserate meters and integrating Tl dosimeters. (author)

[en] Measurements of the background radiation were made in 1978 at 14 locations with a high-pressure ionization chamber, thermoluminiscence dosimeters (TLD's), two NaI(Tl) detectors, and a Ge(Li) spectrometer system. Simultaneous measurements with the ionization chamber and the spectrometer system provide reliable estimates of the total background exposure rate, of the individual contributors to the terrestrial exposure rate, and of the exposure rate from the secondary cosmic radiation. The TLD results agree with those of the ionization chamber. The NaI(Tl) detector results show that accurate estimates of the terrestrial exposure rate can be obtained if empirical corrections are applied. (author)

[en] Since the beginning of the 1990s the exploration of optically stimulated luminescence in retrospective accident dosimetry has driven an intensive investigation and development programme at Ris deg. into measurement facilities and techniques. This paper reviews some of the outcomes of this programme, including the evaluation of the single-aliquot regenerative-dose measurement protocol with brick quartz and the determination of dose-depth profiles in building materials as a guide to determining the mean energy of the incident radiation. Investigations into heated materials are most advanced, and a lower detection limit for quartz extracted from Chernobyl bricks was determined to be <10 mGy. The first results from the measurement of doses in unheated building materials such as mortar and concrete are also discussed. Both small-aliquot and single-grain techniques have been used to assess accident doses in these cement based building materials more commonly found in workplaces. Finally some results of a preliminary investigation of the OSL properties of household chemicals are discussed with reference to their potential as accident dosemeters. (author)

[en] A beta source attached to an automatic TL/OSL apparatus was calibrated against ⁶⁰Co gamma radiation using thermally and optically stimulated luminescence on quartz. This report presents the results obtained and discusses different problems encountered, including sensitivity change, effort of using different TL glow curve integration areas, difference between TL and OSL calibrations and, finally, the effect of using different growth line fitting procedures. (au)

[en] Calibration experiments were carried out at Risoe National Laboratory 28-30 August 1985 with the aim of testing calibration methods for instruments used for background gamma radiation monitoring. Two calibration methods using certified gamma sources were tested: 1) A shadow-shield calibration method, and 2) A freefield calibration set-up. The experiments comprised studies og 25 instruments from 11 European laboratories. For most of the instruments the two methods gave identical results. The shadow-shield calibration, however, proved to be more accurate. Additional measurements of the natural background and the cosmic component gave useful information on the energy dependency of the detectors. (author)

[en] The ceramic material AlN-Y₂O₃ is proposed as a potential ultraviolet radiation (UVR) dosemeter using optically stimulated luminescence (OSL) and thermally stimulated luminescence (TL). Experimental studies have shown that AlN ceramics exhibit attractive characteristics suitable for practical UV dosimetry applications. The features are: (1) the spectral sensitivity covers the 200 - 350 nm range, in the UV-B region it is similar to that of the human skin, (2) the angular dependence of the incident radiation follows the cosine law, (3) high yields of both UVR-induced OSL and TL signals compared to those of Al₂O₃:C, and (4) a large dynamic range TL signal (5 orders of magnitude). Although there is relatively high fading, we demonstrate that AlN is a feasible material for UVR dosimetry using short integration times. (author)

[en] Optically stimulated luminescence (OSL) measurements have been made of over 3000 sand-sized grains of quartz. Analysis at this scale highlights the variability in the luminescence sensitivity and the dose saturation characteristics of individual quartz grains. Using a new instrument capable of measuring single grains it is feasible to routinely measure the equivalent dose from many hundreds of grains from each sample. Analysis of such datasets requires assessment of the uncertainties on each equivalent dose since these may vary significantly. This paper assesses the significance of signal intensity, dose saturation characteristics and instrument uncertainty in equivalent dose calculation

[en] To allow the determination of the dose in quartz in the presence of feldspar contamination, the quartz-to-feldspar Optically Stimulated Luminescence (OSL) ratio needs to be maximised. Experiments were carried out to find the optimum procedure to bleach the feldspar by exposure to infrared light, without seriously affecting the quartz OSL signal. A single-aliquot regenerative-dose protocol is proposed which, in our samples, allows accurate measurement of the dose in quartz in the presence of feldspar contamination. The protocol also has potential use for quartz dose determination in mixed-mineral samples. (author)

[en] Two calibration methods for controlling environmental gamma exposure rate meters have been outlined and properly tested, and results from routine calibration experiments with high-pressure ionization chambers demonstrate that a reproducibility for both methods can be obtained within 1% (1 SD) when regularly performed over a prolonged period. (author)