The effects of deep trap population on the thermoluminescence of Al2O3:C

The influence of deep traps on the 450 K thermoluminescence (TL) peak of Al₂O₃:C is studied. Depending upon the sample and on the degree of deep trap filling, features such as the TL width, area and height can vary considerably. These effects are interpreted to be due to: (a) sensitivity changes introduced by competition mechanisms involving deep electron and hole traps, and (b) the multiple component nature of the 450 K TL peak. The influence of the deep traps on the TL was studied using different excitation sources (beta irradiation or UV illumination), and step annealing procedures. Optical absorption measurements were used to monitor the concentration of F- and F⁺-centers. The data lead to the suggestion that the competing deep traps which become unstable at 800–875 K are hole traps, and that the competing deep traps which become unstable at 1100–1200 K are electron traps. Both the dose response of the TL signal and the TL sensitivity are shown to be influenced by sensitization and desensitization processes caused by the filling of deep electron and hole traps, respectively. Changes in the TL peak at low doses were also shown to be connected to the degree of filling of deep traps, emphasizing the influence of deep trap concentration and dose history of each sample in determining the TL properties of the material. Implications of these results for the optically stimulated luminescence properties are also discussed.     

Inter-comparison among fast neutron dosimetric services using PADC material of different composition

A trial inter-comparison has been performed among four fast neutron dosimetric services: PSI(CH), ENEA (I), DRPS (UK), LANL (US). The PADC used for the tests has been produced by Intercast Europe S.p.A. Three sets of detectors have been employed: two of PADC standard material from two different batches, and one of PADC with the addition of 0.1% dioctylphthalate. Each set consisted of 50 detectors.

For each set of detectors, 20 have been irradiated free-in-air at 1 mSv of H^*(10) with an ²⁴¹Am–Be source at ENEA-IRP, whilst the other detectors have been used as background samples. For each batch the value of the average background signal, B, the average neutron sensitivity, S, and minimum detectable dose equivalent, MDDE, have been determined. Two identical tests have been completed and separated with a time of 4 months in order to evaluate the ageing effect on the material stored in different conditions. Each dosimetric service processed the detectors according to local routine procedures. Three laboratories used an Autoscan60 reader, whilst one laboratory has an in-house reading system. Therefore, the results of the tests allowed a comparison of either the performance PADC materials, of different batches and of different compositions, or to evaluate how different etching, reading and storage conditions affect the results.     

Particularism and the contingent a priori

Particularism renders the options for a sound moral epistemology few and the prospects dim. One leading approach treats basic knowledge of particular cases as derivable from an a priori moral principle and a posteriori knowledge of the contingent non-moral facts to which the principle applies. Particularists must forgo this approach because it requires principles. Yet a purely a posteriori moral epistemology is also implausible, especially when combined with particularism. Particularists such as Jonathan Dancy are thus led to the view that our basic moral knowledge is a priori knowledge of contingent moral facts. We argue that this epistemology is unsound. While some cases of a priori knowledge of (even deeply) contingent facts may be defensible, they are not sufficient for particularist purposes. Moreover, neither Dancy’s appeal to the distinction between positive and negative dependence nor his discussion of intuitive examples provides sufficient support for this epistemology.     

Application of the optically stimulated luminescence (OSL) technique in space dosimetry

This paper reviews the state of the optically stimulated luminescence (OSL) technique for space dosimetry applications, focusing on the properties of carbon-doped aluminum oxide (Al₂O₃:C). New data presented include the most complete and recent values for the relative efficiency η_HCP,γ for heavy charged particles as a function of the incident radiation's linear energy transfer (LET), obtained through ground-based experiments at heavy ion accelerators. We also discuss the factors influencing the OSL efficiencies, the LET-dependent properties of Al₂O₃:C, and the experience gained from past space experiments using Al₂O₃:C. The characterization of the OSL efficiency values as a function of LET allows the use of the OSL of Al₂O₃:C in combination with plastic nuclear track detectors for personal dosimetry of astronauts, as proposed by the NCRP Report 142.     

Molecular mobility of nitroxide spin probes in glassy polymers. Quasi‐libration model

ESR spectra of three spin probes with different molecular volumes: 2,2,6,6‐tetramethyl‐4‐oxopiperidine‐1‐oxyl, di‐p‐anisylnitroxide, and nitroxide derivative of fullerene in glassy polystyrene, polyvinyl trimethylsilane, and Teflon AF‐2400 were calculated numerically within the model of quasi‐libration motions. Temperature ranges, where the model is capable to reproduce spectra within experimental errors, were defined. It was found that simulation of X‐band ESR spectra allows to determine quasi‐libration amplitudes around molecular axes X and Y with accuracy ～ 3° and around Z axis with accuracy ～ 15–20°. A shape of distribution of quasi‐libration amplitudes was also determined qualitatively by ESR spectra simulations. It was established that the average amplitude of quasi‐libration motion depends on the free volume of each polymer and geometrical molecular volume of a spin probe. Quasi‐libration amplitudes increase as the temperature increases, and reach the value of 40 degrees. We found that upon further temperature increase, quasi‐libration model becomes inapplicable for quantitative numerical spectra simulation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 107–120, 2009     

Characterization of nonlinearities in the dose dependence of thermoluminescence

Nonlinearities often occur in the dose dependence of thermoluminescence (TL). These include sublinearity, usually when there is an approach to saturation in the dose dependence, as well as supralinearity, also termed superlinearity in the literature. Different researchers in the field have viewed the effect of supralinearity/superlinearity from two somewhat different points of view. One point of view has to do with the rate of change with dose of the dose dependence function. The other approach is related more to the applications of TL in dosimetry and archaeological and geological dating, and basically has to do with the correction to be made in extrapolation in cases where supra(super) linearity occurs following an initial linear dose range, or prior to such a linear range. In the present work we propose quantitative methods to characterize these nonlinearities. We suggest the use of two different nonlinearity indices, depending upon how one wishes to describe the nonlinearity. We propose use of the term “supra linearity index”, ƒ(D), in cases where the feature of interest is the deviation from linearity, namely, when the correction in extrapolation is the main issue. We propose the term “superlinearity index”, g(D), in dose ranges where the growth is “more than linear” and when extrapolation is not the main issue. We mathematically define each of these indices and give examples of their use for different dose dependencies.     

Rapid colorimetric determination of indoxyl acetate

A rapid colorimetric method is presented for the determination of submilligram amounts of indoxyl acetate. The method depends upon the conversion of the indoxyl acetate into indigo.