No abstract available

[en] The supralinear behaviour of the optically stimulated luminescence (OSL) signal is examined in an annealed quartz sample. Such investigations are important in luminescence dating and retrospective dosimetry, especially when the supralinearity intercept comprises a significant component of the paleodose in the sample. The sensitivity-uncorrected OSL growth curve of the annealed quartz sample 3-1/1 is observed to be supralinear in the dose range 0-5 Gy; it is then linear until about 20 Gy; and becomes sublinear beyond 20 Gy. The low-dose supralinearity is completely removed after a correction for sensitivity change. It is shown that the competing trap model (Kristianpoller, N., Chen, R., Israeli, M., 1974. Dose dependence of thermoluminescence peaks. Journal of Physics D: Applied Physics, 7, 1063-1072) and the competing centre model (McKeever, S.W.S., Chen, R., 1997. Luminescence models. Radiation Measurements, 27, 625-661) originally proposed to explain the supralinearity in thermoluminescence of quartz, can also be applied to explain supralinearity in the OSL response of the annealed quartz sample. Furthermore, cycle-dependent sensitivity changes are observed in another annealed quartz sample (NLT-28199) during repeated regeneration cycles. The OSL sensitivity decreases with cycle in this sample; this decrease is explained in terms of a recent model proposed by McKeever et al. (McKeever, S.W.S., Agersnap Larsen, N., Boetter-Jensen, L., Mejdahl, V., 1997. OSL sensitivity changes during single aliquot procedures: computer simulations. Radiation Measurements 27, 75-82)

[en] In a recent paper Bailey proposed a general model to describe many optically stimulated luminescence (OSL) and thermoluminescence properties of natural quartz. This model consists of five electron trapping centres and four recombination centres; one of the recombination centres is assumed to be radiative and the remaining non-radiative. This paper investigates some additional aspects of the Bailey model. Firstly, the single-aliquot regenerative-dose (SAR) method has been simulated using the model. We show that the simulated natural dose (2 Gy) given to the 'sample' in our simulation can be estimated to within ∼2% using the SAR method. Furthermore, sensitivity-corrected OSL growth curves have been calculated over a dose range of 0 to 2500 Gy. Using the model, we also demonstrate that the shape of the sensitivity-corrected OSL growth curve is independent of dose rate, for dose rates of 0.001 Gy.s^-1 and 0.1 Gy.s^-1, over a dose range of 0-500 Gy. (author)

[en] Magnetoresistance and the Hall coefficient of single crystals of bismuth doped with gallium and indium have been measured as functions of temperature between 80 and 300 K and as functions of magnetic field up to 0.6 T. An attempt has been made here to explain the observed temperature variations of the Hall coefficient and magnetoresistance at different constant magnetic fields by considering the relative variation of the free carrier concentrations with temperature in different bands in alloys of bismuth in addition to variation of other parameters. The calculations have been made on the basis of the ellipsoidal band model of bismuth

[en] We present the first quartz optically stimulated luminescence (OSL) ages for palaeochannel sediments from the Riverine Plain in southeastern Australia. For young fluvial sediments, we agree with the notion that analysis of the leading edge of a dose distribution curve provides an objective method for determining the OSL age. For a modern flood deposit (less than 200 years old), the OSL ages estimated using the leading edge method (250±50 years) and by using the lowest 5% of the measured dose in single aliquots (230±50 years) agree within experimental errors. For older sediments, we suggest that the mean estimate of the dose distribution is likely to provide a reliable estimate of the OSL age. The luminescence ages suggest that the Coleambally and Kerarbury palaeochannel systems were active between 105 and 80 and 55 and 35 thousand years ago; the Yanco palaeochannel system could have been active as recently as 9000 years ago. (author)

[en] In retrospective dosimetry, the total dose absorbed by some pre-existing dosemeters such as house bricks or tiles, is used to derive the dose to the population arising from a nuclear accident. This paper uses the newly developed SAR protocol to determine the total dose in young house bricks from the vicinity of the Chernobyl reactor site and from Roskilde, Denmark. For these samples, it is shown that high precision (γ1%) on the mean estimates of total dose can be achieved with γ20 independent measurements. The SAR total dose estimates of two Danish house bricks agree with the expected values based on their known age and confirms the absolute accuracy of the SAR method. It is concluded that a γ18 mGy fallout dose component can be detected on a background of γ100 mGy; this detection limit is controlled by uncertainties in the natural dose rate measurement rather than in the estimation of total dose. (author)

[en] We shall explore here the relationship between chiral anomaly and Berry phase from the view-point of the topological investigations of anomaly. This will be extended in the coherent state representation of a quantized spinor. The relevance of Berry phase will also be studied in an unified formalism of integral and fractional quantum Hall effect. Finally we shall study the role of this topological phase in polarised light. (orig.)

[en] The results of various experiments which characterise the optically stimulated luminescence signals from polymineral fine grains of a Martian soil simulant sample (JSC Mars-1) are presented. The blue-green stimulated luminescence signal has greater thermal stability than the infrared stimulated luminescence signal for pre-heat temperatures between 250 deg. C and 400 deg. C. Fading tests over a 2 month storage period at 20 deg. C indicate that in some aliquots of JSC Mars-1 both the blue-green stimulated luminescence and the infrared stimulated luminescence signals fade by as much as 50%, whereas in others there is no evidence of significant fading. Dose recovery experiments demonstrate that equivalent dose (measured/given) ratio varies from aliquot to aliquot, and the underestimation in dose is less than 5% for at least one aliquot, for both the infrared and blue-green stimulated luminescence signals. (author)

No abstract available

[en] In a recent series of papers, describing aging transformations in plasma sprayed Ti-24Al-11Nb, Hsiung and co-workers proposed a new ordered tetragonal structure as the first metastable phase to form in a series of transformations from quenched-in B2 to the equilibrium phase. They describe this new phase as a ''DO₃ like tetragonal structure'' with a composition Ti₅Al₂Nb, and lattice parameters, a = 0.65 nm and c/a ≅ 1.02. Their unit cell is constituted by 8 bcc unit cells, and the atomic coordinates of their structure are given in Table 1 on this basis. The symmetry of this structure is P4/mm. Though it is not the smallest possible unit cell for the structure, comparison with other bcc binary derivative structures is easily possible on this basis. The atomic coordinates for the latter, for a ternary composition Ti₂AlNb, are also given. They note that the site occupation for the Hsiung et al. structure is quite distinct from that for a ternary DO₃ phase or any of the other possible bcc derivative structures (neglecting 2 possibilities with 128 or 432 atoms per unit cell(8) and interstitial ordering)