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  • 1
    Publication Date: 2018-06-30
    Description: Publication date: Available online 28 June 2018 Source: Radiation Measurements Author(s): A. Timar-Gabor Different optically stimulated luminescence (OSL) single aliquot regenerative (SAR) saturation characteristics have been previously reported for quartz of diverse grain sizes. This preliminary electron spin resonance (ESR) study documents on paramagnetic signals in natural sedimentary quartz extracts of different grain sizes (4–11 μm, 63–90 μm, 90–125 μm, 125–180 μm, 180–250 μm) extracted from loess and sand samples that are amendable to OSL and ESR dating. Spectra recorded at room temperature and low power (〈1 mW) are dominated by the E 1 ’ centre, whose intensity in natural samples was found to decreases with increasing grain size. The signature of titanium centre could not be detected in fine (4–11 μm) quartz. For coarse fractions (>63 μm) titanium-lithium [TiO 4 /Li + ] 0 signals increase with increasing grain size. Aluminium-hole ([AlO 4 ] 0 ) signals are observed in all natural and laboratory irradiated investigated samples when spectra are recorded at low temperature (90 K). The intensity of these signals appears to decrease with increasing grain size, however, room temperature measurements show that these signals are highly interfered by a variety of signals tentatively attributed to peroxy (g ≈ 2.007 and g ≈ 2.004) with significantly higher intensities in fine grains (4–11 μm). A decrease of their intensity is reported when grain size increases and partial evidence that these defects are preferentially located in damaged regions of the grains is presented. A dose dependent paramagnetic signal at g ≈ 2.011 was detected only in 4–11 μm quartz. The stronger signature of the [TiO 4 /Li + ] 0 signals in larger grains coupled with the weaker signals of peroxy signals interfering with [AlO 4 ] 0 signal measurement is suggesting that coarser fractions should be preferred for conventional ESR dating using aluminium-hole and titanium signals. The understanding of the implication of these defects in OSL dating alongside with their concentration dependency on grain size requires further investigations.
    Print ISSN: 1350-4487
    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 2
    Publication Date: 2018-06-30
    Description: Publication date: Available online 28 June 2018 Source: Radiation Measurements Author(s): Eren Şahiner, M. Korhan Erturaç, Georgios S. Polymeris, Niyazi Meriç In this study, two different equivalent dose protocols using Infrared stimulated luminescence (IRSL), namely post IR (pIRIR) and Multi-Elevated temperature post IRSL MET-pIRIR were applied to geological samples collected from terrace staircases formed along the Sakarya River, western Anatolia, Eastern Marmara Region, Turkey. Methodological aspects were studied, as the IRSL signal, which is measured at elevated temperatures, yields unusual shape, consisting of an initial increasing part which is followed by the well-known decaying shape. Therefore, according to signal shape, instead of de-convolving the IRSL signals, equivalent dose estimations were performed using different time integration intervals of the emission. The results constitute of two groups, yielding equivalent dose values, in the range between 55 and 110 Gy for selected sample. Since de-convolution of the IRSL signals is both time consuming as well as difficult, mostly due to the presence of tunneling localized transitions, the selection of the appropriate/optimum time integration interval was discussed. The outcomes of this study indicate that IR stimulations at higher temperatures ranging from 200-250 °C are useful for feldspar dating, providing that initial increasing part will be eliminated. The thermal activation energy of that unusual part was calculated around 0.035 ± 0.005 eV using Arrhenius plot, indicating that it may arise from phonon lattice interactions.
    Print ISSN: 1350-4487
    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 3
    Publication Date: 2018-06-30
    Description: Publication date: Available online 28 June 2018 Source: Radiation Measurements Author(s): X.J. Ou, H.M. Roberts, G.A.T. Duller, M.D. Gunn, W.T. Perkins There is growing interest in rock surface burial and exposure luminescence dating for use in Quaternary science and in archaeology. Such methods have enormous potential both in increasing the range of sedimentary contexts that can be dated, and improving the accuracy and the precision of dating within those contexts. Bleaching of the luminescence signal with depth into the rock surface is likely to vary with lithology. However, previous work on rock surface dating has not systematically studied the differences in light attenuation for rocks of different lithologies, or directly quantified the attenuation of light in different rock surfaces. This study investigates the attenuation of light in different rock types (greywacke, sandstone, two granites and quartzite) using two different approaches: 1) sunlight bleaching experiments, to assess the residual infrared stimulated luminescence signal measured at 50 °C (IRSL 50 ) and the post-IR IRSL signal measured at 225 °C (post-IR IRSL 225 ) at different depths within the rocks after different durations of exposure to daylight; and, 2) direct measurement of light attenuation in rock slices using a spectrometer. Data from the spectrometer shows that for all rocks, attenuation is greater for shorter wavelengths (∼400 nm) than longer ones. A consistent difference in attenuation coefficient is seen when comparing the IRSL 50 and the post-IR IRSL 225 signals; this is thought to reflect the different sensitivity of these two signals to infrared and visible light. Direct measurement using a spectrometer is much more rapid than undertaking a bleaching experiment, and also provides wavelength-resolved attenuation data. Comparison of the numerical values from the two approaches is complex, but they yield consistent results. For the samples analysed here, the rocks that appear lightest in colour show the least attenuation of light and the luminescence signals are bleached to the greatest depths, and are thus the most suitable for dating using luminescence.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 4
    Publication Date: 2018-06-30
    Description: Publication date: Available online 28 June 2018 Source: Radiation Measurements Author(s): Yan Li, Sumiko Tsukamoto, Hao Long, Jingran Zhang, Linhai Yang, Zhong He, Manfred Frechen The reliability of the fading correction methods for feldspar infrared stimulated luminescence (IRSL) dating in the non-linear part of the dose response curve proposed by Wallinga et al. (2007) (modified from Lamothe et al., 2003) and Kars et al. (2008) was evaluated using samples from the Chinese loess-palaeosol sequence in Luochuan with the reference ages. Two protocols, the post-infrared (IR) IRSL at 225 °C (pIRIR 225 ) and the pulsed IR at 50 °C, were applied in this study. The natural dose response curve (DRC) for the IR 50 (pre-pIRIR 225 ), pIRIR 225 and pulsed IR 50 was first constructed. The simulated-natural DRC and the fading corrected ages were then determined. The characteristic saturation dose ( D 0 ) of the simulated-natural DRC was found to be larger than that of the natural DRC for the IR 50 (pre-pIRIR 225 ) and pIRIR 225 signals, whilst the two D 0 values agreed with each other for the pulsed IR 50 . The saturation ratio ( n/N ) of the simulated-natural DRC agreed with the natural one within 10% uncertainty for all three signals. The fading corrected ages using these two methods agreed with the reference ages, confirming the reliability of the two fading correction methods. However, our numerical simulation on the fading correction showed that the method of Wallinga et al. (2007) significantly overcorrect ages when the fading rates are larger than ca. 4–5%/decade.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 5
    Publication Date: 2018-06-29
    Description: Publication date: September 2018 Source: Radiation Measurements, Volume 116 Author(s): Agnieszka Marciniak, Bartłomiej Ciesielski, Paweł Czajkowski, Karolina Krefft, Piotr Boguś, Anita Prawdzik – Dampc, Joanna Lipniewicz Electron paramagnetic resonance (EPR) measurements of human's nails is a newly proposed method of retrospective biodosimetry based on quantitative ex vivo determination of EPR signals originating from free radicals induced in nails by ionizing radiation. In the presented study the nails were irradiated in vivo under controlled exposure conditions during total body irradiation (TBI) procedures with doses in nails about 15 Gy delivered through 3 days in 2 fractions per day. The authors applied two methods of reconstruction of the doses: one based on individualized calibration of the radiation-induced EPR signal (RIS) and the second one based on determination of the dose of maximum response (DMR) of so-called RIS5 EPR signal. The first method yielded doses from −3.5 Gy to 22.1 Gy for seven TBI patients. In all but one patient the reconstructed doses were considerably lower than the actual doses calculated by treatment plan, probably due to decay of the dosimetric EPR signal caused by contact of the nails with water during the patients' personal hygiene activities. The second method, based on the RIS5 signal, did not allow for reconstruction of the TBI doses mostly due to lack of the dose saturation features characteristic to RIS5. Further studies on the RIS5 method suggested, that its applicability can be related to the samples' geometry, i.e. the ratio of the total length ( l ) of cut edges to the mass ( m ) of the nail clippings: the dose saturation effect, characteristic for RIS5 radicals, was not observed for samples of relatively high l/m ratio. In addition, the study showed only limited resistance of the RIS5 radicals to water – water treatments longer than 10 min resulted in a decrease in the RIS intensity up to complete decay of the RIS for 60 min exposures of the irradiated clippings to water. Therefore it is concluded, that both methods are of limited reliability – only the method of direct calibration can provide, under conditions of minimized contact of nails with water before and after cutting, an indication of the radiation exposure in the examined dose range.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 6
    Publication Date: 2018-06-27
    Description: Publication date: Available online 26 June 2018 Source: Radiation Measurements Author(s): P. Bilski, B. Marczewska, M. Kłosowski, W. Gieszczyk, M. Naruszewicz Fluorescent nuclear track detectors (FNTD) based on nat LiF crystals were successfully applied for measurements of neutron doses. FNTDs were exposed on a phantom to Hp(10) doses ranging from 1 mSv to 20 mSv. The number of observed tracks was found to be linear with the dose. The actual limit of detection is certainly much lower than 1 mSv and it depends on the scanned volume of a crystal. The very advantageous feature of LiF FNTDs is that the unirradiated detectors show no tracks similar to that produced by thermal neutrons, which means that background (zero-dose signal) is basically equal to zero. These results were obtained with detectors based on natural lithium and might be substantially improved if 6 Li enriched lithium is used for crystal growth. It was also found that LiF FNTDs can be used for direct detection (without any converter) not only of thermal, but also of fast neutrons by using recoil of lithium nuclei.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 7
    Publication Date: 2018-06-23
    Description: Publication date: Available online 21 June 2018 Source: Radiation Measurements Author(s): R. Kumar, M. Kook, A.S. Murray, M. Jain Prasad et al. (2017) recently developed a new method of measuring the dosimetric signal in feldspar, based on a Stokes-shifted photoluminescence emission (excitation energy ∼ 1.40eV (885 nm), emission energy ∼ 1.30eV (955 nm)). The new signal, termed as infrared photoluminescence (IRPL), was shown to arise from radiative relaxation of the excited state of the principle trap (dosimetric trap), and allows non-destructive probing of the dosimetric information. Thus, IRPL provides a unique tool to study physical characteristics of these metastable states in feldspar, e.g., number density and spatial distribution, trap depth, photo-ionisation and capture cross-section, excited state lifetime, and tunneling probabilities. The IRPL emission is apparently related to the infrared radioluminescence (IR-RL) in K-feldspar (Trautmann et al., 1998); in the latter, however, the electrons relax after being trapped as a result of exposure to ionising radiation, rather than as a result of excitation within the trap. In this study, we report the discovery of a second IRPL emission centred at ∼ 1.41eV (880 nm) in a K- feldspar which arises in response to excitation with 1.49eV photons. Based on the temperature- and dose-dependent behaviour of IRPL and IR-RL, we conclude that the same defect(s) participates in these two emissions. However, IRPL emission is governed by the characteristics of the principle trap (defect) alone, whereas IR-RL depends additionally on thermally assisted transport within the band-tail states. Since IRPL is a site selective technique, it does not, unlike IR-RL, suffer from contamination from higher energy emissions (e.g. from Fe 3 + ). This lack of contamination, and the possibility for thermal/optical pre-treatments and repeated measurements of the same trapped electrons, suggest that IRPL is a robust alternative to IR-RL.
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 8
    Publication Date: 2018-06-23
    Description: Publication date: Available online 22 June 2018 Source: Radiation Measurements Author(s): P. Palczewski, A. Chruścińska Recently it was shown that making use of the dependency of optical cross-section (OCS) of trap on the experimental parameters can help to enhance the ability to separate signals from different traps. When the light source applied for stimulation delivers the spectral band of a finite width, the physical quantity that governs the luminescence process is not the OCS value but rather a kind of weighted average of the OCS value over the range of the stimulation band. Changes of the shape of the stimulation band allow to regulate the shape of OSL curve. The band shape modulation can be easily attained using at least two sources of light. The shape of a band that is the sum of bands from two sources can be controlled by changing the emission intensity of each source. The presented results of simulations and experiments demonstrate what can be achieved by means of such a band shape modulation. The ability to separate the signal from different kinds of traps depends significantly on the selection of the experimental parameters such as the energy of the maxima of the component spectral bands, the difference of these maxima as well as the rate and the character of light intensity changes. When the experimental parameters are properly selected the OSL curve for a single trap has the form of a peak.
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    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 9
    Publication Date: 2018-06-23
    Description: Publication date: Available online 22 June 2018 Source: Radiation Measurements Author(s): Ryo Kakino, Akihiro Nohtomi, Genichiro Wakabayashi We previously evaluated ambient neutron dose equivalent by using the self-activation of a CsI scintillator around a high-energy medical linear accelerator (linac) 128 I saturated activities were successfully converted to neutron spectrum and ambient neutron dose equivalent by neutron spectrum unfolding with the “three-group approximation.” The principle of the three-group approximation is based on the assumption of fixed shapes of neutron energy spectra for each of the three energy regions to evaluate the neutron spectrum effectively. However, such a neutron dose evaluation with the unfolding method might be affected by the difference between the actual fast neutron energy spectrum and the assumed spectrum. In the present work, we modified the unfolding method by taking into account the differences in the shapes of fast neutron energy spectra for various medical linacs. We verified the unfolding method using Monte Carlo simulation with several neutron spectra obtained from published research articles. The modified three-group approximation evaluates the neutron doses more accurately than the conventional unfolding method.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 10
    Publication Date: 2018-06-23
    Description: Publication date: Available online 22 June 2018 Source: Radiation Measurements Author(s): Julie A. Durcan Signal stability is a key consideration when using luminescence dating techniques. The stability, or lifetime, of a signal is one of the factors determining the upper age constraint for luminescence dating, and it has been suggested that the signal being used for dating should have a lifetime at least ten times the age being dated in order to limit age underestimation to an upper loss of 5%. Accurate derivations of signal stability and associated kinetic parameters, such as trap depth and frequency factor, are also important parameters for constraining rock cooling histories in thermochronometric techniques. This paper aims to assess the reproducibility of lifetime determinations derived isothermal decay measurements. Variability arising from changing the isothermal decay protocol used is tested. Simulating Arrhenius plot from fixed trap depth and frequency values shows that whilst trap depth can be relatively well constrained, significant variability in the frequency factor, hence signal lifetime, should be expected. This paper also uses luminescence signals measured using different wavelengths to better understand the impact of signal from non-fast quartz OSL components in lifetime calculations. The presence of contributions from non-fast OSL components in the initial part of the OSL signal can result in the lifetime being calculated from charge contributions from multiple traps, not solely the 325 °C TL peak, as has been previously assumed. This effect can be reduced however by stimulating luminescence signals with longer wavelengths to better isolate the signal from the fast component.
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    Electronic ISSN: 1879-0925
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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