Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): M. Kook, R. Kumar, A.S. Murray, K.J. Thomsen, M. Jain A facility for the measurement of infrared photoluminescence (IRPL) has been developed for the Risø TL/OSL reader. The new IRPL measurement system uses an external laser light source at 1.49 eV (830 nm) and two photomultiplier tubes (PMT) for detecting emissions at ∼1.41 eV (880 nm) and ∼1.3 eV (955 nm) and an EMCCD. Pulsed IRPL measurement ensures a low background count rate by allowing the rejection of breakthrough from excitation light. We present the results of integrated IRPL measurements on both multiple- and single-grain aliquots, and finally demonstrate the potential of imaging natural K-feldspar samples and a granite rock slice.

Description: Publication date: July 2018 Source: Radiation Measurements, Volume 114

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): M.L. Chithambo, J.M. Kalita We report the dosimetric features of ultra-high molecular weight polyethylene (UHMWPE) using luminescence optically stimulated using 470 nm blue light. Samples irradiated to between 1 and 1000 Gy produces luminescence that increases with irradiation dose to produce a linear dose response between 1 and 1000 Gy. The sample was determined not to be affected by pre-dose in tests using a pre-dose of 4000 Gy. This characteristic precludes the need for elaborate background erasing routines typical of dosimetry experiments. The signal has good reproducibility. We used this property to test recovery of ‘unknown’ doses with encouraging results. It was observed that luminescence can also be stimulated using 870 nm infrared light. The dose response, fading, pre-dose effect and the ability to optically stimulate luminescence from the polymer is discussed in terms of curing involving free-radicals.

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): K.J. Thomsen, M. Kook, A.S. Murray, M. Jain It is desirable to be able to establish the relationship between the spatial distribution of luminescence and chemical composition/mineralogy. This is especially true in complex, heterogeneous samples such as solid coarse-grained rock slices and separated feldspar grains, where the internal dose rate is very dependent on the effective size of luminescent regions of the sample. The addition of spectral information would then help to give further insights into luminescence production mechanisms. A high sensitivity imaging attachment to the Risø TL/OSL Reader for investigating the spatial distribution of OSL and TL from natural and artificial phosphors has recently been developed (Kook et al., 2015). When combined with a Bruker μ-XRF facility and a high sensitivity spectrometer attachment, it is possible to investigate the relationship between the spatial distribution of luminescence, the distribution of chemical composition/mineralogy and the associated excitation and emission spectra. Here laboratory measurements undertaken using solid rock samples are presented and the observed relationships and their dosimetric implications are discussed.

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): J.-P. Buylaert, G. Újvári, A.S. Murray, R.K. Smedley, M. Kook Previous work has been unable to establish a relationship between K concentration and D e in single-grains of feldspar. Here we use four well-bleached sediments with low external dose rate (typically ≤1.5 Gy ka −1 ) to investigate this relationship. Single and multi-grain pIRIR measurements and μ-XRF analyses are made on Na- and K-rich extracts; μ-XRF is directly applied to grains sitting in single-grain discs to minimise uncertainty in grain identification. Micro-XRF is shown to be sufficiently precise and accurate and luminescence instrument reproducibility is confirmed using dose recovery measurements on heated feldspar. We are again unable to establish any correlation between single-grain D e and K concentration, even in feldspar grains for which the internal dose rate should dominate. We also measure highly variable Rb concentrations in these grains and are unable detect, at the single-grain level, the correlation between K and Rb previously observed in multi-grain investigations. Nevertheless, these results are unable to explain the lack of D e correlation with K. Finally, we investigate the dependence of D e on grain size (isochrons). Linear correlations are observed but slopes are inconsistent with model prediction. We conclude that this surprising absence of the expected relationships between dose and K concentration and grain size does not arise from analytical precision, incomplete bleaching, sediment mixing or fading. It appears that we cannot measure feldspar doses in these samples as accurately as we thought.

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): R.R. Dawam, M.L. Chithambo The thermoluminescence of synthetic quartz annealed at various temperatures up to 900 °C is reported. Glow curves measured at 1 o Cs −1 following beta irradiation to 40 Gy from a sample annealed at 500 °C and from an unannealed one consist of a prominent peak at 70 °C and secondary peaks at 110, 180 and 310 °C. In comparison, the glow peak from the sample annealed at 900 °C consists of three peaks but with the main peak at 86 °C and other lower intensity peaks at 170 and 310 °C. Kinetic analysis was carried out on the main peak only in each case. The order of kinetics of this peak was determined to be first order using various methods. The activation energy was evaluated as an average of 0.90 ± 0.02 eV for the unannealed sample and the one annealed at 500 °C. However, when the synthetic quartz is annealed at 900 °C, the activation energy decreases to 0.65 ± 0.02 eV. The main point of interest however concerns thermal quenching. It was noted that for the sample annealed at 500 °C as well as the unannealed one, the maximum intensity of the main peak decreases with heating rate. This phenomenon is associated with thermal quenching. When the same experiment is carried out using quartz annealed at 900 °C and irradiated to the same dose, namely 40 Gy, the intensity increases with heating rate. This would imply that this sample is not affected by thermal quenching. Using the notion that the radiative and non-radiative recombination routes are competitive, we repeated the experiment using a low dose of 3 Gy. In this case, the intensity decreased with heating rate showing that the process can be tuned. The activation energy for thermal quenching for the samples annealed at 900 °C, 500 °C and unnannealed one was found as 0.65 ± 0.02 eV, 0.82 ± 0.02 eV and 0.95 ± 0.06 eV. Evidently, annealing affects recombination processes in synthetic quartz.

Description: Publication date: Available online 4 June 2018 Source: Radiation Measurements Author(s): Sunil Thomas, M.L. Chithambo We report the thermoluminescence of Sm 3+ -doped P 2 O 5 -K 2 O-MgO-Al 2 O 3 -ZnF 2 glass. A glow-curve measured at 1 °C/s after beta irradiation to 10 Gy shows two peaks; a broad high intensity one at 214.0 ± 0.4 °C and a weaker intensity peak at 75.2 ± 0.8 °C. The dependence of peak position on partial heating as well as on irradiation suggest that the main peak at 214 °C is a combination of several overlapping peaks. The activation energy of the different components of the main peak, calculated using the initial-rise method, differ showing that the components are distinct. The reproducibility, fading and dose response were examined by considering the dominant component of the main peak. The intensity of the peak changes with heating rate in a manner consistent with thermal quenching.

Description: Publication date: Available online 29 May 2018 Source: Radiation Measurements Author(s): Vicki Hansen, Andrew Murray, Kristina Thomsen, Mayank Jain, Martin Autzen, Jan-Pieter Buylaert The ability to deliver accurate and precise calibration doses is a central part of all trapped charge dating methods. Usually, the radiation source (alpha, β, X-ray) used to deliver these doses is, in turn, calibrated against an absolutely known reference source (usually a γ source) and many laboratories make use of Risø calibration quartz for this purpose. We have previously described this material in detail (Hansen et al., 2015) and discussed the over-dispersion (OD) of 3.2 ± 0.3% in calibrated dose rate observed over 16 years. This dispersion highlights the danger of relying on individual calibrations, and is clearly undesirable. Here we continue our investigation into providing reliable calibration materials for trapped electron dating. A comparison of the apparent quartz β source dose rates shows that there is no significant dependence on geological source. However the β dose rate decreases by 25% with increasing grain size from about 100 μm to 1 mm, and backscatter leads to a dose rate increase of ∼1% per unit atomic number of the substrate. It is concluded that, for the multi-grain aliquots used in this study, the contributions to dose rate variability from grain size and substrate variations are likely to be negligible. Nevertheless there may be a practical advantage in using a high Z substrate because of the higher dose rate. Finally we test the measured to given dose (dose recovery) ratio for five heated feldspar samples and use the pIRIR 290 signal for β source calibration; surprisingly this gives an apparent β dose rate 15% lower than that to quartz despite their almost identical stopping power and mass absorption characteristics. Our results are discussed in terms of their significance for reproducibility and accuracy of β dose-rate estimates.

Description: Publication date: Available online 25 May 2018 Source: Radiation Measurements Author(s): K. Mayakannan, C.S. Sureka, R. Venkatesh, R. Sathish Kumar, R.K. Jeevanram In-vitro dose response curves were built with 6 MV X-ray for a dose range of 0.1–6 Gy, at a dose rate of 300 cGy/min, using Linear Accelerator (LINAC, SIMENS PRIMUS) for Cytokinesis-Block Micronucleus (CBMN) and Dicentric Chromosome Aberration assay (DCA). The dose response curves constructed up to 6 Gy and also up to 4 Gy using the manual method were compared to those curves obtained with the software program such as CABAS (V.2) and Dose Estimate software (V.5.2). The alpha and beta coefficients for MN and CA obtained for the curves constructed up to 6 Gy showed variation compared to those obtained in dose response curve constructed up to 4 Gy. However, the doses estimated based on these coefficients did not show much variation. The results are discussed in this paper.

Description: Publication date: Available online 26 May 2018 Source: Radiation Measurements Author(s): W.B. Li, W. Hofmann, W. Friedland In this review, the multiscale approach in radiation dosimetry in relation to biological effects is first briefly introduced. The need of dosimetry in microscopic regions, for example in cells, is then addressed, followed by a review of the basic microdosimetric quantities of internal emitters. The requirement of understanding the molecular biological effects of radiation leads to the dosimetric concept in the nanometer ranges, where the initial events produced at the molecular level cause the subsequent cellular and tissue effects that may lead to cancer. Track structure theory is particularly introduced in nanodosimetry for internal emitters. The relationship between the quantities in macroscopic dosimetry, e.g. absorbed dose, the microdosimetric quantities, e.g. specific energy and lineal energy, and the nanodosimetric characteristics, the track structures is inherently established in a derivational way. The significance of microdosimetric and nanodosimetric quantities in understanding and interpreting the mechanisms of radiobiological effects is addressed. Several applications of microdosimetry and nanodosimetry for internal emitters in radon and thoron progeny dosimetry and risk analysis, in targeted radionuclide therapy, in modelling of DNA damages and as a tool in the potential interpretation of dose-response relationship at low doses and dose rates are given. Finally, the potential future development of internal microdosimetry and nanodosimetry is outlined.