Radiation Measurements最新文献

The goal of the present work was to conduct an initial screening survey of several types of TL and OSL detectors, aimed at searching for the indication of the presence of dose rate effects. The study has been performed on ten different materials: LiF:Mg,Ti; LiF:Mg,Cu,P; CaF₂:Dy; Al–P glass; YAP:Mn; CaSO₄:Dy; Al₂O₃:C; BeO; MgB₄O₇:Ce.Li and quartz. Gamma-ray dose rates ranged from 0.1 mGy/h to 90 Gy/h. No clear evidence of dose rate effects was found for any material. In two cases (MgB₄O₇:Ce,Li and BeO) some irregularities of the response were observed, which require further investigations but most probably they are not attributable to the dose rate influence.

Screen protectors for smartphone are investigated in attempts for emergency dosimetry as for example in case of malicious attacks with radioactive sources or accidental overexposure. Electron Paramagnetic Resonance (EPR) measurements were carried out on six different types of screen protectors (SPs). The inter and intra batch variability of the EPR signals characteristics (sensitivity, stability, signal shape) were studied. Contrary to touch screen (De Angelis et al., 2015; Juniewicz et al., 2020), UVB exposure for SP is not a limiting confounding factor. All samples under irradiation exhibit same EPR signals. The nature of the radio-induced point defects was identified (HC₁ and HC₂) as well as their evolution according to dose. The linear dose response was studied in the 0–5 Gy dose range with a detection limit estimated of 750 mGy with a field deployable benchtop EPR spectrometer. Large variability of the dose response prevents presently from using universal calibration curve. Therefore, further work is needed to consider possible application for triage in the case of large-scale accidents scenarios.

Dose evaluation and direct measurements are fundamental for radiation protection in non-conventional accelerator facilities, both before and after the primary and secondary shielding. In this paper, we will report about the experimental setup, data acquisition and analysis, together with FLUKA modeling, of the dose measurements test carried out in the Beam Test Facility (BTF) of the INFN - Frascati’s National Laboratories (LNF), where an intense mixed field is produced and measured with thermoluminescent dosimeters. BTF is an extraction and transport line of DA$\Phi$NE LINAC (Buonomo et al. 2021; Mazzitelli et al. 2003). It is optimized for electrons and positrons production in a wide range of intensity, energy (30 MeV–800 MeV), beam spot dimensions and divergence, using both primary and secondary beam of the DA$\Phi$NE LINAC. Through the years, the BTF has gained an important role in particle detectors test and development with electron/positron beam. A small fraction of the BTF’s shifts have been dedicated to radiation damage test using LINAC electron primary beam up to $5\times 10^{10}$ e-/s. As radiation protection group of the LNF, we evaluated the dose when electrons impinging on a Pb target from: (i) photon Bremsstrahlung production; (ii) photoneutron production. Three dedicated tests with 503 MeV electrons impinging on a $\sim$16 cm thick Pb target have been carried out in February, June 2022 and in January 2023, using TLD700 and TLD600, measuring doses at several charge intervals. The aim of this study focuses on evaluating dosimetric quantities produced by the mixed field, air kerma for the photon component, and ambient dose equivalent for the neutron one, using thermoluminescence dosimeters calibrated with low-energy standards: Cs-137 and Am-Be. The approach adopted involves the use of Monte Carlo simulations of the experiment, both to benchmark against experimental measurements and to validate the results obtained for energies higher than those of calibration. The results of this comparison show excellent agreement between measured and simulated quantities in the forward direction, allowing us to conclude and confirm the validity of the calibrations themselves.

The objective of this work is to assess the photon energy and angular response of various dosimetry systems in terms of the operational quantities for external radiation exposure personal dose, $H_{\text{p}}$, and personal absorbed dose in local skin, $D_{\text{local skin}}$, defined in Report 95 of the International Commission on Radiation Units and Measurements (ICRU). The dosimetry systems in Switzerland offer an opportunity to evaluate the status quo in personal dosimetry, due to variety of techniques employed and the possibility of accessing commissioning data from the various services.

The photon energy and angular responses in terms of the ICRU Report 51 personal dose equivalents $H_{\text{p}}\left(10\right)$ and $H_{\text{p}}(0.07)$ were compiled for the dosimetry systems used by the Paul Scherrer Institute (radiophotoluminescence and direct ion storage), the Lausanne University Hospital (optically stimulated luminescence), the CERN (direct ion storage), Dosilab (thermoluminescence), and the SUVA (thermoluminescence). From this data, the response of the systems to the ICRU Report 95 quantities for whole body dosimetry ($H_p$) and skin dosimetry ($D_{\text{local skin}}$) was calculated using conversion coefficients from air kerma to the respective operational quantities. Regardless of the detector material, whole-body dosimeter design, or technique, each system over-estimated the personal dose, $H_{\text{p}}$, in the low-energy range ($<70$  keV) up to a factor of 3 or 4. The indicated values for the personal absorbed dose in local skin, $D_{\text{local skin}}$, remains within the limits $(0.71-1.67)$. These estimates highlight the impact of the ICRU 95 Report at a country’s scale and prompts discussion regarding potential solutions and challenges.

This work proposed the development of CaSO₄:Tm,Li, CaSO₄:Tb,Li and CaSO₄:Eu,Li composites for application in radiation dosimetry, using luminescent techniques such as thermoluminescence (TL) and optically stimulated luminescence (OSL). The CaSO₄ crystals were produced by the adapted slow evaporation route and characterized using X-ray diffraction (XRD), TL and OSL techniques. XRD analyses showed that the doped CaSO₄ samples presented a single phase. The CaSO₄:Eu,Li composites showed TL signals with peaks around 145 °C and 180 °C. The CaSO₄:Tb,Li and CaSO₄:Tm,Li composites showed TL signals with peaks centered at 165 °C and 275 °C. For the CaSO₄:Tb and CaSO₄:Tm samples, the addition of lithium as co-dopant resulted into a significant increase (2x) in the total TL signal of the samples. The CaSO₄:Tm,Li samples presented a very intense OSL signal, about 80x greater than the signal of the other samples produced. This allows the applicability of TL/OSL detectors even more sensitives. The TL emission spectra of the samples showed typical emissions of Eu²⁺ ions (280 nm), Eu³⁺ (614 nm), Tb³⁺ (544 nm) and Tm³⁺ (455 nm). No emission corresponding to lithium was identified. All the samples produced showed linearity in the dose range used and good reproducibility, with variations below 10%. The CaSO₄:Tm,Li samples showed the lowest limit of detection and fading. The evaluated dosimetric characteristics denote that these developed composites have potential application as TL/OSL detectors.

In luminescence thermochronometry, the thermal stability of feldspar minerals is conventionally constrained from isothermal decay experiments. However, despite recent refinement of the measurement protocol, measurements take several days and are routinely done for each individual sample. Following that most other thermochronometric methods usually use only a single reference set of thermal kinetic parameters, and that recent studies on direct physical probing of feldspar sample properties have shown that trap depth and band-tail width are broadly similar despite large variations in chemical composition, we sought to optimise luminescence thermochronometry measurements by exploring whether a single set of thermal kinetic parameters can describe luminescence thermal decay in feldspar. We explored the effect of using averaged thermal kinetic parameters rather than sample-specific thermal kinetic parameters to model luminescence signal accumulation under different thermal conditions. A set of K- and Na-feldspar minerals extracted from all over the world were analysed after being measured with a multi-elevated temperature protocol, comprising four different IRSL signals at 50, 100, 150, and 225 °C. Comparisons were done between the thermal kinetic parameters of each IRSL signal depending on different variables such as geographic region, transect, lithology, or mineralogy of the analysed feldspar grains. Even though it is not possible to generalise the thermal kinetic parameters between IRSL signals measured at different temperatures, the variance between the thermal kinetic parameters of different samples measured at the same IRSL temperature is consistent with the uncertainties on the individual parameters (i.e., <2–10%), suggesting that averaged, rather than sample-specific values may be appropriate. We then explored the effect of using these averaged parameters to model luminescence signal accumulation under different synthetic and natural thermal conditions. For our dataset, results show minimal impact on the obtained cooling histories and exhumation rates. We therefore propose the use of averaged rather than sample-specific thermal kinetic parameters for rapid investigation of luminescence thermochronometry samples. Based on careful initial characterisation of a few samples to verify the validity of using averaged thermal kinetic parameters, this would reduce measurement times by ca. 50% (i.e., 3–4 days per sample), allowing higher resolution sampling and measurement.

This study investigates the impact of particle size on the radioluminescence (RL) response of (C₄₄H₃₈P₂)MnCl₄ coatings, which have been made with five crystal size fractions ranging from ≈200 nm to 75 μm. These coatings underwent testing using a bespoke 2D real time prototype system, comprising a camera affixed to the head of a linear accelerator and oriented towards the flexible RL coatings positioned at the beams' isocentre. Upon irradiation, a consistent RL peak at 525 nm was observed across all particle size fractions, albeit with varying light intensities. Minimum detectable dose-rate values were determined to be 0.05 Gy/min, and even for the coating exhibiting the lowest light intensity (Nano-01), individual pulses could be discerned, yielding a minimum detectable dose of 0.28 mGy. Basic dosimetric tests were conducted to characterize these coatings, evaluating their response with respect to dose-rate, dose, and small field relative responses. Subsequently, the coating demonstrating the most favorable dosimetric properties underwent further analysis to assess its suitability for machine quality assurance (QA). These tests included the standard alternating leaves, chair, and pyramid checks routinely employed for QA purposes.

In this study, we examined the response of Allium cepa sprout stem cells, or meristems, to UVB and UVC radiation. The choice of Allium cepa, or onion, was made to avoid the controversial use of animal models. Allium cepa is a well-established in vivo standard model that is frequently used in cytogenetic research connected to various environmental contaminants. Indicators such as micronuclei and chromosomal abnormalities were used to evaluate the genotoxicity of UVB and UVC radiation, and the mitotic index was used to investigate the cytotoxicity of the radiation, providing information on cellular proliferation. The Shapiro-Wilk test (p < 0.05) confirmed the normality of the data. The analysis of the Pearson linear correlation coefficient (r = 0.97), conducted across all dose points considered, including the negative control, revealed an almost perfect positive linear relationship between the dose and the number of cells with micronuclei, for both UVB and UVC. The frequency of induction of micronuclei as a function of dose for both radiation types was found to be similar. However, a difference in the morphology of the cells exposed to UVB radiation compared to those exposed to UVC radiation was observed. In conclusion, the mitotic index analysis showed no significant differences in cell activity between UVC and UVB irradiation compared with control samples. The results from this study support the use of Allium cepa and cytogenetic endpoints as a biodosimetric method for ultraviolet radiation.

Gamma-ray coded-aperture imaging technology plays an important role in nuclear security, decommissioning of nuclear facilities, and nuclear medicine diagnosis. However, under near-field imaging condition, artifacts in the reconstructed image can interfere with identifying the shape and position of the radioactive source. In this paper, a gamma-ray coded-aperture imaging method based on mask and anti-mask functions was proposed to suppress imaging artifacts and speed up the acquisition of low-noise reconstructed images. Through simulation, the effects of the number of iterations and the thickness of the coded-aperture collimator on the imaging quality were studied, and the range of the optimal correction factor in the method was determined. Imaging experiments were conducted using a compact coded-aperture gamma camera based on CdZnTe detector to verify the applicability of the optimal correction factor range. The limitations of the proposed method were analyzed through complex-shaped source imaging simulations and multi-source imaging experiments. This method has an insufficient suppression effect on random artifacts and requires further improvement in imaging irregular radioactive sources. However, it has good imaging performance for single-point source and multi-point sources, effectively reducing regular cross-shaped and stripe-like artifacts. In the non-uniform radioactive background, it can eliminate a part of artifacts, significantly improving imaging quality. Therefore, this method has potential applications in complex radioactive environments.

In this work, thermally assisted OSL (TA-OSL) of natural fluorite was investigated, aiming to understand better the role of traps in both TL and OSL. TA-OSL is the luminescence simultaneously stimulated by light and heat; from this combination it is possible to access deeper traps in the analyzed material, that, in general, need more energy to be accessed. Irradiations were performed at room temperature using the Sr-90/Y-90 source incorporated in the TL/OSL reader at a dose rate of about 10 mGy/s. The optical stimulus was blue light at 470 nm. The dosimeters were also irradiated with X and gamma-rays of various energies (from 20 keV to 1.25 MeV) for comparing the energy dependence of the OSL and the TA-OSL signals. Residual TL curves were acquired after OSL readouts for checking trap participation in OSL emission. The OSL measurements were done at temperatures from 25 °C to 400 °C. For readout temperatures from 25 to ∼185 °C, decay curves were observed, and they were modeled by one stretched-exponential function, giving rise to a good fit to the experimental data. The dependence of the fitting parameter (β) on the photon energy was studied, and it was observed that β increases with the X-ray beam effective energy. The energy dependence of OSL signal is 1.5 times larger than that of TA-OSL signal, pointing to the reduction in energy dependence with the combination of thermal and optical stimuli. The total light emitted (TA-OSL + residual TL) is highly increased by the simultaneous stimulation by light and heat, indicating that light promotes charges to thermally active traps (phototransfer), and heat promotes charges to optically active traps, facilitating their release during illumination.