Radiation Measurements最新文献

Radiophotoluminescence (RPL) has been a key phenomenon in dosimetry. Most materials exhibiting RPL are inorganic single crystals, glasses, and ceramics. Recently, similar phenomena (i.e., fluorescence after irradiation) have been realized in soft matters, such as liquids, gels, and organic solids, on the basis of the radiation-induced production of fluorescent molecules. Dosimeters showing such phenomena are attractive from the viewpoints of their tissue equivalence, flexibility, scalability, and workability. The objective of this paper is to present an overview of such dosimeters with emphasis on the radiation chemical reactions used in the materials. Moreover, the sensitivity and the measurable range is introduced.

A constant value of the Relative Biological Effectiveness ($RBE$), equal to 1.1, to weight the physical dose of proton therapy treatment planning collides with the experimental evidence of an increase of effectiveness along the depth dose profile, especially at the end of the particle range. In this context, it is desirable to develop new optimized treatment planning systems that account for a variable RBE when weighting the physical dose. In particular, due to the increasing interest on microdosimetry as a possible methodology for measuring physical quantities correlated with the biological effectiveness of the therapeutic beam, the development of new Tissue-Equivalent Proportional Counters (TEPCs) specifically designed for the clinical environment are in progress.

In this framework, the silicon technology allows to produce solid state detectors of real micrometric dimensions. This is a valid alternative to the TEPC from a practical point of view, being simple, easy-of-use and more versatile. The feasibility of a solid state microdosimeter based on a monolithic double stage silicon telescope has been previously proposed and deeply investigated by comparing its response to the one obtained by reference TEPCs in various radiation fields. The device is constituted by a matrix of cylindrical elements, 2 μm in thickness and 9 μm in diameter, coupled to a single E stage, 500 μm in thickness. Each segmented ΔE stage acts as a solid state microdosimeter, while the E stage gives information on the energy of the impinging proton up to about 8 MeV.

This work is dedicated to the description of the microdosimetric characterization of the 148 MeV energy-modulated proton beam at the radiobiological research line of the Trento Proton Therapy Centre by means of a pixelated silicon microdosimeter. All measurements were carried out at different positions across the spread-out Bragg peak (SOBP) and the corresponding microdosimetric distributions were derived by applying a novel extrapolation algorithm. Finally, microdosimetric assessment of Relative Biological Effectiveness was carried out by weighting the dose distribution of the lineal energy with the Loncol's biological weighting function. Benefits and possible limitations of this approach are discussed.

Bone Mineral Density (BMD) can be determined by applying the Digital Image Processing (DIP) method using medical X-ray diagnosis. Although only the second metacarpal bone is analyzed in this approach, other parts of the body are exposed to X-ray radiation. We here propose a novel procedure in which parts of the hand surrounding the area of interest are shielded with an X-ray shielding sheet having low shielding performance. In our procedure, the main diagnostic area is not shielded, and other areas are covered with an X-ray shielding sheet with a low shielding performance. The sheet was fabricated by embedding Bi₂O₃ particles in resin sheet. We assessed the clinical performance of this method using three types of hand phantoms and conventional diagnostic X-ray equipment. The dose reduction for the entire hand region was evaluated by the Dose Area Product (${DAP}_{\text{Hand}}$), which was measured with a small dosimeter, and the hand area was determined from the X-ray image. The X-ray image of the second metacarpal bone is affected by the contribution of X-rays that penetrate the object of interest and are scattered in other areas of the hand. Because our X-ray shielding sheet suppressed the generation of scattered X-rays, the pixel value of the second metacarpal bone and corresponding BMD value are varied. To address this issue, we developed a correction algorithm. We found that the X-ray shields with Dose Reduction Factor ($DRF$) values of 40–60% were appropriate for our methodology. Our method was estimated to have a percentage uncertainty of approximately 5% for the derivation of BMD values. Morphological information of the hand and bones could thus be clearly observed. We verified that both morphological diagnosis and quantitative determination of BMD are possible when DIP procedure is conducted using our shield.

The advantages of proton and light ion beam therapy compared to conventional photon radiation therapy are well-known, mainly thanks to the characteristic depth dose distribution of ions and their radio-biological effectiveness. Nevertheless, the use of ions implies different nuclear reactions that generate secondary particles, with neutrons among them. These secondary neutrons can travel far away from the treatment volume, their measurement is a challenging complex task, and their biological effects are particularly high for neutrons with energies in the MeV range. In this review, a comprehensive description of secondary neutron dosimetry in proton and light ion beam therapy is given. Many studies have been conducted on the quantification of the secondary neutron dose, most of them have been performed for proton beams, whereas for other ions like carbon, the available information is scarce. The main measurement campaigns are summarised, focusing on the type of detectors used. In line with the detectors’ advantages and limitations, measurements performed inside and outside anthropomorphic phantoms are considered. The role of Monte Carlo radiation transport simulations is discussed since many experimental detection techniques need additional simulations to provide dose estimates. A focus on the current challenges for the measurements of neutrons with energies above 20 MeV is given, as this is one of the main components of secondary neutrons produced by therapeutic ion beams. Finally, the potential clinical relevance of the available and needed secondary neutron dose data is discussed, in terms of its impact on the treatment of patients. For this, the relative biological effectiveness of neutrons and the potential risk of cancer induction re-incidence or secondary cancer due to secondary neutron doses play a key role.

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.