Radiation Measurements最新文献

Innovative Treatment Planning Systems (TPS) in proton therapy based on a variable radiation quality with depth with respect to the conventional one with a fixed Relative Biological Effectiveness (RBE) of 1.1 are under study. Experimental methods are needed to verify the consistency between what is planned and what is delivered in terms of radiation quality. Microdosimetry studies the stochastics of the energy deposition process at micrometric and sub-micrometric level which is known to be related to the biological effectiveness of ionising radiation fields. For this reason, it is recognised by the scientific community that it is a useful tool to monitor the radiation quality of hadron therapy beams where the effectiveness varies with the penetration depth in patients. Detectors are needed to perform a microdosimetric characterization of a clinical beam and they need to satisfy specific requirements to enter the clinical practice as instruments for the Quality Assurance (QA). With this aim, at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (LNL-INFN) a technological transfer project was carried out with the final goal of developing engineered miniaturized Tissue Equivalent Proportional Counters (mini-TEPCs) for clinical applications. This work presents the characterization performed on the new detectors and the results obtained in neutron and proton fields.

Optically stimulated luminescence detectors (OSLDs) have been utilized for various dosimetry applications for many years. The use of ${\text{Al}}_2{\text{O}}_3\text{:C}$ OSLDs for proton dosimetry began over a decade ago, taking advantage of the correlation between the ionization density of the radiation field and the ratio of intensities of the material’s two emission bands. The correlation allows for determining both linear energy transfer (LET) and dose in proton beams, with corrections for ionization quenching derived from the LET. However, the previous methodology for proton dosimetry and simultaneous LET determination with ${\text{Al}}_2{\text{O}}_3\text{:C}$ OSLDs was cumbersome and occasionally associated with large uncertainties, while carbon beam dosimetry posed further challenges due to an elevated LET.

This paper reviews the recent advancements in ion beam dosimetry and LET determination using OSLDs. Employing ${\text{Al}}_2{\text{O}}_3\text{:C,Mg}$ OSLDs alongside improved, automatized read-out techniques, and the use of other radiation quality metrics than averaged LET, has removed most of the previous obstacles for ion beam dosimetry with OSLDs.

The feasibility of simultaneous LET determination and dosimetry in ion beams is demonstrated through two case studies involving realistic proton and carbon ion therapy scenarios.

Handling the ²⁵²Cf radionuclide source poses a potential hazard of skin surface contamination in case of an unexpected occurrence. Consequently, there is a growing need to establish precise dose conversion coefficients tailored to each type of emitted primary particle and various radionuclides. Nevertheless, the current body of literature does not provide specific data or methodologies for evaluating skin contamination dose and its associated coefficients, particularly with regard to the ²⁵²Cf source. Thus, this study aims to quantify the dose rate received by the skin and its associated coefficients after contamination scenario. Utilizing the established MCNPX environment, the Equivalent dose rate and Absorbed dose, along with Skin contamination dose coefficient (SCDC), have been calculated within the skin tissue. Two methodologies, specifically Watt Fission distribution and the Doppler Effect, are proposed to analyze particle spectra within skin phantom, enabling the calculation of Equivalent dose rate. In accordance with ICRP recommendations regarding the optimal depth for assessing skin doses, the designated scoring volume within the skin is located between depths of 50–100 μm. This volume is tasked with evaluating the dose. The SCDC results were entirely consistent with previously published data from MCNPX, with statistical uncertainties of less than 15%, demonstrating the efficacy of the methodologies employed in this study. This research presents an innovative method for generating data related to skin contamination doses. The novel outcomes in the current research facilitate the assessment of skin dose contamination for the targeted radionuclides and radiotherapy purposes due to staff oversight and radiobiological effects.

Objective

To investigate the consistency of the recommended methodology, we analyzed the dosimetric results obtained for each setup beam shaping filter and tube voltage and evaluated the uncertainty associated with the full dose measurement process.

Methods

A 300-mm PTIC was used to validate the results obtained with the 100-mm PTIC. Considering the other dosimetric parts, a cylindrical 160-mm diameter PMMA phantom and a cylindrical 320-mm diameter PMMA phantom were also used in the experimental protocol.

Results

For the lowest and highest tube voltages available, the CTDI_air,160 values obtained by 1-step dosimetry with the 300-mm PTIC were greater than the respective values obtained by 2- and 3-step dosimetry with the 100-mm PTIC.

Conclusion

This study established that careful positioning of the 100-mm PTIC in 2 or 3 steps, as well as proper execution of the other dosimetric parts recommended by the IAEA, represents a validated approach within up to 20% uncertainty for wide cone beam CT dosimetry.

The hybrid K-edge/X-ray fluorescence densitometer (HKED) is a combination of K-edge absorption technology (KED) and characteristic X-ray fluorescence (XRF), which has the advantages of direct, fast and non-destructive determination, and is an ideal non-destructive measurement technology for uranium and plutonium concentrations. In this paper, a new HKED was developed, primarily utilizing an X-ray tube from COMET, alongside high-purity germanium (HPGe) and cadmium telluride (CdTe) detectors from AMETEK ORTEC. This manuscript delves into several variables that influence measurement outcomes under predefined experimental conditions and operational prerequisites to pinpoint critical parameters. It was discerned that the adoption of a 160 kV high voltage setting markedly diminishes experimental interferences, while the beam current, optimally set at 2 mA, not only ensures a linear correlation with the count rate but also maximizes the effective count detected. The incorporation of a 2 cm fixed-length iron rod along the trajectory between the sample and the detector, complemented by an additional 3 mm external absorber before the KED detector, effectively mitigates direct X-ray exposure, thereby enhancing transmittance values to attainable extents. Subsequent to the determination of these pivotal parameters, validation of the HKED system's efficacy was conducted via performance evaluation tests on a laboratory-scale HKED setup. Measurements undertaken for both KED and XRF across an interval ranging from 300 to 3000 s fell within the 2σ boundary, affirming the system's stability. Repeated measurements of 50 g/L and 150 g/L uranium solutions yielded KED precision rates of 0.56% and 0.19%, respectively. Moreover, linear regression analyses linking transmittance, characteristic X-ray fluorescence, and uranium concentrations across a spectrum of 0–150 g/L underscored the laboratory HKED instrument's robust analytical capabilities. Notably, the relative discrepancy between theoretical predictions and empirical findings for the 150 g/L uranium sample was minimized to a commendable 0.58%.

Radiation damages to genes and cells occur at the DNA level, and therefore they are directly related to the spatial distribution of events caused by radiation at nanometer scale. Nanodosimetry introduces new quantities to correlate the initial features of radiation interactions and the likelihood of late radiobiological effects by means of Monte Carlo codes and, experimentally, with gas-detectors operating at low pressure.

Within this context, the aim of this work is to develop a numerical approach based on the implementation of different simulation tools to accurately describe the low energy electron transport processes within nanodosimetric devices. This approach was directly applied to perform a proof-of-concept study of the response of the electron collector of the STARTRACK nanodosimeter. Garfield++ was used to simulate the primary track structure of 5.8 MeV He-4 particles, while COMSOL Multiphysics was used to model the geometry and the electrostatic field of the electron collector. Available experimental data, measured with the STARTRACK nanodosimeter, were used to validate Garfield++ nanodosimetric spectrum before proceeding with the simulation of the electron transport stage in the drift volume, again performed with Garfield++. In order to verify the performance and reliability of the implemented codes, the nanodosimetric distributions were studied with the threefold objective of characterizing the time, space, and energy distributions of particles collected at the end of the drift volume. These results can offer a valuable insight into the overall working principle of nanodosimeters: this understanding can be pivotal in optimizing and refining the design of such devices, ultimately extending their effectiveness in particle track characterization during radiation therapy.

In this work, a novel sensitive composition of Fricke radio-chromic gel dosimeter based on polyvinyl alcohol (PVA), xylenol orange (XO), and physical cross-linking agent gellan gum (GG) is presented and evaluated with two optically detection methods. The Fricke dosimeter was irradiated up to 30Gy using medical linear accelerator and analyzed optically using ultraviolet visible (UV–Vis) spectrophotometry technique at wavelengths of 585 nm (i.e., within the visible range) and two-dimensional optical imaging system of charge-coupled-device (CCD) camera with a uniform red light-emitting-diode (LED) array source. The Fricke dosimeter demonstrated important properties including independence of beam energy and dose rate over the range studied. In addition, these dosimeters have high sensitivity in the range of 0–10Gy, and significant low diffusion coefficient of 0.070 mm² h⁻¹. In addition, the composition shows a lower diffusion coefficient with respect to those reported so far for a Fricke dosimeter. The total uncertainty of the estimated doses for the Fricke dosimeter was 3.96% at 95% confidence level.

In the MARE experiment onboard the NASA Artemis 1 mission of the ORION spacecraft to lunar orbit, two anthropomorphic female phantoms, equipped with a large number of active and passive radiation detectors were flown. Among the detectors were both LiF:Mg,Ti and LiF:Mg,Cu,P TL detectors as well as Al₂O₃:C OSL detectors. In order to correctly interpret the measured doses, the effective relative TL/OSL efficiency for cosmic radiation of these detectors was calculated by combining simulated radiation spectra for the cis-lunar space conditions with the efficiency functions based on experimental data for different ions and on a microdosimetric model.

The obtained results show that for the ORION shielding conditions, the relative efficiency of LiF:Mg,Ti is close to unity (0.95), while the remaining detectors show somewhat smaller efficiency: 0.90 for Al₂O₃:C and (0.81–0.86) for LiF:Mg,Cu,P. The analysis of the influence of the shielding thickness on the relative TL/OSL efficiency revealed, that for low shielding conditions, the relative efficiency may be more significantly decreased, reaching values between 0.71 (LiF:Mg,Cu,P) and 0.85 (LiF:Mg,Ti) for 1 g/cm².

Luminescence-based thermometry and dating often requires determination of the saturation level for specific signals and the corresponding dose. However, previous studies found non-monotonic dose responses for some monochromatic thermoluminescence (TL) and optically stimulated luminescence (OSL) signals from quartz as well as spectral overlap of emission bands, substantially complicating data interpretation. Therefore, the present study examines (1) the variability in the TL emission spectrum of quartz and feldspar from bedrock and sediment of different provenances and, (2) the saturation characteristics of the blue emission band for both quartz and feldspar in the dose range from 0.25 kGy to 50 kGy. The experimental results confirm differences in the spectra which appear to be characteristic of their geological origin and chemical composition. Spectral analysis shows that in the temperature range 175–220 °C the blue emission band at ∼2.5 eV dominates over other bands for all quartz samples studied. A broad UV-blue TL signal peaking at ∼2.5−3.0 eV and composed of probably three overlapping, individual bands is characteristic for K-feldspar, while one Na-feldspar exhibits an additional band at ∼2.2 eV.

In the studied dose range, the emissions at ∼2.5 eV and ∼2.6 eV increase as a function of dose up to 6 kGy for both quartz and feldspar. A difference in dose response was observed for high doses (>6 kGy) where feldspar samples reached a stable saturation level while for quartz the blue emission band intensity decays until 50 kGy after having attained a maximum. Our results suggest the suitability of feldspar TL for palaeothermometry and thermochronometry from the perspective of signal saturation characteristics. However, the spectral overlap of several bands in the UV-blue emission requires careful optical filter selection to isolate the signal of interest. The non-monotonic dose response of the ∼2.5 eV emission of quartz around 200 °C glow curve temperature probably precludes its use for temperature sensing based on relative trap saturation levels.

X-rays generated by high-energy pulsed electron sources can be utilized in tumor treatment. The time spectrum measurement of pulsed electron sources enables precise treatment and provides feedback to the design and construction of accelerators. In this paper, silica aerogel samples of different densities and thicknesses were prepared as Cherenkov radiator. The transmittance and refractive index of these samples were measured, then the absorption and scattering lengths were calculated on the basis of the obtained transmittance. The obtained results were input into Geant4 software to get the intrinsic luminescence time of the silica aerogel of different densities and thicknesses. Finally, a measurement system was constructed with the silica aerogel samples, and the rise time of this system and the silica aerogel were measured by using a picosecond electron accelerator. The results demonstrate that the rise time of the measurement system is below 180 ps and that of the silica aerogel is less than 54.32 ps. It is also proved that the silica aerogel can be used as the Cherenkov radiator for the measurement of the time spectrum of high-energy pulsed electron sources.