Radiation Measurements最新文献

The effect of non-monotonic dose dependence of TL intensity on the irradiation dose has been reported in some materials in the past. As opposed to the regular case in which the intensity of the emitted TL light increases monotonically with the applied dose until it reaches saturation, in some reported cases, the light intensity reached a maximum and then declined at higher doses. The effect has been explained by using an energy level model including two electron traps and two hole centers competing with each other, thus yielding the effect. In the present work we show that with the use of certain sets of trap and center parameters, the effect can be seen with a reduced model of one trapping state and two recombination centers. Also, in recent years some experimental results showed more complex non-monotonic dose dependence, namely that following a maximum in the dose-intensity curve, and a certain range of decline, the TL intensity starts to increase again with the dose. We offer a new physical model that may explain this wiggly dose dependence. The energy-level diagram we propose is the same as before, with one electron trap and two kinds of recombination centers, one of which is radiative. In addition, we assume that the high energy radiation can produce more defects in the material which form more radiative recombination centers, this in addition to the filling of new and existing traps and centers by the irradiation. We consider the simultaneous differential equations governing the processes during irradiation, relaxation and heating with the variable dose-dependent concentration of the radiative recombination centers. We solve the equations numerically and by an analytical way with plausible approximations. The wiggly dose dependence results with certain sets of the relevant parameters.

Fast neutron spectrometry and dosimetry at a specified location in a compact radiation environment is difficult due to large size of the conventional neutron spectrometers. In such situations, a small-size bare CR-39 detector can be used as a neutron detector to quantify the fast neutron fraction. In the present study, CR-39 detectors were placed very close to natural lithium and carbon targets during the proton irradiations to acquire the emission neutron spectra. The neutron spectra and the ambient dose equivalents in the forward and lateral directions with respect to the incident proton beam were estimated for both targets at incident proton energies between 8 and 20 MeV. The measured neutron spectra using CR-39 detectors could identify the quasi mono-energetic neutron features from the Li(p,n) and ¹³C(p,n) reactions effectively. An important observation of the present study is the identification of the fast neutron signature from the ¹³C(p,n) system from the discrete state de-excitations of excited ¹⁴N composite nuclei. The theoretical evaluation of the neutron spectral features and relative neutron energy distributions were performed using the FLUKA: FLUktuierende KAskade, a Monte Carlo simulation package, and the estimates agreed with the experimental results for both systems. The neutron ambient dose equivalents were also estimated from the measured spectra. These neutron fluence and dose estimates at close vicinity to the target can serve as an essential basis for shielding calculations and planning the pertinent radiation protection strategies.

The alpha-particle targeted radionuclide therapy (TRT) has been actively investigated for cancer treatment, and astatine-211 (²¹¹At) is one of the promising alpha-particle emitters. To evaluate the efficacy of radioactive pharmaceuticals, it is necessary to understand the ²¹¹At distribution in a body to accurately assess radiation dose in the targeted cells. In this study, an X-ray imaging camera was developed to investigate an in vivo ²¹¹At imaging technique for the alpha-particle TRT, especially to apply for small animal investigations. The design of the X-ray imaging camera was optimized to measure Po K X-rays (77–92 keV) emitted during ²¹¹At decay. It comprised a monolithic NaI(Tl) scintillator, a position-sensitive photomultiplier, and a tungsten pinhole collimator. The intrinsic performance evaluation of the position-sensitive X-ray detector exhibited good energy resolution, spatial resolution, and response uniformity. Using point-like ²¹¹At sources, the ²¹¹At distribution was successfully obtained by the X-ray camera with a useful field-of-view of 20.4 × 20.4 mm², a system spatial resolution of 1.6 mm, and a sensitivity of 2.4 × 10⁻⁴, equivalent to 101 cps/MBq, on the collimator axis at a 12.5 mm distance. This study demonstrated the imaging capability of ²¹¹At with high sensitivity and spatial resolution by the X-ray imaging camera with a pinhole collimator.

A Cockcroft–Walton accelerator from High Voltage Engineering Europa BV was installed at the Korea Research Institute of Standards and Science in June 2022 to generate monoenergetic neutron fields. In this study, the fluences of monoenergetic neutron fields with energy peaks at 2.5, 2.8, and 3.2 MeV from the D(d,n) reaction and at 14.8 MeV from the T(d,n) reaction were measured. To measure neutron fluence, Bonner spheres with diameters of 17.78, 20.32, and 25.40 cm were placed at a distance of 1.50 m from the target. Additionally, a small size long counter was used separately as a neutron reference detector to monitor the stability of neutron production rate. For a deuteron beam current of 1 $\mu$A, the neutron fluences of monoenergetic neutron fields with energy peak at 2.5, 2.8, 3.2, and 14.8 MeV were determined to be 0.71 ± 0.03, 1.10 ± 0.04, 13.9 ± 0.5, and 258.0 ± 8.1 cm${}^{-2}$s${}^{-1}\mu$A⁻¹, respectively.

In this study, we investigate the halide perovskite material ${\mathrm{Cs}}_2{\mathrm{LiLuCl}}_6$ using both density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Our analysis focuses on the structural, electronic, and optical properties of the material, conducted with the Quantum Espresso code. In order to confirm the structural stability of the material, we performed various tests including analysis of elastic constants, formation energy, tolerance factor, and phonon dispersion. Employing the generalized gradient approximation (GGA) and GGA+U, we determine that the material behaves as an insulator with a direct band gap of 5.3042 eV and 5.4245 eV, respectively. Additionally, DFT+U calculations were performed to study the dielectric function, reflectivity, absorption coefficient, and refractive index, revealing a high transmittance rate exceeding 90%. Under ideal conditions, the upper light yield (LYsc) is estimated to be $75411$ ph/MeV and $73739$ ph/MeV for the DFT and DFT+U methods, respectively. These results, along with the presence of lithium in ${\mathrm{Cs}}_2{\mathrm{LiLuCl}}_6$, highlight its potential for use in scintillation-based thermal-neutron detection applications.

The ongoing war in Ukraine is associated with unprecedented radiological threats to the public in Ukraine and the neighboring countries. This calls for fundamental revision of the preparedness plans and established approaches to radiological monitoring of the populations affected by potential radiological emergencies. Dosimetric information will be needed for triage of victims and support to decision makers for prioritizing mitigation actions. Retrospective dosimetry methods strive to find a solution that would achieve this and enable fast and accurate feedback with information on individual doses to the concerned public. All known approaches to emergency dosimetry, both in biological and physical (instrumental) dosimetry have limitations, in particular – preventive cost, limited availability of samples for analysis, insufficient sensitivity (high dose threshold) and/or stability of radiation-induced markers (i.e. high fading). At the moment each of considered dose assessment methods possesses some combination of the aforesaid limitations. A suggestion to overcome these deficiencies is to use ordinary table salt (NaCl), read by optically stimulated luminescence (OSL), with well-known good dosimetric properties, and which allows anybody to prepare improvised individual dosemeters at home to be carried like a regular personal dosemeter until readout of the OSL signal is possible. This paper considers pros and cons of the use of NaCl as an OSL dosemeter in an emergency situation, with emphasis on practical aspects of its application for mass dose assessments for individuals among populations affected by radiological emergency situations.

ESR (electron spin resonance) spectra of quartz samples irradiated with varying gamma ($\gamma$) dose were measured at different microwave power levels (0–200 mW). The microwave power saturation characteristics of Al and E${}^{\prime }$ centers were systematically investigated, and the mechanisms by which the power saturation characteristics affected equivalent dose ($D_e$) fitting results in ESR dating were revealed. The experimental results demonstrated that irradiation reduces the spin-lattice relaxation time, resulting in the inability to intrinsically characterize the number of spins in a series of aliquots when the ESR intensity exhibits significant saturation. The simulation results indicated that changes in spin-lattice relaxation characteristics can cause distortion in the dose response curve (DRC) at high power levels, leading to deviations in $D_e$ values. A method that uses the slope of the approximate linear regime of the power saturation curve (PSC) as an intrinsic metric of ESR intensity is proposed; this method has been preliminarily validated in both experiments and simulations.

NaI:Tl single crystals codoped with ⁶LiI have been considered as promising neutron-gamma scintillators due to low cost, scalability, and high efficiency in detecting and discriminating neutrons and gamma-rays. This study aims to study the effects of ⁶LiF and ⁶LiCl codoping on the NaI:Tl single crystals grown by the multi-ampoule Bridgman method. The impact of ⁶LiF and ⁶LiCl on the optical properties, gamma spectroscopy, and pulse shape discrimination (PSD) of neutron and gamma detection performance were analyzed. Both ⁶LiF and ⁶LiCl caused a decrease in gamma-ray light yield and a deterioratrion of energy resolution with increasing codoping concentrations, similar to the scenarios of ⁶LiI codoping. Nonetheless, for NaI:Tl,⁶LiF, the light yield and PSD Figure-of-Merit (FoM) are almost unchanged about 37,500 photons/MeV and 4.6 when the Li content reaches 2 at%, which is better than the scenario of ⁶LiI codoping. Combing with the advantages of non-hygroscopic nature of LiF and a higher utilization yield of Li element in LiF comparing with LiI, NaI:Tl,⁶LiF single crystals could be regarded as more cost-effective scintillators for neutron detection applications.

In warhead verification, physical encryption technology could play a critical role in protecting confidential information on geometric structure and isotopic composition of a true warhead. As an important supplement to physical encryption, algorithmic encryption still has great potential in improving defense-in-depth security for nuclear arms control verification. To further supplement feasible nuclear arms control verification technologies, we propose a verification method based on neutron induced fission reactions employing both physical field flux encryption and algorithm encryption. Physical encryption processes the classified geometry or composition information by encrypting the fission neutron signal of the tested item with a randomly shielded mask. Algorithm encryption adopts pixel scrambling, pixel diffusion for secondary encryption. To verify the robustness and security of this new verification method, numerical simulations are performed using the Monte Carlo toolkit Geant4. Verification results indicate a high level of robustness and security with a low level of noise (∼<0.5%).

Ultra-high dose rate radiation therapy (FLASH) based on proton irradiation is of major interest for cancer treatments but creates new challenges for dose monitoring. Amorphous hydrogenated silicon is known to be one of the most radiation-hard semiconductors. In this study, detectors based on this material are investigated at proton dose rates similar to or exceeding those required for FLASH therapy. Tested detectors comprise two different types of contacts, two different thicknesses deposited either on glass or on polyimide substrates. All detectors exhibit excellent linear behaviour as a function of dose rate up to a value of 20 kGy/s. Linearity is achieved independently of the depletion condition of the device and remarkably in passive (unbiased) conditions. The degradation of the performance as a function of the dose rate and its recovery are also discussed.