keV Gamma Rays Research Articles

A feasibility study on 3D interaction position estimation using deep neural network in Cherenkov-based detector: a Monte Carlo simulation study

Cherenkov-based radiation detectors have been developed for time-of-flight positron emission tomography. As Cherenkov photons are emitted in an extremely short time, their use can improve time resolution. However, only up to 10 Cherenkov photons are yielded when a 511 keV gamma ray interacts with Cherenkov radiators, such as lead tungstate and lead fluoride (PbF2). Therefore, accurate estimation of the interaction position was difficult, and intense effort has been devoted to its improvement. We propose an estimation method for the 3D interaction position using a deep neural network. The network was evaluated by Monte Carlo simulations. For the simulations, a Cherenkov-based detector with a monolithic PbF2 radiator of 40 × 40 × 10 mm3 and a photodetector array were used. The gamma-ray interaction position in the radiator was estimated in 3D space by the neural network, whose inputs were the detection positions on the photodetector plane (xy plane) and timestamps of each photon from the detector. Training and validation datasets were generated while varying the single photon time resolution (SPTR) and readout pitch of the photodetector. By comparing several neural network architectures, we determined the best configuration to be the multilayer perceptron with 3 layers and 256 units. The full widths at half maximum of the xy plane and z axis (i.e., depth of interaction) were 1.54 and 1.59 mm with SPTR σ = 10 ps, respectively, and their cumulative histograms at half maximum were 0.65 and 0.81 mm also with σ = 10 ps, respectively. The proposed method retrieved higher estimation accuracy of the interaction position than an existing method based on the center of gravity and principal component analysis. Therefore, it is feasible to estimate the 3D interaction position in the Cherenkov-based detectors using deep neural networks.

Effect of annealing temperature on K-shell X-ray fluorescence parameters of zinc oxide thin films prepared by the sol-gel method

Zinc oxide thin films were grown on a glass substrate by a sol-gel process using a spin-coating technique. The obtained thin films were annealed between 350 °C and 550 °C in 50 °C steps and were then characterized using X-ray diffraction, scanning electron microscopy, and X-ray fluorescence techniques. The samples were stimulated by 59.5 keV gamma rays emitted from an Americium-241 annular radioisotope source. K X-rays emitted by samples were counted using an ultra-low energy germanium detector with a resolution of 150 eV at 5.96 keV. It was found that there was generally a decrease in both the Kβ/Kα X-ray intensity ratios and the K X-ray fluorescence cross sections for zinc oxide between 350 °C and 500 °C, but not at 550 °C. In addition, the X-ray diffraction patterns of the films showed that the transition phase from an amorphous to a polycrystalline hexagonal wurtzite structure was complete at an annealing temperature of 500 °C. The results show that variations in these parameters can be explained by the reorganization of atoms and the charge transfer process due to the effect of the annealing temperature on the elements forming the compounds.

Efficient design of a ∅2×2 inch NaI(Tl) scintillation detector coupled with a SiPM in an aquatic environment

Abstract After the Fukushima accident in 2011, there has been increased public concern about radioactive contamination of water resources through fallout in neighboring countries. However, there is still no available initial response system that can promptly detect radionuclides. The purpose of this research is to develop the most efficient gamma spectrometer to monitor radionuclides in an aquatic environment. We chose a thallium-doped sodium iodide (NaI(Tl)) scintillator readout with a silicon photo multiplier (SiPM) due to its compactness and low operating voltage. Three types of a scintillation detector were tested. One was composed of a scintillator and a photomultiplier tube (PMT) as a reference; another system consisted of a scintillator and an array of SiPMs with a light guide; and the other was a scintillator directly coupled with an array of SiPMs. Among the SiPM-based detectors, the direct coupling system showed the best energy resolution at all energy peaks. It achieved 9.76% energy resolution for a 662 keV gamma ray. Through additional experiments and a simulation, we proved that the light guide degraded energy resolution with increasing statistical uncertainty. The results indicated that the SiPM-based scintillation detector with no light guide is the most efficient design for monitoring radionuclides in an aquatic environment.

Industrial gamma computed tomography using high aspect ratio scintillator detectors (A Geant4 simulation)

Gamma-ray Computed Tomography is an important tool for accessing the internal details of large objects in different industries such as oil, gas, petrochemical, etc. In this paper, a Geant4 study was performed to develop a new approach for this type of tomography by using high aspect ratio scintillators. In this method, a NaI(Tl) rectangular cube scintillator, coupled to a PMT on each side in a coincidence setup, was considered as a position sensitive detector. Different responses of the detector including the scintillation processes in presence of 662 keV gamma-rays of a Cs-137 were simulated. Spectral response, position and energy resolutions were obtained and compared to the experimental data. The comparisons showed a good agreement between the simulation results and experimental data. Furthermore, the detector was simulated in a gamma-ray tomography setup and the related projections and cross sectional images of a standard phantom were obtained. The obtained results showed that the high aspect ratio scintillator detector can be used instead of array detector in industrial applications where there is no need to very high position resolutions.

Radiological risk assessment of fuel fabrication facility at Al- Tuwaitha nuclear site

The specific activity of 29 soil samples collected from FuelFabrication Facility FFF at AL-Tuwaitha site, 20 km south ofBaghdad were determined using HPGe detector in a low backgroundconfiguration, it's relative efficiency of 40%, and resolution of 2keVfor the 1332 keV gamma ray emission of 60Co. The range of activityconcentrations of 226Ra, 232Th and 40K were between (12.56-31.96),(10.2-18.4) and (47.47-402.1) Bq/kg respectively. In order to assessany radiological hazard to human health, the absorbed gamma doserate D in air at 1m above the ground surface was calculated in therange (18.87 to 36.46) nGy/h; the outdoor annual effective doseequivalent AEDE was evaluated to vary from 0.0039 to 0.0076mSv/y with the mean value 0.0059 mSv/y, this value comparable tothe worldwide effective dose 0.48mSv/y. The Radium EquivalentRaeq for all samples were evaluated and were lower than the acceptedsafety limit value of 370 Bq/kg. The results indicated that theradiation of hazards from primordial radionudlides in all samples inthis study is not significant.

Improvement of a PET Detector Performance by Setting Reflectors in Parallel With PMT Face

A whole-body positron emission tomography scanner must be equipped with many detectors so that they are often composed of low-cost photomultiplier tubes (PMTs), that is, large anode-type PMTs. The general detector structure has a scintillation crystal element array coupled on an array of the large anode PMTs, and for crystal element identification, the method is needed to get sufficient spread of scintillation light for distribution among distant PMT anodes. Besides the common method of using a light guide, some methods have been proposed for better element identification performance. In this paper, we introduce a new method, in which the scintillation light spread is promoted not only by removing reflectors between crystal elements but also by restricting light exit to the PMTs by placing additional reflectors at the bottom of the crystal element array. Because the additional reflectors are parallel to the PMT surface, we call them parallel reflectors. We verified our method with a detector consisting of the 2.45 mm $\times \,\, 5$ mm $\times \,\,15$ mm Lu2 x Gd2(1– x )SiO5:Ce crystal elements and two dual-photocathode PMTs. Each photocathode was 8 mm $\times \,\,18$ mm in size. We set a $9 \times 10$ crystal element array on the two PMTs and tried to identify the elements by the $2\times 2$ PMT signals. Detector performance was evaluated with 137Cs point sources (662-keV gamma rays). The results showed that despite a significant decrease in light output at the boundary of the two PMTs, the method made crystal element identification possible. We measured energy resolutions of 13.1% and 17.8% for the elements on the PMT photocathode area and the PMT boundary, respectively. Our method is applicable to the depth-of-interaction detector consisting of multilayer crystal element arrays. By inserting parallel reflectors between the layers, we would be able to control the path of scintillation light originating in the upper layer. The effect was first examined in a basic study with two layers of a $2 \times 5$ crystal element array. Then, the array of each layer was increased to $9\times 9$ for performance evaluation. It was difficult to identify all 162 crystal elements with four PMT signals; however, results suggest the possibility of scintillation light path control in each layer separately by the parallel reflectors and the potential for better performance by more precise adjustment of parallel reflectors.

Preparation and characterization of bismuth-filled high-density polyethylene composites for gamma-ray shielding

An attempt has been made to prepare the nonlead-based gamma shielding materials by adding different weight percentages (0%, 10%, 20%, and 40%) of bismuth in high-density polyethylene (HDPE) matrix. Gamma shielding parameters such as linear attenuation coefficient (μ), mass attenuation coefficient (μm), half-value layer, tenth value layer relaxation length (λ), and percentage attenuation were determined for all synthesized samples using 3“×3” NaI (Tl) detector for 59.54 keV energy. The results obtained from attenuation studies have shown that the shielding efficiency of synthesized HDPE+Bi composites increases with an increase in the weight percentage of bismuth. The experimentally obtained mass attenuation coefficient values are compared with Monte Carlo simulation using Monte Carlo N-particle code and XCOM code and are in good agreement with each other. The mechanical parameters such as tensile strength, tensile modulus, and elongation at the break were also determined for synthesized composites. Among the prepared composites, HDPE containing 40 wt% of bismuth (HDPE+40% Bi) has shown good radiation shielding property for 59.54 keV gamma rays along with good mechanical properties. Therefore, HDPE+40% Bi can be considered as a better lead-free shielding material for low-energy gamma rays.

Experimental study on fission reaction rate induced by D-T neutron in depleted uranium shell

Fission reaction rate is an important index for validating and checking the neutron transportation and fission power in nuclear engineering. The experimental data can be used in benchmark validation of cross sections, and in studying the correlation of fission power with the thickness of uranium sphere shell. There are five assemblies of depleted uranium shells used in this work, the inner radii of which are all fixed at 13.1 cm, while their outer radii are 18.1, 19.4, 23.35, 25.4 and 28.5 cm, respectively. The D-T neutron source is generated in the center of the assemblies, the yield of which is about 3 × 10<sup>10</sup>−4 × 10<sup>10</sup> s<sup>–1</sup>. In horizontal plane across the center of the assemblies, the fission rates at positions along the radial direction are measured in the direction with 45° inclining with respect to the incident D<sup>+</sup> beam. Due to the disturbance to assemblies and neutron field, the activation foil of uranium is a suitable choice rather than fission chamber or capture detector. The material of activation foil is the same as that in the experimental assemblies. Considering the accurate fission yield of <sup>143</sup>Ce, the objective nuclides are selected. The total fission yield of <sup>143</sup>Ce is contributed by <sup>238</sup>U and a little <sup>235</sup>U. For calculating the total fission yiled of <sup>143</sup>Ce, the neutron energy range of 0−15 MeV is divided into eight subranges. By measuring the 293 keV gamma rays from the fission product <sup>143</sup>Ce in activation foils with a TRANS-SPEC-DX100 HPGe detector, with a relative efficiency 40%, the fission rates and the trends at positions along the radial direction in the five assemblies are obtained based on the <sup>143</sup>Ce fission product yield. The fission rate ranges from 5.28 × 10<sup>–29</sup> to 7.58 × 10<sup>–28</sup> sn<sup>-1</sup>·nuclide<sup>–1</sup>, with the relative uncertainty in a range from 6% to 11%. The Monte Carlo transport code MCNP5 and continuous energy cross section library ENDF/BV.8 are used for analyzing the fission rate distribution in the assemblies, and the experiemtal configuration, including the wall of the experimental hall is described in detail in the model. The calculated results are compared with the experimental ones and their agreement is found to be in an uncertainty range.

Effective Atomic Number and Electron Density Determination of Some Amino Acids by Using Scattering Intensity Ratio of 59.54 keV Gamma Rays

In this study the specific atomic arguments have been determined for F-Glycine (C2H5O2N), Alenine (L, D) (C3H7O2N), Leucine (L, D) (C6H13O2N), L-Proline (C5H9O2N) amino acids. The calculation procedure of the experimental values of atomic parameters was carried out by using scattering intensity ratios of γ-rays. These γ-rays were obtained from 5 Ci 241Am annular radioactive source. In traditional studies, these arguments were determined by transmission technique. The scattered γ-rays were counted by using an HPGe semiconductor detector. Our detecting system was connected to a separate amplifier and an Accuspec card. Theoretical values of related atomic parameters for amino acid targets were calculated and cross checked with our experiential values. Our deliberated values are in good concordance with theoretical calculations.

Using the 90–105 keV gamma-rays for isotopic composition determination of plutonium in dilute solutions

Using the 90–105 keV gamma-rays for determining Pu isotopic composition is studied for dilute Pu solutions (0.0001–0.05 μg/mm3) as well as Pu-U mixed solutions. It is shown that for concentrations higher than 0.001 μg/mm3 Pu, results match well with those of mass spectrometric results. However, in mixed solutions, beyond 0.005 mg/mm3 U concentration, the errors on isotopic compositions of Pu increased as U content increased.

Tailoring lattices of Bi2WO6 crystals via Ce doping to improve the shielding properties against low-energy gamma rays

In this study, lattices of Bi2WO6 crystals were tuned by cerium doping in a hydrothermal process in order to enhance the shielding properties against low-energy gamma rays. The products obtained were characterized by Raman, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques. The results demonstrated that cerium ions were successfully introduced into the lattices of the Bi2WO6 crystals and they partially replaced the bismuth ion sites. The shielding results showed that 10 mol% cerium doping allowed the Ce-doped Bi2WO6 crystals to shield against 59.5 keV gamma rays at a 49.41% better level compared with the original crystals. The enhanced shielding against low-energy gamma rays was ascribed to the expanded K-edge absorbing area of bismuth after cerium doping. In this study, we developed a facile synthetic method for obtaining Ce-doped Bi2WO6 materials. Importantly, these crystals could be used as functional fillers in rubber composites to prepare wearable products (such as clothing) with desirable shielding properties and no requirement for lead.

The mass attenuation coefficients, effective atomic numbers and effective electron numbers of some concrete containing barite for 511, 835 and 1275 keV gamma rays

The linear attenuation coefficients (μl) of concretes including barite fractions of 0%, 50% and 100% were measured at the gamma energies of 511, 835 and 1275 keV.The measurements have been performed using a low level gamma counting spectrometer including a 3”x3” NaI(TI) detector by ORTEC Inc., connected to a multichannel pulse height analyzer. Total mass attenuation coefficients, effective atomic numbers and effective electron numbers valuesf or concretes are calculated in the energy range from1keVto 100GeV. The values of mass attenuation coefficients used in calculations are taken from the XCOM. The results from the measurements were compared with the theoretically calculated results. The measured results of mass attenuation coefficients, effective atomic numbers and effective electron density were found to be in good agreement with the calculations.

Determination of the Mass Attenuation Coefficient, Effective Atomic Number and Electron Density for Manganese Nano Hydroxyapatite by using 778-1457 keV Gamma Rays

In this study, Nano Manganese substituted hydroxyapatite artificial bone powders (nMnHAp) have been investigated by means of mass attenuation coefficients, effective atomic numbers and electron densities experimentally. The samples were excited with using 778 keV, 964 keV, 1085 keV, 1111 keV, 1408 keV and 1457 keV gamma photons from Europium-152 (Eu 152 ).The gamma photons from the source were counted by using gamma spectroscopy, a High Purity Germanium (HPGe) detector. The mass attenuation coefficients of the hydroxyapatites artificial bone powders (including hydroxyapatite without any substituted metal and real bone powder) were compared with each other. This study has been dealt with as a guide to medical field. Also the results have been evaluated in terms of the electron density and effectice atomic number.

Determination of valence electronic structure of Ni in Ni-B alloy coatings using Kβ-to-Kα X-ray intensity ratios

In this study, Kβ-to-Kα X-ray intensity ratios of Ni in Ni-B alloy coatings were investigated. These samples were excited by 59.5 keV gamma-rays from a 241Am annular radioactive source. K X-rays emitted by the samples were counted using an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. The Kβ-to-Kα X-ray intensity ratios of Ni-B alloys are compared with pure Ni and each other. Deviations between the results were explained by the change in valence electronic structures of Ni in Ni-B alloy coatings.

Variation of scattering intensity ratios with mean atomic number using a dilution technique in EDXRF

The variation of different intensity ratios with mean atomic number for qualitative analysis was investigated in EDXRF. Ten different samples with a mean atomic number between 4.268 and 5.786 were obtained by mixing zirconyl chloride octahydrate (Cl2OZr·8H2O) and cellulose (C6H10O5) powders. The samples were excited by 59.54 keV gamma rays emitted from a 241Am annular radioactive source with 5 Ci activity. The high purity germanium (HPGe) semiconductor detector with a resolution of 182 eV at 5.9 keV was used to detect the photons. (Icoh/2(μ/ρ)λ+Icomp/(μ/ρ)λ+(μ/ρ)λ−Δλ), (Icoh+IComp)/(μ/ρ)λ, (Icoh/2(μ/ρ)λ, IKα/Isc and IKβ/Isc intensity ratios in XRF spectrum for the assessment of information regarding the mean atomic number of the samples are studied. It has been observed that the total scattering intensity ratios can be used with high reliability in qualitative analysis for complex materials.

Structural, elastic, thermodynamic and electronic properties of covellite, CuS

Covellite, the CuS, is a unique compound owing to both superconducting and metallic behavior at different temperatures. We model and characterize the elastic, electronic and associated properties of the CuS launching the state-of-art first-principles calculations taking the exchange and correlation energy functionals based on the gradient generalized approximation and hybrid functionals. After settling the crystal structure, we find elastic constants and related mechanical constants. As the crystal satisfies the stability criterion, so we compute the sound velocity, Debye temperature and lower bound of the thermal conductivity also. The electronic bands dispersion and the density of states exhibit the metallic behavior of the compound. The isotropic and the anisotropic parts of the electron momentum density are calculated by means of the Compton profiles. The isotropic Compton profile is compared with our measurement deploying the 5Ci 241Am spectrometer based on the 59.54 keV gamma-rays and a good agreement is found. The anisotropies in the directional Compton profiles are also presented. The Mulliken population analysis is performed to see nature of bonding and occupied charges on the crystallographically distinct Cu and S atoms in CuS.

Effects of hematite-lead oxide combination in ethylene-propylene-diene-monomer on shielding 59.54 keV gamma rays

Ethylene-propylene-diene-monomer (EPDM) was filled with metal oxides like PbO and Fe2O3 and analysed for peroxide vulcanisation kinetics, radiation shielding ability, and thermal stability. Increase in crosslinking density was observed with Fe2O3 concentration in the lead oxide-hematite-EPDM (LHE) composites, and radiation shielding property upon addition of total 60 phr fillers was discussed. Among the synthesised composites, P60F0 and P40F20 showed good shielding ability for 59.54 keV gamma rays. All the composites showed good electrical insulation up to 50 kHz AC frequency. Moreover, the P40F20 composite contained relatively less lead content than the P60F0 composite, and also, the mechanical strength and thermal stability of P40F20 was greater than that of the P60F0 composite and therefore, it can be considered as a good shielding material.

Albedo factor determination of rare-earth oxides

ABSTRACTGamma-ray albedo factors of rare-earth oxides were determined experimentally. The detection of albedo factors for selected materials includes albedo number, albedo energy and albedo dose calculations. 59.54 keV gamma rays of 5 Ci annular 241Am were used as a gamma source. Gamma rays were scattered by selected samples and collected by High Purity Germanium semiconductor detector. The albedo factors were plotted as a function of atomic number of target materials.

In vivo simultaneous imaging with 99mTc and 18F using a Compton camera

We have been developing a medical imaging technique using a Compton camera. This study evaluates the feasibility of clear imaging with 99mTc and 18F simultaneously, and demonstrates in vivo imaging with 99mTc and/or 18F. We used a Compton camera with silicon and cadmium telluride (Si/CdTe) semiconductors. We estimated the imaging performance of the Compton camera for 141 keV and 511 keV gamma rays from 99mTc and 22Na, respectively. Next, we simultaneously imaged 99mTc and 18F point sources to evaluate the cross-talk artifacts produced by a higher energy gamma-ray background. Then, in the in vivo experiments, three rats were injected with 99mTc-dimercaptosuccinic acid and/or 18F-fluorodeoxyglucose and imaged. The Compton images were compared with PET images. The rats were euthanized, and the activities in their organs were measured using a well counter. The energy resolution and spatial resolution were measured for the sources. No apparent cross-talk artifacts were observed in the practical-activity ratio (99mTc:18F = 1:16). We succeeded in imaging the distributions of 99mTc and 18F simultaneously, and the results were consistent with the PET images and well counter measurements. Our Si/CdTe Compton camera can thus work as a multi-tracer imager, covering various SPECT and PET probes, with less cross-talk artifacts in comparison to the conventional Anger cameras using a collimator. Our findings suggest the possibility of human trials.

Field dependence of electronic recoil signals in a dual-phase liquid xenon time projection chamber

We present measurements of light and charge signals in a dual-phase time projection chamber at electric fields varying from 10 V/cm up to 500 V/cm and at zero field using 511 keV gamma rays from a 22Na source. We determine the drift velocity, electron lifetime, diffusion constant, and light and charge yields at 511 keV as a function of the electric field. In addition, we fit the scintillation pulse shape to an effective exponential model, showing a decay time of 43.5 ns at low field that decreases to 25 ns at high fields.