keV Gamma Rays Research Articles

Resolving the Energy of γ-Ray Photons with MAPbI3 Single Crystals

Halide perovskites exhibit remarkably high-performance as semiconductors compared to conventional materials because of an unusually favorable combination of optoelectronic properties. We demonstrate here that solution-grown single-crystals of organic–inorganic hybrid perovskite CH3NH3PbI3 (MAPbI3), implemented in a Schottky-type device design, can produce outstanding hard radiation detectors with high spectral response and low dark current for the first time. Schottky-type MAPbI3 detector achieves an excellent energy resolution of 6.8% for 57Co 122 keV gamma ray. The high detector performance is achieved due to the balanced charge collection efficiency for both electrons and holes, reflected in the high mobility-lifetime (μτ) products of both carriers (∼0.8 × 10–3 cm2/V). MAPbI3 also demonstrates remarkably long electron and hole lifetimes (τe = 10 μs and τh = 17 μs) and impressive operational stability over time. Furthermore, dual-source detection of α particle (5.5 MeV) and γ-ray (59.5 keV) from the 241...

Experimental calculations of number, energy and dose albedos for various materials using 662 keV gamma rays

ABSTRACTNumber, energy and dose albedos are measured at a scattering angle of 180° for a broad beam of 662 keV gamma rays obtained from a radioactive source of 137Cs (having strength in µCi; 1 Ci = 3.7 × 1010 disintegrations per second). The gamma beam is incident on semi-infinite thick targets of variable atomic numbers. The scattering media is divided into three sets, which are pure elements, alloys and composite materials. Experiments are carried out using a 3″ × 3″ NaI(Tl) scintillation detector. To obtain precision in data, the response unfolding of a scintillation detector is used, which converts the observed pulse-height distribution to a true photon spectrum over the energy range of 2.5 to 640 keV. The detector response unfolding results in the true intensity of back-scattered gamma flux by shifting the events resulting from partial absorption of photons to the full energy peak of the spectrum. In the present study, albedo factors are studied as a function of target thickness and their atomic number. The experimentally calculated numbers of back-scattered gamma photon are in good agreement with theoretically generated numbers of multiple back-scattered counts by using a Monte Carlo simulation code. The experimental data on energy and intensity of 662 keV gamma photons are used to evaluate the number, energy and dose albedos for different materials under investigation.

A non-destructive analytical technique for low level detection of praseodymium using epithermal neutron activation analysis and compton suppression gamma-ray spectroscopy

When NAA is used to analyze geological samples a common issue arises in which certain radioisotopes produce gamma-ray peaks and Compton plateaus that ultimately overshadow the peaks of interest. This is the case when analyzing geological samples for trace concentrations of the rare earth element praseodymium. We report for the first time the determination of the rare earth element praseodymium using the 141Pr(n,γ)142Pr reaction with its only single 1575.6 keV gamma ray and 19.12 h half-life using a 5–10 min epithermal neutron irradiation and Compton suppressed gamma-ray spectroscopy. Preliminary results using this method have shown a minimum detectable concentration of 5 μg/g.

Growth and Luminescent Properties of Cs2HfCl6 Scintillators Doped With Alkaline Earth Metals

Nondoped Cs2HfCl6 (CHC) and alkaline earth metal-doped CHC (AE:CHC) crystals were grown by the vertical Bridgman–Stockbarger method. The spectra of the AE:CHC under X-ray excitation were similar to those for the AE-free crystal; thus, AE doping did not change emission wavelength of CHC. We determined the light outputs and energy resolutions of nondoped CHC and AE:CHC by measuring pulse-height spectra under 662-keV gamma-ray excitation of a 137Cs source. Both light output and energy resolution were deteriorated with AE doping. For example, nondoped CHC had a light output of ~44 000 photons/MeV and energy resolution of ~5.2%; on the other hand, Sr 0.5 at.%-doped CHC had a light output of only ~28 000 photons/MeV and energy resolution of ~10%. Scintillation decay also did not change. The nonproportional response values of light output versus gamma-ray energy did not improve in AE:CHC either. Therefore, doped AEs can be responsible for creation of defect trap levels which would hamper the carrier transport in CHC structure.

Analysis of Pulse Height Distributions of a Gas Electron Multiplier Detector by Using Cs-137 and Sr-90 Radioactive Sources

A double-layer gas electron multiplier (GEM) chamber was developed at the Physics Department, Changwon National University. Its performance was evaluated using Cs-137 and Sr-90 radiation sources. Using a gas mixture filling of 85% argon and 15% carbon dioxide, in the one-channel GEM chamber (5 cm × 5 cm), the pulse height distributions were detected at atmospheric pressure and room temperature. The signals from the 32-keV and the 36-keV characteristic X-rays emitted owing to internal conversion in the Cs-137 source, as were signals from the beta emissions and 662-keV gamma rays. The signals due to the 662-keV gamma rays were separated from the other signals by placing 1 mm or 1.6 mm intercepting copper plates under the source. Furthermore, regions of the GEM detector in which the photo- and Compton electrons were produced by the X-rays (32 keV and 36 keV) and gamma rays (662 keV) were analyzed.

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using an alpha–gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478 keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024%. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058%. We discuss the principle of the alpha–gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.

X- and gamma-ray irradiation effects on vanadium pentoxide thin films

Thickness and composition of thin films can be measured with X- and gamma-rays. In this work, thickness and composition of vanadium pentoxide thin films are investigated by energy dispersive and wavelength dispersive X-ray fluorescence systems. Also, the surface analysis of vanadium pentoxide thin films irradiated with Rhodium Kα X-rays and 59.54 keV gamma-rays emitted from 100 mCi and 5 Ci Americium-241 radioactive sources is performed by scanning electron microscope. It is observed that X- and gamma-rays are destructive for vanadium pentoxide thin films. Also, the composition of vanadium pentoxide thin films changes by irradiation with X- and gamma-rays.

Shielding 140 keV Gamma Ray Evaluation of Dose by Depth According to Thickness of Lead Shield

Shielding 140 keV Gamma Ray Evaluation of Dose by Depth According to Thickness of Lead Shield

Characteristic X-ray detector with a large sensitive area: Its sensitivity to environmental radioactive cesium and imaging performance as confirmed in an area of Fukushima

An X-ray detector which we call the characteristic X-ray detector (CXRD) with a large sensitive area of 199 cm2 was studied as a candidate imaging device with high sensitivity, light weight and low-cost features to visualize environmental 137Cs deposited after the Fukushima Dai-ichi Nuclear Power Station accident. The CXRD has a directionality for its sensitivity and it is able to visualize a spatial distribution of 137Cs by scanning the flux of 32 keV characteristic X-rays due to disintegration of 137Cs instead of imaging the 662 keV gamma-rays from 137Cs. Our experimental results showed that the counting efficiency of the CXRD was 105 counts per second for a 1 MBq 137Cs source at a distance of 1 m and the CXRD had a very high counting efficiency for a certain direction. We estimated the potential sensitivity of the CXRD when it was used in the scanning mode to image an area of 2π sr. The CXRD was tested in a contaminated forest in Fukushima Prefecture and images of the spatial distribution of 137Cs in the forest were successfully obtained. We found that most of the 137Cs was present in the forest floor and no 137Cs was detected in the atmosphere and the tree canopy. The CXRD is useful because of its low cost, light weight and high sensitivity as a 137Cs imaging device for monitoring post devices in forests and as a portable imaging device to confirm the effectiveness of decontamination work.

Effect of an external magnetic field on the mass attenuation coefficients of p-Si and n-Si

Abstract In this study, the mass attenuation coefficients of p-Si and n-Si semiconductor samples have been determined in an external magnetic field. The semiconductor samples were located to the external magnetic field of intensities 0.2 T, 0.4 T, 0.6 T and 0.8 T. The samples were bombarded by 59.5 keV, 80.1 keV, 121.8 keV and 244.7 keV gamma-rays emitted from Am241, Ba133 and Eu152 radioactive sources. The transmitted photons were detected by a CdTe detector. It was observed that the mass attenuation coefficients of p-Si and n-Si semiconductor samples decrease with increasing gamma-ray energy. Also, the mass attenuation coefficients of the samples increase with applying magnetic field intensity.

Determination of Mass Attenuation Coefficients of Cement Paste Containing Ilmenite and Barite for γ-Rays

The gamma ray shielding properties of cement paste containing ilmenite and barite (BaSO4) at different concentration were investigated using beam transmission method for 59.5 keV gamma ray energy of 241Am radioactive isotopes by using NaI(Tl) scintillation detector. The mass attenuation coefficients (μm) of these shielding materials were calculated. It was found that the mass attenuation coefficients increase with increasing of ilmenite and barite content up to a value of 60% by weight. The highest value of μm was 0.425 ± 0.003 cm2/g for cement paste containing ilmenite and 1.598 ± 0.039 cm2/g for the cement paste containing barite. The mass attenuation coefficient values were compared between cement pasted containing ilmenite and barite. The result show that cement paste containing barite showed good gamma ray shielding performances than that for the cement paste containing ilmenite.

Effective Atomic Number Dependence of Radiological Parameters of Some Organic Compounds at 122 KeV Gamma Rays

Mass attenuation coefficient is a fundamental parameter of radiation interaction, from which the other radiological parameters like half Value Layer [HVL], tenth Value Layer [TVL], total atomic and electronic cross-sections, mass energy absorption coefficient, KERMA, CT number and effective atomic number are deduced. These parameters are extensively required in a number of fields such as diagnostic radiology, gamma ray spectroscopy, fluorescence analysis and reactor shielding. In the present work, mass attenuation coefficients are determined experimentally for some organic compounds at 122 keV incident photons using narrow-beam transmission geometry to establish a relation between effective atomic number (Zeff) and other deduced parameters. The experimental data for all these parameters are compared with the values deduced from WinXcom software package and are found to agree within experimental estimated errors. This study gives some insight about the photon interaction in some organic compounds whose effective atomic numbers match with some human body fluids.

Explanation of the 511 keV line: cascade annihilating dark matter with the ^8Be anomaly

A possible dark matter (DM) explanation about the long-standing issue of the Galactic 511 keV line is explored in this paper. For DM cascade annihilations of concern, a DM pair pi _d^{+} pi _d^{-} annihilates into unstable pi _d^{0} pi _d^{0}, and pi _d^{0} decays into e^+ e^- with new interactions suggested by the ^8Be anomaly. Considering the constraints from the effective neutrino number N_{mathrm {eff}} and the 511 keV gamma-ray emission, a range of DM is obtained, 11.6 lesssim m_{pi _d^{pm }} lesssim 15 MeV. The typical DM annihilation cross section today is about 3.3 times 10^{-29} cm^3 s^{-1}, which can give an explanation about the 511 keV line. The MeV scale DM may be searched by the DM-electron scattering, and the upper limit set by the CMB s-wave annihilation is derived in DM direct detections.

Position-sensitive NaI(TL) detector module for large-area Compton camera

In the present study, we developed a position-sensitive NaI(Tl) scintillation detector module for use in the development of a large-area Compton camera. The developed detector module employs a large (i.e., 27 × 27 × 2 cm3) monolithic NaI(Tl) scintillator coupled with a closely packed array of 6 × 6 square PMTs. A multiplexer-based signal processing circuit and a data acquisition system were developed to estimate the interaction position in the scintillator from the signals of the PMTs by using the maximum likelihood position estimation algorithm (MLPE). The performance of the developed detector was evaluated experimentally, showing that the energy and the time resolution of the detector are 7.88% (for 662-keV gamma ray) and 9.6 ns FWHM, respectively, which are comparable to those of a commercial three-inch cylindrical NaI(Tl) scintillation detector. In addition, the spatial resolutions were about 3-to-6-mm FWHM for a wide energy range (59.5 - 1173 keV) and various interaction positions on the detector (from center to edge), which are satisfactory results considering that a 3-mm-diameter collimated gamma-ray beam was used in the experiments.

Characterization of the new scintillator Cs2LiYCl6:Ce3+

The first domestic inorganic scintillator, Cs2LiYCl6:Ce3+ (CLYC), was grown at Beijing Glass Research Institute using the vertical Bridgman method. In this work, we evaluated the performance of this new CLYC crystal in terms of its gamma-ray energy resolution and pulse shape discrimination (PSD) capability between neutrons and gamma rays. The decay times associated with different scintillation mechanisms were obtained by fitting decay functions to the neutron and gamma-ray waveform structures. We found an energy resolution of ~ 4.5% for 662-keV gamma rays and efficient neutron/gamma PSD with a figure of merit of ~ 2.6. Under gamma-ray excitation, there is an ultrafast scintillation mechanism in CLYC with a decay time of approximately 2 ns, whereas there is no evidence of ultrafast decay under thermal neutron excitation. This work contributes to the promotion of domestic development of CLYC.

Synthesis and targeting of gold-coated 177Lu-containing lanthanide phosphate nanoparticles-A potential theranostic agent for pulmonary metastatic disease.

Targeted radiotherapies maximize cytotoxicity to cancer cells. In this work, we describe the synthesis, characterization, and biodistribution of antibody conjugated gold-coated lanthanide phosphate nanoparticles containing 177Lu. [177Lu]Lu0.5Gd0.5(PO4)@Au@PEG800@Ab nanoparticles combine the radiation resistance of crystalline lanthanide phosphate for stability, the magnetic properties of gadolinium for facile separations, and a gold coating that can be readily functionalized for the attachment of targeting moieties. In contrast to current targeted radiotherapeutic pharmaceuticals, the nanoparticle-antibody conjugate can target and deliver multiple beta radiations to a single biologically relevant receptor. Up to 95% of the injected dose was delivered to the lungs using the monoclonal antibody mAb-201b to target the nanoparticles to thrombomodulin receptors. The 208 keV gamma ray from 177Lu decay (11%) can be used for SPECT imaging of the radiotherapeutic agent, while the moderate energy beta emitted in the decay can be highly effective in treating metastatic disease.

235U enrichment determination on UF6 cylinders with CZT detectors

Measurements of uranium enrichment in UF6 transit cylinders are an important nuclear safeguards verification task, which is performed using a non-destructive assay method, the traditional enrichment meter, which involves measuring the count rate of the 186 keV gamma ray. This provides a direct measure of the 235U enrichment. Measurements are typically performed using either high-resolution detectors (Germanium) with e-cooling and battery operation, or portable devices equipped with low resolution detectors (NaI). Despite good results being achieved when measuring Low Enriched Uranium in 30B type cylinders and natural uranium in 48Y type containers using both detector systems, there are situations, which preclude the use of one or both of these systems.The focus of this work is to address some of the recognized limitations in relation to the current use of the above detector systems by considering the feasibility of an inspection instrument for 235U enrichment measurements on UF6 cylinders using the compact and light Cadmium Zinc Telluride (CZT) detectors.In the present work, test measurements were carried out, under field conditions and on full-size objects, with different CZT detectors, in particular for situations where existing systems cannot be used e.g. for stacks of 48Y type containers with depleted uranium.The main result of this study shows that the CZT detectors, actually a cluster of four μCZT1500 micro spectrometers provide as good results as the germanium detector in the ORTEC Micro-trans SPEC HPGe Portable spectrometer, and most importantly in particular for natural and depleted uranium in 48Y cylinders.

Characterization of a 2 [formula omitted] 2 array of large square bars of LaBr3:Ce detectors with [formula omitted]-rays up to 22.5 MeV

LaBr3:Ce scintillators have recently become commercially available in sizes large enough for measurements of high energy gamma-rays. In this communication, we report our studies on properties and response of large volume square bars (2′′×2′′×8′′) of LaBr3:Ce detectors, individually, and in a compact array of four square bars, with gamma-rays up to 22.5 MeV. The properties studied are, uniformity of the crystal, internal radioactivity, energy resolution, timing resolution, linearity of the response and detection efficiencies. The response of the detectors for 22.5 MeV γ-rays produced from 11B(p,γ)12C capture reaction and for 15.1 MeV γ-rays produced from 12C(p,p′γ)12C inelastic scattering reaction are studied in detail. The measured absolute efficiencies (both total detection and photo-peak) for 662 keV gamma-rays from 137Cs are compared to those obtained using realistic GEANT4 simulations. The primary aim of the array is to measure high energy gamma-rays (5–50 MeV) produced from the de-excitation of excited Giant Dipole Resonance (GDR) states, radiative capture reactions, nuclear Bremsstrahlung process and inelastic scattering process. The highly satisfactory performance of the array provides the impetus for future efforts toward building a bigger array.

A gamma and neutron phoswich read out with SiPM for SPRD

A gamma and neutron phoswich was developed for spectroscopic personal radiation detectors (SPRDs). It consisted of a Φ25 × 25 mm NaI(Tl) crystal for gamma detection and a Φ25 × 3 mm LiI(Eu) crystal for neutron detection. The phoswich was read out by 8 × 8 ch SiPM array (24 × 24 mm2). Radiations in NaI(Tl) and LiI(Eu) were discriminated by pulse shape, while gammas and neutrons in LiI(Eu) were separated by pulse amplitude. For the LiI(Eu), the gamma equivalent energy for thermal neutrons was measured as 3.6 ± 0.1 MeV, providing satisfactory gamma rejection. For NaI(Tl), the response of SiPM array was well linear in the energy range up to 1408 keV, at which a deviation less than 2% was measured. Digital pulse shape discrimination (PSD) was implemented with an 8-bit digitizer running at 50 MSPS sampling rate and offline analysis. The signal pulses from NaI(Tl) and LiI(Eu) showed significant difference in falling edge allowing effective PSD. The best figure of merit (FOM) was measured as 4.4 ± 0.2 with optimized parameters, providing excellent PSD performance. The energy resolutions for 661.6 keV gamma rays in NaI(Tl) and thermal neutrons in LiI(Eu) were measured as 7.0 ± 0.2% and 11.2 ± 0.2% respectively, with selected PSD threshold.

Study of a generalized birks formula for the scintillation response of a CaMoO4 crystal

We have investigated the scintillation characteristics of CaMoO4 (CMO) crystals by using a gamma source and various internal alpha sources. A 137Cs source with 662-keV gamma-rays was used for the gamma-quanta light yield calibration. Internal radioactive contaminations provided alpha particles with different energies from 5.41 to 7.88 MeV. We developed a C++ program based on the ROOT package for the fitting of parameters in a generalized Birks semi-empirical formula by combining the experimental and the simulation data. Results for the fitted Birks parameters are k b1 = 3.3 × 10 −3 (g/MeVcm2) for the 1st parameter and k b2 = 7.9 × 10 −5 (g/MeVcm2)2 for the 2nd parameter. The χ2/n.d.f. (Number of Degree of Freedom) is calculated as 0.1/4. We were able to estimate the 238U and 234U contaminations in a CMO crystal by using the generalized Birks semi-empirical formula.