Low Energy Gamma Research Articles

Performances of different efficiency calibration methods of high-purity-germanium gamma-ray spectrometry in an inter-comparison exercise

This study reports the performances of efficiency calibrations for high-purity-germanium gamma-ray spectrometry using the source-, Laboratory Sourceless Object Calibration Software (LabSOCS)- and ANGLE-based methods in an inter-comparison exercise. Although the results of LabSOCS and ANGLE for 241Am emitting low-energy gamma rays were not very satisfactory, all of the three efficiency calibration methods passed acceptance criteria. The results confirmed the reliability of the calculation codes ANGLE and LabSOCS as alternative efficiency calibration methods in high-purity-germanium gamma spectrometry. This study is likely to promote the further application of the ANGLE and LabSOCS calculation codes in radioactivity measurements.

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ∼20 MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ∼0.01° and ∼1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.

Broad Beam and Gamma Spectrometric Parameters of Some Granites

Using a g-ray spectrometer with 3x3 NaI (Tl) detector the linear and mass attenuation coefficients (m/r) and (mb/r) from narrow and broad beam experimental arrangements have been measured and compared with the theoretical values for the granites Double Black, DB, from India, Rose Al-Howdy, RH, from Aswan, south Egypt and Bianco Halayeb, BK, from Halayeb, south Egypt. The photon energies lei in the range 0.081-1.332 MeV from the radioisotopes 133Ba, 137Cs and 60Co. The build-up factor B, the effective atomic number Zeff, and the total atomic cross-section st for the granites as a function of photon energy were determined and discussed. It is found that the experimental results are consistent, within the experimental errors, with the theoretical values. The effective atomic number Zeff, the build-up factor B, and the total atomic cross-section st were calculated and discussed as a function of photon energy. The B factor is large at low gamma energy and not sensitive for discrimination between the granites. The maximum Zeff corresponds to minimum B factor at the photon energy 0.356 MeV. The broad beam geometry is more efficient than narrow beam geometry in characterizing the shielding properties of the studied granites.

The Threshold of Detection of Fission Materials by ZnWO4 and Bi4Ge3O12 Scintillation Detectors

In the present work we found the maximum discovery distance for 239Pu-Be source using the detectors based on ZWO (ZnWO4) and BGO (Bi4Ge3O12) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.

Retrosternal Ectopic Thyroid Mimicking Esophagus in Tc-99m Pertechnetate Thyroid Scan.

Abnormal Pertechnetate distribution can occur due to many reasons such as retrosternal extension of eutopic thyroid gland, ectopic functioning thyroid gland, physiological uptake in esophagus, teratoma having functioning thyroid tissue component, metastatic lymph nodes and sequestered thyroid nodule. We present a case of thyrotoxicosis with hyper functioning thyroid gland and two abnormal foci of uptake in the mediastinum in a linear fashion that mimcked esophageal activity. These foci persisted even after consuming water. SPECT localised these foci in retrosternal and likely to be ectopic functioning thyroid. Retrosternal ectopic thyroid tissue may not usually be detected on Tc-99m scan due to attenuation of low-energy gamma rays by sternal bone. However, hyperfunctioning tissue enabled visualization of the retrosternal ectopic thyroid.

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.

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.

Study of energy and timing characteristics of 38.1mm × 38.1mm CeBr3 scintillator detectors

We report the results of measurements and GEANT4 simulation for the performance of two 38.1mm × 38.1mm CeBr3 detectors. The linearity and energy resolution of both the detectors have been measured using low energy gamma sources in the range from 121.8 keV to 4.44 MeV. Maintaining the energy linearity condition, the best time resolution value of 423 ± 14 ps was measured for 1173–1332 keV photon pair from a 60Co source. A GEANT4 simulation was performed to reproduce the measured experimental spectrum and to estimate the absolute photopeak efficiencies at several energies up to 4.44 MeV.

An ultrahigh spatial resolution radiation-imaging detector using 0.1 mm × 0.1 mm pixelated GAGG plate combined with 1 mm channel size Si-PM array

Spatial resolution of a pixelated scintillator-based radiation-imaging detector is sometimes limited by the pixel size of the scintillators. We developed a small-size pixelated GAGG scintillator using a dicing method and combined it with a small channel-size Si-PM array for the development of an ultrahigh resolution radiation-imaging detector. The developed pixelated GAGG scintillator had a pixel size of 0.1 mm × 0.1 mm arranged in 0.15-mm separations. It was combined with a Si-PM array made of 1 mm × 1 mm channels to form a radiation-imaging detector. With the developed radiation imaging detectors, the 0.1 mm × 0.1 mm pixels could be resolved for Am-241 alpha particles (5.5 MeV). The spatial resolutions of this imaging detector were better than 0.31-mm FWHM for Am-241 alpha particles and Ca-45 (maximum energy: 0.257 MeV) beta particles. The spatial resolutions for Am-241 gamma photons (60 keV) and Cs-137 X-ray (∼32 keV) were better than 0.6-mm FWHM. Separation of the images of alpha particles and gamma photons was possible using the scintillation decay time difference of GAGG between alpha particles and gamma photons. The developed ultrahigh spatial resolution pixelated GAGG radiation-imaging detector is promising for the imaging of alpha particles, beta particles, low-energy gamma photons and X-ray.

Improvement on Gamma Energy Resolution of Plastic Scintillator by Adding PMMA Light Guider or Chamfer

Traditional plastic scintillator has respectively low gamma energy resolution. Space radiation detection need the plastic scintillator to keep a relatively better energy resolution for gamma. Thus we did experiments to study how to get it enhanced by adding light guider and chamfer. A 9000Bq radioactive source 60Co has been utilized to make the experiment and results came that when keeping other conditions same, the height of poly methyl methacrylate (PMMA) light guider changes from 12mm to 40mm and the energy resolutions varied from 72.3% to 63.5% respectively. Furthermore, another contrast experiment was made to decide whether plastic scintillator with light guiders or integrated chamfer can get better energy resolution. In conclusion the plastic scintillator with integrated chamfer got 55.0%. Through the study of adding light guider or chamfer to plastic scintillator, the gamma energy resolution has been improved greatly from 72.3% to 55.0%.

Toward an understanding of aging in plutonium from direct measurements of stored energy

ABSTRACTWe present here the first direct measurement of the radiation-damage-induced energy stored in δ-phase plutonium. The primary mode of radioactive decay of 239Pu occurs with a time constant of τ=1.1 × 1012 s. Each decay imparts about 85 keV of recoil energy to the uranium byproduct, 5.2 Mev to the alpha particle, and a spectrum of mostly low energy gamma rays with the most probable at 51 keV [1]. Most of the decay energy is converted immediately to heat, releasing about 1.9 mW/g. However, some thermally-recoverable energy remains trapped. Reported here are measurements of that stored energy using differential scanning calorimetry (DSC) applied to 239Pu-2.0 at.%Ga δ-phase alloy. Retained energy of ∼2 J/g saturates at about 5 months and is unchanged after 30 years. The magnitude of the stored energy agrees with a short-bond defect model that that we present here. This model treats radiation damage as a Pu impurity with shortened bond lengths. It explains the change in known properties with age and predicts that density increases with age, contrary to current thinking. The short-bond impurities proposed are expected to act like other impurities, affecting strength, phase transitions, grain boundaries and other metallurgical properties.

A SiPM-Readout ASIC for SPECT Applications

In this paper, we present ANGUS, an application specific integrated circuit (ASIC) for silicon photomultiplier (SiPM) readout designed for low-energy gamma imaging (140 keV), specifically targeting clinical single photon emission computed tomography (SPECT) applications based on Anger-type detectors. The chip is composed of 36 channels, each featuring a current conveyor input followed by an RC filter with a time constant programmable from 200 ns up to 10 $\mu \text{s}$ , a baseline holder and a peak stretcher stage. Multichannel readout is performed with a polling strategy thanks to two analog multiplexers. The chip has been designed to cope with input capacitance values of several nanofarad, like the ones featured by the large-sized SiPM pixels (8 mm ${\times }$ 8 mm) of the application. Despite being conceived for operation with slow scintillator crystals like cesium-iodide (CsI), this ASIC can successfully manage the readout of faster crystals like lutetium-yttrium oxyorthosilicate. Measurements of the ASIC carried out on a fully equipped SPECT detection module have shown an energy resolution of 13.7% at the 140-keV line of 99mTc, for a 5 cm ${\times }$ 5 cm gamma camera consisting of a continuous CsI crystal and a SiPM detection plane cooled at 0 °C.

Depletion measurements using a new gamma transparency method of irradiated MTR-type fuel assemblies

An innovative method for the determination of the depletion in research reactor fuel assemblies (FAs) based on gamma transparency was developed, tested, and presented. The basic concept is the assessment of the uranium content from the attenuation of gamma rays passing through the FA, which is placed between a gamma-emitting source and a spectroscopic detector. With increasing depletion, more uranium transforms into fission products, which causes a significant decrease in the gamma-rays attenuation at energies higher than ∼116 keV, thus increasing the count rate at the detector. The attenuation from the fuel assembly was compared to that of a fresh (highest known uranium content, most opaque to gamma-rays) and dummy (Aluminum-only; most transparent) fuel assemblies, and subsequently, a logarithmic interpolation to determine the current uranium content was performed. In this study, a low-energy gamma ray of 155 keV (emitted from 188Re) was used, which exhibited significant contrast between the attenuation through the uranium versus its fission products, while obtaining sufficiently high count-rate at the detector at relatively short count durations. The 188Re source was generated prior to the experimental campaign through the 187Re(n,γ) reaction by irradiation of natural rhenium in IRR1 (Israel Research Reactor 1, 5MW open-pool HEU MTR-type fuel, Soreq Nuclear Research Center, Israel). Five FAs of different irradiation histories previously used in the IRR1 reactor were studied. The determined depletions were found to be in the range of 47%–59%, with absolute uncertainties of 2%–3%. The axial distribution of the depletion along the FAs was determined with high resolution (20 axial points per FA) using the low-energy photons and found to be in good agreement compared to the axial distributions obtained from fission products such as 137Cs. Experimental results of the present study were also compared to results of a different experiment that used the traditional gamma ray spectroscopy technique (i.e., using 137Cs activity) for one of the studied fuel assemblies (FS-5), giving good agreement in both the axial depletion distribution, as well as the whole assembly depletion. Thus, the method described in this paper demonstrates improved accuracy compared to other non-destructive spectroscopy-based methods. Furthermore, we managed to obtain spectroscopic signatures of relatively short-lived fission products such as 140Ba (T1∕2=12.7 days) from an FA that was irradiated 65 days before the measurement.

Development of an event-by-event based radiation imaging detector using GGAG: A ceramic scintillator for X-ray CT

For a radiation imaging detector, low cost, high light output and short decay time scintillator is required. Although ceramic scintillators developed for X-ray computed tomography (CT) are possible materials for this purpose, the performance of the scintillation imaging detector using ceramic scintillators was not reported. For this purpose, we tested a ceramic scintillator originally developed for X-ray CT, Gd3(GaAl)5O12:Ce (GGAG), combined with a position sensitive photomultiplier (PSPMT) to test whether an event-by-event based radiation imaging detector is possible to develop. The radiation imaging detector consists of a 0.1 mm thick GGAG plate, light guide and a 1-inch square PSPMT. The GGAG plate was optically coupled to the PSPMT with a 1 mm thick light guide between them. Anger principle was used for the position calculation of the radiations. We also conducted the comparison of the imaging detectors using 0.5 mm thick GGAG and single crystal Ce doped Gd3(Ga, Al)5O12 (GAGG) plates. The spatial resolution and energy resolution of the developed imaging detector were 0.53mm FWHM and 11.5 % FWHM for 5.5 MeV alpha particles, respectively. The uniformity of the imaging detector at the central part of the field of view (FOV) was ±11%. We could obtain variable phantom images with the developed imaging detector for alpha particles. Reasonable performance was also obtained for beta particles, low energy gamma photons and X-ray. The spatial resolution of the imaging detector used GGAG plate was twice better and distortion was smaller than that of GAGG. We conclude that GGAG ceramic scintillator is promising for the development of radiation imaging detectors.

Development of ultrahigh resolution radiation imaging detector using 1 mm channel size Si-PM array combined with 0.2 mm × 0.2 mm pixelated GAGG plate

For precise distribution measurements of gamma photons or beta particles, high resolution radiation imaging detectors are required. Reducing the size of the photodetectors combined with small pixel scintillators is a possible method to improve the spatial resolution of the scintillator based radiation imaging detectors. In this paper, we used a 1mm channel size silicon photomultiplier (Si-PM) array combined with a small pixel scintillator array and evaluated the performance for gamma photons and beta particles. For the radiation imaging detector, a Si-PM array with 1mm × 1mm channel size arranged in 8 × 8 (Hamamatsu, S13615-1025N-08) was optically coupled to a 0.2 mm × 0.2 mm pixelated GAGG plate. For 662 keV high energy gamma photons, 0.2mm GAGG pixels were clearly resolved in the position histogram. The peak to valley ratio (P/V) of the position histogram was not improved when only photo-peak events were used while it was improved when the events lower energy than the Compton edge was used. We could also resolve the position histograms for both 122 keV and 60 keV gamma photons. For beta particles, although the position histogram showed good separation for relatively low energy beta particles of Ca-45 (245 keV max), separation became worse for higher energy beta particles from Sr-Y-90 (545keV and 2280keV max). The separation of the position histogram for Sr-Y-90 improved when only lower energy events were used. Using 1mm size Si-PM array, high resolution detectors was realized for low energy gamma photons and beta particle but the spatial resolution was decreased for high energy beta particles from Sr-Y-90.

14 MeV neutrons for medical application: a scientific case for 99Mo/99Tcm production

99Tcm is a widely used radionuclide for SPECT (Single Photon Emission Computed Tomography) diagnostics thanks to its short half-life (about 6h) and the low-energy gamma ray emission (140 keV) well suited for diagnostic devices. The specific method for producing 99Tcm via 100Mo(n,2n)99Mo reaction, as it was investigated in ENEA, is discussed in detail in this paper. The 99Mo activity achieved by means of 14 MeV neutron irradiation on natural Molybdenum sample irradiated at the Frascati Neutron Generator (FNG) facility, at the Research Centre of ENEA-Frascati, was accurately assessed, by tracing it to the activity standards provided by the Italian National Institute of Ionizing Radiation Metrology (INMRI), located at the Research Centre of ENEA-Casaccia. The whole experiment carried out in ENEA was supported by simulations performed with the Fluka Monte Carlo code, whose predictions have been benchmarked against the experimental data collected at ENEA-FNG, relying on the traceability to the activity standards developed and maintained at the ENEA-INMRI Radioactivity laboratories.

Impurities Behaviors in Indium Iodide Materials

Environmentally friendly 99.998%-pure indium iodide (InI), one candidate materials for the room-temperature operating radiation detector, was purified more than 250 times using the zone-refining method to reduce the impurities. Segregation coefficient of major positive and negative impurities of the purified InI ingot was analyzed using time-of-flight secondary ion mass spectroscopy. Electrical and spectroscopic properties of the purified Pd/InI/Pd detector were also determined. Planar Pd/InI/Pd detector showed the 59.5-keV gamma peak of Am-241 clearly. However, low-energy gamma peaks were buried in the noise. Mechanical or electrical degradation under an ambient condition was not observed for six months. Electrical resistivity and electron mobility-lifetime product of the multiple-refined InI were $4\times 10^{11}\,\,\Omega \cdot \textrm {cm}$ and $1.3\times 10^{-3}\,\,\textrm {cm}^{2}/\textrm {V}$ , respectively.

A compact fast low energy gamma ray detector insensitive to high magnetic field

One step of the IRFU GBAR project aims at producing a dense low temperature positronium gaz. In order to characterize the positronium cloud we have tested a detector able to measure gamma energies in the 511 keV domain or lower, which is compact, fast, and insensitive to high magnetic fields. It uses the PreLude 420 scintillating crystal from Saint Gobain and large area Hamamatsu avalanche photodiodes. The performances of the system are presented. It could be used for other purposes.

Thermal resistance, tensile properties, and gamma radiation shielding performance of unsaturated polyester/nanoclay/PbO composites

Composites of unsaturated polyester containing 5wt% nanoclay and different amounts of lead monoxide particles (0, 10, 20, and 30wt%) were prepared. XRD patterns showed the exfoliation of nanoclay layers in the polymer. Morphological properties of the composites were studied using SEM micrographs. The prepared composites were investigated for their thermal resistance and mechanical properties using thermogravimetric analysis and tensile testing method, respectively. Addition of lead monoxide to the polymer worsened its thermal resistance and tensile properties, whereas the observed negative effects could be moderated by the clay nanoparticle. Gamma attenuation performance of the composites was evaluated by 192Ir, 137Cs, and 60Co gamma radiation sources. Linear attenuation coefficient and mass attenuation coefficient of the composites were found to be increased with the increase of PbO content. Shielding efficiency of the prepared composites was compared with some conventional shielding materials regarding their half value layer thickness. UP/nanoclay/PbO composites were found to be suitable materials for the low-energy gamma radiation shielding applications.

Pulse Shape Analysis and Discrimination for Silicon-Photomultipliers in Helium-4 Gas Scintillation Neutron Detector

Using natural helium (helium-4), the Arktis 180-bar pressurized gas scintillator is capable of detecting and distinguishing fast neutrons and gammas. The detector has a unique design of three optically separated segments in which 12 silicon-photomultiplier (SiPM) pairs are positioned equilaterally across the detector to allow for them to be fully immersed in the helium-4 gas volume; consequently, no additional optical interfaces are necessary. The SiPM signals were amplified, shaped, and readout by an analog board; a 250 MHz, 14-bit digitizer was used to examine the output pulses from each SiPMpair channel. The SiPM over-voltage had to be adjusted in order to reduce pulse clipping and negative overshoot, which was observed for events with high scintillation production. Pulse shaped discrimination (PSD) was conducted by evaluating three different parameters: time over threshold (TOT), pulse amplitude, and pulse integral. In order to differentiate high and low energy events, a 30ns gate window was implemented to group pulses from two SiPM channels or more for the calculation of TOT. It was demonstrated that pulses from a single SiPM channel within the 30ns window corresponded to low-energy gamma events while groups of pulses from two-channels or more were most likely neutron events. Due to gamma pulses having lower pulse amplitude, the percentage of measured gamma also depends on the threshold value in TOT calculations. Similarly, the threshold values were varied for the optimal PSD methods of using pulse amplitude and pulse area parameters. Helium-4 detectors equipped with SiPMs are excellent for in-the-field radiation measurement of nuclear spent fuel casks. With optimized PSD methods, the goal of developing a fuel cask content monitoring and inspection system based on these helium-4 detectors will be achieved.