keV Γ-rays Research Articles

Neural MLAA for PET-enabled Dual-Energy CT Imaging.

The PET-enabled dual-energy CT method allows dual-energy CT imaging on PET/CT scanners without the need for a second x-ray CT scan. A 511 keV γ-ray attenuation image can be reconstructed from time-of-flight PET emission data using the maximum-likelihood attenuation and activity (MLAA) algorithm. However, the attenuation image reconstructed by standard MLAA is commonly noisy. To suppress noise, we propose a neural-network approach for MLAA reconstruction. The PET attenuation image is described as a function of kernelized neural networks with the flexibility of incorporating the available x-ray CT image as anatomical prior. By applying optimization transfer, the complex optimization problem of the proposed neural MLAA reconstruction is solved by a modularized iterative algorithm with each iteration decomposed into three steps: PET activity image update, attenuation image update, and neural-network learning using a weighed mean squared-error loss. The optimization algorithm is guaranteed to monotonically increase the data likelihood. The results from computer simulations demonstrated the neural MLAA algorithm can achieve a significant improvement on the γ-ray CT image quality as compared to other algorithms.

Measurement of Photon Matter Interaction Parameters for some Iodine Compounds

In this study, total atomic cross-section (σta), total moleculer cross-section (σtm) total electronic cross-section (σte), effective atomic number (Zeff), effective electron density (Neff) and Kerma (K) were determined both experimentally and theoretically values for some iodine compounds. Experimental mass attenuation coefficient (µ/ρ) values for some iodine compounds were calculated with the data obtained from the test results. The theoretical mass attenuation coefficient values of these compounds were calculated with the WinXCOM data program. Also, we have performed the measurements for the calculations of experimental values mass attenuation coefficient using direct transmission experimental geometry. The transmission photon intensity of halogene iodine compounds were measured in a narrow beam experiment geometry was used 59.543 keV γ-ray from an 241Am radioactive source. The tranmissions spectra from iodine compounds were recorded with a Si (Li) detector having a resolution of 155 eV FWHM at 5.9 keV (55Fe) and coupled to a 1024 channel analyzer through a spectroscopic amplifier. This study was provided that new insights into the literature since mass attenuation coefficient experimental values of some I compounds have not been determined previously. More research should be done to observe the changes in the chemical structure of iodine compounds with gamma-ray interaction. This study will shed light on further research.

Characterisation of the charge collection properties in a segmented planar HPGe detector

Segmented germanium semiconductor detectors provide excellent γ-ray spectroscopic information whilst also being sensitive to the position of interactions within their active volume. Understanding the detector response to γ-ray interactions throughout its volume is required for interpreting the signal output. This work is the first assessment of the response and charge collection properties of an electrically-cooled Mirion Technologies-manufactured planar HPGe detector with boron implanted p+ and amorphous germanium based n+ strip contacts. The signal response of the detector as a function of γ-ray interaction position has been characterised by performing collimated beam scans with 59.5 keV and 661.7 keV γ-rays. A database of average signals, generated through the detector volume and across the detector surfaces, has been produced. A map of parameterised rise time response through depth has been generated and used to apply pulse shape analysis techniques, improving the position resolution within the detector.

Dosimetry and Calorimetry Performance of a Scientific CMOS Camera for Environmental Monitoring.

This paper explores the prospect of CMOS devices to assay lead in drinking water, using calorimetry. Lead occurs together with traces of radioisotopes, e.g., , producing -emissions with energies ranging from 10 to several 100 when they decay; this range is detectable in silicon sensors. In this paper we test a CMOS camera (Oxford Instruments Neo 5.5) for its general performance as a detector of X-rays and low energy -rays and assess its sensitivity relative to the World Health Organization upper limit on lead in drinking water. Energies from 6 to 60 are examined. The CMOS camera has a linear energy response over this range and its energy resolution is for the most part slightly better than 2%. The Neo sCMOS is not sensitive to X-rays with energies below . The smallest detectable rate is , corresponding to an incident activity on the chip of . The estimation of the incident activity sensitivity from the detected activity relies on geometric acceptance and the measured efficiency vs. energy. We report the efficiency measurement, which is 0.08(2)% (0.0011(2)%) at ( ). Taking calorimetric information into account we measure a minimal detectable rate of ( ) for ( ) -rays, which corresponds to an incident activity of ( ). Toy Monte Carlo and Geant4 simulations agree with these results. These results show this CMOS sensor is well-suited as a - and X-ray detector with sensitivity at the few to 100 ppb level for in a sample.

A cryogenic setup for multifunctional characterization of luminescence and scintillation properties of single crystals.

This article reports on a cryogenic setup that can be used for multifunctional experimental purposes. The temperature of the setup can be set from 10 K to 300 K. Different kinds of experiments were carried out in this experimental setup such as (1) luminescence emission, light yield, and decay time measurement under excitation of 266 nm laser and 280 nm LED sources, (2) thermoluminescence (TL) measurement under an x-ray excitation source, (3) scintillation property measurements such as light output, energy resolution, and decay time under 137Cs (662 keV γ-rays) and 241Am (5.4 MeV α) isotope sources, and (4) scintillation measurement under a 90Sr beta source through the continuous single-photon counting technique. The luminescence and scintillation properties of various molybdate and tungstate crystals such as CaMoO4, Na2Mo2O7, Pb2MoO5, CdWO4, and ZnWO4 are characterized and reported in the present work. The TL measurement of a CaMoO4 crystal is carried out from 10 K to 300 K, and various kinetic parameters such as order of kinetics, frequency factor, activation energy, and figure of merit are calculated for different TL peaks. As the temperature goes down from room to 10 K, the light yield of all studied crystals increases. Since the light yield of the crystal increases as temperature decreases toward 10 K, this experimental setup can be used for the characterization of luminescence and scintillation properties of a single crystal for rare event searches such as neutrinoless double-beta decay and dark matter.

Dual MRI-SPECT imaging system realized with Timepix pixel detector inserted into MR small animal scanner

Although MRI and SPECT are routine tools in medical imaging individually, the combination of these two modalities in multimodal imaging is still unexplored. By hybridizing high-resolution anatomical with functional imaging, combined MRI-SPECT could be a valuable addition to existing medical imaging methods, reducing overall scanning time and image co-registration errors. In contrast to PET, SPECT offers a cost-efficient range of applicable radioisotopes. This proof-of-principle study shows a modified experimental MRI-SPECT insert system consisting of an MR-compatible SPECT unit with hybrid semiconductor detectors Timepix. The insert system is equipped with CdTe pixelated sensors, tungsten collimators and a radiofrequency coil (RF). To increase the number of projections acquired, the setup is also equipped with an electromagnetic step motor Microcon SX 16-0503 for a sample rotation. Measurements were performed our own invented multimodal (1H/99mTc) inhomogeneous phantom filled with a liquid 99mTc radiotracer, emitting 140.5 keV γ-rays inside the RF coil by the Bruker BioSpec 47/20 (4.7 T) MR animal scanner. For the evaluation of measured data, SPECT-back projection software was developed in Matlab. Our results pave the way for a preclinical MRI-SPECT insert system. This research was performed in the framework of the Medipix Collaboration.

Synthesis of nanometer-sized PbZrxTi1-xO3 for gamma-ray attenuation

Nanometer-sized PbZrxTi1-xO3 powder was fabricated by the tartrate precursor method with different Zr contents, x = 0, 0.25, 0.52, and 0.75. All samples were annealed at 850 °C. These annealed samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and thermogravimetric analysis (TGA). The γ-ray attenuation coefficients of the annealed PbZrxTi1-xO3 samples were measured as a function of the Zr content for 661.7 keV γ-rays from a137Cs source. Positron annihilation spectroscopy was used to study the microstructural changes of the prepared samples. The XRD patterns indicate the presence of a tetragonal perovskite structure with a main peak corresponding to the (101) plane at 2θ of nearly 31°. The FTIR spectra show the presence of two absorption bands at around 620 and 390 cm−1, which are due to stretching and bending vibrations of the Ti–O bond, respectively. The nanometer-sized structure of synthesized PbZrxTi1-xO3 particles was confirmed by XRD and TEM. The TGA curves show a high decomposition temperature of more than 800 °C for PbZr0·52Ti0·48O3 and more than 650 °C for the other samples. PbZr0.52Ti0.48O3 shows the highest γ-ray mass attenuation coefficient among the samples studied. The positron annihilation lifetimes show that the main defect types are Pb monovacancies and Pb–O divacancies, and the samples with x ≥ 0.52 have the lowest average defect density. PbZr0.52Ti0.48O3 shows the highest value of the W parameter, which means that the chemical environment of its defects has more core electrons compared with the other samples. Finally, PbZr0·52Ti0·48O3 has novel properties for γ-ray shielding.

Scintillation characteristics of YAlO3:Pr perovskite single crystals

Abstract The luminescence and scintillation characteristics of YAlO3:Pr (0.05, 0.51 and 1.1 mol%) single crystals were investigated. At 662 keV γ-rays, the light yield of 22,290 ± 1150, 13,070 ± 650 and 13,240 ± 650 ph/MeV was obtained, respectively, for YAP:Pr (0.05%), YAP:Pr (0.51%) and YAP:Pr (1.1%). In scintillation decays the intensity of fast component (9–12 ns) becomes enhanced with increasing Pr concentration in the crystals. The time resolution at 511 keV annihilation quanta was measured for YAP:Pr-PMT detector in coincidence experiment with a BaF2-PMT detector. The time resolution of 357 ± 19, 333 ± 18 and 268 ± 15 ps was obtained, respectively, for YAP:Pr (0.05%), YAP:Pr (0.51%) and YAP:Pr (1.1%). High concentration of shallow traps in both YAP:Pr (0.51%) and YAP:Pr (1.1%) samples was evidenced by means of thermoluminescence in the 20–350 K temperature range. The lower light yield obtained for YAP:Pr (0.51%) can be caused by the enhanced delayed radiative recombination at Pr3+ luminescence centers.

Charge transport properties in CdZnTeSe semiconductor room-temperature γ-ray detectors

CdxZn1−xTeySe1−y (CZTS) has emerged as a next-generation compound semiconductor for high energy gamma-ray detection. In the present study, we report for the first time the hole transport property measurements in CZTS based gamma-ray detectors in the planar configuration. Current–voltage measurements revealed a bulk resistivity of ∼5 × 108 Ω cm and the fabricated detectors produced well-resolved 5486 keV alpha particle peaks, for both electrons and holes drifting alike, when pulse-height spectra (PHS) were recorded using a 241Am radiation source. The PHS measurements were enabled to measure the charge transport properties for both the charge carriers. The mobility–lifetime product (μτ) for electrons and holes was calculated to be 6.4 × 10−4 cm2 V−1 and 8.5 × 10−5 cm2 V−1, respectively, using a single polarity Hecht plot regression method. The pre-amplifier pulses were also recorded and processed digitally to obtain electron and hole drift mobilities of 692 cm2 V−1 s−1 and 55 cm2 V−1 s−1, respectively, using a time-of-flight method. The measured transport properties indicated the hole lifetime to be greater than the electron lifetime by a factor of ∼1.5. Gamma-ray PHS were recorded using fabricated detectors that showed tailing of the 662 keV photopeak due to hole trapping effects. Depth dependent PHS were digitally generated from 2D biparametric plots to reveal the effects of hole trapping on the gamma PHS at different detector depths. Digital correction procedures were applied to generate well-resolved PHS with an energy resolution of ∼2% for 662 keV γ-rays.

Study of charged particle activation analysis (II): Determination of boron concentration in human blood samples

Boron Neutron Capture Therapy (BNCT) is a radiotherapy for the treatment of intractable cancer. In BNCT precise determination of 10B concentration in whole blood sample before neutron irradiation of the patient, as well as accurate neutron dosimetry, is crucial for control of the neutron irradiation time. For this purpose ICP-AES and neutron induced prompt γ-ray analysis are generally used. In Ibaraki Neutron Medical Research Center (iNMRC), an intense proton beam will be accelerated up to 8 MeV, which can also be used for Charged Particle Activation Analysis (CPAA). Thus, in this study, we apply the CPAA utilizing the proton beam to non-destructive and accurate determination of 10B concentration in whole blood sample.A CPAA experiment is performed by utilizing an 8 MeV proton beam from the tandem accelerator of Nuclear Science Research Institute in Japan Atomic Energy Agency. The 478 keV γ-ray of 7Be produced by the 10B(p, α)7Be reaction is used to quantify the 10B in human blood. The 478 keV γ-ray intensity is normalized by the intensities of the 847 keV and 1238 keV γ-rays of 56Co originating from Fe in blood. The normalization methods were found to be linear in the range of 3.27 μg 10B/g to 322 μg 10B/g with correlation coefficients of better than 0.9999.

Experimental and Monte Carlo investigations of gamma ray transmission and buildup factors for inorganic nanoparticle/epoxy composites

The integration of inorganic nanoparticles into a polymer matrix presents a category of advanced materials, known as polymer inorganic nanocomposites (PINCs). In present work, the γ-ray shielding parameters of epoxy resin loaded with two different proportions (5 and 25 wt%) of Pb, Zn, ZnO, Ti and TiO2 inorganic nanoparticles have been investigated. The prepared samples were characterized through structural investigations including SEM, EDS, XRD and FT-IR analyses. Furthermore, mechanical properties of the nanocomposites were evaluated on the basis of compressive strength. To evaluate the γ-ray attenuation performance of the nanocomposites, the transmission and flux buildup factors have been measured experimentally. The 59.54 and 662 keV γ-rays emitted from 241Am and 137Cs point sources were counted by a 2″ × 2″ NaI(Tl) detector. In addition, experimental results has been confirmed by a theoretical study using MCNPX code. The results showed that γ-ray shielding effectiveness was enhanced by the increment of the filler loading. The experimental and theoretical calculations of transmission and buildup factors were found to be in a good agreement. As expected, 25 wt% Pb/epoxy nanocomposites indicated better shielding properties than their counterparts. However, it has to be notices that the mechanical strength of Pb/epoxy nanocomposites were determined significantly lower than those of Zn, ZnO, Ti and TiO2/epoxy nanocomposites. To design and choose an appropriate shielding material, therefore, a number of factors have to be considered.

Characterizations of a New Tl-based Elpasolite Scintillator: Tl2LiScCl6

A new Tl2LiScCl6 (TLSC) single crystal was grown by using the two-zone vertical Bridgman method. The TLSC belongs to the cubic chloro-elpasolite crystal family. Under X-ray excitation at room temperature, an emission spectrum from 300 to 550 nm was obtained, with the maximum emission being at 385 nm. The scintillation properties, such as the energy resolution, light yield and decay time of the TLSC crystal, were measured at room temperature by using a 137Cs γ-ray source. The energy resolution at the 662 keV photopeak was found to be 8.3% (full width at half maximum). Using the LYSO light yield as a reference, we obtained the light yield of the TLSC crystal as 26000 ± 2600 ph/MeV under excitation by 662 keV γ-rays. The developed crystal shows a single exponential decay time of 1.147 µs under 662 keV γ-ray excitation from a 137Cs source. Due to the high effective Z-number (67) and density of the TLSC crystal, it can be used for efficient detection of X- and γ-rays in various applications. It also has a potential to be used for detection of thermal neutrons via the 6Li(n, α) reaction. Further improvements in the scintillation properties are expected with rare-earth doping in this compound, which is the subject of our future work.

PbMoO4 Synthesis from Ancient Lead and Its Single Crystal Growth for Neutrinoless Double Beta Decay Search

A powder synthesis of PbMoO4 (PMO) from ancient lead (Pb) and deeply purified commercial MoO3 powders was performed using a wet chemistry technique to achieve the low radioactivity scintillator for neutrinoless double beta decay search in 100Mo. The synthesized powders were used to grow single crystals of PbMoO4 by the Czochralski technique in an Ar environment. The luminescence and scintillation properties were measured with excitations using UV, X- and γ-rays in the temperature range of 10–300 K. Annealing of the grown PMO crystal in an air atmosphere significantly enhanced the scintillation light yield compared to that measured before annealing. The scintillation light yield of grown PMO crystal at 10 K was found to be 127% to that of a reference PMO crystal under 662 keV γ-rays excitation from a 137Cs source. The background measurement of the grown crystal performed at 50 K shows a lower internal activity from 210Pb compared to that of reference PMO (grown from modern Pb) crystal. These preliminary performances show that the PMO crystal grown from ancient Pb and deeply purified MoO3 powders has a great potential to be used as a cryogenic scintillator for the neutrinoless double beta decay search in 100Mo.

Electronic response of hydrogen storage intermetallics LaNi5 and LaNi4.5Co0.5: inelastic scattering experiment and ab initio calculations

Electron momentum densities of intermetallic compounds LaNi5 and LaNi4.5Co0.5 using inelastic scattering of 662 keV γ-rays are presented. To check the usefulness of different exchange and correlation potentials for such type of hydrogen storage compounds, the resulting experimental Compton profiles (CPs) have been compared with the Compton lines deduced using linear combination of atomic orbitals (LCAO) scheme. It is seen that the LCAO with HISS scheme (middle range separated hybrid approach) leads to a better agreement with the experimental CPs than other considered schemes based on LDA, GGA, SOGGA, B3LYP and short range separated hybrid HSE06. In addition, energy bands and density of states of these systems derived using LCAO and the full potential linearized augmented plane wave methods are discussed. Anisotropies in momentum densities with respect to [001] direction namely (J001−J110 and J001–J100) show almost similar trend for both the intermetallics. It is noticed that the energy states corresponding to d states of Ni (2c), Ni (3 g) and Co atoms dominate near Fermi level (EF). The Fermi surface (FS) topology and real space CPs of LaNi5 and LaNi4.5Co0.5 show non-spherical character of FS and failure of free electron theory for such intermetallics.

Crystal growth and Ce3+ concentration optimization in Tl2LaCl5: An excellent scintillator for the radiation detection

High effective atomic number (70) and density (5.17 g/cm3) among the known halide scintillators with excellent scintillation performance make Tl2LaCl5 (TLC) a new potential candidate for X- and γ-ray detection. The preliminary scintillation performance of TLC was reported earlier for small crystal pieces without any detail information of synthesis, crystal growth optimization conditions and Ce3+ doping concentration, which are investigated in this study. The newly developed melt rotation technique was found to be the best one for the synthesis of TLC and probably for other Tl-based compounds among the known melting techniques. Pure and nominal Ce3+ concentration of 1%, 3%, 5%, 7% and 10% TLC crystals were grown with two zones vertical Bridgman technique in two different type of homemade furnaces and found the optimum thermal gradient, pulling and cooling rate as 25 °C/cm, 0.5 mm/h and 20 °C/h, respectively. The best energy resolution of ∼3.3% (FWHM) and light yield of ∼82,000 ph/MeV were obtained for TLC:3%Ce3+ under 662 keV γ-rays excitation. The promising scintillation performance of TLC revealed that this crystal could be used in Positron Emission Tomography (PET), environmental radiation monitoring and homeland security applications.

Transmission of X and γ-rays to differentiate tumbaga from gold and gilded copper

In many cases, the differentiation between an artefact on gold alloy, or on tumbaga (the last being a poor gold alloy subject to depletion gilding), and, sometimes, on gilded copper, is not easy. Their aspect is often similar, and energy-dispersive X-ray fluorescence analysis, which is one of the few non-destructive and non-invasive technique suited to analyze gold sheets, is sometimes not able to solve the question on the basis of altered Au-L, Cu-K, Cu-K/Au-L- ratios, as in other similar cases. For that reason, X-rays from a Sn secondary target, and 26.4 and 59.6 keV γ-rays emitted by an Am-241 radioactive source were employed in transmission mode as an additional differentiation method.

Search for WIMP-129Xe inelastic scattering using particle identification in the XMASS experiment

The inelastic scattering of Weakly Interacting Massive Particles (WIMPs) and 129Xe nuclei was searched for in the XMASS experiment. When excited by the inelastic scattering, the nuclei emit 39.6 keV γ-ray. The exposure of the data was 327 kg × 800.0 days. To improve the sensitivity of the signal, the events were classified by their pulse shapes, which discriminates between γ-rays and β-rays. As no significant signal was found, the upper limits of the inelastic channel cross section at the 90% confidence level were set. For a 200 GeV/c 2 WIMP, the limit was 4.1 × 10−39 cm2. This is the most stringent limit of the SD WIMP-neutron interaction.

Measurement of talc in flour by the 14 MeV neutron activation analysis method

The 14 MeV neutron activation analysis method was used to measure talc in flour. The neutron yield of a D-T neutron generator was maintained at 1.32 × 107n∙s−1 to irradiate flour samples for one hour. A 1779 keV characteristic γ-ray produced by the 28Si(n,p)28Al reaction and 1369 and 2754 keV characteristic γ-rays produced by the 24Mg(n,p)24Na reaction were measured by a 3-inch NaI(Tl) detector and a 2-inch LaBr3(Ce) detector, respectively. The accuracy and detection limit of the talc content measured by the two detectors with different characteristic γ-rays were discussed. The results show that the best scheme for measuring talc content is measuring the 1779 keV γ-ray with the 3-inch NaI(Tl) detector. The detection limit reaches 0.07%, and the relative error of multiple measurements of the same sample is 2.07%. The relationship among the mass thickness of the sample, the talc content and the characteristic peak area was plotted.

Fast neutron inelastic scattering from 7Li

The inelastic scattering of fast neutrons from 7Li nuclei was investigated at the nELBE neutron-time-of-flight facility. The photon production cross section of 478 keV γ-rays from the first excited state of 7Li was determined by irradiating a disc of LiF with neutrons of energies ranging from 100 keV to about 10 MeV. The target position was surounded by a setup of 7 LaBr3 scintillation detectors and 7 high-purity germanium detectors to detect the de-excitation γ-rays. A 235U fission chamber was used to determine the incoming neutron flux. The number of detected photons was corrected for the detection efficiency, multiple scattering and the time-of-flight dependent data acquisition dead time. The preliminary results show reasonable agreement with some previous measurments but are about 15 % below the recent data taken at the GELINA facility.

Production yields of 𝛽+ emitters for range verification in proton therapy

In-vivo Positron Emission Tomography (PET) range verification relies on the comparison of the measured and estimated activity distributions from β+ emitters induced by the proton beam on the most abundant elements in the human body, right after (looking at the long-lived β+ emitters 11C, 13N and 15O) or during (looking at the short-lived β+ emitters 29P, 12N, 38mK and 10C) the irradiation. The accuracy of the estimated activity distributions is basically that of the underlying cross section data. In this context, the aim of this work is to improve the knowledge of the production yields of β+ emitters of interest in proton therapy. In order to measure the long-lived β+ isotopes, a new method has been developed combining the multi-foil technique with the measurement of the induced activity with a clinical PET scanner. This technique has been tested successfully below 18 MeV at CNA (Spain) and will be used at a clinical beam to obtain data up to 230 MeV. However, such method does not allow measuring the production short-lived isotopes (lower half-life). For this, the proposed method combines a series of targets sandwiched between aluminum foils (acting as both degraders and converters) placed between two LaBr3 detectors that will measure the pairs of 511 keV γ-rays. The first tests will take place at the AGOR facility at KVI-CART, in Groningen.