Gamma-ray Pulse-height Spectra Research Articles

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.

Evaluation of gamma-ray strength function based on measured gamma-ray pulse-height spectra in time-of-flight neutron capture experiments

In order to develop an evaluation method of gamma-ray strength function (GSF), neutron capture pulse-height (PH) spectrum of gold was employed, where it was measured with the NaI(Tl) spectrometer of AN-NRI installed at the Material and Life Science Experimental Facility in J-PARC. The neutron capture gamma-ray spectrum of gold was calculated using the nuclear reaction model code CCONE. In order to obtain the information on GSF from the measured data, a gamma-ray response function for the NaI(Tl) spectrometer was calculated by the Monte-Carlo particle-transport simulation code PHITS. As a result, the PH spectrum comparable with measured one was derived by applying the gamma-ray response function to the calculated gamma-ray spectrum. By evaluation with measured PH spectra, we obtained GSF which reasonably explains measured PH spectrum in the continuum region.

Bulk Organic-Inorganic Methylammonium Lead Halide Perovskite Single Crystals for Indirect Gamma Ray Detection.

Scintillators that convert ionization radiation photons to UV-visible photons have attracted extraordinary attention. Traditional scintillators are associated with a vacuum photomultiplier tube that faces strict constraints of fragility, magnetic fields, and operated voltage, or coupled to a silicon photomultiplier (SiPM) with optical silicone grease. Here, we report a high-performance radiation detector with an indirect photon-to-photon conversion radiation detection model based on perovskite single crystals (SCs), where perovskite SCs have been directly integrated into the window of SiPM by using the solution growth method at low temperature. Tunable X (γ)-ray excited light emission in the range of 414 to 600 nm is obtained with different concentrations of Br doping, which greatly matches the response wavelength of SiPM. Small Br-doped CH3NH3PbBr0.05Cl2.95 SCs exhibit high transmittance and weak self-absorption, resulting in improved scintillation light emissions. Moreover, we have successfully collected a 137Cs source gamma-ray pulse height spectrum with the SiPM readout. The MAPbBr0.05Cl2.95 scintillator exhibits a decay time of 0.14 ± 0.02 ns and a light yield of 18 000 photons/MeV with an energy resolution of 10.5 ± 0.4% at 662 keV. The results indicate that the CH3NH3PbBrxCl3-x perovskite SCs could enable the next generation of low-cost, fast, and fine-energy resolution scintillators.

Spectroscopic and neutron detection properties of rare earth and titanium doped LiAlO2 single crystals

In this study, LiAlO2 crystals doped with rare-earth elements and Ti were produced by the CZ method and spectroscopic and neutron detection properties were investigated. Photoluminescence revealed no clear luminescent activation of LiAlO2 by the rare-earth dopants though some interesting luminescence was observed from secondary phases within the crystal. Gamma-ray pulse height spectra collected using a 137Cs source exhibited only a Compton edge for the crystals. Neutron modeling using Monte Carlo N-Particle Transport Code revealed most neutrons used in the detection setup are thermalized, and while using natural lithium in the crystal growth, which contains 7.6% 6Li, a 10mm Ø by 10mm sample of LiAlO2 has a 70.7% intrinsic thermal neutron capture efficiency. Furthermore, the pulse height spectra collected using a 241Am-Be neutron source demonstrated a distinct neutron peak.

Study on the impact of pair production interaction on D-T controllable neutron density logging

This paper considers the effect of pair production on the precision of D-T controllable neutron source density logging. Firstly, the principle of the traditional density logging and pulsed neutron density logging are analyzed and then gamma ray cross sections as a function of energy for various minerals are compared. In addition, the advantageous areas of Compton scattering and pair production interactions on high-energy gamma ray pulse height spectrum and the errors of a controllable source density measurement are studied using a Monte Carlo simulation method. The results indicate that density logging mainly utilizes the Compton scattering of gamma rays, while the attenuation of neutron induced gamma rays and the precision of neutron gamma density measurements are affected by pair production interactions, particularly in the gamma rays with energy higher than 2MeV. By selecting 0.2−2MeV energy range and performing proper lithology correction, the effect of pair production can be eliminated effectively and the density measurement error can be rendered close to the precision of chemical source density logging.

Neutron Capture Cross Section Measurement on91Zr at J-PARC/MLF/ANNRI

The neutron capture cross section measurement on 91Zr was performed at neutron TOF beam line ANNRI installed at J-PARC/MLF. Prompt capture gamma rays from the sample were detected with an array of large Ge detectors at a distance of 21.5 m from the spallation neutron source by the time-of-fligh (TOF) method. The neutron capture gamma-ray pulse-height spectra from the 182-eV p-wave resonance and the 292-eV s-wave resonance were obtained by gating on the TOF regions, respectively. Though the decay patterns of primary transitions from the capture state were quite different between resonances, the prominent characteristics common to both resonances was the very strong ground-state transition from the 935-keV state. Therefore, a ground-state transition method was applied to obtain the capture yield, so that the background components due to impurities were successfully eliminated. The preliminary result of the neutron capture cross section for 91Zr up to 5 keV is presented.

Measurements of keV-neutron Capture Cross Sections and Capture Gamma-ray Spectra of Pd Isotopes

The capture cross sections and capture gamma-ray spectra of 104,105,106,108,110Pd were measured in the neutron energy region from 15 to 100 keV. A neutron time-of-flight method was utilized by means of an anti-Compton NaI(Tl) spectrometer and a 1.5 nsec pulsed neutron source via the 7Li(p,n)7Be reaction. The capture yields were obtained by applying a pulse-height weighting technique to the net gamma-ray pulse-height spectra. The capture cross sections of 104,105,106,108,110Pd were determined with uncertainties of less than 6%, using the standard capture cross sections of 197Au. The capture gamma-ray spectra of 104,105,106,108,110Pd were also derived by unfolding the respective observed capture gamma-ray pulse-height spectra.

Study on the keV neutron capture reaction in 56Fe and 57Fe

The neutron capture cross-sections and the radiative capture gamma-ray spectra from the broad resonances of 56Fe and 57Fe in the neutron energy range from 10 to 90keV and 550keV have been measured with an anti-Compton NaI(Tl) detector. Pulsed keV neutrons were produced from the 7Li\( (p,n)\) 7Be reaction by bombarding the lithium target with the 1.5ns bunched proton beam from the 3MV Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a time-of-flight (TOF) method with a 6Li -glass detector. The number of weighted capture counts of the iron or gold sample was obtained by applying a pulse height weighting technique to the corresponding capture gamma-ray pulse height spectrum. The neutron capture gamma-ray spectra were obtained by unfolding the observed capture gamma-ray pulse height spectra. To achieve further understanding on the mechanism of neutron radiative capture reaction and study on physics models, theoretical calculations of the \( \gamma\) -ray spectra for 56Fe and 57Fe with the POD program have been performed by applying the Hauser-Feshbach statistical model. The dominant ingredients to perform the statistical calculation were the Optical Model Potential (OMP), the level densities described by the Mengoni-Nakajima approach, and the \( \gamma\) -ray transmission coefficients described by \( \gamma\) -ray strength functions. The comparison of the theoretical calculations, performed only for the 550keV point, show a good agreement with the present experimental results.

Measurements of keV-neutron capture cross sections and capture gamma-ray spectra of 105Pd

The neutron capture cross sections and capture gamma-ray spectra of 105Pd were measured in the region from 15 to 100 keV and at 585 keV. A neutron time-of-flight method was utilised with an anti-Compton NaI(Tl) spectrometer and a 1.5-ns pulsed neutron source by the 7Li(p,n)7Be reaction. The capture yields were obtained by applying a pulse-height weighting technique to the observed net capture gamma-ray pulse-height spectra. The capture cross sections of 105Pd were derived with errors less than 5%, using the standard capture cross sections of 197Au. The evaluated capture cross sections of JENDL-4.0 and ENDF/B-VII.1 were compared with the present results. The evaluations of JENDL-4.0 and ENDF/B-VII.1 were larger than the present results by 3%–15% in the region from 15 to 100 keV and at 585 keV. The capture gamma-ray spectra of 105Pd were also derived by unfolding the observed net capture gamma-ray pulse-height spectra. The multiplicities of capture gamma rays of 105Pd were obtained from the capture gamma-ray spectra.

Precise Numerical Simulation of Gamma-ray Pulse Height Spectrum Measured with a CdTe Detector Designed for BNCT-SPECT

Precise Numerical Simulation of Gamma-ray Pulse Height Spectrum Measured with a CdTe Detector Designed for BNCT-SPECT

Automated nondestructive assay of UF6 cylinders: Detector characterization and initial measurements

Abstract International Atomic Energy Agency (IAEA) inspectors currently perform periodic inspections at uranium enrichment plants to verify UF6 cylinder enrichment declarations. Measurements are typically performed with handheld high-resolution sensors on a sampling of cylinders taken to be representative of the facility's entire cylinder inventory. These measurements are time-consuming and assay only a small fraction of the total cylinder volume. An automated nondestructive assay system capable of providing enrichment measurements over the full volume of the cylinder could improve upon current verification practices in terms of manpower and assay accuracy. Pacific Northwest National Laboratory is developing an Integrated Cylinder Verification System (ICVS) intended for this purpose and has developed a field prototype of the nondestructive assay (NDA) components of an ICVS. The nondestructive assay methods would combine the “traditional” enrichment-meter signature (i.e. 186-keV emission from U-235) as well as “nontraditional” high-energy photon signatures derived from neutrons produced primarily by F-19(α,n) reactions. This paper describes the design, calibration and characterization of the NaI(Tl) and LaBr3(Ce) spectrometers utilized in the field prototype. An overview of a recent field measurement campaign is then provided, supported by example gamma-ray pulse-height spectra collected on cylinders of known enrichment.

Effect of Electron Traps on Scintillation of Praseodymium Activated Lu$_3$Al$_5$O$_{12}$

In this paper we present the studies performed on a set of Lu3Al5O12:Pr (LuAG:Pr) crystals with praseodymium concentration between 1.5 and 10%, grown by the micro-pulling-down (muPD) technique. The research comprises the measurements of X-ray excited emission spectra and 137Cs gamma-ray pulse height spectra in a range from 78 to 600 K, and thermoluminescence glow curves. Based on experimental data we discuss the dependence of scintillation properties of Lu3Al5O12:Pr on praseodymium content and temperature. The main attention is focused on a distinct increase of scintillation yield with temperature, which we attribute to existence of shallow electron traps and their temperature-dependent contribution to scintillation of LuAG:Pr. An active role of traps is demonstrated by a novel experiment combining X-ray and laser excitation.

Automated spectroscopy of X-ray and gamma-ray pulse height spectra using energy space subdivision

A new model for the automated analysis of X-ray and gamma-ray multi-channel pulse height spectra is presented. The goal of the algorithm is to efficiently and accurately converge on the background and elemental factors while limiting human influence to the a priori defined knowledge of the detector characteristics. This information includes generic estimates of the continuum with defined elemental response functions. The energy space of the spectrum is subdivided and each subspace is fit independently. By considering all possible elemental line combinations within each energy subspace an optimal line combination is determined from the minimal squared error over each reconstructed elemental line combination. In this paper, we briefly review the background issues and motivations for the present research. The paper will present the algorithms and discuss related issues for elemental analysis of actual integrated spectra obtained from the Mars Odyssey Gamma-ray spectrometer.

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 99Tc

The capture cross sections of 99Tc were measured in the incident neutron energy region from 8 to 90 keV and at 190, 330, and 540 keV. A neutron time-of-flight method was adopted with a ns-pulsed neutron source by the 7Li(p, n) 7Be reaction and with a large anti-Compton NaI(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture gamma-ray pulse-height spectra to derive capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of 99Tc were obtained with the error of about 5%. The present results were compared with other measurements and the evaluated values in JENDL-3.2 and 3.3 and ENDF/B-VI. Capture gamma-ray spectra were obtained by unfolding observed capture gamma-ray pulse-height spectra. A change of slopes was observed at 2.2 MeV in the spectra. The multiplicities of observed gamma rays were obtained from the gamma-ray spectra.

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 99Tc.

The capture cross sections of 99Tc were measured in the incident neutron energy region from 8 to 90 keV and at 190, 330, and 540 keV. A neutron time-of-flight method was adopted with a ns-pulsed neutron source by the 7Li(p, n) 7Be reaction and with a large anti-Compton NaI(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture gamma-ray pulse-height spectra to derive capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of 99Tc were obtained with the error of about 5%. The present results were compared with other measurements and the evaluated values in JENDL-3.2 and 3.3 and ENDF/B-VI. Capture gamma-ray spectra were obtained by unfolding observed capture gamma-ray pulse-height spectra. A change of slopes was observed at 2.2 MeV in the spectra. The multiplicities of observed gamma rays were obtained from the gamma-ray spectra.

PCGAP: Application to analyze gamma-ray pulse-height spectra on a personal computer under Windows NT®

PCGAP is a software code, which was written to provide gamma-ray pulse height spectrum analysis on a personal computer platform. The code was specifically developed for Windows NT for either an Intel® or DEC Alpha® based processor. PCGAP includes programs which can be used to control data collection using a Canberra INSPECTOR® multichannel pulse-height analyzer. With suitable spectrum conversion routines PCGAP can be used to analyze data from almost any multi-channel analyzer. Besides the normal functions associated with a robust spectrum analysis package, PCGAP can be used for radionuclide analysis for actinides via L-X and gamma-ray spectrometry. It can be used to control and analyze data from an INEEL developed pulse injection system for individual spectrum validation. The package includes programs for the manual analysis of spectra using displays which permit the spectroscopist to interactively define the spectral continuum and peak fitting limits, and display the resulting function fitting forms.

The use of pulse processing techniques to improve the performance of Cd/sub 1-x/Zn/sub x/Te gamma-ray spectrometers

Cd/sub 1-x/Zn/sub x/Te (CZT) has recently shown great promise for use as a room temperature gamma-ray detector material. The availability of large volume (>1 cm/sup 3/) high resistivity CZT crystals has allowed the demonstration of detectors much larger than can be built with the similar material CdTe. However, CZT-like many other room-temperature materials-suffers from the poor transport properties of holes. The poor hole drift properties of CZT cause the characteristic "hole tailing" in gamma-ray pulse height spectra. We have applied pulse processing methods to reduce the hole tailing effects and improve the energy resolution of CZT detectors. We have used two signal processing methods to reduce hole tailing in CZT detectors: digital rise-time compensation and dual time-constant sampling. We discuss the implementation of these techniques, demonstrate results obtained in the laboratory, and compare the performance obtained with other detector systems.

An algorithm for intrinsic gain and offset stabilization of gamma-ray pulse height spectra

A new algorithm for the intrinsic stabilization of the pulse height spectra (PHSs) of multiply scattered gamma -rays that makes gain and offset corrections based on spectral shape is described. In the implementation, the input spectrum is transformed from assumed values of gain and offset to a set of standard values. The PHSs are projected onto four spectral principal components, and the mean square error between the transformed input spectrum and its rank four representation is minimized. For noise-free spectra, it was found that the algorithm can estimate gain with a root mean square (RMS) error of 1%, and offset with an RMS error of 0.6 keV when the spectral components were determined from the test data. For noisy spectra the RMS errors for gain and offset were 4% and 1.7 keV, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Indium phosphide particle detectors

The authors fabricated particle detectors made from InP:Fe, InP:Zn, and InP:Cu and evaluated the performance of these devices. The InP detectors were suggested for gamma-ray detection with varying degrees of success. Gamma-ray pulse-height spectra were acquired and stored for detectors of each type. It was found that the InP:Fe detector performance is currently limited by the trapping of charge carriers by the iron dopant in the material InP:Zn detectors are limited by the low mobilities ( approximately=3 cm/sup 2/ V/sup -1/ s/sup -1/) existing in the material at the operating temperature of 14 K. The InP:Cu detectors fabricated are limited by defects induced in the material by the thermal cycling of the copper diffusion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monte Carlo simulation of gamma ray spectra from semiconductor detectors

Monte Carlo techniques have been used to simulate gamma-ray pulse-height spectra from rectangularly shaped CdTe detectors in the energy range of a few keV to approximately 1 MeV. The simulation results were found to agree well with measured CdTe gamma-ray pulse-height spectra. The various physical events occurring within the detector are simulated in a naturally sequential manner. Specifically, the algorithm simulates such effects as exponentially absorbed radiation, multiple Compton scattering within the detector, charge-carrier trapping, and electronic noise (Gaussian). Advantages of this simulation method are the compactness of the code (allowing the use of microcomputers) and speed of operation (approximately 15 events per second).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>