Alireza Kargar

• Kansas State University

The detector that converts X-ray intensity into a digitized electronic signal, processed into an image, often limits the performance of modern X-ray imaging systems, whether for medical, research, or industrial applications. Digital radiography uses the following two types of detectors: indirect detectors, where a scintillating film converts X-ray...

The material family halide perovskites has been critical in recent room-temperature radiation detection semiconductor research. Cesium lead bromide (CsPbBr3) is a halide perovskite that exhibits characteristics of a semiconductor that would be suitable for applications in various fields. In this paper, we report on the correlations between material...

Lithium indium diselenide (LISe) is a semiconductor that holds promise for neutron imaging sensor technologies because of its high neutron absorption efficiency and its corresponding ability to discriminate between gamma rays and neutrons. However, being a semiconductor, LISe may not be sufficiently radiation hard for practical application in radia...

Arrays of 3D position-sensitive detectors (3DPSD), operating at room temperature and using cadmium zinc telluride (CZT) and thallium bromide (TIBr) sensors, are suitable for gamma-ray spectrometry in many applications. One detector configuration, the 3D position-sensitive Virtual Frisch-Grid detector (VFG), is particularly advantageous for integrat...

Lithium Indium Diselenide ”LiInSe2” is a semiconducting material considered as a potential option for energy resolved neutron imaging. Its high neutron detection efficiency and excellent spatial resolution make it attractive to be used in the development of a neutron imager for DOE facilities. A neutron imager with an overall enhancement of detecti...

Lithium indium selenide (LiInSe2) is being developed for use as a room temperature semiconductor detector for thermal neutrons. The material has been studied for a number of applications including non-linear optics such as parametric oscillators, as anode material for lithium ion batteries, piezoelectrics, as a scintillation detector material, and...

Thallium bromide (TlBr) is a compound semiconductor with a band gap of 2.68 eV making it ideal for room temperature radiation detection. The high atomic numbers, 81 and 35, and the high density of 7.56 g/cm3 give it excellent gamma-ray stopping power. TlBr is a cubic material that melts congruently at a relatively low temperature (~480°C). These pr...

The detection of thermal neutrons has traditionally been accomplished with ³He-tubes, but with the recent shortage of ³He, much research has gone into finding suitable replacements. Both relatively inefficient ¹⁰B- and ⁶LiF-coated silicon diodes and HgI2 have been known for many years, and engineered structures in Si that have been filled with ¹⁰B...

Four thallium bromide planar detectors were fabricated from materials grown at RMD Inc. The TlBr samples were prepared to investigate the effect of guard ring on device gamma-ray spectroscopy performance, and to investigate the leakage current through surface and bulk. The devices’ active area in planar configuration were 4.4 × 4.4 × 1.0 mm3. In th...

Thermal neutron detectors in planar configuration were fabricated from B2Se3 (Boron Selenide) crystals grown at RMD Inc. All fabricated semiconductor devices were characterized for the current-voltage (I-V) characteristic and neutron counting measurement. In this study, the resistivity of crystals is reported and the collected pulse height spectra...

Thallium bromide (TlBr) has been under development for room temperature gamma ray spectroscopy. As a result of improvements in material processing and detector fabrication over the last several years, the electron and hole mobility-lifetime products of TlBr are close to those of CdTe. This has allowed us to fabricate 10 mm thick arrays. Without any...

Thallium bromide (TlBr) has been under development for room temperature gamma ray spectroscopy due to high density, high Z and wide bandgap of the material. Furthermore, its low melting point (460 °C), cubic crystal structure and congruent melting with no solid-solid phase transitions between the melting point and room temperature, TlBr can be grow...

In this paper the fabrication and characterization of lead gallium selenide (PbGa2Se4) semiconductor devices are reported. PbGa2Se4 semiconductor crystals were grown by vertical Bridgman method and planar devices were fabricated from cleaved crystals. The resistivity of the samples with chromium gold contacts was measured to be in the 1013 Ω cm ran...

In recent years, progress in processing and crystal growth methods have led to a significant increase in the mobility-lifetime product of electrons in thallium bromide (TlBr). This has enabled single carrier collection devices with thickness greater than 1-cm to be fabricated. In this paper we report on our latest results from pixellated devices wi...

In this study, a 2.1×2.1×4.1mm3 HgI2 Frisch collar device was characterized through probing the device with a highly collimated 662keV gamma rays (137Cs check source) along the length and width of the device. In a systematic series of experiments, the detector was probed along its central line under different operating voltages of 1600, 1300, 1000,...

The efficient detection of fast neutrons is essential for nuclear non-proliferation monitoring. Although semiconductor devices such as silicon sensors have been used for thermal neutron detection using Gd, B or Li based converter layers, direct fast-neutron detection with hydrogen-containing semiconductor devices has not yet been accomplished. In t...

Thermal neutron detectors in planar configuration were fabricated from LiInSe2 and B2Se3 crystals grown at RMD Inc. All fabricated semiconductor devices were characterized for the current-voltage (I-V) characteristic and neutron counting measurement. Pulse height spectra were collected from 241AmBe (neutron source on all samples), as well as 137Cs...

In this study, the charge collection efficiencies (CCEs) of a 7.8- × 7.8- × 15.6-mm3 CdZnTe Frisch collar detector and a 2.1- × 2.1- × 4.1-mm3 HgI2 Frisch collar detector were measured and compared. Two Frisch collar devices were designed and fabricated to have identical aspect ratios of 2.0 to maintain similar weighting potential distributions. Pu...

Being a high-Z material, mercuric iodide (HgI2) has a relatively high gamma-ray absorption coefficient. Its low charge carrier mobilities, however, have somewhat hampered the interest in using this material as a roomtemperature gamma-ray spectrometer. By using the Frisch collar technology, the influence of the low charge carrier can be significantl...

Tetragonal prismatic HgI₂ crystals are obtained from growth with low M_w polyethylene. Thermal desorption studies coupled with gas chromatography/mass spectroscopy (TDGC/MS) reveal the existence of normal alkanes and ketones in the growth ampoules with low molecular weight polyethylene. Polar bonds, such as carbonyl bonds found...

A tetragonal prismatic HgI2 crystal grown with low molecular weight polyethylene addition in a horizontal furnace has been fabricated into a 2.1×2.1×4.1 mm3 Frisch collar spectrometer. With no electronic correction nor LN2 cooling, an energy resolution of 1.8% FWHM at 662 keV (137Cs) is achieved. Spectra from 241Am (4.7% FWHM at 59.5 keV), 57Co (4....

Many homeland security applications involving gamma-ray detectors require energy resolution of better than 1%-2% for isotope identification. Existing High-Purity germanium (HPGe) detectors have the needed energy resolution but suffer from large size and the need for liquid-nitrogen or electromechanical cooling. Compact, inexpensive, room-temperatur...

Thallium bromide (TlBr) and related ternary compounds, TlBrI and TlBrCl, have been under development for room temperature gamma ray spectroscopy due to several promising properties. Due to recent advances in material processing, electron mobility-lifetime product of TlBr is close to Cd(Zn)Te's value which allowed us to fabricate large working detec...

An alternative method for the detection of thermal neutrons has been investigated utilizing the Pockels effect with CdZnTe and LiNbO3. A photodiode was used to indicate a change in light intensity transmitted through an assembly consisting of polarizer, Pockels cell, and analyzer. Ionization due to neutron reaction products can perturb an establish...

A 4.7 ×4.7×9.5 mm3 CdZnTe Frisch collar device was characterized through probing the device with a highly collimated Cs137 662 keV gamma ray source. In a systematic series of experiments, the detector was probed along the length and width with a Cs137 gamma ray source using a 43.0 mm long Pb-collimator with a 0.6 mm circular hole. The detector was...

CdZnTe crystals equipped with Frisch collars are studied at the Semiconductor Materials and Radiological Technologies Laboratory (S.M.A.R.T. Lab) at Kansas State University for use as room-temperature, high-resolution, semiconductor gamma-ray detectors. Obtaining plots of Relative Pulse Height vs. Input Photon Energy by testing with monoenergetic r...

In this study, the impact of crystal length on CdZnTe Frisch collar detector spectroscopic performance is investigated. Four different Frisch collar devices were designed to have identical aspect ratios of 2.0 for simulation purposes, and all four devices were later fabricated and tested. Pulse height spectra were acquired from all Frisch collar de...

A 4.7×4.7×9.5 mm3 Frisch collar device was fabricated from CdZnTe materials grown by the Traveling Heater Method (THM). The device was then characterized through probing with a highly collimated 662 keV gammaray source of 137Cs. In a systematic series of experiments, the detector, at its best design, was probed using a collimated 137Cs source. The...

The spectral performance as a function of the dielectric layer thickness for several CdZnTe Frisch collar devices was investigated. Seven different planar bar shaped detectors were fabricated from Redlen Technologies CdZnTe, and many Frisch collar devices were prepared from each planar device. The optimum dielectric layer thickness was experimental...

New methods, designed for the commercial-scale production of Frisch collar CdZnTe gamma ray spectrometers, are described in detail in the following work. Past methods required considerable skilled labor, were not readily automatable, and batch processing was only supported through a portion of the fabrication process. Advances in dielectric materia...

Cadmium Zinc Telluride (CdZnTe) has been used for many applications, such as medical imaging and astrophysics, since its first demonstration as a room temperature operating gamma-ray detector in 1992. The wide band gap, high effective Z-number and high resistivity of CdZnTe make it a good candidate for use as a room temperature operated detector wi...

Frisch-ring CdZnTe detectors have demonstrated both good energy resolution, <1% FWHM at 662 keV, and good efficiency in detecting gamma rays, highlighting the strong potential of CdZnTe materials for such applications. We are designing a hand-held gamma-ray spectrometer based on Frisch-ring detectors at Brookhaven National Laboratory. It employs an...

Surface passivation and final surface treatment on the lateral sides of CdZnTe/CdTe gamma ray detectors have been studied by many research groups. However, systematic studies of spectroscopic performance and the current voltage (I-V) characteristic behavior of devices as a result of surface treatments have not been conducted. Additionally, few stud...

New methods for the commercial-scale production of CdZnTe Frisch collar spectrometers were developed to reduce fabrication costs, increase process yields, and improve uniformity of performance across batches. Past methods required considerable skilled labor, were not readily automatable, and did not fully support batch processing. Low dielectric ma...

Compact neutron detectors are being designed and tested for use as wireless low-power real-time personnel dosimeters and for remote neutron sensing. The neutron detectors are pin diodes that are mass produced from high-purity Si wafers. Each detector has thousands of perforations etched vertically into the device. The perforations are backfilled wi...

The effects of crystal geometry and aspect ratio on a CdZnTe Frisch collar device were investigated. A 19.08x19.34x4.95mm3 device fabricated from CdZnTe grown by Redlen Technologies was used as the starting material. The crystal was re-fabricated many times to achieve several aspect ratios while the device length was held constant at 4.75+/-0.15mm....

Low dislocation density, high-purity, and low inclusion concentration Cd_0.9Zn_0.1Te (CZT) and CdTe crystals were grown by a vertical Bridgman technique using in-house zone refined precursors. The grown crystals were sequentially processed using optimized chemo-mechanical processes to fabricate planar and Frisch collar detectors...

Frisch-ring CdZnTe detectors have demonstrated good energy resolution for identifying isotopes, <1% FWHM at 662 keV, and good efficiency for detecting gamma rays. To facilitate the application of this detector in radiation detection, we are designing a portable device that can incorporate with an 8times8 Frisch-ring detector array. A prototype syst...

A collimated 198Au source was used to determine the charge collection efficiency (CCE) at several locations along the length of a 3.4×3.4×5.5 mm3 CdZnTe bar detector, both in planar configuration and with Frisch collars of varying length. For each configuration, a 0.50-mm-long region spanning the width of the device was irradiated with 411-keV gamm...

New methods, designed for the commercial-scale production of Frisch collar CdZnTe gamma ray spectrometers, are described in detail in the following work. Past methods required considerable skilled labor, were not readily automatable, and batch processing was only supported through a portion of the fabrication process. Advances in dielectric materia...

Frisch-ring CdZnTe detectors have demonstrated both good energy resolution, <1% FWHM at 662 keV, and good efficiency in detecting gamma rays, highlighting the strong potential of CdZnTe materials for such applications. We are designing a hand-held gamma-ray spectrometer based on Frisch- ring detectors at Brookhaven National Laboratory. It employs a...

Frisch-ring CdZnTe detectors have demonstrated good energy resolution for identifying isotopes, <1% FWHM at 662 keV, and good efficiency for detecting gamma rays. We will fabricate and test at Brookhaven National Laboratory an integrated module of a 64-element array of 6times6times12 mm³ Frisch-ring detectors, coupled with a readout elec...

A process has been developed to mass-produce CdZnTe bar-shaped pieces for Frisch ring detectors. Researchers at Brookhaven National Laboratory have assisted with the process, and have taken a special interest in this particular NEER project. The devices are cut and polished with precision lapping tools. Contacts are applied with electroless gold, a...

Low-energy γ-ray spectra were collected from 241Am, 57Co, 133Ba, 198Au, 137Cs and 235U using a 3.4×3.4×5.7 mm3 CdZnTe detector utilizing an insulated Frisch ring. The CdZnTe detector was fabricated from a single crystal and a copper shim was used as the Frisch collar. Room-temperature energy resolution of 1.45% full-width half-maximum (FWHM) was ob...

Cadmium Zinc Telluride (CdZnTe) has been used for many applications, such as medical imaging and astrophysics, since its first demonstration as a room temperature operating gamma-ray detector in 1992. The wide band gap, high effective Z-number and high resistivity of CdZnTe make it a good candidate for use as a room temperature operated detector wi...