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Research in ceramic scintillators has steadily progressed alongside the research in bulk single crystal scintillator growth. As interest in faster scintillation material production with lower cost increases, more research on scintillating ceramics is needed. Research targeting optimization of optically transparent ceramics that can rival bulk-grown crystals grown may lower cost, increase yield, increase volume, and improve energy resolution in applications and systems currently using sodium iodide and alike. Ceramic scintillators that are dense (>5 g/cm3), have high effective Z (>60), are bright (>40,000 photons/MeV), and are not sensitive to moisture as well as those that can be handled without protection are desired. Ultra-fast ceramic materials are also of interest. This paper presents an equipment design and technique to produce inorganic halide ceramic scintillators Cs2HfCl6 (CHC) and Tl2HfCl6 (THC). Improvements and optimization of CHC and THC ceramic scintillator fabrication are gauged by monitoring the energy resolution and peak position of 137Cs full energy peak at 662 keV. With a 1-inch diameter CHC ceramic scintillator, energy resolution of 5.4% (FWHM) and light yield of 20,700 ph/MeV are achieved, while with a 16-mm diameter THC ceramic scintillator, energy resolution of 5.1% (FWHM) and light yield of 27,800 ph/MeV are achieved. Decay times of 0.6 microseconds (21%) and 3.0 microseconds (79%) are measured for CHC and 0.3 microseconds (13%) and 1.0 microseconds (87%) for THC. Both ceramic CHC and THC scintillators have similarly good proportionality data when compared to their single crystal counterparts.

Gamma-ray detection and spectroscopy is the quantitative determination of their energy spectra, and is of critical value and critically important in diverse technological and scientific fields. Here we report an improved melt growth method for cesium lead bromide and a special detector design with asymmetrical metal electrode configuration that leads to a high performance at room temperature. As-grown centimeter-sized crystals possess extremely low impurity levels (below 10 p.p.m. for total 69 elements) and detectors achieve 3.9% energy resolution for 122 keV 57Co gamma-ray and 3.8% for 662 keV 137Cs gamma-ray. Cesium lead bromide is unique among all gamma-ray detection materials in that its hole transport properties are responsible for the high performance. The superior mobility-lifetime product for holes (1.34 × 10−3 cm2 V−1) derives mainly from the record long hole carrier lifetime (over 25 μs). The easily scalable crystal growth and high-energy resolution, highlight cesium lead bromide as an exceptional next generation material for room temperature radiation detection., Detection and spectroscopic measurements of gamma-ray used to rely on expensive materials such as CdZnTe crystals. Here He et al. develop a melt method to grow large size CsPbBr3 perovskite crystals and the devices achieve low cost, high energy resolving capabilities and stability.

For radiation detection, sensitivity, response time, and energy resolution are important. Scintillating nanoparticles, in principle, can have enhanced light output in comparison with their bulk materials due to quantum size confinement and increased overlap of electron and hole wave function. However, the aggregation and the loss of transparency at high loading into polymers are the challenging issues for practical applications. Here, for the first time, we report a new method to fabricate the blue-emitting nanocomposites with up to 30 wt% nanoparticle loading. First, the polymerizable surfactant coated La0.6Ce0.4F3 nanoparticles are synthesized, and then, they are loaded up to 30 wt% in a polystyrene matrix. The nanocomposites show an intense luminescence and a good transparency, performing much better than the commercial EJ-200 plastic scintillator. The gamma spectra acquired with the nanocomposite show a photopeak for the Co-57 isotope. The gamma spectra of Cs-137 show a full energy peak at around 622 keV, due to the escape of La and Ce Kα X-rays. The observation of the photopeaks is attributed to the enhanced photoelectric effect as a result of increased effective atomic number (Zeff). All these indicate that the high loaded nanocomposites are promising for radiation detection and nuclear material surveillance for homeland security.

Lithium based chalcogenides have many uses in the nuclear science field. 6LiInSe2 (or LISe) has been researched extensively because of its ability to operate in both scintillator and semiconductor modes. This makes it useful in applications including nuclear material detection for national security, space applications, and medical imaging. In some applications growth and fabrication costs are of concern, as it takes upwards of 40 days to synthesize a charge, grow a crystal and fabricate a detector. Ceramics are a solution for this long route of preparation. This research shows that using a 6LiInSe2 ceramic instead of a single crystal significantly decreases the time required to make a detector. In the present work, ceramic wafers can be formed using a mechanical press equipped with a heating attachment. The resulting ceramic wafer performs very similar to a slow-growth single crystal when used in the scintillator mode.

Strontium iodide (SrI 2 ), an important new scintillator crystal having a high light yield and excellent energy resolution, was grown for the first time by the edge-defined film-fed (EFG) growth method. Using high purity starting materials and floating dies made of graphite, fused quartz or AlN, large cylindrical, planar or square cross-section single crystals (12–15 mm across and >7 cm long) were produced at growth rates up to 15 mm/h, significantly faster than the current Bridgman growth technology. Details on the equipment used to grow this deliquescent material and on its growth behavior are given along with some discussion of crystalline quality.

Strontium iodide doped with europium (SrI 2:Eu2+ ) is a new scintillator being developed for use in high-energy astrophysical detectors with excellent energy resolution. Nonproportionality is the primary limiting factor to improving its energy resolution, although the physics of nonproportionality is not yet fully understood. In the past few years, co-dopants have been used to alter nonproportionality. By irradiating a SrI 2:Eu2+ sample with a 2255 Ci 137Cs source, we explore both the crystal's potential for space-based applications in a radiation environment and this new method of altering nonproportionality. At ~6200 Gy irradiation, a drop of 7.8% at 700 nm and a drop of 14.1% at 450 nm were seen in the transmission spectrum. Nonproportionality was also reduced after irradiation, shifting from 87% to 101% of the theoretical light yield at 32.1 keV, while the 4.7 keV peak decreased 40% closer to its theoretical value. We propose a novel method of altering the nonproportionality of scintillators, using radiation-induced F-centers in place of co-dopants.

Semiconducting lithium indium diselenide, 6 LiInSe 2 or LISe, has promising characteristics for neutron detection applications. The 95% isotopic enrichment of 6 Li results in a highly efficient thermal neutron-sensitive material. In this study, we report on a proof-of-principle investigation of a semiconducting LISe pixel detector to demonstrate its potential as an efficient neutron imager. The LISe pixel detector had a 4×4 of pixels with a 550 µm pitch on a 5×5×0.56 mm 3 LISe substrate. An experimentally verified spatial resolution of 300 µm was observed utilizing a super-sampling technique.

Cerium-doped lutetium aluminum garnet (LuAG:Ce) and yttrium aluminum garnet (YAG:Ce) transparent ceramics of same dimension were fabricated and their optical and scintillation properties were studied. LuAG:Ce transparent ceramic showed higher light yield under UV and X-ray excitation with respect to YAG:Ce transparent ceramic. YAG:Ce transparent ceramic showed higher light yield under gamma excitation and better energy resolution, which could be due to the considerable amount of slower emission (38.5%) in LuAG:Ce as well as lower optical transparency with respect to YAG:Ce ceramic.

6LiInSe2 has gained attention recently as a semiconducting thermal neutron detector. As presented herein, the chalcogenide compound semiconductor also detects incident neutrons via scintillation, making 6LiInSe2 the only lithium containing semiconductor to respond to neutrons via both detection mechanisms. Both yellow and red crystals, which appear in the literature, were investigated. Only the yellow crystal responded favorably to ionizing radiation, similar to the semiconducting operation utilizing electrodes. The obtained light yield for yellow crystals is 4400 photons/MeV, referenced to Bi4Ge3O12 (BGO).The estimated thermal neutron light yield was 21,000 photons/thermal neutron. The two measured decay time components were found to be 31±1 ns (49%) and 143±9 ns (51%).This crystal provides efficient, robust detection of neutrons via scintillation with respectable light yield and rapid response, enabling its use for a broad array of neutron detection applications.

The performance of Cd1−x Zn x Te (CZT) materials for room-temperature gamma/x-ray radiation detection continues to improve in terms of material quality and detector design. In our prior publications, we investigated the use of multiple wavelengths of light (in the visible and infrared) to target charge carriers at various trap energies and physical positions throughout crystals. Light exposure significantly alters the charge mobility and improves carrier collection at the anode contact. This study presents an investigation of material performance as a radiation detector during such illumination. The decrease in charge trapping and increase in charge collection due to a higher probability of free electron release from traps contributed to an increase in the resolution-based performance of the detector through controlled illumination. We investigated the performance improvement of CZT crystals with previously known levels of intrinsic defects and secondary phases, at various voltages, light-emitting diode (LED) light wavelengths, and shaping times. Although our setup was clearly not optimized for radiation detector performance, it demonstrated substantial resolution improvements (based on full-width at half-maximum using 662-keV gamma rays from 137Cs upon illumination with 950-nm light) of 16% to 38% in comparison with unilluminated CZT under similar conditions. This manuscript includes discussion of the electrooptic behavior and its effect on performance. Additional testing and fabrication of a detector that incorporates such LED light optimization could lead to improved performance with existing detector-grade materials.

The material lithium indium diselenide, a single crystal neutron sensitive semiconductor, has demonstrated its capabilities as a high resolution imaging device. The sensor was prepared with a 55 μ m pitch array of gold contacts, designed to couple with the Timepix imaging ASIC. The resulting device was tested at the High Flux Isotope Reactor, demonstrating a response to cold neutrons when enriched in 95% 6 Li. The imaging system performed a series of experiments resulting in a

Intrinsic materials can offer advantages over doped materials for some important applications. The doped material might suffer from non-uniform distribution of the dopant, such as fine-scale striations and larger scale segregation, which might affect the overall device response, especially for large-volume detectors such as those in demand for homeland security applications for gamma spectroscopy. Cs2LiCeCl6 (CLCC), being an intrinsic scintillator, can be grown in large volume to produce large detectors with good performance, provided the crystals are free from unwanted scattering centers. CLCC belongs to the elpasolite family and the structure is cubic, so large-volume ingots can be grown without the strains resulting from anisotropic thermal expansion coefficients. In this presentation, we will discuss extensive material characterization and device response of CLCC for gamma and thermal neutron detector applications.

Gadolinium Garnet transparent ceramics doped with Ce, ((Gd,Y,Ce)3(Ga,Al)5O12), for gamma-ray spectroscopy provide high density, high light yield, high energy resolution , high Z, mechanical robustness, and they are unreactive to air and water. Gadolinium garnet single crystals are costly to grow, due to their high melting points, and suffer from non-uniform light yield, due to Ce segregation. In contrast, transparent polycrystalline ceramic Garnets are never melted, and therefore are less costly to produce and provide the uniform light yield required to achieve high energy resolution with a scintillator. GYGAG(Ce) transparent ceramics offer energy resolution as good as R(662 keV) = 3.5%, in a pixelated detector utilizing Silicon photodiode array readout. We have developed a modular handheld detector based on pixelated GYGAG(Ce) on a photodiode array, that offers directional detection for point source detection as well as gamma spectroscopy. Individual modules can be assembled into detectors ranging from pocket-size to large panels, for a range of applications. Large GYGAG(Ce) transparent ceramics in the 2-5 in3 size range have been fabricated at LLNL. Instrumentation of these ceramics with Silicon photomultipliers (SiPMs) and super bi-alkali PMTs has been explored and energy resolution as good as R(662 keV) = 5% has been obtained. Further improvements with SiPM readout will leverage their high quantum efficiency in the 500-650 nm range where GYGAG(Ce) emits, and implement electronics that minimize the effect of SiPM dark current and capacitance on the pulse height spectra. This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded IAA HSHQDC-12-X-00149 under Contract No. DE-AC03-76SF00098. LLNL-ABS-724480.

Alloying of CdZnTe (CZT) with selenium has been found to be very promising and effective in reducing the overall concentration of secondary phases (Te precipitates/inclusions) and sub-grain boundary networks in the crystals. These two types of defects are the main causes for incomplete charge collection, and hence they affect the yield of high-quality CZT, resulting in a very high cost for large-volume, high-quality detector-grade CZT detectors. The addition of selenium was also found to very effective in increasing the compositional homogeneity along the growth direction of the CdZnTeSe (CZTS) ingots grown by the traveling heater method (THM) technique. The compositional homogeneity along the growth direction can enhance the overall yield of detector-grade CZTS, which should therefore be possible to produce at a lower cost compared to CZT. The electrical properties and detector performance of the CZTS crystals will be presented and discussed.

High-resolution position-sensing has been proposed to correct response non-uniformities in Cadmium Zinc Telluride (CZT) gamma ray detectors by virtually subdividing the area into small voxels and equalizing responses from each voxel. 3D pixelated detectors coupled with multichannel readout electronics are the most advanced type of CZT devices offering many options in signal processing and enhancing detector performance. The main hurdle in achieving high sub-pixel position resolution is the relatively low signal induced on the neighboring pixels because of the electrostatic shielding effect caused by the collecting pixel. In addition, to achieve high position sensitivity one should rely on time-correlated transient signals, which means that digitized output signals must be used. Previous results have shown the benefit of using a focused laser beam to study position resolution in 3D pixelated detectors. We present the results of our studies to measure the amplitude of the pixel signals so that these can be used to measure positions of the interaction points. This is done with the processing of digitized correlated time signals measured from several adjacent pixels taking into account rise-time and charge-sharing effects. In these measurements we used a focused pulsed laser to generate a 10-micron beam at one milliwatt (650-nm wavelength) over the detector surface while the collecting pixel was moved in cardinal directions. The results include measurements that present the benefits of combining conventional pixel geometry with digital pulse processing for the best approach in achieving sub-pixel position resolution with different pixel dimensions ranging from 0.5 mm to 1.72 mm.

Eu-doped strontium iodide single crystal growth has reached maturity and prototype SrI2(Eu)-based gamma ray spectrometers provide detection performance advantages over standard detectors. SrI2(Eu) offers a high, proportional light yield of >80,000 photons/MeV. Energy resolution of

We present a preliminary design for a novel neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide ( 6 LiInSe 2 ), the first crystal to include 6Li in the crystalline structure, and a silicon avalanche photodiode (Si-APD). The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha, gamma and neutron radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10 cm x 10 cm x 15 cm, weighs 670 grams and requires 5 V direct current at 3 Watts.

Inspired by biological multicontrollability, we have devised the concept of multicontrollable metasurfaces. Comprising electrically small elements called MetaAtoms, a metasurface could be either homogeneous or graded on the wavelength scale for operation in the terahertz regime. The MetaAtoms would comprise diverse pixels each of which is made of magnetically controlled, thermally controlled, electrically controlled, or optically controlled material. Stacks of parallel multicontrollable metasurfaces would function as multicontrollable metamaterials.

In the pursuit of ultrasmall electronic components, monolayer electronic devices have recently been fabricated using transition-metal dichalcogenides. Monolayers of these materials are semiconducting, but nanowires with stoichiometry MX (M = Mo or W, X = S or Se) have been predicted to be metallic. Such nanowires have been chemically synthesized. However, the controlled connection of individual nanowires to monolayers, an important step in creating a two-dimensional integrated circuit, has so far remained elusive. In this work, by steering a focused electron beam, we directly fabricate MX nanowires that are less than a nanometre in width and Y junctions that connect designated points within a transition-metal dichalcogenide monolayer. In situ electrical measurements demonstrate that these nanowires are metallic, so they may serve as interconnects in future flexible nanocircuits fabricated entirely from the same monolayer. Sequential atom-resolved Z-contrast images reveal that the nanowires rotate and flex continuously under momentum transfer from the electron beam, while maintaining their structural integrity. They therefore exhibit self-adaptive connections to the monolayer from which they are sculpted. We find that the nanowires remain conductive while undergoing severe mechanical deformations, thus showing promise for mechanically robust flexible electronics. Density functional theory calculations further confirm the metallicity of the nanowires and account for their beam-induced mechanical behaviour. These results show that direct patterning of one-dimensional conducting nanowires in two-dimensional semiconducting materials with nanometre precision is possible using electron-beam-based techniques.

Cd0.9Zn0.1Te (CZT) based pixelated radiation detectors have been fabricated and characterized for gamma ray detection. Large area CZT single crystals has been grown using a tellurium solvent method. A 10 ×10 guarded pixelated detector has been fabricated on a ~ 19.5 ×19.5 ×5 mm3 crystal cut out from the grown ingot. The pixel dimensions were 1.3 ×1.3 mm2 and were pitched at 1.8 mm. A guard grid was used to reduce interpixel/inter-electrode leakage. The crystal was characterized in planar configuration using electrical, optical and optoelectronic methods prior to the fabrication of pixelated geometry. Current-voltage (I-V) measurements revealed a leakage current of 27 nA at an operating bias voltage of 1000 V and a resistivity of ~ 3.1 ×1010 Ω-cm. Infrared transmission imaging revealed an average tellurium inclusion/precipitate size less than 8 μm. Pockels measurement has revealed a near-uniform depth-wise distribution of the internal electric field. The mobility-lifetime product in this crystal was calculated to be 6.2 ×10 - 3 cm2/V using alpha ray spectroscopic method. Gamma spectroscopy using a 137Cs source on the pixelated structure showed fully resolved 662 keV gamma peaks for all the pixels, with percentage resolution (FWHM) as high as 1.8%.

Our review offers an overview of the Traveling Heater Method (THM) for growing crystals of CdZnTe, the most important semiconductor material available today for fabricating nuclear detectors operable at room temperature. The review compares the advantages of the THM technique with respect to melt growth techniques, and details the development and improvements in the technique from its start to the present day. It is known that the optimization of the growth parameters is highly dependent on the height of the Te-rich CZT molten zone, which in turn governs the shape of the growth interface. Special attention is paid to understand the effect of the Te-rich CZT molten zone on the growth interface (both microscopic and macroscopic) to improve the uniformity and overall quality of the grown crystals. We conclude that this technique affords us the best method today for consistently producing large homogenous detectors in mass quantities with a thickness up to 15 mm. Such detectors are need for many national-security and medical-imaging applications.

We present a review on mercuric iodide technology for room temperature gamma radiation detection. After four decades of research and development the material is attractive for a number of applications for x-ray and gamma-ray imagers with performances that match all competing materials. The crystal growth of large single crystals is challenging; however the high resistivity of 1013 Ω cm, the undoped, as-grown crystals and the high radiation damage remaining features that are not exhibited by any other wide bandgap semiconductor materials.

The variation in bulk resistivity during infrared (IR) illumination above 950 nm of state-of-the-art CdZnTe (CZT) crystals grown using the traveling heating method or the modified Bridgman method is documented. The change in steady-state current with and without illumination is also evaluated. The influence of secondary phases (SP) on current–voltage (I–V) characteristics is discussed using IR transmission microscopy to determine the defect concentration within the crystal bulk. SP present within the CZT are connected to the existence of deep, IR-excitable traps within the bandgap.

CdZnTe-based gamma detectors require a reduction of electronic noise contributed by apparent device and surface leakage current, especially for advanced readout schemes such as the Co-planar Grid or Pixelated Grid. In this work, we describe a combination of surface treatments and amorphous semiconductor layers that result in a reduction of both apparent device and surface leakage current compared to metal contacts on Br:MeOH etched devices. Characterization by scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), current-voltage (IV), and pulse height spectra is performed.

Lithium Indium Selenide (LiInSe2) has been under development in RMD Inc. and Fisk University for room temperature thermal neutron detection due to a number of promising properties. The recent advances of the crystal growth, material processing, and detector fabrication technologies allowed us to fabricate large detectors with 100 mm2 active area. The thermal neutron detection sensitivity and gamma rejection ratio (GRR) were comparable to 3He tube with 10 atm gas pressure at comparable dimensions. The synthesis, crystal growth, detector fabrication, and characterization are reported in this paper.

Recent renewed emphasis placed on gamma-ray detectors for national security purposes has motivated researchers to identify and develop new scintillator materials capable of high energy resolution and growable to large sizes. We have discovered that SrI2(Eu) has many desirable properties for gamma-ray detection and spectroscopy, including high light yield of ∼90,000 photons/MeV and excellent light yield proportionality. We have measured

In this article we report the evaluation of thick (up to 10 mm) as-grown Cd0.9Zn0.1Te(CZT):In detectors fabricated from ingots grown by traveling heater method (THM). The crystals were investigated by mapping the electron mobility (μe), (μτ)e and the internal electric field of as-grown CZT samples. The detector performance was also evaluated in co-planar grid geometry. The excellent (μτ)e value and the detector performance of 10 mm thick as-grown detectors is the indication that the THM technique can be employed successfully to fabricate the detectors directly from the as-grown boule at substantially lower cost.

New scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized. Our development efforts have focused on two classes of high-light-yield materials: europium-doped alkaline earth halides and cerium-doped garnets. Of the halide single crystals we have grown by the Bridgman method-SrI2, CaI2, SrBr2, BaI2 and BaBr2-SrI2 is the most promising. SrI2(Eu) emits into the Eu2+ band, centered at 435 nm, with a decay time of 1.2 mus and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3% FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramic fabrication allows the production of gadolinium- and terbium-based garnets which are not growable by melt techniques due to phase instabilities. The scintillation light yields of cerium-doped ceramic garnets are high, 20,000-100,000 photons/MeV. We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance the energy resolution.

Synthetic Cd1–xZnxTe or “CZT” crystals are highly suitable for γ-spectrometers operating at room temperature. Secondary phases (SP) within CZT, presumed to be Te metal, have detrimental impacts on the charge collection efficiency of fabricated device. Using analytical techniques rather than arbitrary theoretical definitions, we identify two SP morphologies: (i) many void, 20-μm “negative” crystals with 65-nm nanoparticle residues of Si, Cd, Zn, and Te and (ii) 20-μm hexagonal-shaped bodies, which are composites of metallic Te layers with cores of amorphous and polycrystalline CZT material that surround the voids.

We present a preliminary design for a novel neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide ($^6$LiInSe$_2$), the first crystal to include $^6$Li in the crystalline structure, and a silicon avalanche photodiode (Si-APD). The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10 cm x 10 cm x 15 cm, weighs 670 grams and requires 5 Volts direct current at 3 Watts., Comment: 14 pages, 6 figures

AgInSe2 (AIS) films were grown on n-type Si substrates by the ultra-high-vacuum pulsed laser deposition technique from the AIS target synthesized from high-purity materials. The X-ray diffraction and microscopic studies of the films show that films are textured having terrace-like surface morphology. The optical studies of the films show that the optical band gap is about 1.24 eV. The electrical conductivity of AgInSe2/Si films shows excellent diode characteristics. The photoconductivity of the AgInSe2/Si device shows photocurrent of 2.8 mA at a bias-voltage of − 1 V with an open circuit voltage of 0.15 V. This shows that AIS films are very good absorber material for solar cell technology.

Lithium indium diselenide (6LiInSe2) has drawn interest in recent years as a thermal neutron detector due to its high volumetric thermal neutron detection efficiency. Enriched in 6Li, the single crystalline semiconductor can reach thermal neutron detection efficiencies approaching 80% at thickness of 0.5 cm. With a Q-value of 4.78 MeV, the material also offers neutrongamma discrimination capabilities. Identification and implementation of a contact scheme that is both robust and reproducible is important for its commercial potential. Thorough testing of a myriad of contact schemes yielded a viable Ohmic contact with sufficient adhesion to endure gold wire wedge bonding. Furthermore, characterization of the semiconducting properties, such as the charge carrier mobility-lifetime constant of this material as a radiation detector is important to identify the application space of this material. Using the single charge carrier approximation to the Hecht relation, the electron mobility-lifetime product was found to be on the order of 3.8–90 cm2/V with a mean ionization energy of 400 eV/e-h pair.

The detection of thermal neutrons has traditionally been accomplished with 3 He-tubes, but with the recent shortage of 3 He, much research has gone into finding suitable replacements. Both relatively inefficient 10 B- and 6 LiF-coated silicon diodes and HgI 2 have been known for many years, and engineered structures in Si that have been filled with 10 B and 6 LiF have shown promise. These devices are intended to realize an optimal juxtaposition of neutron-sensitive material and semiconductor and thereby simulate a semiconductor containing B or Li. Such material has been realized for the first time in the form of 6 LiInSe 2 in which collectable charge from the 6 Li(n,t) reaction indicates a neutron event. In this paper we report neutron and gamma responses of 6 LiInSe 2 , we show pulse height spectra from pure gamma sources and from a thermal neutron source, and we derive the μτ product from the position of spectral features as a function of bias voltage. In addition, we demonstrate the observation of the beta decay of 116m In in samples exposed to thermal neutrons. This feature of the response serves as an additional confirmation of exposure to neutrons.

The three most important desirable features in the search for room temperature semiconductor detector (RTSD) candidate as an alternative material to current commercially off-the-shelf (COTS) material for gamma and/or thermal neutron detection are: low cost, high performance and long term stability. This is especially important for pager form application in homeland security. Despite years of research, no RTSD candidate so far can satisfy the above 3 features simultaneously. In this work, we show that mercurous halide materials Hg2X2 (X= I, Cl, Br) is a new class of innovative compound semiconductors that is capable of delivering breakthrough advances to COTS radiation detector materials. These materials are much easier to grow thicker and larger volume crystals. They can detect gamma and potentially neutron radiation making it possible to detect two types of radiation with just one crystal material. The materials have wider bandgaps (compared to COTS) meaning higher resistivity and lower leakage current, making this new technology more compatible with available microelectronics. The materials also have higher atomic number and density leading to higher stopping power and better detector sensitivity/efficiency. They are not hazardous so there are no environmental and health concerns during manufacturing and are more stable making them more practical for commercial deployment. Focus will be on Hg2I2. Material characterization and detector performance will be presented and discussed. Initial results show that an energy resolution better than 2% @ 59.6 keV gamma from Am-241 and near 1% @ 662 keV from Cs-137 source can be achieved at room temperature.

The common methods of neutron detection are reviewed with special attention paid to the application of cryogenics and semiconductors to the problem. The authors' work with LiF- and boron-based cryogenic instruments is described as well as the use of CdTe and HgI{sub 2} for direct detection of neutrons.

Cadmium zinc telluride (CZT) is one of the most promising materials for large-volume gamma-ray spectrometers and imaging arrays. However, because of deficiencies in the high quality material, high-resolution CZT spectrometers are still limited to relatively small dimensions (

The effects of polishing on the electron mobility-lifetime product of a detector-grade Cd/sub 1-x/Zn/sub x/Te (CZT) crystal is reported. The two surfaces of the crystal were deposited with Au layers and illuminated with subband light. A direct current (dc) photocurrent technique was used to measure the electron mobility-lifetime product as a function of the illuminating power. The measured dependence of the electron mobility-lifetime product on the photogenerated electron concentration was highly affected by the condition of the irradiated surface. This discovery has important implications for processing of CZT surfaces for radiation detector applications.

We report the effects of different etchants on the mobility-lifetime product (/spl mu//spl tau/) of cadmium zinc telluride (CZT). The /spl mu//spl tau/ values were obtained via the Hecht relation. The effects of surface recombination were also investigated using photoconductivity measurements. Results were obtained for a {111} oriented CZT single crystal. We find that the surfaces behave differently after etching. Values for surface recombination rates for [111]A and [111]B surfaces can vary by up to two orders of magnitudes for the same etchant. This large variation in surface recombination rates affects the charge collection efficiency and detector performance. We report surface treatments that enhance the charge collection efficiency for [111]A and [111]B surfaces. Data describing the detector response for Am/sup 241/ spectra current-voltage relationship, and bulk /spl mu//spl tau/ values and surface recombination rates are shown for different etchants.

The change in bulk resistivity of CdZnTe (CZT) crystals was measured during infrared (IR) light between 950 and 1000 nm. The crystals are grown using one of the state-of-the-art methods either the traveling heating method or the modified Bridgman method. The change resistivity was evaluated using the steady-state current with and without light. Additionally, the change in current with both IR sources were correlated to the influence of secondary phases (SP) in each crystal using IR transmission microscopy to determine whether the number and size of the impurities has a drastic effect based on the current-voltage (IV) characteristics. SP at various depths within CZT are connected to the existence of variable depth, IR-excitable traps that lie within the bandgap. The release of these traps will significantly affect the overall current in the system. However, the current increase may not match the overall energy of the light utilized are more dependent on the size and quantity for each energy range.

The development of a thermal neutron imaging sensor constructed with semiconducting lithium indium diselenide is presented. Both a computational and experimental investigation were conducted. In the computational investigation, it is shown that the imaging potential of Lithium Indium Diselenid (LISe) is excellent, even when using a large pixel pitch through the use of super sampling. In the experimental investigation, it was found that a single pixel LISe detector using detector super sampling shows a spatial variation in the count rate, which is a clear sign of imaging capability. However, a good image was not obtained in the first experiment and may be caused by a variety of experimental conditions. Finally, a search is still underway to find a suitable contact metal with good mechanical adhesion for wedge bonding.

Alkaline-earth scintillators such as strontium iodide and other alkaline-earth halides activated with divalent europium represent some of the most efficient and highest energy resolution scintillators for use as gamma-ray detectors in a wide range of applications. These applications include the areas of nuclear nonproliferation, homeland security, the detection of undeclared nuclear material, nuclear physics and materials science, medical diagnostics, space physics, high energy physics, and radiation monitoring systems for first responders, police, and fire/rescue personnel. Recent advances in the growth of large single crystals of these scintillator materials hold the promise of higher crystal yields and significantly lower detector production costs. In the present work, we describe new processing protocols that, when combined with our molten salt filtration methods, have led to advances in achieving a significant reduction of cracking effects during the growth of single crystals of SrI 2 :Eu 2+ . In particular, we have found that extended pumping on the molten crystalgrowth charge under vacuum for time periods extending up to 48 hours is generally beneficial in compensating for variations in the alkaline-earth halide purity and stoichiometry of the materials as initially supplied by commercial sources. These melt-pumping and processing techniques are now being applied to the purification of CaI 2 :Eu 2+ and some mixed-anion europium-doped alkaline-earth halides prior to single-crystal growth by means of the vertical Bridgman technique. The results of initial studies of the effects of aliovalent doping of SrI 2 :Eu 2+ on the scintillation characteristics of this material are also described.

Room temperature direct current (DC) photocurrents were measured for detector grade Cd1−xZnxTe (CZT) crystals in the spectral range of 400–1000 nm as a function of light intensity and voltage. The photocurrent data were analyzed and fit to a theoretical model to extract the electrical transport properties for high-resistivity detector grade CZT material. Using the DC photocurrent measurements, the mobility-lifetime () products and the surface recombination velocities for both electrons and holes were measured. For this study the CZT detectors had Au contacts, and the surfaces were treated in a standard 5% bromine in methanol etching solution. The correlation of the DC photocurrent measurements and detector performance is also reported.

This paper reviews some of the progress obtained in the understanding of defects in detector grade cadmium zinc telluride material (CZT). Several techniques have been utilized to elucidate some of the issues related to compositional uniformity, effects of precipitates, grain boundaries, and surface defects related to mechanical and chemical treatments. In few cases, special mapping capabilities had to be developed to allow correlations with detector performance.

A large photorefractive effect was measured in CdS0.8Se0.2:V and Cd0.55Mn0.45Te:V ternary crystals which shows promise for many device applications such as optical signal processing and optical limiting. In this study, we compared the results obtained from two-wave mixing experiments with Cd0.55Mn0.45Te:V and CdS0.8Se0.2:V crystals at the 633 nm wavelength. As the signal to pump beam ratio was varied from 10−1 to 10−4, Cd0.55MN0.45Te:V and CdS0.8Se0.2:V showed a maximum photorefractive gain of 0.17 and 0.20 cm−1, respectively. The grating formation time of both the crystals were measured to be in the milli-second range at an incident intensity of 200 mW/cm2.

We report for the first time on the characteristics of large volume (4 cm×4 cm×0.5 cm) cadmium zinc telluride gamma-ray imaging arrays produced by IMARAD Imaging Systems. These arrays are shown to posses high uniformity of response to gamma-photons in the energy range of about 50 to over 600 keV. High resolution photopeaks have been obtained without any pulse processing or compensation techniques. Excellent peak-to-valley ratios, good efficiencies, and acceptable leakage currents have been measured. In addition measurements of the internal electric field indicate that the field is uniform and does not appear to be confined to only one region of the detector volume. Low temperature photoluminescence spectroscopy shows that the dominant peaks are different than those typically observed in high quality HPB material of the same composition obtained from other vendors. We believe that this material and the arrays that may be produced from it represent a significant step forward in the technology of room temperature semiconductor gamma and x-ray spectrometers.

In the past several years significant progress has been made in building a database of physical properties for detector quality Cd x Zn 1− x Te (CZT) ( x =0.1–0.2) crystal material. CZT's high efficiency combined with its room temperature operation make the material an excellent choice for imaging and spectroscopy in the 10–200 keV energy range. For detector grade material, superior crystallinity and high bulk resistivity are required. The surface preparation during the detector fabrication plays a vital role in determining the contact characteristics and the surface leakage current, which are often the dominant factors influencing its performance. This paper presents a surface and contact characterization study aimed at establishing the effects of the surface preparation steps prior to contacting (polishing and chemical etching), the choice of the metal and contact deposition technique, and the surface oxidation process. A photoconductivity mapping technique is used for studying the effects of different surface treatments on the surface recombination.

Cadmium manganese telluride (Cd 1− x Mn x Te) is a diluted magnetic semiconductor material which forms the basis for many important devices such as IR detectors, solar cells, magnetic field sensors, optical isolators, and visible and near IR lasers. High resistivity (>10 10 Ω cm) and high μ τ (>10 −6 cm 2 /V) material, which are the two prerequisites in the fabrication of radiation detectors, has recently been demonstrated at Brimrose Corp. This paper presents the crystal growth of intentionally vanadium doped crystals, the surface preparation and contacting procedure, as well as the best detector performance obtained so far. Dark current characteristics, and low temperature photoluminescence results are also presented and discussed.

The material showing the greatest promise today for production of large-volume gamma-ray spectrometers operable at room temperature is cadmium zinc telluride (CZT). Unfortunately, because of deficiencies in the quality of the present material, high-resolution CZT spectrometers have thus far been limited to relatively small dimensions, which makes them inefficient at detecting high photon energies and ineffective for weak radiation signals except in near proximity. To exploit CZT fully, it will be necessary to make substantial improvements in the material quality. Improving the material involves advances in the crystallinity, purity, carrier lifetimes, and control of the electrical compensation mechanism. A more detailed understanding of the underlying material problems limiting the performance of CZT gamma-ray detectors is required; otherwise, problems with supply, delivery times, and unit cost of large-volume (>5 cm3 active volume) CZT spectrometers are expected to continue. A variety of analytical and numerical techniques have been employed to quantify crystallinity, strain, impurities, compositional and stoichiometric variations, bulk and surface defect states, carrier mobilities and lifetimes, electric field distributions, and surface passivation. Data from these measurements were correlated with spatial maps of the gamma-ray and alpha particle spectroscopic response, and feedback on the effectiveness of crystal growth and detector fabrication procedures has been generated. The results of several of these analytical techniques will be presented in this paper.

Transition-metal-doped zinc chalcogenide crystals have recently been investigated as potential mid-infrared lasers. Tetrahedrally coordinated Cr/sup 2+/ ions are especially attractive as lasants on account of high luminescence quantum yields for emission in the 2000-3000-nm range. Radiative lifetimes and emission cross sections of the upper /sup 5/E state are respectively /spl sim/10 /spl mu/s and /spl sim/10/sup -18/ cm/sup 2/. The associated absorption band peaked at /spl sim/1800 mm enables laser-diode pumping of the Cr/sup 2+/ systems. Laser demonstrations with ZnS:Cr and ZnSe:Cr (using a MgF/sub 2/:Co/sup 2+/ laser pump source) gave slope efficiencies up to 30%. Excited-state-absorption losses appear small, and passive losses dominate at present. Tuning experiments with a diffraction grating produce a tuning range covering at least 2150-2800 nm. Laser crystals can be produced by Bridgman growth, seeded physical vapor transport, or diffusion doping. Zinc chalcogenide thermomechanical properties of interest for medium-to-high-power operation compare favorably with those of other host materials, except for the larger refractive-index derivative dn/dT.