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A novel type of Yb:YAG transparent ceramic thin disk laser amplifier is demonstrated, based on fabricating a composite gain element with a paraboloidal interface between gain and no-gain regions and employing side-pumping of the thin disk. The pump-induced gain and the impact of amplified spontaneous emission on the achievable inversion are reported.

Perovskites are particularly promising for flexible solar cell applications, because of low-cost and facile integration to flexible substrates. Flexible substrates, however, require lower processing temperatures. Reducing the processing temperature to accommodate inexpensive flexible substrates was a central challenge in this work. Air stability and moisture resistance were improved through molecular engineering of the perovskite materials using an advanced formula containing multiple cations, and through device structure optimization. A spin-coating based solution process was optimized to grow highly crystalline perovskite films within a few seconds in air. Integrated perovskite solar cell module shows enhanced air stable and moisture resistance, with an average efficiency reaching 17% on flexible substrates. We also demonstrate the feasibility of scale-up using slot die coating, up to 100 mm x 75 mm in size.

Nuclear power plants regularly generate spent fuel that must be stored on the decade timescale. Often this is done in dry nuclear waste storage casks. Long-term monitoring would provide data that improves the safe maintenance of stored spent fuel. This requires measuring the conditions within waste casks using a self-contained sensor system. Radiation Monitoring Devices, Inc. is developing a system that detects damaged fuel rod cladding by sensing and quantifying the amount of 85Kr present using a diamond sensor. A potential means for power and data transfer through the cask wall uses an ultrasonic transmission method. The work described here advances the prototype toward inclusion in a specific model fuel cask, the NUHOMS® 32 PTH1 manufactured by Orano (formally, Areva Transnuclear, Inc.). The results include extensive radiological modeling studies, an estimation of the leaked activity due to 85Kr after a cladding breach (~ 1013Bq) derived from a literature review, a design for a prototype, and the characterization of a diamond detector at room temperature and in the presence of 85Kr.

Results from testing of position-sensitive capacitive Frisch-grid (PSCFG) TIBr gamma-ray detectors are presented. Due to its high atomic number, high density, and low Fano factor, TIBr offers excellent energy resolution and high detection efficiency over a wide energy range, thus providing significant advantages over other detector materials commonly used in hand-held instruments. Using high-fidelity 3-D position sensing enables the response non-uniformity caused by defects in the TIBr crystal to be corrected, thereby offering an approach to overcome one of the technical barriers limiting the use of this promising semiconductor material. By utilizing the 3-D position information, temporal and spatial variations of the charge collection efficiency are presented, which provide microscopic characterization of the PSCFG devices. Using the 3-D response correction technique, the best energy resolution measured is

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 as a semiconductor detector material. The recent advances of the crystal growth, material processing, and detector fabrication have led to semiconductor neutron detectors with up to 100 mm2 active area. The theoretical thermal neutron detection sensitivity and gamma rejection ratio (GRR) are comparable to 10 atm, 3He tubes of similar size. Detector fabrication and characterization are described and the results are discussed.

Room-temperature operable semiconductor gamma-ray detectors offer the potential of superior energy resolution compared to scintillators, which can be valuable in the design of radionuclide identification equipment. To achieve the best energy resolution and simultaneously provide good sensitivity, multiple detection elements must be arrayed to operate in parallel. This paper describes efforts to construct such an array from multiple elements of thallium bromide (TlBr), a material that inherently offers a high interaction probability and photopeak efficiency for gamma rays. The base design of the array comprises capacitive Frisch grid (CFG) elements. A key objective is optimizing the energy resolution of each element, for which the single-carrier characteristics of the CFG design were chosen. Gains are realized through signal processing that accounts for 1-D or 3-D material inhomogeneity and charge collection variations. Fully corrected energy resolution reaches values of 1.6% FWHM at 662 keV.

Radiation therapy is one of the primary therapeutic techniques for treating cancer, administered to nearly two-thirds of all cancer patients. Although largely effective in killing cancer cells, radiation therapy, like other forms of cancer treatment, has difficulty dealing with hypoxic regions within solid tumors. The incomplete killing of cancer cells can lead to recurrence and relapse. The research presented here is investigating the enhancement of the efficacy of radiation therapy by using scintillating nanoparticles that emit UV photons. UV photons, with wavelengths between 230 nm and 280 nm, are able to inactivate cells due to their direct interaction with DNA, causing a variety of forms of damage. UV-emitting nanoparticles will enhance the treatment in two ways: first by generating UV photons in the immediate vicinity of cancer cells, leading to direct and oxygen-independent DNA damage, and second by down-converting the applied higher energy X-rays into softer X-rays and particles that are more efficiently absorbed in the targeted tumor region. The end result will be nanoparticles with a higher efficacy in the treatment of hypoxic cells in the tumor, filling an important, unmet clinical need. Our preliminary experiments show an increase in cell death using scintillating LuPO4:Pr nanoparticles over that achieved by the primary radiation alone. This work describes the fabrication of the nanoparticles, their physical characterization, and the spectroscopic characterization of the UV emission. The work also presents in vitro results that demonstrate an enhanced efficacy of cell killing with x-rays and a low unspecific toxicity of the nanoparticles.

The Majorana nature of neutrinos is one of the most important questions being pursued in physics today. This has given the search for neutrinoless double-beta decay (0 ν β β ) a high priority among proposed nuclear physics experiments. In this work, the objective was to evaluate several crystal compositions for possible use as a scintillating bolometer in 0 ν β β research. A crucial characteristic of the investigated crystals is that their compositions must include one of the few elements known to decay with double-beta emission. Therefore, we grew crystals containing molybdenum or selenium as a major constituent. Results are presented here for single-crystals of sodium molybdate and lithium indium diselenide. Scintillating bolometer data were measured at milli-Kelvin temperature and show good discrimination between alpha and beta/gamma emissions, which is crucial for background reduction. The lithium indium diselenide crystal was also used to measure the energy spectrum for the beta emission of indium decay, the first time a beta decay spectrum has been measured from self-emission in a scintillating bolometer.

Background and purpose Radiation therapy is the gold standard treatment for inoperable malignant tumors. However, due to the heterogeneity of the tumor, some regions are more radio resistant and can lead to metastasis and tumor recurrence. In this study, we propose combining traditional X-ray treatment with UVC-emitting LuPO4:Pr3+ nanoparticles (NPs) to increase the tumor control as well as to reduce tumor recurrence and metastasis. These NPs convert ionizing radiation into UVC-photons (UVC range: 200–280 nm) locally at the tumor site. Unlike X-ray, UVC-photons damage DNA directly via an oxygen-independent mechanism, which could improve treatment of radioresistant tumors such as hypoxic tumors. Materials and methods The effect of X-ray generated UVC-photons was tested on human fibroblasts incubated with NPs prior to radiation treatment. The surviving fraction of the cells was assessed by means of colony formation assay. Experiments were performed on normal and UVC sensitive cell lines to demonstrate the presence of UVC photons during treatment. In addition, UV-specific DNA damages were investigated using an immunofluorescence assay to measure cyclopyrimidine dimers (CPDs). Results Combined treatment showed an increased cell death of over 50%, compared to radiation alone. This results in a dose equivalent of 4 Gy for the combined treatment with 2 Gy irradiation. The formation of CPDs and the increased effect on UV sensitive cells indicate the presence of UV photons. The generated amount of CPDs is comparable to an UVC exposure of about 15 J × m−2. Conclusion Combining NPs with ionizing radiation results in a localized dose surge, which could increase tumor control. It could also allow lowering the total applied dose to minimize unwanted side effects to the surrounding normal tissue while maintaining tumor control.

Recently, RMD has investigated the use of CLYC (Cs2LiYCl6 :Ce), a new and emerging scintillation material, in a gamma–neutron coded aperture imaging system based on RMD׳s commercial RadCam TM instrument. CLYC offers efficient thermal neutron detection, fast neutron detection capabilities, excellent pulse shape discrimination (PSD), and gamma-ray energy resolution as good as 4% at 662 keV. PSD improves the isolation of higher energy gammas from thermal neutron interactions (>3 MeV electron equivalent peak), compared to conventional pulse height techniques. The scintillation emission time in CLYC provides the basis for PSD; where neutron interactions result in a slower emission rise and decay components while gamma interactions result in a faster emission components. By creating a population plot based on the ratio of the decay tail compared to the total integral amplitude (PSD ratio), discrimination of gammas, thermal neutrons, and fast neutrons is possible. Previously, we characterized the CLYC-based RadCam system for imaging gammas and neutrons using a layered W-Cd coded aperture mask and employing only pulse height discrimination. In this paper, we present the latest results which investigate gamma-neutron imaging capabilities using PSD. An FPGA system is used to acquire the CLYC–PSPMT last dynode signals, determine a PSD ratio for each event, and compare it to a calibrated PSD cutoff. Each event is assigned either a gamma (low) or neutron (high) flag signal which is then correlated with the imaging information for each event.

For many applications including medical imaging, homeland security, nondestructive testing and scientific research, solid-state radiation detectors provide the best combination of sensitivity per unit volume, flexibility in packaging, cost, and efficient conversion of ionizing radiation into electrical signals suitable for measurement with modern instrumentation. Solid-state detectors are used for sensing all of the main forms of ionizing radiation including X-rays, gamma rays, charged particles, and neutrons. Charged particles include electrons, beta particles, positrons, protons, alpha particles, fission fragments, and other ions. Solid-state detectors include semiconductors, such as silicon and cadmium telluride, and scintillators coupled to solid state photodetectors such as NaI(Tl) coupled to silicon photodiodes. After more than 50 years of development, this remains an exciting area of research with regular reports of significant advances. The factors which make this such a thriving and growing area in radiation detection technology are the inherent advantages in size, weight, power, the need for high resolution digital imaging, low cost, as well as the availability of high performance computers capable of handling large amounts of data generated by large number of solid-state detector elements. This article reviews the primary mechanisms by which ionizing radiation interacts with matter, how these interactions create electronic signals within the various types of solid-state sensors, the properties of many of the more common solid-state nuclear detectors, and a comparison of their properties as they relate to choosing among them for a particular application. Keywords: ionizing radiation; nuclear radiation; photodiode; scintillator; semiconductor

LaBr3:Ce and CeBr3 are novel inorganic scintillators for gamma-ray detection and spectroscopy. Both materials exhibit exceptional scintillation properties, such as very high light output, fast response and excellent energy resolution. Custom equipment was built for crystal growth and handling of the moisture- and oxygen-sensitive materials. Crystal growth runs of large diameter crystals of LaBr3:Ce and pure CeBr3 were conducted in vertical multizone-zone Bridgman systems due to their operational simplicity and the potential for reduced thermal shock to the crystals. Procedures were developed to prepare clean charges, inhibit the formation of oxyhalides, and reduce the residual stresses and cracks in the crystals.

Avalanche photodiodes (APDs) have been investigated as the basis for a very high angular resolution coded aperture telescope with sensitivity over a wide energy range. Using custom electronics, software and a unique shadow-masking technique, we have achieved angular resolution from an X-ray point source of about 30 arcsec. In addition we have demonstrated imaging of higher gamma-ray energies by coupling to a CsI scintillator. Imaging from energies from few keV to an MeV with

Gamma-ray detector technologies, capable of providing adequate energy information, use photomultiplier tubes (PMTs) or silicon avalanche photodiodes to detect the light pulse from a scintillation crystal. A new approach to detect the light from scintillation materials is to use an array of small photon counting detectors, or a “detector-on-a-chip” based on a novel “Solid-state Photomultiplier” (SSPM) concept. A CMOS SSPM coupled to a scintillation crystal uses an array of CMOS Geiger photodiode (GPD) pixels to collect light and produce a signal proportional to the energy of the radiation. Each pixel acts as a binary photon detector, but the summed output is an analog representation of the total photon intensity. We have successfully fabricated arrays of GPD pixels in a CMOS environment, which makes possible the production of miniaturized arrays integrated with the detector electronics in a small silicon chip. This detector technology allows for a substantial cost reduction while preserving the energy resolution needed for radiological measurements. In this work, we compare designs for the SSPM detector. One pixel design achieves maximum detection efficiency (DE) for 632-nm photons approaching 30% with a room temperature dark count rate (DCR) of less than 1 kHz for a 30-μm-diameter pixel. We characterize after pulsing and optical cross talk and discuss their effects on the performance of the SSPM. For 30-μm diameter, passively quenched CMOS GPD pixels, modeling suggests that a pixel spacing of approximately 90 μm optimizes the SSPM performance with respect to DE and cross talk.

Active Pixel Sensors (APSs) in complementary metal-oxide-semiconductor (CMOS) technology are augmenting Charge-Coupled Devices (CCDs) as imaging devices and cameras in some demanding optical imaging applications. Radiation Monitoring Devices are investigating the APS concept for nuclear detection applications and has successfully migrated avalanche photodiode (APD) pixel fabrication to a CMOS environment, creating pixel detectors that can be operated with internal gain as proportional detectors. Amplification of the signal within the diode allows identification of events previously hidden within the readout noise of the electronics. Such devices can be used to read out a scintillation crystal, as in SPECT or PET, and as direct-conversion particle detectors. The charge produced by an ionizing particle in the epitaxial layer is collected by an electric field within the diode in each pixel. The monolithic integration of the readout circuitry with the pixel sensors represents an improved design compared to the current hybrid-detector technology that requires wire or bump bonding. In this work, we investigate designs for CMOS APD detector elements and compare these to typical values for large area devices. We characterize the achievable detector gain and the gain uniformity over the active area. The excess noise in two different pixel structures is compared. The CMOS APD performance is demonstrated by measuring the energy spectra of X-rays from 55Fe.

In this paper we report on the thermoluminescence of Cs2LiYCl6, Cs2LiYCl6: Ce3+ and Cs2LiYCl6: Pr3+ crystals. Low-temperature glow curves and isothermal decay spectra are presented. All three crystals exhibit prominent glow peaks below 300 K: The Cs2LiYCl6 sample shows a major peak at 58 K in addition to a broad band between 75 K and 150 K. The glow curve of Cs2LiYCl6: Pr3+ is similar to that of Cs2LiYCl6 but shows additional peaks at 222 K and 277 K. The glow curve of Cs2LiYCl6: Ce3+ is dominated by a major glow peak at 214 K with minor peaks at 50 K and 88 K. Lifetimes of traps derived from isothermal decay spectra measured at the temperature maximum of selected glow peaks are of the order of tens of seconds.

An aliovalently calcium-doped cerium tribromide (CeBr3:Ca2+) crystal was prepared with a gamma-energy resolution (FWHM) of 3.2% at the 137 Cs 662 keV gamma energy. We completed a crystal assessment and calculated the predictive performance and physical characteristics using density functional theory (DFT) formalism. Detector performance, characteristics, calcium doping concentration, and crystal strength are reported. The structural, electronic, and optical properties of CeBr3 crystals were investigated using the DFT within generalized gradient approximation. Specifically, we see excellent linearity of photons per unit energy with the aliovalent CeBr 3 :Ca 2+ crystal. Proportionality of light yield is one area of performance in which Ce-doped and Ce-based lanthanide halides excel. Maintaining proportionality is the key to producing a strong, high-performance scintillator. Relative light yield proportionality was measured for both doped and undoped samples of CeBr 3 to ensure no loss in performance was incurred by doping. The light output and proportionality for doped CeBr 3 , however, appears to be similar to that of undoped CeBr 3 . The new crystal was subjected to additional testing and evaluation, including a benchmark spectroscopy assessment. Results, which present energy resolution as a function of energy, are summarized. Typical spectroscopy results using a 137 Cs radiation source are shown for our crystallites with diameters 241 Am, 60 Co, 228 Th, and background to illustrate the spectrosocopic quality of CeBr 3 :Ca 2+ over a broader energy range.

Radiation Monitoring Devices, Inc., has recently investigated Cd(Zn)Te detector with three electrodes. Planar devices were refabricated as three-electrode devices after recording pulse height spectra. From the spectroscopy measurements at room temperature, photon energy resolutions of 8.3% and 3.5% FWHM were obtained, without noticeable loss of the detector efficiency, with the "three-electrode detector" for gamma ray energies of 122 and 662 keV, respectively, while no discernable full energy peaks were apparent with the planar detectors. The full contact cathode was grounded while two different bias voltages were applied to each anode electrode, even though the induced signal was collected only from the center anode. By investigation of the real and weighting electric field of the detector, the possible reasons for the improved spectra with the three-electrode detector were determined. The strong real electric field around the two anodes very likely enhances the created charge velocity and results in increasing the possibility to induce full charge collection. From additional measurements with increased differences between two bias voltages applied to the anodes, the effects of the strong real electric field on the improved energy spectrum have been confirmed.

The tracking of radiation contamination and distribution has become a high-priority US DOE task. To support DOE needs, Radiation Monitoring Devices Inc. has been actively carrying out research and development on a gamma-radiation imager, RadCam 2000 TM . The imager is based upon a position-sensitive PMT coupled to a scintillator near a MURA coded aperture. The modulated gamma flux detected by the PSPMT is mathematically decoded to produce images that are computer displayed in near real time. Additionally, we have developed a data-manipulation scheme which allows a multi-dimensional data array, comprised of x position, y position, and energy, to be used in the imaging process. In the imager software a gate can be set on a specific isotope energy to reveal where in the field of view the gated data lies or, conversely, a gate can be set on an area in the field of view to examine what isotopes are present in that area. This process is complicated by the FFT decoding process used with the coded aperture; however, we have achieved excellent performance and results are presented here.

Polycrystalline lead iodide (PbI2) is one of only a few materials commonly mentioned as a potential direct converter for digital X-ray sensors. Previous evaluations have noted higher than desirable leakage currents and commented on imaging characteristics from sensors constructed with PbI2 films deposited onto amorphous Si thin film transistor arrays. Changes in film growth parameters show a significant reduction in leakage current, to 10's of pA/mm2 (or less than 1 pA/pixel). Sensitivity remains good but is limited by incomplete X-ray absorption and lag. Image samples are derived from two different a-Si TFT designs, demonstrating high resolution and good contrast.

Numerous instruments have been developed for performing gamma-ray imaging and neutron imaging for research, nondestructive testing, medicine and national security. However, none are capable of imaging gamma-rays and neutrons simultaneously while also discriminating gamma-rays from the neutron. This paper will describe recent experimental results obtained using a gamma/neutron camera based on Cs 2 LiYCl 6 :Ce (CLYC) scintillation crystals, which can discriminate gamma-rays from neutrons. The ability to do this while also having good energy resolution provides a powerful capability for detecting and identifying shielded special nuclear materials for security applications. Also discussed are results obtained using a LaBr 3 scintillation crystal.

In this paper, we discuss a new X-ray imaging detector which consists of lead iodide polycrystalline films as sensor and amorphous silicon flat panel arrays as read out. We present our investigation of such a detector in 5 cm x 5 cm format with 100 μm pixels. The signal amplitude, and sensitivity of the films have been measured along with spatial resolution properties such as line spread function (LSF) and modulation transfer function (MTF). Real-time imaging performance at 30 frames/s of lead iodide films has also been evaluated using vidicon tube approach. Important properties of lead iodide film are also discussed. Finally, the potential applications of this detector are analyzed.

The use of high atomic number, room-temperature semiconductors for radiation detectors always involves making compromises to optimize the performance for specific applications. In recent years, a number of sophisticated device configurations and a variety of new read-out methods have been developed to extract the desired information from the detector signal. These approaches have significantly mitigated the effects of the inherent deficiencies found in available materials and have opened the way for promising new applications. The benefits of such approaches and their limitations are reviewed for CdTe and Cd1−xZnxTe (CZT) devices.

Vapor deposited films of thallium bromide are evaluated as potential photoconductive layers in new large-area radiographic detectors. The attractiveness of the material lies in its inherent high effective atomic number and high density. Polycrystalline films up to 200 /spl mu/m have been grown and show a columnar structure with grains reaching 100 /spl mu/m in diameter. Current-voltage (IV) tests indicate a bulk resistivity of 10/sup 9/-10/sup 10/ /spl Omega//spl middot/cm, limited by ionic conduction. The instability of current with time is also observed, but it can be minimized with cooling. The films demonstrate high gain at relatively low field strengths as compared to other photoconductive layers. Benefits and drawbacks of TIBr are compared to other materials, and possible solutions are discussed.

New third generation X-ray sources such as the Advanced Photon Source have created a need for a detector that can provide multiple frames of detailed X-ray images on the millisecond time scale. Such detectors will prove invaluable in applications such as time-resolved X-ray diffraction, X-ray microtomography, as well as materials science applications like polymer processing. Currently, detectors capable of acquiring high resolution X-ray images at such high speed do not exist, thus limiting progress in many of these important areas of research. To address these needs we have developed a prototype fast X-ray imaging system, using a structured CsI(Tl) scintillator coupled to a fast-frame 1 K/spl times/1 K CCD. The system has been successfully employed to capture 1024/spl times/64 pixel X-ray images at a rate of 1000 frames per second (fps) with a 12 bit dynamic range. The system exceeds the capabilities of the current high speed X-ray imaging systems which typically operate at the rate of 30 fps. Fabrication of a large area detector is currently underway, using a microstructured CsI(Tl) scintillator coupled to a fast-frame CCD with a 3:1 fiberoptic taper. The camera will operate in a burst mode, acquiring 8 1 K/spl times/1 K images at rates up to 1000 frames per second with 12 bit dynamic range. Higher image capture speeds can be accomplished by reducing the image area. This paper discusses the specific characteristics of the CsI(Tl) screens, experimental details of the prototype and the new design for the large area detector being developed specifically for time-resolved X-ray diffraction experiments in structural biology.

Imaging gamma-ray sources and distributions of low intensity is difficult using current commercially available radiation imagers. Radiation Monitoring Devices, Inc. has carried out the research and development necessary to construct a novel, compact radiation-imaging device, RADCAM, for low-intensity applications. The device consists of a position-sensitive photomultiplier tube (PSPMT) coupled to a CsI(Na) scintillation crystal, which is an excellent candidate for such applications due to its high light output. A tungsten coded-aperture mask, placed in front of the scintillator, creates a gamma-ray intensity pattern across the face of the crystal. The PSPMT detects the resulting scintillation pattern and the analog output signals are captured and converted to digital signals by the RMD PSPMT interface card. The digital data is stored and processed by a portable personal computer. The gamma-ray “shadowgram” is then mathematically decoded to yield the original source image. The pseudo-color radiation-source image is overlaid on a video picture of the same area captured by a high-resolution CCD. The combined image is displayed on screen as an accurate map of radioactive gamma-ray sources in the physical environment. Data acquisition and image display are controlled by the IMager Acquisition and Graphical-user-interface Environment (IMAGE), a Windows-NT program developed for the imager.

A small pixellated CdZnTe array is tested for suitability in a prototype SPECT system designed to acquire both emission and transmission data. Determining the optimum contact design and obtaining performance estimates of single photon acquisition are the primary focus. Flood field and collimated 57 Co sources irradiated the 16 pixel array (5 mm thick and 1.5 mm pixels) to determine photopeak efficiencies and detector response with different event collection techniques. Intrinsic full energy peak efficiency averaged 72% for an 18 keV acceptance window. A small irradiation spot scanned an array region, revealing detector response from nearby pixels. Post processing spectra compare coincident and anti-coincident acquisition. Additionally, current mode tests compare linearity with a CdWO 4 /Si p-i-n detector.

A small pixellated gamma-ray detector has been constructed from a 5 mm thick CdZnTe substrate and characterized for spectroscopic and spatial properties. Emphasis has been placed on revealing 'pixel-level' results to further understand optimum array design and operation. The anode design is (1.5/spl times/1.5) mm/sup 2/ pixels on a 1.625 mm pitch. Spectroscopic results with a /sup 57/Co source display an average energy resolution of 3.9 keV FWHM. Analysis of the electronic noise for different pixels showed good agreement with a theoretical model and similar performance between edge and interior pixels. A test of spatial response with scanned sources incident on the anode face showed good agreement with the pixel geometry and an undetectable amount of dependence on interaction depth.

Film radiography has long served the aerospace industry as a principal method for hardware flaw detection. Although excellent in performance, this method is extremely time consuming, labor intensive, costly, and is unsuitable for real time inspections. Modern digital radiographic systems overcome some of these difficulties but are also limited in terms of speed of operation due to persistence of the sensor and a problematic tradeoff between the X-ray detection efficiency and spatial resolution. We are developing an innovative X-ray imaging detector consisting of a novel microstructured CsI scintillator coupled to a fiberoptic taper-based CCD. Thin-film deposition techniques, previously developed to produce thin, structured CsI screens have been extended to fabricate CsI screens, up to 450 mg/cm/sup 2/ (1,000 /spl mu/m) in thickness. These sensors are suitable to provide high detection efficiency with high image quality for NDE applications. A prototype high energy imaging system was constructed by integrating these screens into a fiber-optic-based CCD camera. The performance was compared to that of the same system using a standard polycrystalline phosphor for NDE imaging applications. The experimental evaluations were carried out at Scientific Measurement Systems, Inc., Austin, TX.

Position sensitive detectors constructed from compound semiconductors (CdTe, CdZnTe, HgI 2 ) are being developed for a variety of applications where high sensitivity and improved energy resolution are significant advantages over scintillator or gas based systems. We have investigated the possibility of using a CdTe detector array in a SPECT gamma camera that would require a high efficiency at 140 keV. The problem of worsening photopeak efficiencies in thick detectors (due to incomplete charge collection) makes it difficult to maintain a high efficiency which, ironically, is the primary reason for choosing a thicker detector. Recent research has shown that following a simple geometrical design criterion can greatly reduce this deleterious effect. This paper reports on the results from a small prototype pixellated array fabricated using this design. We verify the ‘small pixel effect’ for a detector thickness and pixel size significantly larger than those used in most other work. A 9-element detector (1×1 mm pixels, 4 mm thick) has been fabricated and characterized in terms of energy resolution, peak-to-valley ratio and detection efficiency. Testing of the detector in a fast pulse mode to obtain its high count rate response has also been performed.

Semiconductors photodetectors have long seemed an attractive alternative for scintillation detection, but only recently have semiconductor photodiodes been proven suitable for some room temperature applications. There are many applications, however for which the performance of standard silicon p-i-n photodiodes is not satisfactory. This article reviews recent progress in two different families of novel semiconductor photodetectors: (1) wide bandgap compound semiconductors and (2) silicon photodetectors with enhanced signal-to-noise ratio. The compounds discussed and compared in this paper are HgI 2 , PbI 2 , InI, TlBr, TlBr 1− x I x and HgBr 1− x I x . The paper will also examine unity gain silicon drift diodes and avalanche photodiodes with maximum room temperature gain greater than 10 000.

Despite the outstanding scintillation performance characteristics of cerium tribromide (CeBr3) and cerium-activated lanthanum tribromide (LaBr3:Ce), their commercial availability and application is limited due to the difficulties of growing large, crack-free single crystals from these fragile materials. The objective of this investigation was to employ aliovalent doping to increase crystal strength while maintaining the optical properties of the crystal. One divalent dopant (Ca2+) was investigated as a dopant to strengthen CeBr3 without negatively impacting scintillation performance. Ingots containing nominal concentrations of 1.9% of the Ca2+ dopant were grown. Preliminary scintillation measurements are presented for this aliovalently doped scintillator. Ca2+-doped CeBr3 exhibited little or no change in the peak fluorescence emission for 371 nm optical excitation for CeBr3. The structural, electronic, and optical properties of CeBr3 crystals were investigated using the density functional theory within generalized gradient approximation. The calculated lattice parameters are in good agreement with the experimental data. The energy band structures and density of states were obtained. The optical properties of CeBr3, including the dielectric function, were calculated.

Some long-term, remote applications do not have access to conventional harvestable energy in the form of solar radiation (or other ambient light), wind, environmental vibration, or wave motion. Radiation Monitoring Devices, Inc. (RMD) is carrying out research to address the most challenging applications that need power for many months or years and which have undependable or no access to environmental energy. Radioisotopes are an attractive candidate for this energy source, as they can offer a very high energy density combined with a long lifetime. Both large scale nuclear power plants and radiothermal generators are based on converting nuclear energy to heat, but do not scale well to small sizes. Furthermore, thermo-mechanical power plants depend on moving parts, and RTG’s suffer from low efficiency. To address the need for compact nuclear power devices, RMD is developing a novel beta battery, in which the beta emissions from a radioisotope are converted to visible light in a scintillator and then the visible light is converted to electrical power in a photodiode. By incorporating 90Sr into the scintillator SrI2 and coupling the material to a wavelength-matched solar cell, we will create a scalable, compact power source capable of supplying milliwatts to several watts of power over a period of up to 30 years. We will present the latest results of radiation damage studies and materials processing development efforts, and discuss how these factors interact to set the operating life and energy density of the device.

We report on the results of a number of investigations into the material properties of lead iodide and their relation to x- and gamma-ray spectrometers. The effectiveness of zone refining as determined by inductively coupled plasma optical emission spectroscopy is demonstrated. We show that zone refining is effective in producing lead iodide with a higher degree of purity in terms of extrinsic dopants and we determine the segregation coefficients for a number of these impurities. Low temperature photoluminescence also indicates an improvement in the material properties of the purified lead iodide. The chemical etching characteristics, including etch rates, of lead iodide are presented for a number of etching solutions. Triple axis x-ray diffraction measurements have been employed to determine the structural perfection of the lead iodide after diamond sawing and etching and recovery of the crystallinity of the material is seen after Nal etching.

A wide variety of applications require high resolution, high sensitivity, gamma ray spectrometers which are portable, compact, and rugged enough for field operations. We are developing a laboratory prototype of a semiconductor detector system meeting these requirements. This spectrometer uses multiple CdTe radiation detectors for high counting efficiency, digital nonlinear pulse risetime compensation circuitry for high energy resolution and high sensitivity, and a low power thermoelectric cooler for low electronic noise. The use of digital compensation allows arbitrary, very accurate compensation with no rejection. These three techniques were integrated in the prototype, which achieved an energy resolution of 5 keV (0.75%) FWHM at 662 keV, without rejecting any counts, using a detector volume of 4 × 4 × 2 mm CdTe. With a 1.6 cm diam × 2 mm CdTe detector, a resolution of 15 keV (2%) FWHM at 662 keV was measured. The same technology has been successfully applied to other compound semiconductors which also have performance limited by poor charge collection, such as CdxZn1 − xTe. A low power, compact, very portable, rugged implementation has been designed.

Recent progress in the development of room-temperature lead iodide (Phi,) X-ray detectors is reported. Progress has been made in the areas of detector fabrication and preamplifier electronics, and this has resulted in improved detection performance. An energy resolution of 415 eV (FWHM) has been reported for 5.9 keV X-rays (“Fe source) with 1 mm’ detector at room temperature. A better estimation of the Fano factor in PbIz has been carried out and the upper limit of the Fano factor is calculated to be 0.19. Larger lead iodide detectors (up to 2.5 mm*) have been fabricated and their spectroscopic performance has been evaluated. The timing characteristics of lead iodide detectors have been investigated. A compact, portable lead iodide probe assembly has been designed and built for X-ray spectroscopic applications. Finally, optical and charge particle detection properties of lead iodide detectors have also been characterized.

Cadmium telluride has been investigated for potential use in a prototype imaging system capable of acquiring both X-ray CT and SPECT data. The system is being designed to accumulate SPECT images with 140 keV gamma rays, thus requiring 4 mm detector thicknesses to achieve satisfactory stopping power. This study primarily investigates whether an alternative pixel orientation can be used with thick detectors to preserve the higher photopeak efficiencies normally associated with smaller thicknesses. Using /sup 57/Co (122 keV) as a substitute isotope to /sup 99m/Tc, small 2 mm CdTe cubes were investigated along with 'edge irradiated' 2/spl times/4/spl times/2 mm bars of both CdTe and CdZnTe. The photopeak efficiency of the large bars can be increased through the use of cooling but energy resolution remains less than desired. Small cubes of either material meet the resolution requirements, but the efficiency of patient dose would be sacrificed.

A new scintillator material, lutetium orthoaluminate (LuAlO/sub 3/:Ce or LuAP), has been characterized by measuring its light output, scintillation decay time and energy resolution. Successful detection of 511 keV /spl gamma/-rays has been accomplished using LuAP coupled to semiconductor photosensors (silicon avalanche photodiode and silicon p-i-n photodiode). The background spectrum due to the radioactive isotope /sup 176/Lu in LuAP has been measured and characterized, and potential applications of LuAP are addressed.

A combined video and gamma ray imaging system has been developed to rapidly determine the location, distribution, and intensity of gamma ray sources. This instrument includes both a conventional video camera and a gamma ray imaging system, which is based upon a position sensitive photomultiplier tube, a scintillator, and a pinhole collimator. The gamma camera records the position and energy of each interaction, determining the energy spectrum and count rate from each direction. The design of the instrument and results of preliminary field tests will be presented. We have used a prototype of such an instrument in preliminary field tests to image radioactive sources with gamma ray energies between 120 keV and 2.4 MeV. This new system achieves an angular resolution for the nuclear image of 60 with an efficiency of 3/spl times/10/sup -6/ at 1 meter, a performance suitable for many nuclear applications. The sensitivity of the system is sufficiently high that, in a low background environment, a 1 mCi /sup 137/Cs source at 5 meters can be located in

RadCam™ is a detection system developed by RMD for gamma ray imaging. The system images and tracks radiation contamination and its distribution. The current system is based on a CsI:Na scintillator coupled to a position-sensitive photomultiplier tube (PS-PMT). The image is obtained either using MURA coded aperture or pin-hole masks. Detected signals are decoded to produce radiation distribution that is overlaid on an image from a video camera (real-time). Due to increased focus on neutron detection, we recently started upgrading the system with a new scintillating material capable of simultaneous gamma ray and neutron detection - Cs2LiYCl6 (CLYC). Due to excellent pulse-shape discrimination, CLYC provides dual-mode detection of gamma-rays and neutrons while cleanly separating the signals from these two types of radiation. In addition, CLYC delivers better energy resolution than classical scintillators, such as CsI:Na. In this paper we present our initial results obtained with a system in which the original CsI:Na crystal was replaced with a CLYC scintillator.

An integrated imaging sensor system is being developed to enhance operations of robots and telerobotic systems used in nuclear industry. This system combines a gamma ray image of the distribution of radioactivity with a video image of the area, allowing a rapid and intuitive determination of the source location. The gamma ray imaging system is based upon a position sensitive photomultiplier tube, a segmented scintillator, and a pinhole collimator which provides high quality images in the energy range of 0.1 to 1.5 MeV. The design and measured performance of a prototype of this system will be discussed.

Lead iodide (PbI2) is a wide bandgap semiconductor (Eg = 2.32 eV) and has been studied over the past several years as a semiconductor material for use in solid state X-ray and gamma-ray detectors. Small lead iodide detectors have been found to operate with low noise and good energy resolution (500 eV FWHM for 5.9 keV 55Fe X-rays). In the interest of reducing the electronic noise in lead iodide detection systems we have characterized the measured noise in the lead iodide detectors, and have compared the measurements with known noise models. It has been assumed that the noise sources in the lead iodide detectors would take form of a combination of series thermal noise, detector shot noise, and 1ƒ noise. Detectors with differing areas and thicknesses were analyzed by measuring their noise as a function of the amplifier integration time. A computer fitting program was used to obtain the magnitude of each noise source. Based on this analysis, 1ƒ noise was found to be the dominant noise source in most detectors at larger integration times of 4 μs to 12 μs, in which range the detectors are normally operated. The 1ƒ noise was also found to be proportional to the input capacitance, indicating that it is dominated by the series1ƒ noise. The 1ƒ noise magnitude appears to be dependent on the detector fabrication procedures, and may be reduced in future detectors by using more suitable fabrication procedures.

Large area silicon avalanche photodiodes (APDs) have been fabricated with maximum avalanche gains exceeding 10 000 and with relatively flat signal-to-noise performance from gains of a few hundred to gains of a few thousand. Gain and noise performance as well as detector speed of response is presented for APDs with active areas of 4 mm2 and 64 mm2. An overview of the performance of these devices as radiation detectors includes pulse height spectra using the APD as a scintillation spectrometer coupled to CsI(Tl) and to plastic scintillator, and also for direct detection of low energy X-rays.

A compact, high resolution X-ray and gamma ray spectroscopy system has recently been developed which provides excellent energy resolution over a wide range of photon energies. Two detector types have been tested, a cooled silicon PIN photodiode for X-ray energies from 2keV to 30 keV and a CdTe detector for energies from 20 keV to 1 MeV. The CdTe detector can be operated cooled or at room temperature. The heart of the system is a miniature preamplifier developed at AMPTEK which is used in combination with a small thermoelectric cooler to reduce the leakage current of the detectors. Using the cooled Si-PIN detector, 660 eV FWHM was achieved at 5.9 keV and using a CdTe detector 1.3 keV was achieved at 60 keV both with nearly 100% counting efficiency. Good resolution was also achieved at higher energies. >

It has recently been shown that lead sulfate (PbSO/sub 4/) is a promising scintillator material for use in PET detector systems. However, for lead sulfate scintillators to be useful in such an application, a technique must be developed to grow large optical quality crystals of this material. This paper describes our research into the high-temperature solution growth of PbSO/sub 4/ crystals. We report on the systematic selection of solvent materials including KCl, LiCl, PbCl/sub 2/, Na/sub 2/SO/sub 4/ and Li/sub 2/SO/sub 4/. Our studies indicate that Na/sub 2/SO/sub 4/ is the best solvent. With Na/sub 2/SO/sub 4/ as the flux, we obtained PbSO/sub 4/ single crystals of several millimeters in size by Bridgman crystal growth method. We employed ACRT (accelerated crucible rotation technique), to resolve the constitutional supercooling problem, thus increased the crystal yield and reduced the number of grains. Finally, we compared the scintillation properties of synthetic PbSO/sub 4/ crystals we grew with previous measurements on natural anglesite and other synthetic crystals, and found them nearly identical. >