This PDF file contains the front matter associated with SPIE Proceedings Volume 6707, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

As new scintillation materials are developed, great care is taken so that the scintillation properties of the material are optimized. Of equal importance, however, is ensuring that the new detector material is capable of reliable performance over an extended time period under a variety of environmental conditions. Careful consideration of the scintillation properties, mechanical properties, and the intended use of the final detector assembly is essential to the successful design and fabrication of reliable packaging. This paper discusses the important scintillation characteristics and properties that influence detector design. Also presented are the important design features that should be implemented when fabricating reliable inorganic scintillation detectors.

The ability of Compton telescopes to perform imaging and spectroscopy in space depends directly on the speed and energy resolution of the calorimeter detectors in the telescope. The calorimeter detectors flown on space-borne or balloon-borne Compton telescopes have included NaI(Tl), CsI(Na), HPGe and liquid organic scintillator. By employing LaX scintillators for the calorimeter, one can take advantage of the unique speed and resolving power of the material to improve the instrument sensitivity and simultaneously enhance its spectroscopic performance and thus its imaging performance. We present a concept for a space-borne Compton telescope that employs LaX as a calorimeter and estimate the improvement in sensitivity over past realizations of Compton telescopes. With some preliminary laboratory measurements, we estimate that in key energy bands, typically corrupted with neutron-induced internal nuclear emissions, this design enjoys a twenty-fold improvement in background rejection.

Single crystals of LaBr₃:1% Pr and CeBr₃:1% Pr have been grown by the vertical Bridgman technique. Crystals of these scintillators can be used in the fabrication of gamma-ray spectrometers. The LaBr₃:1% Pr and CeBr₃:1% Pr crystals we have grown had light outputs of ~73,000 and ~50,000 photons/MeV, respectively, and principal decay constants of 11μs and 26 ns, respectively. There were a number of emission peaks observed for these compounds. The emission wavelength range for the LaBr₃:1% Pr and CeBr₃:1% Pr scintillators were from about 400 to 800 nm. The CeBr₃:1% Pr scintillator had a dominating emission peak due to CeBr₃ at 390 nm. These two materials had energy resolutions of 9 and 7% FWHM, respectively, for 662 keV photons at room temperature. In this paper, we will report on our results to date for vertical Bridgman crystal growth and characterization of Pr-doped LaBr₃ and Pr-doped CeBr₃ crystals. We will also describe the special handling and processing procedures developed for these scintillator compositions.

Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl₃ type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.

The ability to manufacture large scale scintillating crystals is directly linked to the mechanical properties of the crystal. In this paper, estimated mechanical properties, including hardness, modulus, and fracture toughness of novel and established scintillating single crystals including CsI(Tl), CdWO₄, NaI(Tl), and LaBr₃(Ce). Lanthanum and cerium halide crystals have shown particular promise as scintillating materials because of their high luminosity and proportional response. However, the ability to manufacture large crystals of these materials is limited by their low fracture toughness. The mechanical properties of all the crystals are discussed in terms of the materials' deformation and fracture mechanisms and resulting manufacturability.

This paper will summarize our work on rare-earth nanomaterials for infrared photonic applications. Our research focuses the use of solvothermal methods to prepare these materials in particulate and molecular form with controlled physical and chemical characteristics. Thermochemical computations are used to facilitate direct crystallization of the desired material from the solvothermal medium. The impact of the chemical and physical characteristics of nanopowder and molecular characteristics on optical properties will be discussed in reference to conventional glasses and single crystals.

Anhydrous cerium bromide (CeBr₃) and cerium doped lanthanum bromide (Ce+³-LaBr₃) were obtained by the dehydration of hydrates synthesized by a direct acidification process. The dehydration process involves heating in vacuum through three phase changes - hydrate, amorphous, and crystalline LaBr₃. Incomplete removal of the bound water leads to the formation of oxybromides and the partial reduction of the lanthanum at high temperatures. It was found that upon the completion of dehydration (< 200 °C) a complete solid solution can be formed between LaBr₃ and CeBr₃. These two compounds form a simple binary phase diagram. Challenges associated with the dehydration process are discussed.

Lanthanide halide alloys have recently enabled scintillating gamma ray spectrometers comparable to room-temperature semiconductors (< 3% FWHM energy resolutions at 662keV). However brittle fracture of these materials hinders the growth of large volume crystals. Efforts to improve the strength through non-lanthanide alloy substitution, while preserving scintillation, are being pursued. Isovalent alloys nominal Ce_0.9Al_0.1Br₃, Ce_0.9Ga_0.1Br₃, Ce_0.9Sc_0.1Br₃, Ce_0.9In_0.1Br₃ and Ce_0.8Y_0.2Br₃, as well as aliovalent alloys nominal (CeBr₃)_0.99(CdCl₂)_0.01, (CeBr₃)_0.99(CdBr₂)_0.01, (CeBr₃)_0.99(ZnBr₂)_0.01, (CeBr₃)_0.99(CaBr₂)_0.01, (CeBr₃)_0.99(SrBr₂)_0.01, (CeBr₃)_0.99(PbBr₂)_0.01, (CeBr₃)_0.99(ZrBr₄)_0.01, (CeBr₃)_0.99(HfBr₄)_0.01 were prepared. All of these alloys exhibit bright fluorescence under UV excitation, with varying shifts in the spectral peaks and intensities relative to pure CeBr₃. Further, these alloys scintillate when coupled to a photomultiplier tube (PMT) and exposed to ¹³⁷Cs gamma rays. These data and the potential for improved crystal growth will be discussed.

The aim of this work was to explore the limits of polycrystalline ceramic scintillator in countering the nuclear threat. The goal was to develop a polycrystalline LaBr₃:Ce, which can be processed from ceramic forming techniques and can be produced in large size scintillator panels with lower cost and high production rate. Three high purity raw powders were used as the starting materials including LaBr₃, LaCl₃, and CeBr₃. Powder characteristics were measured. A melt spinning method was used to synthesize the nanoparticle LaBr₃:Ce with stoichiometric compositions. The synthesized nanoparticles were characterized and the average particle size of the synthesized nanoparticle LaBr₃:Ce was about 50 nm. The melt spun powders were consolidated using a "Nanosintering" method to achieve a high density while maintaining the stoichiometric composition. The grain size of the sintered polycrystalline is about 50 nm, which shows no grain growth during the densification process.

While a wide variety of new scintillators are now available, CsI:Tl remains a highly desired material for medical and industrial applications due to its excellent properties, low cost, and easy availability. Despite its advantages, however, its use in high-speed imaging applications has been hindered by an undesirably high afterglow component in its scintillation decay. To address this specific issue and to make the material suitable for applications such as volumetric CT and high-speed radiography, we have discovered that codoping the material with certain dipositive rare earth ions is particularly effective for such afterglow suppression. We have extensively studied the manner in which one such ion, Eu²⁺, alters the spectroscopic and kinetic properties of the scintillation, and have developed a coherent mathematical model consistent with the experimental results. Unfortunately, the beneficial effect of Eu²⁺ appears to be restricted only to relatively short times (say ≤200 ms) after the end of the excitation pulse. At longer times, the carriers whose diversion into deep traps is responsible for suppression of the short-term afterglow begin to escape those traps, resulting in enhancement of the low-level persistence on a time scale of seconds or minutes. What is needed is to provide some nonradiative means to annihilate the trapped carriers before their escape can enhance the low-level long-term emission. And, as predicted by the mathematical model, this is exactly what Sm²⁺ does. In this paper we compare the respective effects of the two additives on the afterglow and hysteresis characteristics of the host CsI:Tl material system. We find that while Eu begins to exert its afterglow-suppressive effect sooner after termination of excitation, the influence of Sm lasts much longer. Moreover, the suppressive effect of the latter is always found, regardless of the conditions of excitation, and becomes more profound the greater the duration of the exciting pulse. Various aspects of these effects and some their consequences for imaging performance are also discussed.

We have synthesized and tested new highly fluorescent metal organic framework (MOF) materials based on stilbene dicarboxylic acid as a linker. The crystal structure and porosity of the product are dependent on synthetic conditions and choice of solvent and a low-density cubic form has been identified by x-ray diffraction. In this work we report experiments demonstrating scintillation properties of these crystals. Bright proton-induced luminescence with large shifts relative to the fluorescence excitation spectra were recorded, peaking near 475 nm. Tolerance to fast proton radiation was evaluated by monitoring this radio-luminescence to absorbed doses of several hundred MRAD.

We report on developments of an intraoperative probe, capable of functioning in real time with high spatial resolution and high sensitivity. This probe combines two novel technologies and is based on an electron multiplying charge coupled device (EMCCD) bonded to a high spatial resolution microcolumnar CsI(Tl) scintillator via a flexible fiberoptic cable. Our data demonstrates that the probe can be used with such beta-emitting radiolabels as ¹⁸F, ¹³1I, and ³²P. The basic design of the probe and its evaluation using standard clinical phantoms is presented. In addition, the operational data obtained on swine models is included to demonstrate the probe's efficacy in practical procedures.

Neutron imaging of Inertial Confinement Fusion (ICF) targets provides a powerful tool for understanding the implosion conditions of deuterium and tritium filled targets at Mega-Joule/Tera-Watt scale laser facilities. The primary purpose of imaging ICF targets at that National Ignition Facility (NIF), sited at Lawrence Livermore National Laboratory, Livermore, California, is to determine the asymmetry of the fuel in an imploded ICF target. The image data are then combined with other nuclear information to gain insight into the laser and radiation conditions used to drive the target. This information is requisite to understanding the physics of Inertial Confinement Fusion targets and provides a failure mode diagnostic used to optimize the conditions of experiments aimed at obtaining ignition. We present an overview of neutron aperture imaging including a discussion of image formation and reconstruction, requirements for the future (NIF) neutron imaging systems, a description of current imaging system capabilities, and ongoing work to affect imaging systems capable of meeting future system requirements.

Cadmium zinc telluride (CdZnTe, or CZT) is a room-temperature semiconductor radiation detector that has been developed in recent years for a variety of applications. CZT has been investigated for many potential uses in medical imaging, especially in the field of single photon emission computed tomography (SPECT). CZT can also be used in positron emission tomography (PET) as well as photon-counting and integration-mode x-ray radiography and computed tomography (CT). The principal advantages of CZT are 1) direct conversion of x-ray or gamma-ray energy into electron-hole pairs; 2) energy resolution; 3) high spatial resolution and hence high space-bandwidth product; 4) room temperature operation, stable performance, high density, and small volume; 5) depth-of-interaction (DOI) available through signal processing. These advantages will be described in detail with examples from our own CZT systems. The ability to operate at room temperature, combined with DOI and very small pixels, make the use of multiple, stationary CZT "mini-gamma cameras" a realistic alternative to today's large Anger-type cameras that require motion to obtain tomographic sampling. The compatibility of CZT with Magnetic Resonance Imaging (MRI)-fields is demonstrated for a new type of multi-modality medical imaging, namely SPECT/MRI. For pre-clinical (i.e., laboratory animal) imaging, the advantages of CZT lie in spatial and energy resolution, small volume, automated quality control, and the potential for DOI for parallax removal in pinhole imaging. For clinical imaging, the imaging of radiographically dense breasts with CZT enables scatter rejection and hence improved contrast. Examples of clinical breast images with a dual-head CZT system are shown.

This paper discusses the criteria underlying the design of an innovative X-ray active pixel sensor in CMOS technology. This X-ray detector is used in a Full Field-of-view Digital Mammography (FFDM) camera. The CMOS imager is a three-side buttable 29mm x 119mm, 48 μm active pixel CMOS sensor in 0.18 μm technology. The 1^st silicon FFDM devices were fabricated at the end of June, 2007. The device suffers a common failure mode of high current and currently is in failure analysis at Bioptics foundry. Current target for revision A1 tape out is at the end of August, 2007.

Maximum-likelihood estimation methods offer many advantages for processing experimental data to extract information, especially when combined with carefully measured calibration data. There are many tasks relevant to x-ray and gamma-ray detection that can be addressed with a new, fast ML-search algorithm that can be implemented in hardware or software. Example applications include gamma-ray event position, energy, and timing estimation, as well as general applications in optical testing and wave-front sensing.

A Monte Carlo model has been developed for epitaxial silicon active pixel sensor arrays. Ionization generation of ⁵⁵Fe X-rays and high energy electrons are modeled directly using random numbers that follow an exponential distribution and a Bichsel distribution, respectively. Both the simulation and measurement have identified a considerable bulk-silicon substrate contribution to collected ionization electrons, which is important in accurate modeling of sensor response to high energy electrons.

The development of faster more reliable techniques to detect radioactive contraband in a portal type scenario is an extremely important problem especially in this era of constant terrorist threats. Towards this goal the development of a model-based, Bayesian sequential data processor for the detection problem is discussed. In the sequential processor each datum (detector energy deposit and pulse arrival time) is used to update the posterior probability distribution over the space of model parameters. The nature of the sequential processor approach is that a detection is produced as soon as it is statistically justified by the data rather than waiting for a fixed counting interval before any analysis is performed. In this paper the Bayesian model-based approach, physics and signal processing models and decision functions are discussed along with the first results of our research.

A prototype x-ray imaging system was built and tested for high-resolution x-ray radiography and tomography. The instrument consists of a microspot x-ray tube with a multilayer optic, a parabolic compound refractive lens (CRL) made of a plastic containing only hydrogen and carbon, and an x-ray detector. A rotation stage was added for tomography. Images were acquired of both grid meshes and biological materials, and these are compared to images achieved with spherical lenses. We found the best image quality using the multilayer condenser with a parabolic lens, compared to images with a spherical lens and without the multilayer optics. The resolution was measured using a 155 element parabolic CRL and a multilayer condenser with the microspot tube. The experiment demonstrates about 1.1 μm resolution.

A fluorescent x-ray tomography system is useful in performing fluorescent x-ray analysis for target atoms in biomedical objects utilizing a drug deliverly system. This tomography system is employed in order to measure iodine distribution in objects, and the system consists of a cerium x-ray generator, a 58-μm-thick stannum filter, a tungsten collimator, and a computed radiography system. Because K-series characteristic x-rays from the cerium target are absorbed effectively by iodine-based contrast media, iodine fluorescent x-rays from iodine atoms in the objects are produced. In the tomography system, when the objects are exposed by fan beams, the stannum filter easily transmits iodine Kα rays from a slice plane, and tomograms are obtained using the CR system and the collimator.

A novel identification technique suited to security screening of liquid and amorphous substances with x-ray diffraction (XRD) is presented. The starting point is to fit the high momentum region (independent atom regime) of the XRD profile with a free-atom scatter function corresponding most closely to the effective atomic number of the sample. The Percus-Yevick formulation of the molecular interference function for hard-sphere liquids then enables features to be extracted from liquid/amorphous XRD profiles. These features correspond to such molecular structure parameters as effective particle radius, packing fraction, effective atomic number, particle homogeneity and inter-particle potential. Amorphous substances may thus be classified into functional groups such as oxidisers and fuels. These considerations are illustrated with synchrotron XRD measurements of acetone and hydrogen peroxide, implicated in the London "transatlantic aircraft plot" of 2006 and representative of hazardous liquid fuel and oxidizer combinations.

We have combined a CMOS color camera with special software to compose a multi-functional image-quality analysis instrument. It functions as a colorimeter as well as measuring modulation transfer functions (MTF) and noise power spectra (NPS). It is presently being expanded to examine fixed-pattern noise and temporal noise. The CMOS camera has 9 μm square pixels and a pixel matrix of 2268 x 1512 x 3. The camera uses a sensor that has co-located pixels for all three primary colors. We have imaged sections of both a color and a monochrome LCD monitor onto the camera sensor with LCD-pixel-size to camera-pixel-size ratios of both 12:1 and 17.6:1. When used as an imaging colorimeter, each camera pixel is calibrated to provide CIE color coordinates and tristimulus values. This capability permits the camera to simultaneously determine chromaticity in different locations on the LCD display. After the color calibration with a CS-200 colorimeter the color coordinates of the display's primaries determined from the camera's luminance response are very close to those found from the CS-200. Only the color coordinates of the display's white point were in error. For calculating the MTF a vertical or horizontal line is displayed on the monitor. The captured image is color-matrix preprocessed, Fourier transformed then post-processed. For NPS, a uniform image is displayed on the monitor. Again, the image is pre-processed, transformed and processed. Our measurements show that the horizontal MTF's of both displays have a larger negative slope than that of the vertical MTF's. This behavior indicates that the horizontal MTF's are poorer than the vertical MTF's. However the modulations at the Nyquist frequency seem lower for the color LCD than for the monochrome LCD. The spatial noise of the color display in both directions is larger than that of the monochrome display. Attempts were also made to analyze the total noise in terms of spatial and temporal noise by applying subtractions of images taken at exactly the same exposure. Temporal noise seems to be significantly lower than spatial noise.

This communication focuses on physical evaluation of image quality of displays for applications in medical imaging. In particular we were interested in luminance noise as well as chromaticity noise of LCDs. Luminance noise has been encountered in the study of monochrome LCDs for some time, but chromaticity noise is a new type of noise which has been encountered first when monochrome and color LCDs were compared in an ROC study. In this present study one color and one monochrome 3 M-pixel LCDs were studied. Both were DICOM calibrated with equal dynamic range. We used a Konica Minolta Chroma Meter CS-200 as well as a Foveon color camera to estimate luminance and chrominance variations of the displays. We also used a simulation experiment to estimate luminance noise. The measurements with the colorimeter were consistent. The measurements with the Foveon color camera were very preliminary as color cameras had never been used for image quality measurements. However they were extremely promising. The measurements with the colorimeter and the simulation results showed that the luminance and chromaticity noise of the color LCD were larger than that of the monochrome LCD. Under the condition that an adequate calibration method and image QA/QC program for color displays are available, we expect color LCDs may be ready for radiology in very near future.

In this paper a new approach to 3D Compton imaging is presented, based on a kind of finite element (FE) analysis. A window for X-ray incoherent scattering (or Compton scattering) attenuation coefficients is identified for breast cancer diagnosis, for hard X-ray photon energy of 100-300 keV. The point-by-point power/energy budget is computed, based on a 2D array of X-ray pencil beams, scanned vertically. The acceptable medical doses are also computed. The proposed finite element tomography (FET) can be an alternative to X-ray mammography, tomography, and tomosynthesis. In experiments, 100 keV (on average) X-ray photons are applied, and a new type of pencil beam collimation, based on a Lobster-Eye Lens (LEL), is proposed.

Detection of high-dose-rate pulse x-rays from a samarium plasma flash x-ray generator utilizing a multipixel photon counter is described. Monochromatic K-series characteristic x-rays are detected by a plastic scintillator, and fluorescent lights are lead to the photon counter through a 10-m-length plastic fiber. The reverse bias was 70.0 V, and x-ray outputs were recorded by a digital storage scope. The samarium plasma flash x-ray generator is useful for performing high-speed enhanced K-edge angiography using cone beams because K-series characteristic x-rays from the samarium target are absorbed effectively by iodine-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x-rays are produced by the discharging. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current are approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic x-ray intensities of samarium increased. Bremsstrahlung x-ray intensity rate decreased with increasing the charging voltage, and K lines were produced with a charging voltage of 80 kV. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 500 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography (CR) system and iodine-based contrast media. In the angiography of nonliving animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

Tellurium (Te) is purified using a multistage vacuum distillation technique. Specially designed quartz ampoules coupled to a 10^-6 torr vacuum system are used for one, two, and three stage distillations. The unique quartz design allows removal of residual materials between stages without handling purified material or exposing it to atmospheric conditions. Average deposition of purified material is 0.93 g/min at a distillation temperature of 525°C. The average overall yield per stage is 84% for single stage distillation, 80% for two stages, and 76% for three stages. Glow discharge mass spectrometry testing (GDMS) is used to analyze samples of purified tellurium. GDMS results show 6N purity (99.9999%) is achieved after the three stage distillation process when starting with 4N+ pure material.

Organic materials, and in particular, poly(p-phenylene vinylene)s, are being investigated for solid state neutron detection. Semiconducting organics can offer direct detection because of high resistivity, high dielectric strength, natural gamma discrimination due to low Z, and room temperature operation. However, the effective charge collection is dependant on several material processing variables, including solvent choice and concentration, substrate, deposition method and conditions, post-deposition processing, and other factors, all of which can influence the local and bulk order of the material. We have investigated the effects of processing variables on the material order through infrared dichroism. The charge collection of the device was measured with visible laser excitation, and related to the order.

CaF₂:Eu is an attractive radiation detection material because it is inert, non-hygroscopic, shock resistant, and can be less expensive than other radiation detection materials. A CaF₂:Eu scintillation detector was constructed to identify whether energy dependent differences in (n,p) and (n,α) cross sections could be exploited to distinguish fission neutrons from D-D neutrons in an active interrogation system. Experimentally, the charged particles are difficult to distinguish from the significantly larger number of γ-rays produced in (n,γ) reactions. In addition, modeling results show that fission neutrons produce only slightly higher charged particle production rates than D-D neutrons. For charged particle production in CaF₂:Eu to succeed in fission neutron detection, a superior γ-ray discrimination technique is required.