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
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
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 Ce0.9Al0.1Br3, Ce0.9Ga0.1Br3, Ce0.9Sc0.1Br3,
Ce0.9In0.1Br3 and Ce0.8Y0.2Br3, 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 1st 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
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
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
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.