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.
We performed a number of comparative MCNPX simulations of gamma energy depositions of scintillation crystals with smooth and rough surfaces. In the study, nine surface patterns (8 micro-roughness + 1 smooth) were coupled with eight common scintillation crystals for a total of 72 possible combinations. Although this was a preliminary study, the outcome was counterintuitive; results generally favored surfaces with micro-roughness over a conventional smooth surface as measured in terms of average energy depositions. The advantage gained through surface roughness is less significant for CdSe and LaCl3, but is most significant for the common NaI and the glass-like SiO2 scintillators. Based on the results of the 64 rough-surface coupled MCNPX simulations, 57 of the 64 (~89%) simulations showed some improvement in energy deposition. The mean improvement in energy deposition was 2.52%. The maximum improvement was about 8.75%, which was achieved when roughening the surface of a SiO2 scintillator using a micro cutting pattern. Further, for a conventional NaI scintillator, MCNPX results suggest that any roughness pattern would improve the energy deposition, with an average improvement of 3.83%. Although the likely causes remain unclear, we intend to focus on presenting simulation results instead of offering a sound explanation of the underlying physics.
In recent years, the concept of embedding composite scintillators consisting of nanosized inorganic crystals in an organic matrix has been actively pursued. Nanocomposite detectors have the potential to meet many of the homeland security, non-proliferation, and border and cargo-screening needs of the nation and, by virtue of their superior nuclear identification capability over plastic, at roughly the same cost as plastic, have the potential to replace all plastic detectors. Nanocomposites clearly have the potential of being a gamma ray detection material that would be sensitive yet less expensive and easier to produce on a large scale than growing large, whole crystals of similar sensitivity. These detectors would have a broad energy range and a sufficient energy resolution to perform isotopic identification. The material can also be fabricated on an industrial scale, further reducing cost. This investigation focused on designing and fabricating prototype core/shell and quantum dot (QD) detectors. Fourteen core/shell and four QD detectors, all with the basic consistency of a mixture of nanoparticles in a polymer matrix with different densities of nanoparticles, were prepared. Nanoparticles with sizes <10 nm were fabricated, embedded in a polystyrene matrix, and the resultant scintillators’ radiation detector properties were characterized. This work also attempted to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy and high-energy gamma rays. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.
It has been reported that detectors made of lanthanum-cerium halides (LaBr3:Ce and CeBr3) have superior energy resolution for gamma-radiation detection compared to what is offered by conventional sodium iodide (NaI:T1) detectors. Although superior energy resolution may be observed, one major barrier that has hindered the rapid adaptation of lanthanum halides is their self-activity, due primarily to the presence of isotope 138La, and the α contamination, due to the trace amount of actinides. It has also been observed that the lanthanum-cerium halides contain a substantial amount of self-activity caused by the radioactive isotope 138La. Additionally, LaBr3:Ce spectra are also affected by β contaminations in the low-energy region. To use either LaBr3:Ce or CeBr3 for high-sensitivity gamma detection, it may be necessary to have the self-activity as well as α and β contaminations removed or reduced. This paper describes a novel algorithmic approach for self-activity and contamination reduction for LaBr3:Ce and CeBr3 detectors using a third reference NaI:T1 detector. We present a computational procedure for separating self-activity from the gamma spectra obtained by LaBr3:Ce detectors. With the self-activity spectra precalculated, it is possible to perform real-time self-activity removal. This procedure can be implemented as an automatic self-activity subtraction module for gamma-radiation detectors made of LaBr3:Ce and/or CeBr3 crystals. With this approach, it is possible to develop a new generation of LaBr3:Ce detectors capable of producing spectra as clean as those obtained by conventional NaI:T1 detectors, but with much improved energy resolutions.
Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and
cerium bromide (CeBr3) without requiring the growth of large crystals. Nanostructured detectors may allow us to
engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution
sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is
much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with
nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may
improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have
been seen in photoluminescence from silicon nanocrystals in a densely packed ensemble. We have fabricated
nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work
investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on
both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy
activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3.
Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.
Energy resolution and detection efficiency were compared between two sizes of cerium bromide (CeBr3) scintillators,
three sizes of lanthanum bromide (LaBr3:Ce) scintillators, three sizes of sodium iodide (NaI:Tl) scintillators, and a lanthanum chloride (LaCl3:Ce) scintillator. Comparisons are made of key parameters such as energy resolution, detection efficiency, linearity, and self-activity of CeBr3, LaBr3:Ce, LaCl3:Ce, and NaI:Tl scintillator detectors. The scintillator detectors are tested by comparing the peak separation and identification in the energy range up to 3.0 MeV using 133Ba, 152Eu, and naturally occurring radioactive materials [1]. The study has shown that CeBr3 scintillator detectors provided by Saint-Gobain offer better resolution than NaI:Tl scintillator detectors. CeBr3 detectors could resolve some closely spaced peaks from 133Ba and 152Eu, which NaI:Tl could not. LaBr3:Ce has slightly better resolution, and a slightly higher
efficiency than CeBr3. In this work, "self-activity" of each of these four detector types was measured by operating the
detectors themselves. A comparison of the intrinsic activity for all of the detectors in this study is demonstrated. For CeBr3, the self-activity present may be reduced, or even eliminated in the future, through improved processes for growing the material. It will be discussed if, and under what conditions, CeBr3 may be better than LaBr3:Ce and LaCl3:Ce for detection of certain special nuclear material γ-rays [2]. An overall advantage of CeBr3 detectors over lanthanum halide and NaI:Tl detectors will be discussed.
To incorporate the georegistration and restoration processes into airborne data processing in support of DOE's nuclear emergency response task, we developed an adaptive restoration filter for airborne Daedalus AADS1268 ATM thermal data based on the Wiener filtering theory. Preliminary assessment shows that this filter enhances the detectability of small weak thermal anomalies in AADS1268 thermal images.
The number of available spaceborne and airborne systems will dramatically increase over the next few years. A common systematic approach toward verification of these systems will become important for comparing the systems' operational performance. The Commercial Remote Sensing Program at the John C. Stennis Space Center (SSC) in Mississippi has developed design requirements for a remote sensing verification target range to provide a means to evaluate spatial, spectral, and radiometric performance of optical digital remote sensing systems. The verification target range consists of spatial, spectral, and radiometric targets painted on a 150- by 150-meter concrete pad located at SSC. The design criteria for this target range are based upon work over a smaller, prototypical target range at SSC during 1996. This paper outlines the purpose and design of the verification target range based upon an understanding of the systems to be evaluated as well as data analysis results from the prototypical target range.
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