New scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized. Our development efforts have focused on two classes of high-light-yield materials: europium-doped alkaline earth halides and cerium-doped garnets. Of the halide single crystals we have grown by the Bridgman method—SrI$_2$ , ${hbox {CaI}}_2$ , SrBr$_2$ , ${hbox {BaI}}_2$ and ${hbox {BaBr}}_2$ —SrI$_2$ is the most promising. SrI$_2({hbox {Eu}})$ emits into the ${hbox {Eu}}^{2+}$ band, centered at 435 nm, with a decay time of $1.2~mu $s and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3%FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramic fabrication allows the production of gadolinium- and terbium-based garnets which are not growable by melt techniques due to phase instabilities. The scintillation light yields of cerium-doped ceramic garnets are high, 20,000–100,000 photons/MeV. We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance the energy resolution.

We are reporting on the latest growth and scintillating properties of a recently discovered intrinsic scintillating compound with the K2PtCl6 simple cubic crystal structure: the Cs-based Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (CHCB), both with the density of 3.9 g/cm(3), as well as the Tl-based Tl2HfCl6 (THC) and Tl2ZrCl6 (TZC). This article presents a successfully developed process of growing crack-free, single crystals of 16 mm diameter to 1-in-diameter CHC by the Bridgman method. The energy resolution of 2.8% [full-width at half-maximum (FWHM)] at 662 keV has been obtained for small diameters and typical 3.5% (FWHM) at 662 keV has been obtained for 1 in x 1 in CHC. The light yield of 30 000 ph/ MeV and the 3.8 mu s primary decay time have been measured for CHC. CHC's excellent linear response to gamma rays compared to those of NaI:Tl and BGO is also reported. The mixed-halides CHC-based compound CHCB performs with a shorter primary decay time of 1.8 mu s. Introducing Tl, a heavier element than Cs, increases both Zeff and density of THC and TZC, and improves gamma-ray detection efficiency. Primary decay times are also reduced to about 1 mu s for THC and 2 mu s for TZC.

We are developing new scintillator materials that offer potential for high resolution gamma ray spectroscopy at low cost. Single crystal SrI 2(Eu) offers ~3% resolution at 662 keV, in sizes of ~1 in 3. We have developed ceramics processing technology allowing us to achieve cubic inch scale transparent ceramic scintillators offering gamma spectroscopy performance superior to NaI(Tl). Our bismuth-loaded plastic scintillator demonstrates energy resolution of ~8% at 662 keV, for samples of ~0.5 cm 3.

The growth and scintillating properties of undoped and Eu(2+) doped Strontium Iodide indicate excellent potential for gamma ray spectroscopy. Energy resolution at 662 keV was found to be as good as 2.7% at 662 keV. The effect of purification by zone refining was also studied and crystal growth of SrI(2) by the Bridgman technique was found to be less subject to cracking compared to the growth of lanthanum halide scintillators.

The lead magnesium niobate-lead titanate is one of the new generations of piezoelectric materials with outstanding properties. Single crystals of 0.67Pb(Mg 1/3Nb 2/3) O 3-0.33PbTiO 3 (PMN-PT) show superior properties as compared to piezoelectric ceramics and piezoelectric films in device applications. Large size crystals are required for specific applications. Previously, transparent and high quality PMN-PT single crystals have been grown in our laboratory using the high temperature flux method. The size of the obtained crystals was small and varied from 2 to 8 mm 3, mostly showing regular prismatic shape. In present attempt, PMN-PT crystals are grown from the vertical gradient freeze method with no flux using congruent melt. Processing conditions and growth parameters have been optimized to increase the size and yield of the perovskite crystals including cooling rate, soak time and soak temperature. The size of the grown crystals obtained by this method is very large relatively and varied from 5 to 30 mm . The microstructure of the as grown single crystals is investigated by scanning electron microscopy. Piezoelectric properties of the grown crystals are also investigated. PMN-PT plates show excellent piezoelectric properties. Samples were poled under an applied electric field of 5 kV/cm. Dielectric properties at a frequency of 1 kHz are examined. Finally, the variation of pyroelectric coefficient with temperature is studied. The grown PMNPT crystals show typical relaxor dielectric properties.

Cs2UYCl6 (CLYC) has generated recent interest as a thermal neutron detector due to its excellent n/gamma-ray pulse-shape discrimination and energy resolution. Here, the capabilities of CLYC as a fast neutron detector and spectrometer are reported. A 1 in. x 1 in. CLYC detector was used to measure the response of mono-energetic neutrons over a range of 0.8-2.0 MeV produced via the Li-7(p,n) reaction at the University of Massachusetts Lowell 5.5 MV Van de Graaff accelerator. A broad continuum from the Li-6(n, alpha) reaction was observed, as well as additional peaks below the thermal capture peak. Based on possible reactions in CLYC, the additional peaks are determined to be due to the Cl-35(n,p)S-35 reaction, with a Q-value of +615 keV, and corroborated in simulations using MCNPX. The average resolution of 9% for these peaks makes CLYC a promising candidate for a fast neutron spectrometer. Published by Elsevier B.V.

Both Te inclusions and point defects can trap the charge carriers generated by ionizing particles in CdZnTe (CZT) detectors. The amount of charge trapped by point defects is proportional to the carriers' drift time and can be corrected electronically. In the case of Te inclusions, the charge loss depends upon their random locations with respect to the electron cloud. Consequently, inclusions introduce fluctuations in the charge signals, which cannot be easily corrected. In this paper, we describe direct measurements of the cumulative effect of Te inclusions and its influence on the response of CZT detectors of different thicknesses and different sizes and concentrations of Te inclusions. We also discuss a means of partially correcting their adverse effects.

Europium-doped barium and strontium iodide crystals are high light yield scintillator materials with excellent energy resolution. In this communication, BaI(2):Eu and SrI(2):Eu single crystals with space groups of Pnma (D(2h)(16)) and Pbca (D(2h)(15)) respectively were grown from the vertical Bridgman method. The crystals were investigated with polarized Raman spectroscopy at temperatures varied from 77 to 300 K. The observed Raman-active modes for each crystal were assigned with the help of group theory analysis. It is found that the absence of the site symmetry leads to splitting of a spectral line in Pnma structure into two lines in the Pbca structure. Structural defects including dark spots formed during crystal growth and new species produced from hydration were characterized. (C) 2011 Elsevier Ltd. All rights reserved.

High resistivity single crystals of AgGaSe2 were grown by the horizontal Bridgman technique. The near band edge photoconductivity of the grown crystal at room temperature was found to be up to 2 x 10(4) times higher than the dark conductivity, under the illumination of 10(-3) W/cm(2). The photoconductivity spectrum consists primarily of three peaks, which are attributed to the transitions from Gamma(7)(A), Gamma(6)(B) and Gamma(7)(C) states of valence band to the conduction band Gamma(6). The crystal field splitting and the spin-orbit splitting were determined from these peak energy positions of the photoconductivity spectrum. (c) 2006 Elsevier Ltd. All rights reserved.