In this communication we report on the application of low temperature thermoluminescence (ltTL) associated with shallow traps in the research on scintillation properties of cerium doped LuAP and YAP crystals. We show that existence of shallow traps and their interference with the scintillation process readily explain changes in light yield and time profiles with temperature. The analysis of two major glow peaks at 183 and 270 K of LuAP:Ce yields trap parameters: The activation energy E

Lutetium iodide (LuI3) is a new addition to the family of Ce-doped lanthanide trihalide scintillating materials. Crystals of this material show hexagonal structure with density of 5.6g/cm3 and have been grown by the Bridgman method. Under X-ray excitation this material exhibits broad, cerium based emission that peaks at 475 and 520nm. The fastest and major component of scintillation time profile of LuI3:Ce emission decays with a 31ns time constant. The light yield of LuI3:Ce for thin samples (0.2mm) was estimated to be 50,000photons/MeV.

This paper describes detectors comprised of Cs2LiYCl6 : Ce(CLYC) scintillators coupled to silicon photomultipliers (MPPC, Hamamatsu). CLYC has been developed for dual gamma ray and thermal neutron detection. MPPCs are compact detectors with a very thin profile (similar to 2 mm), but also a small active area (6 mm x 6 mm). The combination of both can create a compact replacement of a He-3 tube. Three different crystal sizes were tested: a 5 mm x 5 mm x 5 mm cube, a 1 cm x 1 cm x 4 cm cuboid, and a empty set1 in x 1 in cylinder. All three detectors showed a well-resolved thermal neutron peak with energy resolution of 5.4%, 7%, and 11% (FWHM), respectively. The degradation in larger crystals is due to a mismatch between the coupled crystal face and the active area of the light detector. All detectors showed the 662 keV gamma ray peak from a Cs-137 source, indicating capability for limited gamma ray spectroscopy, with energy resolutions of 10%, 17%, and 26%, respectively. The capability for pulse shape discrimination was shown as well. The efficiency of the detectors was measured against a 10 atm He-3 tube (9 cm(3) volume). The best absolute efficiency was shown by the cylinder detector, next by the He-3 tube (almost the same as the cylinder detector), and finally by the cuboid detector. The latter showed the best neutron count per cm(3), twice as high as the two other detectors.

LaCl3:Ce and LaBr3:Ce scintillators are characterized by a high light yield and very fast nanosecond primary emission. To study scintillation mechanisms in these materials, we have measured low-temperature thermoluminescence. Both crystals exhibited prominent glow peaks below 100K: LaCl3:10%Ce sample showed multiple glow peaks with two major ones at 65 and 66K, whereas the LaBr3:0.5%Ce sample showed two major peaks at 65 and 75K. Assuming first-order kinetics, the traps responsible for those peaks can be described by the following parameters: E

The observed discrepancy in the scintillator light output, measured by different PMTs, triggered studies to understand the problem. In that purpose the photoelectrons number were measured by two different methods: the classical one based on comparison of the full energy peak to that of single photoelectron and by a method based on the pulse height resolution of the peak due to the light pulser. Under the test significant number of different PMTs from Photonis and Hamamatsu were used. We concluded that the number of phe obtain by means of classical method was higher than the number of phe calculated from the pulse height resolution of the light pulser peak for all of the PMTs but XP2020Q. It leads to large dispersion in the estimated light output for a given scintillator. In details, the light output of BGO and LSO determined with R6231 and R2095 is comparable to those measured with XP2020Q and S3590-18 pin photodiode, when photoelectron number calculated from the pulse height resolution is used. Further carried on in-depth studies of the photoelectron number at different HV suggested that the effect is related to the space charge created over the dynode structure of PMTs. Operation of PMTs at lower HV/gain minimizes this effect, thus low noise electronics is recommended to get the single photoelectron peak at this conditions. Moreover, the absolute light output of scintillators is affected by differences in the quantum efficiency calibration at Photonis and Hamamatsu.

Numerous instruments have been developed for performing gamma-ray imaging and neutron imaging for research, non-destructive 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 Cs2LiYCl6: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 LaBr3 scintillation crystal.

Radiation Monitoring Devices (RMD) has modified their production of deep diffused, planar silicon avalanche photodiodes (APDs), which resulted in significant performance improvements. This modification involves an alternative planar process to influence the p-n junction contour to create a planar bevel while using 4 Omega cm n-type neutron transmutation-doped silicon wafers, where previously 30 Omega cm silicon wafers were used. These new APDs still offer a high gain (similar to 10(3)), but with an increased quantum efficiency and a reduced noise by a factor of 4-5, compared to our standard planar processed 30 Omega cm APDs with the same detection area. We have characterized these new devices for their intrinsic and spectroscopic properties. In our study a 14 x 14 mm(2) APD, made from 4 Omega cm silicon, was coupled to a 1 cm(3) LaBr(3):Ce scintillator. We measured a FWHM energy resolution at 662 keV to be 2.55% at room temperature (24 degrees C). (C) 2009 Elsevier BIN. All rights reserved.

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.

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. (c) 2007 Elsevier B.V. All rights reserved.

We report on our development of large volume Cs2LiYCl6 (CLYC) detectors for nuclear security applications. Three-inch diameter boules have been grown and 3-in right cylinders have been fabricated. Crystals containing either >95% Li-6 or >99% Li-7 have been grown for applications specific to thermal or fast neutron detection, respectively. We evaluated their gamma and neutron detection properties and the performance is as good as small size crystals. Gamma and neutron efficiencies were measured for large crystals and compared with smaller size crystals. With their excellent performance characteristics, and the ability to detect fast neutrons, CLYC detectors are excellent triple-mode scintillators for use in handheld and backpack instruments for nuclear security applications.

Homeland security applications often require detection of both neutron and gamma radiation. A combination of two detectors registering neutrons and gammas separately is typically used. Recently, a number of scintillators from the elpasolite crystal family were proposed, that provide detection of both types of radiation. The most promising are Cs2LiYCl6, Cs2LiLaCl6, and Cs2LiLaBr6. All are doped with Ce3+. They are capable of providing very high energy resolution. The best values achieved for each material are 3.9%, 3.4%, and 2.9%at 662 keV (FWHM), respectively. Since 6Li has an acceptable cross-section for thermal neutron capture, these materials also detect thermal neutrons. In the energy spectra, the full energy thermal neutron peak typically appears above 3 MeV gamma equivalent energy. Thus very effective pulse height discrimination can be implemented with these materials. The CLLC and CLYC emissions consist of two main components: Core-to-Valence Luminescence (CVL; 220 nm to 320 nm) and Ce emission (350 to 500 nm). The former is of particular interest since it appears only under gamma excitation. It is also very fast and decays with less than 2 ns time constant. The CVL provides a significant difference to temporal responses under gamma and neutron excitation thus it may be used for effective pulse shape discrimination.