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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/cm3, 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 × 1 in CHC. The light yield of 30 000 ph/MeV and the 3.8-μs 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~μs. 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~μs for THC and 2~μs for TZC. [ABSTRACT FROM AUTHOR]

Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far small crystals of this composition have been studied, but for practical applications with affordable price, large-scale crystals are required. In this work, we present successful efforts to grow crack-free single crystals with sizes up to ø1" × 5.5". A variety of experimental techniques were employed to investigate the scintillation properties. A ø1" × 1.2" TLYC cylinder has a light yield of 25,000 ph/MeV, and its energy resolution is better than 4% at 662 keV. The gamma equivalent energy (GEE) produced by thermal neutron is 1.89 MeVee, along with a neutron induced light yield of 47,000 ph/n. Pulse shape discrimination (PSD) between gamma-rays and neutrons has been successfully shown with a current Figure-of-Merit (FOM) of 2.4. This article explores the crystal growth, scintillation properties, and potential applications of TLYC. [ABSTRACT FROM AUTHOR]

Tl2LiYCl6:Ce (TLYC), a new cerium doped-thallium based, dual mode gamma and neutron elpasolite scintillation crystal, has been grown and evaluated at RMD. Energy resolution of 4.2% at 662 keV (FWHM) is measured for samples of this material. From comparison with a 137Cs spectrum collected with NaI:Tl, a gamma-ray induced light yield of 26,000 ph/MeV is estimated for TLYC. The material also shows better proportionality of response than both LaBr3:Ce and NaI:Tl in the energy range between 32 keV to 1275 keV. Single thermal neutron interactions produce a peak measured at a gamma equivalent energy of 1.9 MeVee, corresponding to a (neutron induced) light yield of approximately 47,000 ph/n. Decay times obtained from gamma-ray interactions in TLYC are measured at about 57 ns, 431 ns, and 1055 ns, with slightly shorter values measured for neutron interactions. These differences allow for gamma-neutron pulse shape discrimination (PSD) and a PSD Figure-of-Merit (FOM) of 2 is measured with TLYC. [ABSTRACT FROM AUTHOR]

We report on a new family of scintillators - Lithium alkaline halides, developed based on the alkaline halides by introducing lithium for dual mode gamma-neutron detection. Many different compositions were grown, among which LiSr2I5 (LSI), LiCa2I5 (LCI), LiSr2Br5 (LSB) activated with divalent Europium show good gamma and neutron detection properties. LSI shows the main emission at \sim 497 nm under X-ray excitation. It also shows good proportionality, which in combination with the light yield as high as 60000 photons/MeV, results in an energy resolution of 3.5% at 662 keV. The electron or gamma equivalent energy (GEE) of the thermal neutron peak due to the ^6Li neutron capture is 4.1 MeV, which amounts to a very high neutron light yield of \sim 245000 photons. The decay times for neutrons are faster compared to that for gamma-rays, hence we achieved good pulse shape discrimination (PSD) between gamma and neutron events. Our initial studies on the effects of Eu concentration on the properties of LSI show that 3%–4% Eu concentration is optimal for the best performance in terms of gamma and neutron light yields and pulse shape discrimination. LCI shows the main emission at \sim 475 nm under X-ray excitation and a very high gamma light yield of \sim 90000 photons/MeV. The measured energy resolution is 6% at 662 keV. The electron equivalent energy for neutron detection has been measured to be around 3 MeV, which gives a neutron light yield of \sim270000 photons. The measured decay times for neutrons are faster compared to gamma decays and the PSD between the gamma-rays and neutrons is not as good as LSI. LSB shows two emissions at \sim 410 and 475 nm under X-ray excitation. The measured light yield is \sim 32000 ph/MeV gamma-ray with an energy resolution of 6% at 662 keV. The electron equivalent energy of the ^6Li capture peak was measured to be 3.3 MeV. [ABSTRACT FROM AUTHOR]

Properties of dual-mode scintillation detectors based on CLLBC crystals are reported. Energy resolution and light yield are measured at 2.9% (FWHM) at 662 keV and 45000 photons/MeV, respectively, for a 1-in-diameter and 1-in-long crystal. With less than 2% variation in light yield as a function of energy, CLLBC has better proportionality than \LaBr3 and NaI:Tl. Neutron peak resulting from reactions with neutrons emitted by ^252\Cf (moderated) is measured at a gamma energy equivalent of 3.1 MeVee (electron energy equivalent), making pulse height discrimination between gamma-rays and neutrons easy. The material is also of effective pulse shape discrimination. The figure-of-merit for discrimination of gamma rays and thermal neutrons in CLLBC can be as high as 3.2, which is comparable to that of CLYC. [ABSTRACT FROM AUTHOR]

Abstract: Cs2LiYCl6 (CLYC) is one of the most interesting new scintillators developed during the last fifteen years. Its use as a thermal neutron scintillator was discovered in 1999 at the Delft University of Technology in Netherlands. In 2003, CLYC was selected by Radiation Monitoring Devices (RMD) for further studies and ultimately resulted in a commercial product. RMD's investigation of CLYC showed that it is a very good gamma ray detector with excellent 4% or better energy resolution, making it an ideal choice for dual mode detectors. Recently, Bubble Technology Industries of Canada discovered the possibility of fast neutron detection with CLYC, increasing its versatility even further. In this paper, we present the progress of CLYC’s development since its inception, with a focus on the work conducted at RMD. Our initial results with small crystals are presented, followed by data collected with samples of consecutively larger volumes and quality. We discuss the improvements in the energy resolution from 7% to 3.6%, as well as volume from 1cm3 to 100cm3. In addition, we address basic properties, gamma ray and neutron detection, pulse shape discrimination, and recently discovered fast neutron detection. [Copyright &y& Elsevier]

Abstract: Large diameter Bridgman growth of europium activated strontium iodide SrI2:Eu2+ produces crystals with light yield of up to 115,000ph/MeV with an excellent light yield proportionality. SrI2:Eu2+ exhibits an outstanding energy resolution of better than 3% FWHM at 662keV. Its emission is centered at 435nm. The scintillation decays with a 1μs time constant for small samples and up to 5μs to larger crystals. This paper presents successful progress made in the vertical Bridgman crystal growth of SrI2:Eu2+ and its scintillator properties. Large diameter, crack-free and transparent SrI2:Eu2+single crystals with diameters of 1in., 1.3in., 1.5in. and 2in. were all successfully grown. [Copyright &y& Elsevier]

Up to 1-in-diameter, Eu-doped CsBa 2 {\I} 5 and BaBrI crystals have been grown using the vertical Bridgman method. Scintillation properties of the crystals up to \sim 1 \times 1 \times 1~\cm^3 have been studied under gamma-ray irradiation. Systematic concentration studies have been performed for both these alkaline earth halides with Eu^2+ doping levels ranging from 0% to 10% to optimize growth of large crystals. We have achieved excellent energy resolution of \sim 2.6\% at 662 keV for a 2\,\times\,2\,\times\,1-mm^3 sample of CsBa2 {\I} 5:2%Eu. However, in this paper, the emphasis is on the larger crystals that can be used practically in nuclear nonproliferation applications. Our measurements of a 1.0\,\times\,1.0\,\times\,1.0-cm^3 sample of CsBa2 {\I} 5:3%Eu, processed from a 1-in-diameter crystal, shows very good energy resolution of 3.9% at 662 keV, high light output of \sim 80\,000~photons/MeV, and a principal decay time of \sim 900~ns. The second investigated composition, BaBrI:5%Eu, 1.0-cm-diameter \times\,1.0-cm-thick sample shows high light output of 71\,000 photons/MeV and energy resolution of 4.3% at 662 keV. A decay time of 480 ns was measured for this sample, which is shorter than most Eu^2+ doped materials of this size. The emission in these materials is due to d\rightarrow f transitions of Eu^2+ and occurs over a single band between 400–500 nm. It peaks at \sim 430~nm for CsBa 2 {\I} 5:Eu and at \sim 413~nm for BaBrI:Eu. Since both compositions show high proportionality over a wide range of energies, we expect to see improvements in the energy resolution of large crystals, as better quality of 1-in-diameter crystals are grown. [ABSTRACT FROM PUBLISHER]

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 (\sim2 mm), but also a small active area (6 mm \times 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\times 5\ mm\times 5\ mm cube, a 1\ cm\times 1\ cm\times 4\ cm cuboid, and a \varnothing 1\ in\times 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. [ABSTRACT FROM PUBLISHER]

Abstract: Europium-doped barium and strontium iodide crystals are high light yield scintillator materials with excellent energy resolution. In this communication, BaI2:Eu and SrI2:Eu single crystals with space groups of Pnma () and Pbca () 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. [Copyright &y& Elsevier]

Abstract: Cesium cerium bromide (Cs2CeBr5) and potassium cerium bromide (K2CeBr5) are new scintillator materials for X-ray and gamma ray detector applications. Recently, halide scintillator materials such as Ce-doped lanthanum bromide have been proved to be very important materials for the same purpose. These materials are highly hygroscopic; a search for high-light-yield non-hygroscopic materials was highly desirable to advance the scintillator technology. In this paper, we are reporting the crystal growth of novel scintillator materials, Cs2CeBr5 and K2CeBr5. Crystals were successfully grown from the melt using the vertical Bridgman–Stockbarger technique. In comparison with the high-performance LaBr3 or LaCl3 crystals, cerium-based alkali halide crystals, Cs2CeBr5 and K2CeBr5, have similar scintillation properties, while being much less hygroscopic. Furthermore, cesium-based compounds will not suffer from the self-activity present in potassium and lanthanum compounds. However, the Cs2CeBr5 crystals did not grow properly probably due to non-congruent melting or some phase transition during cooling. [Copyright &y& Elsevier]

Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5 mol % TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21/c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256 °C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ∼0.4 μm to 25 μm and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5 μm, 3 μm, 2.3 μm, and 2 μm corresponding to 7F6–7Fα transitions, for α=2–5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134 cm-1 from Raman scattering spectrum. [ABSTRACT FROM AUTHOR]

Abstract: Single-crystal strontium iodide (SrI2) doped with relatively high levels (e.g., 3–6%) of Eu2+ exhibits characteristics that make this material superior, in a number of respects, to other scintillators that are currently used for radiation detection. Specifically, SrI2:Eu2+ has a light yield that is significantly higher than LaBr3:Ce3+—a currently employed commercial high-performance scintillator. Additionally, SrI2:Eu2+ is characterized by an energy resolution as high as 2.6% at the 137Cs gamma-ray energy of 662keV, and there is no radioactive component in SrI2:Eu2+—unlike LaBr3:Ce3+ that contains 138La. The Ce3+-doped LaBr3 decay time is, however, faster (30ns) than the 1.2μs decay time of SrI2:Eu2+. Due to the relatively low melting point of strontium iodide (∼515°C), crystal growth can be carried out in quartz crucibles by the vertical Bridgman technique. Materials-processing and crystal-growth techniques that are specific to the Bridgman growth of europium-doped strontium iodide scintillators are described here. These techniques include the use of a porous quartz frit to physically filter the molten salt from a quartz antechamber into the Bridgman growth crucible and the use of a “bent” or “bulb” grain selector design to suppress multiple grain growth. Single crystals of SrI2:Eu2+ scintillators with good optical quality and scintillation characteristics have been grown in sizes up to 5.0cm in diameter by applying these techniques. Other aspects of the SrI2:Eu2+ crystal-growth methods and of the still unresolved crystal-growth issues are described here. [Copyright &y& Elsevier]

Abstract: Cs2LiYCl6:Ce (CLYC) has been demonstrated to be sensitive to thermal neutrons via the 6Li(n, )t reaction, and recently to fast neutrons via the 35Cl(n,p) reaction. The scintillation properties of CLYC have been investigated in more detail to further understand its capabilities. Pulses from thermal neutron, fast neutron, and -ray induced excitations were captured, digitized over a time range, and analyzed to identify the scintillation mechanisms responsible for the observed shapes. Additionally, the timing resolutions of CLYC crystals of different sizes were measured in coincidence with a fast CeBr3 scintillator. The effect of high count rates on fast neutron energy resolution and pulse-shape discrimination was investigated up to 45kHz. [Copyright &y& Elsevier]

Abstract: Cs2LiYCl6 (CLYC) has generated recent interest as a thermal neutron detector due to its excellent pulse-shape discrimination and energy resolution. Here, the capabilities of CLYC as a fast neutron detector and spectrometer are reported. A 1in.×1in. CLYC detector was used to measure the response of mono-energetic neutrons over a range of 0.8–2.0MeV produced via the 7Li(p,n) reaction at the University of Massachusetts Lowell 5.5MV Van de Graaff accelerator. A broad continuum from the 6Li(n, ) 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 35Cl(n,p)35S reaction, with a Q-value of +615keV, and corroborated in simulations using MCNPX. The average resolution of 9% for these peaks makes CLYC a promising candidate for a fast neutron spectrometer. [Copyright &y& Elsevier]