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A scintillator-based Timepix3 (TPX3) detector was developed to resolve the high-frequency modulation of a neutron beam in both spatial and temporal domains, as required for neutron spin-echo experiments. In this system, light from a scintillator is manipulated with an optical lens and is intensified using an image intensifier, making it detectable with the TPX3 chip. Two different scintillators, namely, 6LiF:ZnS(Ag) and 6LiI:Eu, were investigated to achieve the high resolution needed for spin-echo modulated small-angle neutron scattering (SEMSANS) and modulation of intensity with zero effort (MIEZE). The methodology for conducting event-mode analysis is described, including the optimization of clustering parameters for both scintillators. The detector with both scintillators was characterized with respect to detection efficiency, spatial resolution, count rate, uniformity, and γ-sensitivity. The 6LiF:ZnS(Ag) scintillator-based detector achieved a spatial resolution of 200 μm and a count rate capability of 1.1 × 105 cps, while the 6LiI:Eu scintillator-based detector demonstrated a spatial resolution of 250 μm and a count rate capability exceeding 2.9 × 105 cps. Furthermore, high-frequency intensity modulations in both spatial and temporal domains were successfully observed, confirming the suitability of this detector for SEMSANS and MIEZE techniques, respectively. [ABSTRACT FROM AUTHOR]

Abstract Recent studies have shown that under certain environmental conditions, plastic scintillators which are used in a variety of applications in outdoor environments develop defects called "fogging", resulting in a reduced useful lifetime and increased maintenance cost. Applications of plastic scintillators include scanning recycled steel going into a processing plant, personnel portals to scan employees, and scanning cargo and cars crossing borders of many countries. In this report, fogging was studied in conventional PVT and PS-based plastic scintillators, both field aged and freshly cast. A new fogging-resistant PVT-based formulation developed by scientists at Lawrence Livermore National Laboratory (LLNL) was tested as well. We used accelerated aging experiments via temperature and humidity cycling in controlled laboratory conditions to create observable temporary fogging defects in small samples (≤ 1 in3). Photoluminescence and optical transmission studies were used to evaluate the effect of the fogging. The time evolution of the induced temporary fogging formation and defogging (i.e. fading of defects in ambient conditions over time) were recorded using optical microscopy, time-lapse photography, and gravimetric analysis. [ABSTRACT FROM AUTHOR]

Abstract KCaI 3 :Eu is a scintillator composition that is promising for national security applications, with a high light yield and good energy resolution (∼ 70,000 ph/MeV and ∼ 3% E.R. at 662 keV, respectively). In addition to its high performance, we have been successful at growing KCaI 3 :Eu at larger sizes (38 mm diameter) without cracking. In this work we utilized a multi ampoule growth station to grow four 38 mm diameter crystals simultaneously. Three of these crystals achieved an energy resolution of ∼ 4% at 662 keV. The three crystals were hermetically packaged and a collimation study was carried out. This study revealed that light yield at a given irradiation location is dominated by photon path lengths and self-absorption, while the energy resolution dependence is affected heavily by local crystal quality. A 50 mm diameter KCaI 3 :Eu crystal was grown that achieved an energy resolution of 4.6% at 662 keV. GEANT4 was used to model a gap-style package that results in reduced photon path lengths, and therefore reduced self-absorption probability. [ABSTRACT FROM AUTHOR]

The distorted-perovskite scintillator materials CsCaI 3 :Eu and CsSrBr 3 :Eu prepared as single crystals have shown promising potential for use in radiation detection applications requiring a high light yield and excellent energy resolution. We present a study using high temperature powder X-ray diffraction experiments to examine a deleterious high temperature phase transition. High temperature phases were identified through sequential diffraction pattern Rietveld refinement in GSAS II. We report the linear coefficients of thermal expansion for both high and low temperature phases of each compound. Thermal expansion for both compositions is greatest in the [0 0 1] direction. As a result, Bridgman growth utilizing a seed oriented with the [0 0 1] along the growth direction should be used to mitigate thermal stress. [ABSTRACT FROM AUTHOR]

In this paper we report on the scintillation properties of TlSr 2 I 5 doped with Eu2+, a novel thallium-containing high-resolution scintillator for gamma-ray spectroscopy. Small diameter, good quality crystals of TlSr 2 I 5 :Eu (TSI) with different Eu2+ concentrations were grown by the vertical Bridgman method. X-ray diffraction measurements show that single crystals of TSI belong to the monoclinic system with space group P2 1 /c. TlSr 2 I 5 has a density of 5.32 g/cm3 and effective Z of 60. The X-ray excited emission of Eu2+ doped TlSr 2 I 5 features a broad emission band peaking between 460–470 nm. The light yield of TlSr 2 I 5 crystal doped with 1% Eu2+ is measured to be ∼ 72,000 ph/MeV with an energy resolution of 2.8% at 662 keV. The scintillation decay time which is characteristic of Eu2+ shows two components, with ∼ 90% of the light in a ∼ 500 ns component and the rest in a longer component of ∼ 3 μ s. [ABSTRACT FROM AUTHOR]

In this paper we report on the crystallographic and scintillation properties of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + , two novel thallium-containing high-resolution scintillators for gamma-ray spectroscopy. Crystals of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + were grown by the Vertical Bridgman method up to 1-inch diameter and 1-inch long. Single crystals of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + belong to the orthorhombic system with space group 62 and have a density of 5.16 and 5.98 g/cm3, respectively. The scintillators show high light yields of up to 68,000 photons/MeV, excellent gamma-ray energy resolution of ≤ 3% at 662 keV, a fast scintillation decay, and a proportional response over a wide range of energies from 32 keV up to 1275 keV. Density Functional Theory calculations show that the Ce 3 + energy levels are inside the bandgap despite the smaller bandgap of Tl 2 LaCl 5 and Tl 2 LaBr 5 compared to K 2 LaCl 5 and K 2 LaBr 5. A systematic Ce 3 + concentration study was performed for Tl 2 LaCl 5 :Ce 3 + and trends observed. [ABSTRACT FROM AUTHOR]

• Mixed scintillator CeBr 3−x I x was investigated. • X-ray diffraction was used to determine the structure both phases that formed. • Five singled crystals were grown via the vertical Bridgman technique. • A light yield of >80,000 ph/MeV was measured for the grown crystal CeBr 2 I. CeBr 3 is an intrinsic scintillator that has promising performance capabilities such as 60,000 ph/MeV and ~4% energy resolution at 662 keV. It has been shown that halide mixing can improve the light yield of single halide scintillators. In this work we attempted to improve on CeBr 3 by creating a mixed halide composition CeBr 3−x I x. Analysis of melt-freeze samples revealed that the light yield of CeI 3 rapidly increases as bromine is substituted. Thirteen mm diameter crystals were grown using the vertical Bridgman technique, with x values between 0.03 and 1. The CeBr 2.5 I 0.5 crystal segregated into two sections, colorless and green, while the CeBr 2 I crystal was entirely green. X-ray diffraction analysis was used to identify the two phases. Decay time increased as iodine concentration increased. All colorless phase crystals reached <4.5% energy resolution at 662 keV and >65,000 ph/MeV, with the CeBr 2.94 I 0.06 crystal achieving 3.9% energy resolution at 662 keV. The green phase crystals both reached light yields of 78,000 ph/MeV, the highest ever recorded for a CeI 3 phase crystal. [ABSTRACT FROM AUTHOR]

Fogging in plastic scintillators is a degradation mechanism that reduces light collection efficiency. In an effort to reduce maintenance costs, multiple groups have attempted to understand and prevent this problem by changing plastic compositions and system level designs. New formulations have been produced that are promising with respect to fogging resistance. In this current work we study a variety of new compositions by subjecting them to an accelerated aging experiment with varying temperature and humidity profiles. Compositions are analyzed for their resistance to degradation after saturation periods, with those containing polymethyl methacrylate and divinyl benzene being the most promising. Pulse height spectra revealed that after environmental aging, many of the samples suffered a reduction in light yield to different degrees, even those that did not fog. This result could be due to heating of the samples and may be prevented by further production optimization. [ABSTRACT FROM AUTHOR]

Inch-sized scintillating crystals are required for practical radiation detectors such as hand-held radio-isotope identification devices. In this work, a transparent and colorless 2-inch diameter KCa 0 . 8 Sr 0 . 2 I 3 : 0 . 5 mo % E u 2 + single crystal was grown by the vertical Bridgman method, and the scintillation properties of a ∅ 50 mm × 45 mm long sample were evaluated. The Eu 2 + 5 d 1 - 4 f emission under X-ray excitation is centered at 472 nm. Its scintillation decay time under 137 Cs source irradiation is 2 . 37 μ s , and the absolute light output is 51,000 ± 3000 photons/MeV. The energy resolution at 662 keV was evaluated for different orientations of the crystals with respect to the PMT, and the effect of 40 K background subtraction on energy resolution was evaluated. The performance of the packaged crystal was also investigated. [ABSTRACT FROM AUTHOR]

A self-activated Cs 4 YbI 6 single crystal was grown by the vertical Bridgman method. Crystal structure refinements verified the phase purity and the trigonal crystal system with a space group of R 3 ̅ c. By using differential scanning calorimetry, the melting and crystallization points were determined to be 550 and 510 °C, respectively. Luminescence and scintillation properties were systematically studied. Upon ultraviolet light (360 nm) excitation, the Cs 4 YbI 6 crystal exhibits bluish-green emission centered at 450 and 480 nm due to spin-allowed and spin-forbidden transitions of Yb 2+ activators. The lifetimes of the corresponding emission bands at room temperature are tens and hundreds of nanoseconds, respectively. X-ray excited radioluminescence spectrum is dominated by the spin-forbidden transition of Yb 2+ at 480 nm. The absolute light yield is 2700 ± 200 photons/MeV with a principal scintillation decay time of 33 ns. The physical explanation for the low light yield observed is proposed from experimental and theoretical insights. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation properties of Bi 3+ , Sb 3+ , and Eu 2+ -doped LaI 3 and LaBr 3 were explored. Out of the three dopants investigated, Eu 2+ was the most promising new activator for small-bandgap LaX 3 (X = Br, I) and was further studied in the mixed-halide LaBr 3−x I x . Crystals were grown from the melt using the vertical Bridgman method. LaBr 3 :Eu 2+ 0.5% (mol) had the most favorable scintillation properties with a light output of 43,000 ph/MeV and 6% energy resolution at 662 keV. Performance of LaBr 3−x I x :Eu 2+ worsened for most samples as iodide concentration was increased. Room-temperature scintillation of LaI 3 :Eu 2+ 0.1% and 0.5% was observed and is the first case of room-temperature emission reported for doped LaI 3 . [ABSTRACT FROM AUTHOR]

We investigate the multi-ampoule growth at 25 mm diameter of ternary iodide single crystal scintillator KCaI 3 :Eu using the randomly oriented self-seeded Bridgman method. We compare scintillation performance between cubic inch scale crystals containing small variations of low nominal europium concentrations previously shown to balance light yield with self-absorption in the host crystal. Growth conditions were optimized in the developmental furnace and four 2 in 3 KCaI 3 :Eu crystals were grown simultaneously producing a total of six 25 mm × 25 mm cylinders. Small variations in activator concentration did not result in significant performance differences among the six measured crystals. A range of energy resolutions of 3.5–4.7% at 662 keV was achieved, surpassing that of NaI:Tl crystals commonly used in spectroscopic detection applications. The function and basic design of the multi-ampoule furnace as well as the process of growing single crystals of KCaI 3 is included here. [ABSTRACT FROM AUTHOR]

CsSrI3/Eu2+ has very promising scintillation properties for gamma-ray spectroscopy applications, but it has proven difficult to grow high quality single crystals in large sizes. This paper reports a composition-engineering strategy, in this case a combination of off-stoichiometric melts and Eu2+ concentration optimization, to obtain large-size CsSrI3/Eu2+ crystals with excellent energy resolution. Crystals of a series of off-stoichiometric compositions, Cs(1+x)(Sr,Eu)(1-x)I(3-x) (x = 0, 0.05, 0.06, and 0.1), were grown by the Bridgman method. The Cs1.06Sr0.94I2.94/Eu2+ single crystal has the highest optical transmittance between 450 and 800 nm. Cs1.06Sr0.94I2.94 single crystals doped with 0.5, 1, 3, 5, and 7 mol % Eu2+ ions were also grown by the Bridgman method. The effects of Eu2+ concentration on the phase purity and optical and scintillation properties were studied. X-ray diffraction patterns confirmed the phase purity of all samples with the exception of a hydrate phase formed during measurement. Increasing Eu2+ concentration leads to longer decay components due to the effect of self-absorption. An unexpected relationship was found between the Eu2+ concentration and the appearance of two photopeaks in a pulse height spectrum acquired under a single gamma-ray energy of 662 keV irradiation. The origins of this phenomenon are proposed from experimental insights. The optimal composition we developed achieved an excellent energy resolution of 3.4% for ϕ22 mm × 2 mm, 3.9% for ϕ22 mm × 15 mm, and 4.1% for ϕ22 mm × 19 mm at 662 keV. The results of this paper lead to a better understanding of the effects of composition-engineering in optimization of nonstoichiometric scintillator compounds. [ABSTRACT FROM AUTHOR]

KCaI 3 :Eu crystals have been identified as very promising for use in spectroscopic detector applications related to nuclear nonproliferation and domestic security efforts. Initial studies have shown for small crystals a few mm 3 in size with 3% europium dopant concentration, a high light yield of >70,000 ph/MeV and energy resolution of ≈3% at 662 keV is attainable which is comparable with the highest performance scintillators discovered. In this work, single crystals of KCaI 3 with a range of Eu 2+ doping between 0 and 5 at% substituting for Ca 2+ were grown at 22 mm diameter and their performance for gamma-ray spectroscopy studied. Comparisons among crystals approximately Ø22 mm×22 mm (8.4 cm 3 or ≈0.5 in 3 ) provide a more accurate understanding of how scintillation performance changes with Eu doping and increased crystal size. KCaI 3 in the undoped form is shown to be a highly efficient intrinsic scintillator with a defect-related emission at 404 nm which coexists with the Eu 2+ 5d–4f emission in low dopant concentrations and is completely re-absorbed in more heavily doped crystals. For larger crystals, effects from self-absorption due to Eu activation become more evident by a near doubling of decay time for 0.5 in 3 crystals as the activator is increased from 0.5 to 5.0 at% Eu. Comparisons of pulse-height spectra obtained for Ø22 mm×22 mm cylinders with varying Eu concentration suggests best performance is achieved using lower Eu additions closer to 0.5–1.0 at%. Using a modified crystal packaging featuring an offset reflector geometry, 0.5 in 3 crystals of KCaI 3 :Eu can attain under 4% energy resolution at 662 keV. [ABSTRACT FROM AUTHOR]

In this paper we report on the crystal growth, density functional theory (DFT) calculations and scintillation properties of Tl 3 LnCl 6 :Ce 3 + and TlLn 2 Cl 7 :Ce 3 + (Ln = Y, Gd). Crystals were grown by the Vertical Bridgman technique up to 16 mm in diameter and 25 mm long. Crystals of Tl 3 YCl 6 :Ce 3 + and Tl 3 GdCl 6 :Ce 3 + belong to the family of the Nesohalides which have the monoclinic crystal structure. Crystals of TlY 2 Cl 7 :Ce 3 + and TlGd 2 Cl 7 :Ce 3 + belong to the family of the Phyllohalides which have either the monoclinic or the orthorhombic crystal structure. The light yields of these Nesohalides and Phyllohalides are typically on the order of 35,000–40,000 ph/MeV. [ABSTRACT FROM AUTHOR]

Europium doped strontium iodide (SrI 2 :Eu 2 +) is one of the cutting-edge halide scintillators for gamma-ray spectroscopy applications due to its low radioactive background, ultrahigh light yield (70,000–100,000 photons/MeV), and excellent gamma-ray energy resolution (2.6%–3% at 662 keV). In this work, we report an improvement in the scintillation characteristics of SrI 2 :Eu 2 + single crystals via tetravalent ion codoping, namely Zr 4 +. High quality SrI 2 :Eu 2 + single crystals codoped with 0, 0.05, 0.1, and 0.2 at.% Zr 4 + were grown by the Multi-ampoule Bridgman method. All of the as-grown crystals are transparent, crack-and inclusion-free. They have high optical quality with a transmittance of over 70%. The effects of Zr 4 + codoping on spectral properties and decay kinetics of SrI 2 :Eu 2 + under optical, and x- and gamma-ray excitation are studied. An enhancement of gamma-ray spectroscopic resolution from 2.8 to 2.5% at 662 keV and 5.4 to 5% at 122 keV is achieved upon Zr 4 + codoping with a slightly enhanced light yield of 95,000 photons/MeV. [ABSTRACT FROM AUTHOR]