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At least 937 records · Page 52

Artificial neural network algorithms for pulse shape discrimination and recovery of piled-up pulses in organic scintillators

We developed two neural-network (NN)-based algorithms (fully-connected neural network (Fc-NN) and recurrent neural network (RNN)) to perform pulse shape discrimination (PSD) and identification of piled-up pulses produced by organic scintillators, upon interaction with neutrons and gamma rays. We tested the algorithms on measured and verification sets of data and compared their classification performances to standard approaches. At a high acquisition count rate (100,000 counts per second, cps), in the presence of a gamma-to-neutron ratio of approximately 400–1, the proposed NN-based algorithm achieves a fraction of misclassified neutron, gamma, and piled-up pulses of approximately 1%, 1.8%, and 0.6%, respectively. Compared to the traditional approach, it exhibits 3×, 14×, and 11× improved (lower) miscalculation rates for neutron, gamma, and piled-up pulses, respectively. Here, we also demonstrate the capability of NN-based algorithms of successfully recovering and identifying neutron and gamma ray compositions from piled-up pulses in challenging, high pulse count rate conditions.

42 ENGINEERING↗

Analysis of 161 Tb by radiochemical separation and liquid scintillation counting

The determination of 161 Tb activity is problematic due to its very low fission yield, short half-life, and the complication of its gamma spectrum. At AWE, radiochemically purified 161 Tb solution was measured on a PerkinElmer 1220 Quantulus TM Liquid Scintillation Spectrometer. Since there was no 161 Tb certified standard solution available commercially, the counting efficiency was determined by the CIEMAT/NIST Efficiency Tracing method. The method was validated during a recent inter-laboratory comparison exercise involving the analysis of a uranium sample irradiated with thermal neutrons. Lastly, the measured 161 Tb result was in excellent agreement with the result using gamma spectrometry and the result obtained by Pacific Northwest National Laboratory.

07 ISOTOPE AND RADIATION SOURCES↗

Chemical stability and Ce doping of LiMgAlF 6 neutron scintillator

We perform density functional calculations to investigate LiMgAlF 6 as a potential neutron scintillator material. The calculations of enthalpy of formation and phase diagram show that single-phase LiMgAlF 6 can be grown but it should be more difficult than growing LiCaAlF 6 and LiSrAlF 6 . Moreover, the formation energy calculations for substitutional Ce show that the concentration of Ce on the Al site is negligible but a high concentration (>1 at.%) of Ce on the Mg site is attainable provided that the Fermi level is more than 5 eV lower than the conduction band minimum. Acceptor doping should promote Ce incorporation in LiMgAlF 6 .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Scintillation properties of Eu 2+ -doped KBa 2 I 5 and K 2 BaI 4

We report two new ternary metal halide scintillators, KBa 2 I 5 and K 2 BaI 4 , activated with divalent europium. Single crystal X-ray diffraction measurements confirmed that KBa 2 I 5 has a monoclinic structure (P2 1 /c) and that K 2 BaI 4 has a rhombohedral structure (R3c). Differential scanning calorimetry showed singular melting and crystallization points, making these compounds viable candidates for melt growth. We grew 13 mm diameter single crystals of KBa 2 I 5 :Eu 2+ and K 2 BaI 4 :Eu2+ in evacuated quartz ampoules via the vertical Bridgman technique. The optimal Eu 2+ concentration was 4% for KBa 2 I 5 and 7% for K 2 BaI 4 . The X-ray excited emissions at 444 nm for KBa 2 I 5 :Eu 4% and 448 nm for K 2 BaI 4 :Eu 7% arise from the 5d-4f radiative transition in Eu 2+ . KBa 2 I 5 :Eu 4% has a light yield of 90,000 photons/MeV, with an energy resolution of 2.4% and K 2 BaI 4 :Eu 7% has a light yield of 63,000 ph/MeV, with an energy resolution of 2.9% at 662 keV. Both crystals have an excellent proportional response to a wide range of gamma-ray energies.

36 MATERIALS SCIENCE↗

Serrated flow in $\mathrm{NaI:Tl}$ scintillator crystals

We report the serrated-flow behavior is an important phenomenon that unveils material-deformation mechanisms, as reported for various kinds of materials. NaI doped with Tl (NaI:Tl) is unique among scintillation materials in that the structure contains glide planes that are linked to serration behavior. In the present work, single crystals of NaI:Tl were subjected to room-temperature compression experiments at different strain rates. The serrated flow was observed, and complexity and multifractal analyses were performed to analyze the serration behavior. The findings revealed that the strain rate had a pronounced effect on the complexity and multifractality of the serrated flow, similar to what has been found in other alloy systems. The results also indicate that there may be a strong link between the complexity of the serrated flow behavior and the heterogeneity of the underlying dynamics. It is expected that the present work could be a step toward a better understanding of the deformation behavior and forgeability of NaI:Tl single crystals.

36 MATERIALS SCIENCE↗

Structure and scintillation yield of Ce-doped Al–Ga substituted yttrium garnet

Highlights: ► Range of Y{sub 3}(Al{sub 1−x}Ga{sub x}){sub 5}O{sub 12}:Ce solid solution crystals are grown from melt by the Czochralski method. ► Light yield of mixed crystals reaches 130% of the YAG:Ce value at x ∼ 0.4. ► ∼1% of antisite defects is formed in YGG:Ce, but no evidence of this is obtained for the rest of crystals. -- Abstract: Structure and scintillation yield of Y{sub 3}(Al{sub 1−x}Ga{sub x}){sub 5}O{sub 12}:Ce solid solution crystals are studied. Crystals are grown from melt by the Czochralski method. Distribution of host cations in crystal lattice is determined. Quantity of antisite defects in crystals is evaluated using XRD and atomic emission spectroscopy data. Trend of light output at Al/Ga substitution in Y{sub 3}(Al{sub 1−x}Ga{sub x}){sub 5}O{sub 12}:Ce is determined for the first time. Light output in mixed crystals reaches 130% comparative to Ce-doped yttrium–aluminum garnet. Luminescence properties at Al/Ga substitution are evaluated.

36 MATERIALS SCIENCE↗

Hydrothermal growth and scintillation properties of γ-CuBr single crystals

Highlights: • Transparent γ-CuBr single crystal with regular shape was successfully grown by hydrothermal method. • The x-ray excited optical luminescence of the γ-CuBr crystal, which exhibits an intensive 430 nm emission, is first reported. • The average decay time of the 430 nm emission is 36.9 ns. - Abstract: A fast scintillation crystal, γ-CuBr, was successfully grown by hydrothermal method with NH{sub 4}Br mineralizer. The element mole ratio of the Cu/Br crystal was about 0.91 caused by the crystal grown in a rich bromine environment. Under ultraviolet excitation, the crystal exhibited an intense 420 nm emission, a shoulder emission at 428 nm and a weak broadband emission at 560 nm, which could be related to free exciton recombination, Cu and Br vacancies, respectively. Furthermore, the X-ray excited optical luminescence of the crystal was first reported, and a strong 430 nm emission was observed. The analysis of luminescence decay kinetics revealed that the 430 nm emission is composed of two components with an average decay time of 36.9 ns. It means that the γ-CuBr crystal is a promising candidate for applications in fast radiation detection.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Neutron light output response and resolution functions in EJ-309 liquid scintillation detectors

Here, the neutron light output response functions and detector resolution functions were measured at Ohio University's tandem Van de Graaff generator for three cylindrical EJ-309 liquid scintillator cells, having dimensions 12.7(circle divide)-by-12.7, 7.6-by-7.6, and 7.6-by-5.1 cm. A 7.44 MeV deuteron beam was used on an Al-27 target generating a continuous spectrum over the energy range from a few hundred keV to over 10 MeV. The light output response functions are determined using an exponential fit. Detector resolution functions are obtained for the 12.7-by-12.7 and 7.6-by-7.6 cm detectors. It is demonstrated that the dependence on detector size is important for the light output response functions, but not to the same extent for the resolution function, even when photomultiplier tubes, detector material, and other detector characteristics are carefully matched.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

An alpha–gamma coincidence spectrometer based on the Photon–Electron Rejecting Alpha Liquid Scintillation (PERALS®) system

Here, an alpha–gamma coincidence spectrometer has been developed for the measurement of selected actinide isotopes in the presence of high beta/gamma fields. The system is based on a PERALS® liquid scintillation counter for beta/alpha discrimination and was successfully tested with both high purity germanium and bismuth germanate, gamma-ray detectors using conventional analog electronics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Neutron response function characterization of 4 He scintillation detectors

Time-of-flight measurements were conducted to characterize the neutron energy response of pressurized 4He fast neutron scintillation detectors for the first time, using the Van de Graaff generator at Ohio University. The time-of-flight spectra and pulse height distributions were measured. This data was used to determine the light output response function, which was found to be linear at energies below 3.5 MeV. The intrinsic efficiency of the detector as a function of incident energy was also calculated: the average efficiency up to 10 MeV was 3.1%, with a maximum efficiency of 6.6% at 1.05 MeV. Furthermore, these results will enable development of neutron spectrum unfolding algorithms for neutron spectroscopy applications with these detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Pulse height model for deuterated scintillation detectors

This work includes the theoretical calculation of pulse height distribution and elaborate measurement at Ohio University using deuterated organic scintillation detector, which allows us to thoroughly investigate the light output spectrum induced by fast neutrons and convincingly compensate the pulse deficiency due to application of threshold to minimize noises either from electronics or environmental background. Specifically, a complete and self-contained analytic model of pulse height distribution for EJ-315 is created. In the model, considering impacts of detector geometry on light output and neutron leakage, a non-uniform angular distribution is also taken into account. An energy range of incident neutron from 1 MeV to 10 MeV is investigated. In return, based on the Peierls-formula, the completed calculation exhibits quantitative probability of fast neutron slowing down history due to stochastic collisions with carbon or deuterium nuclei. The quantitative collision probability conjoining with light output function, which was measured and corrected in view of detector response to several gamma rays, for continuous neutron flux generated by the tandem Van De Graaff Generator gives the light output for various collisions. Furthermore, the individual collision structure of the light pulse spectrum is analyzed and compared to the corresponding pulse height distribution from experimental measurement. Lastly, the resulting light pulse height distribution generated in this model offers intriguing advantages for identifying or characterizing nuclear materials and estimating potentials of various fast recoil detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Time and position resolution of the scintillator strips for a muon system at future colliders

In this study, prototype scintilator+WLS strips with SiPM readout for a muon system at future colliders were tested for light yield, time resolution and position resolution. Depending on the configuration, light yield of up to 36 photoelectrons per muon per SiPM has been observed, as well as time resolution of 0.45 ns and position resolution along the strip of 7.7 cm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Test beam studies of the light yield, time and coordinate resolutions of scintillator strips with WLS fibers and SiPM readout

Prototype scintilator+WLS strips with SiPM readout for large muon detection systems were tested in the muon beam of the Fermilab Test Beam Facility. Furthermore, light yield of up to 137 photoelectrons per muon per strip has been observed, as well as time resolution of 330 ps and position resolution along the strip of 5.4 cm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

A new measurement of the 6 Li(n,α)t cross section at MeV energies using a 252 Cf fission chamber and 6 Li scintillators

We present a new measurement of the 6 Li(n,α)t cross section from 245 keV to 10 MeV using a 252 Cf fission chamber with 6 LiI(Eu) and Cs 2 LiYCl 6 :Ce (CLYC) scintillators which act as both target and detector. Neutron energies are determined from the time of flight (TOF) method using the signals from spontaneous fission and reaction product recoil. Simulations of neutron downscatter in the crystals and fission chamber bring 6 Li(n,α)t cross section values measured with the 6 LiI(Eu) into agreement with previous experiments and evaluations, except for two resonances at 4.2 and 6.5 MeV introduced by ENDF/B-VII.1. Suspected neutron transport modeling issues cause the cross section values obtained with CLYC to be discrepant above 2 MeV.

252Cf fission chamber↗

A novel use of light guides and wavelength shifting plates for the detection of scintillation photons in large liquid argon detectors

Scintillation light generated as charged particles traverse large liquid argon detectors adds valuable information to studies of weakly-interacting particles. This paper uses both laboratory measurements and cosmic ray data from the Blanche dewar facility at Fermilab to characterize the efficiency of the photon detector technology developed at Indiana University for the single phase far detector of DUNE. The efficiency of this technology was found to be 0.48% at the readout end when the detector components were characterized with laboratory measurements. A second determination of the efficiency using cosmic ray tracks is in reasonable agreement with the laboratory determination. In conclusion, the agreement of these two efficiency determinations supports the result that minimum ionizing muons generate ${\mathcal N}_{phot} = 40,000$ photons/MeV as they cross the LAr volume.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Neutron spectroscopy and spectral unfolding with 4 He fast neutron scintillators

Time-of-flight measurements were performed to determine the 4 He pressurized fast neutron scintillation detectors response function and the ability of the detectors to be applied as a spectrometer. An experimentally validated neutron energy response function was used in conjunction with an iterative least squares unfolding technique to unfold a 252 Cf spontaneous fission spectrum, a PuBe (α, n) spectrum, and a deuterium-deuterium (D-D) fusion reaction spectrum. In conclusion, the ability of the detectors to retain incident neutron energies makes them suitable for applications such as nuclear non-proliferation and spent nuclear fuel monitoring.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Intrinsic resolution limits of monolithic organic scintillators for use in rep-rated proton imaging

Rep-rated diagnostics are a necessity for present and future laser facilities focused on the study of high-energy-density (HED) phenomena. Electromagnetic fields in HED systems are of particular interest to the community, but are inherently difficult to diagnose due to the high mass-densities involved. By utilizing high-energy protons that penetrate through dense plasmas, fields may be visualized by detecting variations in proton fluence caused by the Lorenz interaction of the protons with the field. Typical detecting media used for proton imaging are single-use and do not scale well to rep-rated operation. We propose the use of a scintillator-based detector and characterize the energy and spatial responses to demonstrate its feasibility as a viable option for rep-rated proton imaging and other diagnostics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Computational investigation of arranged scintillating particle composites for fast neutron detection

Composite materials have the potential to play an important role in enabling high-performance and cost-effective neutron detectors for fundamental science, global security, and dosimetry applications. This work presents neutron and gamma transport simulation results on composites consisting of 6 Li-containing GS20 scintillator glass particles arranged in an organic matrix. These composites achieve high sensitivity for neutrons while suppressing signals from gamma rays. The simulations successfully identified optimal composite parameters such as particle size, geometry, and inter-particle pitch. This information is key to the subsequent fabrication and scale-up of the desired GS20-in-acrylic composite. Finally, the simulation results presented in this paper demonstrate that arranged composites can provide high neutron detection efficiency with gamma misidentification values of <1 in 10 6 gamma rays, assuming irradiation with a 252 Cf spontaneous fission source.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗