Characterization of a 10B-doped liquid scintillator as a capture-gated neutron spectrometer

Abstract

Accurate measurement of fast neutrons and their energies is essential for many scientific, industrial, and military endeavors. Fields that require fast neutron measurements include material science [1], national security [2], and medical physics [3]. Particularly, national security applications frequently require fast, accurate, and portable methods of neutron spectroscopy [4]. Portability is of particular importance, as identification of nuclear contraband often requires monitoring special nuclear materials outside of a nuclear laboratory [5]. Performing neutron energy measurements in the field is often difficult, since most current methods of neutron spectroscopy require large experimental setups [6]. Capture-gated liquid scintillators are compact and portable, while providing some fast neutron energy resolution. These detectors show promise of becoming one of the standard tools for fast neutron spectroscopy in mixed radiation environments. Standard liquid scintillators have long been used as fast neutron detectors [7]. They have good pulse shape discrimination (PSD) and timing abilities, but often do not provide neutron energies [8] because of their nonlinear light output and the inability to differentiate between fully and partially moderated neutrons. This can be remedied with a technique known as capturegating, which uses standard organic liquid scintillator fluid doped with materials that have a high absorption cross section for thermal neutrons, such as 10 B, 6 Li, or nat Gd [9-11]. A fast neutron striking the detector will lose energy, producing a standard scintillation signal. If the neutron thermalizes and thus deposits all of its energy into the detector, it may capture onto the doping agent (e.g., 10 B). The reaction products (α + 7 Li in the case of 10 B doping) will lose their energy in the active volume, producing a secondary scintillation pulse. This gives rise to a characteristic double-peaked signal, which allows for differentiation between fully and partially moderated neutrons. This differentiation allows capture-gated scintillators to be used as full-energy neutron spectrometers [7]. The BC-523A scintillator used in this work is doped with 10 B, and extensive research has already been performed on this type of detector [12-16]. The physics behind the scattering and capture interactions are well understood [12]. Figure 1 depicts the sequence of events when a fast neutron (shown in red) is incident on the detector. It first interacts with the hydrogen (shown as blue circles) in the scintillator, causing the recoil of the protons and producing a peak (moderation peak) in the waveform. When the neutron loses 1

Neutron-induced thermoluminescence properties of Tb³⁺-doped CaO–Al₂O₃–B₂O₃ glasses

“…Hence, it is necessary to use nuclides that cause a nuclear reaction to convert neutrons to charged particles. 3 He or BF 3 proportional counters, 1),2) LiF/ZnS sheets, 3) Ce 3+ -doped LiCaAlF 6 single crystals, 4) LiCaAlF 6 :Eu 2+ single crystals, 5) ZnS:Ag/LiF, Li-glass, 6) Gd-imaging plates (BaFBr:Eu and Gd 2 O 3 ), 7) and LiF are used for neutron detection in which 3 He, 6 Li, 10 B, and Gd function as converters. Among them, 10 B has a large reaction cross-section for neutrons.…”

“…3 He or BF 3 proportional counters, 1),2) LiF/ZnS sheets, 3) Ce 3+ -doped LiCaAlF 6 single crystals, 4) LiCaAlF 6 :Eu 2+ single crystals, 5) ZnS:Ag/LiF, Li-glass, 6) Gd-imaging plates (BaFBr:Eu and Gd 2 O 3 ), 7) and LiF are used for neutron detection in which 3 He, 6 Li, 10 B, and Gd function as converters. Among them, 10 B has a large reaction cross-section for neutrons. For the nuclear reaction of 10 B and a neutron, 94% of the reactions produce 1.47 MeV ¡-rays and 0.84 MeV 7 Li* ( 7 Li* nuclide in its excited state), and 6% of the reactions produce 1.78 MeV ¡-rays and 1.01 MeV 7 Li.…”

“…Among them, 10 B has a large reaction cross-section for neutrons. For the nuclear reaction of 10 B and a neutron, 94% of the reactions produce 1.47 MeV ¡-rays and 0.84 MeV 7 Li* ( 7 Li* nuclide in its excited state), and 6% of the reactions produce 1.78 MeV ¡-rays and 1.01 MeV 7 Li. For the latter case, 7 Li* relaxes to 7 Li with 0.48 MeV £-rays emission.…”

“…Therefore, £-rays are finally emitted from 10 B (n, ¡) reaction. 8) In addition, 10 B has low reactivity with £-rays because the atomic number of boron is small; boron is also excellent in availability and safety. Hence, it is expected to be applied to detection elements that replace existing detection elements, as reported by many studies, e.g.…”

Monte-Carlo modeling and simulation of neutrons detection process using Boron-10

“…In that case, the properties of charged particle products mainly depend on the neutron energy and its corresponding cross-section. This model is widely applied in various research fields such as in Boron neutron capture therapy in medicine, 10,32 neutron detection and spectrometry in nuclear physics 13,17,19,24,25 and other important applications such as oil well logging. Improving the knowledge related to these reactions allows to optimize the exploitation of this process, specially when precise information on the particle products is needed.…”