Boron-Based Neutron Scintillator Screens for Neutron Imaging

Abstract

In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital neutron imaging systems. Commonly used neutron scintillators are based on 6LiF and gadolinium oxysulfide neutron converters. This work explores boron-based neutron scintillators because 10B has a neutron absorption cross-section four times greater than 6Li, less energetic daughter products than Gd and 6Li, and lower γ-ray sensitivity than Gd. These factors all suggest that, although borated neutron scintillators may not produce as much light as 6Li-based screens, they may offer improved neutron statistics and spatial resolution. This work conducts a parametric study to determine the effects of various boron neutron converters, scintillator and converter particle sizes, converter-to-scintillator mix ratio, substrate materials, and sensor construction on image quality. The best performing boron-based scintillator screens demonstrated an improvement in neutron detection efficiency when compared with a common 6LiF/ZnS scintillator, with a 125% increase in thermal neutron detection efficiency and 67% increase in epithermal neutron detection efficiency. The spatial resolution of high-resolution borated scintillators was measured, and the neutron tomography of a test object was successfully performed using some of the boron-based screens that exhibited the highest spatial resolution. For some applications, boron-based scintillators can be utilized to increase the performance of a digital neutron imaging system by reducing acquisition times and improving neutron statistics.

Fast Neutron Imaging with Semiconductor Nanocrystal Scintillators

“…Consequently, there are two common types of fast neutron imaging detectors: an integrated liquid or plastic scintillator which provides both high proton density and light emission, ,− or a two-part detector consisting of a hydrogen-dense matrix (often a plastic or polymer such as polypropylene (PP) or high-density polyethylene) and a scintillator material such as ZnS:Ag, ZnS:Cu, or Gd 2 O 2 S:Tb. − The latter type has shown the most success to date, , with screens consisting of ZnS:Cu in a PP matrix, denoted hereafter as ZnS:Cu­(PP), showing a good combination of light output and spatial resolution that has led to their commercialization by RC Tritec AG. , However, long exposure times are still required to obtain high-quality images even under high fast neutron fluxes, while spatial resolution decreases substantially with thickness of the scintillator plate, likely due to light scattering at the phosphor–plastic interface, as the typical size of phosphor inclusions are larger than the emission wavelength. Another fundamental drawback is the afterglow of the ZnS:Cu phosphor, which exhibits a several minute decay under fast neutron beam exposure, problematic for the short repeated exposures required for computed tomography and precluding the use of such screens in pulsed neutron experiments with high repetition rates.…”

Extraordinary intense blue Tl+ lone-pair photoluminescence from thallium(i) chloride hydroborate Tl3Cl[B12H12]

“…11 As Tl 3 Cl[B 12 H 12 ] also shows strong blue radioluminescence peaking at 445 nm upon 50 keV excitation (Fig. 14) and has a fairly high density ( ρ = 4.06 g cm −3 ), this novel 6s 2 -cation hydroborate can be regarded as a promising molecular scintillator, which deserves further investigation for application in high-energy physics, neutron detectors, 35 or medical imaging.…”

“…Dalton Transactions be regarded as a promising molecular scintillator, which deserves further investigation for application in high-energy physics, neutron detectors, 35 or medical imaging.…”

Performance of borated scintillator screens for high-resolution neutron imaging

“…However, earlier reports about trial screens containing boron showed much lower light output than expected, to an extent that made those screens practically unusable. Simulations performed in [4] showed the range of the reaction products to be on the order of only 2-3 µm in any boron-containing substance, as shown in Table 1.…”

“…However, due to the low energy of the main conversion electrons from neutron capture in 157 Gd (29 keV + 71 keV), the range of the reaction products in Gadox is very low, on the order of a few micrometers. Also the light yield from the smaller deposition energy is much less than that of 6 LiF in zinc sulfide, only 3.29 photons per neutron capture on average [4]. Due to the much higher cross section of Gd and thus much higher detection efficiency, screens can be thinned to 10-20 µm for nearly full absorption, delivering a resolution about equal to the range of the thickness.…”