Lithium indium diselenide: A new scintillator for neutron imaging

Abstract

Lithium indium diselenide, 6 LiInSe2 or LISe, is a newly developed neutron detection material that shows both semiconducting and scintillating properties. This paper reports on the performance of scintillating LISe crystals for its potential use as a converter screen for cold neutron imaging. The spatial resolution of LISe, determined using a 10% threshold of the Modulation Transfer Function (MTF), was found to not scale linearly with thickness. Crystals having a thickness of 450 µm or larger resulted in an average spatial resolution of 67 µm, and the thinner crystals exhibited an increase in spatial resolution down to the Nyquist frequency of the CCD. The highest measured spatial resolution of 198 µm thick LISe (27 µm) outperforms a commercial 50 µm thick ZnS(Cu): 6 LiF scintillation screen by more than a factor of three. For the LISe dimensions considered in this study, it was found that the light yield of LISe did not scale with its thickness. However, absorption measurements indicate that the 6 Li concentration is uniform and the neutron absorption efficiency of LISe as a function of thickness follows general nuclear theory. This suggests that the differences in apparent brightness observed for the LISe samples investigated may be due to a combination of secondary charged particle escape, scintillation light transport in the bulk and across the LISe-air interface, and variations in the activation of the scintillation mechanism. Finally, it was found that the presence of 115 In and its long-lived 116 In activation product did not result in ghosting (memory of past neutron exposure), demonstrating potential of LISe for imaging transient systems.

Neutron Imaging with Timepix Coupled Lithium Indium Diselenide

“…The technology shows great potential to go even smaller using techniques such as charge centroiding and super sampling with a step size smaller than the 55 µm pixel pitch. The acquisition times rivaled the previous LISe scintillator imaging experiments [14,15], generally requiring 1 second to acquire a single frame and between 1 to 10 minutes to capture high resolution images, given neutron flux at HFIR. Furthermore, the system ran continuously under neutron flux at HFIR for a period of roughly 3 days, capturing data without degradation in sensor performance.…”

“…In the activated LISe sensor, the decay of 116 In will release betas (isomer with a large end-point energy of 3.3 MeV) and the ground state (an end point energy of 1 MeV) where the branching ratio is 0.267 [14].The interaction rate compared to 6 Li is dependent on the incident neutron energy, approximately 20% for this experiment. Therefor the higher isomer decay energy will manifest itself around 4% of the time in all neutron interactions.…”

“…Alternatively, lithium indium diselenide or LISe, has been used as a scintillator to create high resolution neutron radiographs of micro-scale test patterns [14] as well as neutron computed tomography scans of biological material [15]. Demonstrating its capabilities as a scintillating neutron detector, lithium indium diselenide has also been proven as a semiconductor resulting in the 16-channel neutron pixel detector [16].…”

“…Along with resolution tests, the LISe imager was used to capture images of standardized samples for feature detection, mimicking applications in nuclear image analysis. In previous testing, the University of Tennessee "Power T" logo was captured using a standard 50 µm thick LiF scintillating screen and a 650 µm thick single crystal LISe scintillator for neutron imaging comparison [14]. The Power T imaging target (shown in Figure 6) was printed on a Formlabs Form 2 printer using SLA additive manufacturing [25,26].…”

Evaluation of Neutron‐Radiation Tolerance of Lithium Indium Diselenide Semiconductors

“…[ 12,13 ] Recently, lithium‐containing semiconductors have been discovered and show promise in neutron imaging because of their large absorption efficiency per unit volume and adaptability to imaging system readout technologies used in medical, physical, and industrial applications. [ 14,15 ]…”