LISe pixel detector for neutron imaging

Abstract

Semiconducting lithium indium diselenide, 6 LiInSe 2 or LISe, has promising characteristics for neutron detection applications. The 95% isotopic enrichment of 6 Li results in a highly efficient thermal neutronsensitive material. In this study, we report on a proof-of-principle investigation of a semiconducting LISe pixel detector to demonstrate its potential as an efficient neutron imager. The LISe pixel detector had a 4x4 of pixels with a 550 µm pitch on a 5x5x0.56 mm 3 LISe substrate. An experimentally verified spatial resolution of 300 µm was observed utilizing a super-sampling technique. 1 INTRODUCTION Cold neutron radiography and tomography comprise powerful detection tools for investigating both natural and engineered materials. Its sensitivity for real-space imaging relies on the total neutron interaction cross section with the material under investigation, which includes both scattering (neutronnuclei and neutron-lattice) and absorption [1]. Neutron imaging shares many similarities with X-ray imaging systems, albeit the mode of interaction of the interrogating beam is different. The comparison between these two imaging techniques is outside the scope of this study, but many references are available [1-3]. In the advancement of the capabilities of neutron imaging facilities, it has been indicated that there is a need for advances in suitable detection systems to reach the full potential of current and future neutron facilities, such as the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Specifically, a simultaneous enhancement of the detection efficiency (ideally 100%), spatial resolution (less than 10 µm), large signal-to-noise ratio, (good gamma-ray rejection capability), and high temporal resolution (less than 1 µs) is desired [4]. Achieving the desired performance metrics outlined is a challenging prospect, but the use of a semiconductor-based imaging plane may provide the necessary performance.

Neutron Imaging with Timepix Coupled Lithium Indium Diselenide

“…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].…”

“…The primary detection mechanism for imaging is the thermal neutron absorption reaction 6 Li(n, 3 H) 4 He with a 938 b thermal neutron cross section [17]. While the competing reaction 115 In(n,γ) 116 In maintains a thermal neutron cross section of 202 b, the secondary gamma has a high escape probability and has not been observed to affect significantly the neutron signal [16]. To enhance the thermal neutron capture efficiency of the sensor material, the lithium used for crystal synthesis is isotopically enriched to 95% 6 Li [12,13].…”

“…The photolithography process begins with a clean, stainless steel planchet as shown in Figure 2 (process depicts fabrication of the original 16-channel LISe pixel detector for simplicity [16]). …”