Extended Data Fig. 8 | Absorption probability versus^6 LiInP 2 Se 6 thickness
for thermalized neutrons. In addition to charge transport properties, the
neutron-capture cross-section of LiInP 2 Se 6 must be considered, as this directly
correlates with the intrinsic maximum of the detector efficiency. A linear
attenuation coefficient can be used to quantify the percentage of incident
neutrons absorbed in a given material through the equation:
frac tion of neutrons captured (%) = (1 – e−lα) × 10%, where l is the thickness of the
active region and α is the linear attenuation coefficient, which is calculated
using the capture cross-section of thermalized neutrons for each element and
its molar density. The calculated mass attenuation coefficient for thermalized
neutrons is 5.1 cm−1 and 1.4 cm−1 for LiInP 2 Se 6 fully enriched in^6 Li and natural-
abundance Li, respectively. A detector with a thickness of about 9 mm would be
able to absorb 99% of the incident neutrons. Here we achieved the successful
growth of crystals with thickness of ~1 mm, which would absorb ~40% of
incident neutrons. Increases in efficiency would be achievable through scaled-
up growth of thicker crystals or stacking of several thinner detectors^42. When
(^115) In (the most common isotope in natural indium) absorbs a neutron, the
nuclide produces a γ-ray instead of a highly energetic charged particle. Thus,
about 20% of the neutrons absorbed do not contribute to the signal, which sets
the maximum theoretical detector efficiency of^6 LiInP 2 Se 6 to approximately
80%.