Development of a neutron-imaging detector based on pulse–height correlation between two superconducting tunnel junctions on a Li2B4O7 crystal

The spatial resolution of a cryogenic neutron detector comprising two superconducting tunnel junctions (STJs) on a single crystal of Li2B4O7 was measured using a collimated neutron beam. Neutrons are captured in the crystal by the nuclear reactions with 6Li or 10B atoms, and excited non-thermal phonons are propagated in the crystal to the STJs. The incident position of the neutron can be evaluated from the pulse–height correlation between the two STJs. A collimated cold-neutron beam of size 0.4×1.1 mm2 was incident equidistant from two STJs separated by 1.3 mm. The measured counts distribution in the pulse–height correlation plot between the two STJs was consistent with the results calculated using a solid-angle model, confirming the position sensitivity of the developed detector. Moreover, the events caused by the 6Li(n,α)t reaction showed signal heights that were 1.8 times larger than those caused by the 10B(n,α)Li reaction, which indicated that the signal-to-noise ratio of the detector is higher for a 6Li-enriched crystal than for a 10B-enriched crystal.