An ultracold neutron (UCN) detector with Ti/(LiF)-Li-6 multi-layer converter and Ni-58 reflector

摘要

High efficient detectors for ultracold neutrons (UCN) must be developed for the new high flux neutron source Forschungsreaktor Munchen II (FRM II). On silicon PIN diodes 76 mug/cm(2) Ni-58 was deposited as a UCN reflector. On this 100 double layers of Ti-nat (4.7 mug/cm(2)) and (LiF)-Li-6 (1.8 mug/cm(2)) were deposited to function as a UCN converter. On top of this, 33 double layers of Ti-nat (3.4 mug/cm(2)) and (LiF)-Li-6 (0.92 mug/cm(2)) were condensed in addition to provide sensitivity to very low-energy UCN. Finally, 6.0 mug/cm(2) V-nat was deposited to protect the multi-layers. Vanadium has nearly zero optical potential for UCN and thus should not hinder their transmission. Since no expensive isotopes were involved, a source to substrate distance of 24cm could be chosen, leading to excellent uniformity. The setup designed for deposition under ultrahigh vacuum conditions and the evaporation procedures are described. (C) 2001 Published by Elsevier Science B.V. References: 7