Document Type

Article

Publication Date

9-2-2026

Abstract

We report the first commissioning with ultracold neutrons (UCN) of an elevator-based loading system for the UCNτ magneto-gravitational neutron trap at Los Alamos Neutron Science Center. The system replaces the previous trap-door geometry with a moving bin designed to transfer UCN from UCN guide height into the open trap while reducing their kinetic energy through an adiabatic expansion of the accessible volume. UCN cutoff energy scans, direct leakage measurements, and variable bin-hold cycle measurements were used to characterize the incident spectrum and the loading losses. Successive sealing modifications increased the effective bin population lifetime from 26.69 ± 0.62 to 47.64 ± 0.70 s. After normalization for changes in transport to the upstream buffer volume, the best configuration stored 1.3 times more UCN per available upstream neutron than the 2022 trap-door configuration. The UCN cutoff energy data further show that a large higher-energy population is available upstream but does not produce the increase in stored yield expected from ideal elevator transport. A Monte Carlo model constrained by the measured bin lifetimes is consistent with residual loading-bin gaps and identifies the drop from the guide entry into the bin to the bottom of the bin as an additional source of spectral heating. These results establish elevator loading in UCNτ Plus and identify the changes required to approach the projected factor-of-5–10 increase in stored UCN for a next-generation neutron-lifetime measurement.

Comments

Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); USDOE Office of Science (SC). Office of Nuclear Physics (NP) (SC-36); LDRD; Other Publication Sponsor: National Science Foundation
DOE Contract Number: 89233218CNA000001
OSTI ID: 17171713
Report Number(s): LA-UR-26-27879

Download

Share

COinS