Neutron lifetime measurement with the UCN trap-in-trap MAMBO II

We have measured the free neutron lifetime τn${\tau }_n$ by storage of ultra-cold neutrons (UCN) in a Fomblin coated UCN trap of in situ variable size. The method was initially developed by W. Mampe et al. (1989) 10] with MAMBO I and improved by the addition of a prestorage volume yielding a well defined UCN spectrum for storage in the main trap. By extrapolation to infinite trap size using the time scaling method we obtain for the free neutron lifetime τn=(880.7±1.3±1.2) s${\tau }_n=(880.7\pm 1.3\pm 1.2)\text{s}$. Data from different UCN spectra, trap temperatures and storage times were used for the evaluation. The present result is compared with other experimental neutron lifetime data.