Evolution und sozialer Wandel

Internal consistency of neutron coherent scattering length measurements from neutron interferometry and from neutron gravity reflectometry

“…One can in principle improve on the slow neutron beam reflectometry measurements of Koester et al by another 1-2 orders of magnitude by instead using ultracold neutrons (UCN), which can be confined in material bottles at all angles of incidence and therefore correspond to neutrons with kinetic energies less than about 300 neV. One could drop UCN onto a flat level sample surface, change its height, and measure the reflectivity curve as a function of H as in the Koester approach. The GRANIT UCN spectrometer [84] nearing completion at the ILL/Grenoble, which is designed to conduct measurements on UCN gravitational bound states and therefore already possesses a very flat, horizontal surface, could more sharply define the starting height of the neutrons than Koester et al's cold neutron apparatus. With the new superfluid-helium-based UCN source [85] installed to supply GRANIT, one could imagine measuring the neutron optical potential using the neutron reflectivity curve with statistical accuracy 1-2 orders of magnitude better than previous work.…”

Ultracold-neutron infrastructure for the gravitational spectrometer GRANIT

“…UCN are extracted from the intermediate volume via a narrow horizontal semidiffuse extraction channel described in [26,27]. Measurements have shown that such a channel increases the storage time inside the intermediate volume since more than 80% of the neutrons incident on the channel are reflected back.…”

“…Experiments at ILL's present facility PF2 for ultracold neutrons (UCN) are limited by counting statistics and systematic effects [9]. In this paper we describe design and status of a dedicated UCN source and its coupling to the gravitational spectrometer, updating a previous status report [10].…”

“…The UCN production rate density is defined as the conversion rate of neutrons to energies below the Fermi po- tential of the walls of the converter volume. For beryllium with V F = 252 neV the production rate density due to the single-phonon process, calculated from neutron scattering data, is P I = (4.97±0.38)·10 −8 dΦ/dλ| λ * s −1 cm −3 , with the differential flux at λ * = 8.9Å given in cm −2 s −1Å −1 [13].…”

“…Using a monochromator and a secondary guide strongly reduces the background with respect to a converter placed in the direct, white beam. The price to be paid is a reduction in intensity due to imperfection of monochromator and secondary guide, and due to omission of multi-phonon processes [12,13].…”