Quasielastic neutron scattering by diffusive adsorbed hydrogen as a possible cause of the energy spreading of ultracold neutrons during long storage in traps

Study of levitating nanoparticles using ultracold neutrons

“…The first measurements were followed by other studies [19][20][21][22][23][24][25][26][27][28][29] carried out by several research groups, which essentially confirmed the initial observation but suggested controversial estimations of the absolute VUCN production rates. This controversy is explained by several factors: (a) measurements of such a kind, involving low-probability effects, require careful control of many systematic effects, which could imitate or hide the VUCN production; (b) the rate of VUCN detection depends strongly on the ranges (windows) of initial and final energies of UCN, which have not been under control in some experiments, (c) as we will see from analyses of the spectra presented in this work, very high energy resolution is needed; it has been provided so far only in the Big Gravitational Spectrometer (BGS) spectrometer [26,29].…”

“…To summarize the status of all these studies, trap walls (samples) of two kinds were used in these experiments: liquid and solid walls (samples). While the origin of small heating of UCN on liquid surfaces has been still under discussion (31), (22), (20), (21), (32), (33), (34), (13) (see also (35), (36), which rule out some hypotheses), the origin of small heating of UCN on solid surfaces is usually attributed to weakly bound nanoparticles on surface (13), ( 30), (37); note that increase in the scattering cross-section due to clustering of atoms was noted already in ref. (34).…”

“…To summarize the status of all these studies, trap walls (samples) of two kinds were used in these experiments: liquid and solid walls (samples). While the origin of small heating of UCN on liquid surfaces is still under discussion [12,[19][20][21][30][31][32][33] (see also [34,35], which rule out some hypotheses), the origin of small heating of UCN on solid surfaces is usually attributed to weakly bound nanoparticles on the surface [12,29,36]; note that an increase in the scattering cross-section due to clustering of atoms has already been noted in [33]. Here we will compare the theoretical estimations within our model to all precision experimental data available on inelastic scattering of UCN on nanoparticles bound to solid surfaces [29,36].…”