Storage of ultracold neutrons in vessels whose walls are made from graphite, fluorine polymer oil, or heavy-water ice

On the possibility of creating a UCN source on a periodic pulsed reactor

“…If energy E is not too close to the boundary energy, values µ and η differ slightly over a wide range of changes in the parameter y. For a number of good materials, η can be η = (3 ÷ 5) × 10 −5 [28][29][30] and the parameter ΣµT/sτ in the denominator of equation ( 10) can be of the order of unity even for a trap of quite significant volume. In this case, gain factor turns out to be of the order of As an example, we note that for the IBR-2 reactor, the ratio is T/τ ≈ 500.…”

Temperature dependence of the probability of “small heating” and total losses of UCNs on the surface of Fomblin oils of different molecular mass

“…Therefore, it was originally assumed that the main contribution to the 𝜂 𝑡𝑜𝑡 value comes from inelastic scattering of UCNs into the range of thermal energies; the scattering occurs on collective vibrations of atoms located in the near-surface oil layer of ~30 nm deep, available for UCNs [7]. However, the calculated value of the total UCN loss coefficient obtained from experiments on the transmission of neutrons with a velocity of 9 m/s through the bulk layer of oil turned out to be 3 times lower than the value obtained from UCN storage experiments [12][13]. The difference can probably be explained by additional oscillation modes of the atoms, which appear exclusively on the surface of Fomblin oil.…”

“…The experimental data on the spectrum of UCNs that have experienced "small heating" are not sufficient to give preference to one model or another, and to make corrections to the 𝜏 𝛽 experiments. Attempts to eliminate the effect of small heating and reduce the probability of total losses of UCNs by cooling the trap to temperatures below 240 К have led to cracking and peeling of the oil coating [4,12]. It should be noted that the best time of storage of UCNs was obtained in an experiment to measure 𝜏 𝛽 in cryotraps covered with so-called low-temperature PFPE [28].…”

Resonance capture by hydrogenous impurities and losses of ultracold neutrons in solid material traps

“…Losses of ultracold neutrons (UCNs) in material traps have attracted attention in recent years [1]. The matter arises for crystal materials such as beryllium and graphite [1,2,3] especially for beryllium [1,2]. For a liquid or solid Fomblin oil the observed losses could be explained by inelastic scattering processes [4], but it can not [1,3,4,5] explain the UCN losses in beryllium traps.…”

“…The matter arises for crystal materials such as beryllium and graphite [1,2,3] especially for beryllium [1,2]. For a liquid or solid Fomblin oil the observed losses could be explained by inelastic scattering processes [4], but it can not [1,3,4,5] explain the UCN losses in beryllium traps. Indeed, the UCN losses in beryllium traps depend slowly on the temperature T at low temperature [1,2,3].…”