Cold-neutron storage owing to diffusion reflection

UCN anomaly and the possibility for further decreasing neutron losses in traps

“…Upscattered neutrons were observed in special experiments with graphite samples at room temperature irradiated with a UCN flux. Based on this observation and on the weak temperature dependence of UCN losses in the graphite traps, the authors [10] propose the hypothesis of surface hydrogen contaminations with two different vibrational modes with characteristic temperatures of 30 K and 1050 K. This interpretation does not seem correct because multiple excitations of lowfrequency oscillators were omitted in the proposed scenario. The result was-strange temperature behaviour of the UCN upscattering probabilitydecrease of upscattering for the low frequency mode with a rise in temperature.…”

“…It is of interest to compare the loss coefficient directly measured [17][18][19] and extracted from the measured cross-sections [10,20] according to Eq.…”

“…As for heavy water ice, the experimental result at 80 K for the UCN loss coefficient Z ¼ 0:94ð0:2Þ Â 10 À5 [10] is no less than five times greater than the ''theoretical'' one, derived from the measured slow neutron total cross-section [11,12] even if it is assumed that the transmission cross-sections for low-energy neutrons [11,12] do not contain contribution from diffuse scattering from inhomogeneities. In this estimate which differs significantly from the estimate of [10] we took into account the incoherent elastic scattering cross-section for D 2 O ice that does not contribute to UCN losses.…”

“…New data have been published recently on UCN losses in traps made of graphite and heavy water ice [10]. It has been found that at 100 K the UCN loss coefficient in graphite traps Z$5 Â 10 À5 , $25 times greater than the extracted value from the cold neutron transmission data.…”

“…In this estimate which differs significantly from the estimate of [10] we took into account the incoherent elastic scattering cross-section for D 2 O ice that does not contribute to UCN losses. The results of [9] for D 2 O ice at 90 and 7 K give several times larger UCN loss coefficient and do not depend on temperature.…”