AN INVESTIGATION INTO THE ORIGIN OF SMALL ENERGY CHANGES (~ 10^-7eV) OF ULTRACOLD NEUTRONS IN TRAPS

Abstract

We studied the phenomenon of relatively small changes in the energy of ultracold neutrons (UCN) (when compared to thermal motion energy) when these are reflected on a surface. The changes observed involved both increases in UCN energy (their heating) and decreases (cooling) of the order of ~ 10 -7 eV. The probability values of this process on various surfaces ranged between 10 -8 and 10 -5 per one collision; the probability of such a small heating was many times larger than that of such a small cooling. We measured the spectra of such heated neutrons and the dependence of small heating probability on the temperature of sample out-gazing. We found that out-gazing of samples in vacuum at a temperature of 500–600 K could increase the small heating probability on stainless steel surface by a factor of ~ 100; and on copper surface by a factor of ~ 10. We observed, for the first time, extremely intensive small heating of UCN on powder of diamond nanoparticles. Neither small heating of UCN, nor nanoparticles could be found on a sapphire single crystal surface. This set of experimental data indicates that the inelastic scattering of UCN on weakly bound nanoparticles at a surface in a state of thermal motion is responsible for the process investigated.