Study of levitating nanoparticles using ultracold neutrons

Abstract

Physical adsorption of atoms, molecules and clusters on the surface is well known. It is linked to many other phenomena in physics, chemistry and biology and has numerous practical applications. Due to limitations of the analytical tools usually used, studies of adsorption are limited to the particle sizes of up to ∼10 2 -10 3 atoms. Following a general formalism developed in this field, we apply it to even larger objects and discover qualitatively new phenomena. A large particle is bound to the surface in a deep and broad potential well formed by van der Waals/Casimir-Polder forces appearing due to the particle and surface electric polarization. The well depth is significantly larger than the characteristic energy 3 2 k B T of a particle's thermal motion; thus such a nanoparticle is settled in long-living states. Nanoparticles in high-excited states form a two-dimensional gas of objects bound to the surface but quasi-freely traveling along the surface under certain conditions. A particularly interesting feature of this model consists in the prediction of small-energy-transfer inelastic scattering of ultracold neutrons (UCN) on solid/liquid surfaces covered by such levitating nanoparticles/nano-droplets. The change in UCN energy is due to the Doppler shift induced by UCN collisions with nanoparticles/nanodroplets; the energy change is almost as small as the UCN initial energy. We compared theoretical estimations of our model to all existing data on inelastic scattering of UCN with small energy transfers and found that they agree quite well. As our theoretical formalism provides robust predictions of some data

Quantum reflection of antihydrogen from nanoporous media

“…The typical density in powder varies between 5% and 15% of the diamond density, depending on the conditioning of the powder; it can be increased by shaking or pressing the powder, and decreased by blowing air through it. The density close to surface of a nanoparticle powder sample is even lower than that the bulk density of the powder (see for instance [24]).…”

A measurement of the neutron lifetime using the method of storage of ultracold neutrons and detection of inelastically up-scattered neutrons

“…The number of UCNs in the trap is equal respectively to ≈ 7.0 · 10 4 and ≈ 13.7 · 10 4 . Small heating of UCNs [15][16][17] during the storage interval occurred with the probability of 1.3 · 10 −5 per one wall reflection and populated the neutron spectrum at heights H > H d ; the typical energy difference (H − H d ) was lower than (15)(16)(17)(18)(19)(20) cm.…”

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

“…As a possible explanation of the effect of small heating of UCNs on the Fomblin surface, UCN scattering on capillary surface waves was considered [23][24][25]. There are also other hypotheses explaining the small heating of UCNs on the surface of hydrogen-free oil, for example, the scattering of UCNs on near-surface mesoscopic objects such as nanodroplets [26][27]. 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.…”