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Physical adsorption of atoms, molecules and clusters on surface is known. It is linked to many phenomena in physics, chemistry, and biology. Usually the studies of adsorption are limited to the particle sizes of up to ~10^2-10^3 atoms. Following a general formalism, we apply it to even larger objects and discover qualitatively new phenomena. A large particle is bound to surface in a deep and broad potential well formed by van der Waals/ Casimir-Polder forces. The well depth is significantly larger than the characteristic thermal energy. Nanoparticles in high-excited bound states form two-dimensional gas of objects quasi-freely traveling along surface. A particularly interesting prediction is small-energy-transfer scattering of 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; the energy change is about as small as the UCN initial energy. We compare theoretical estimations of our model to all relevant existing data and state that they agree quite well. As our theoretical formalism provides robust predictions and the experimental data are rather precise, we conclude that the recently discovered intriguing phenomenon of small heating of UCN in traps is due to their collisions with such levitating nanoparticles. Moreover, this new phenomenon might be relevant to the striking contradiction between results of the neutron lifetime measurements with smallest reported uncertainties as it might cause major false effects in these experiments; thus it affects fundamental conclusions concerning precision checks of unitarity of the Cabibbo-Kobayashi-Maskawa matrix, cosmology, astrophysics. Dedicated measurements of UCN up-scattering on specially prepared surfaces and nanoparticles levitating above them might provide a unique method to study surface potentials.
Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nano-droplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces resu
Two hypothesizes concerning interaction of neutrons with nanoparticles and having applications in the physics of ultracold neutron (UCN) were recently considered in ref. [Physics of Atomic Nuclei 65(3): 400 (2002)]; they were motivated by the experim
For ultracold neutrons with a kinetic energy below 10 neV, strong scattering, characterized by $2pi l_{c} / lambdaleq 1$, can be obtained in metamaterials of C and $^7$Li. Here $l_{c}$ and $lambda$ are the coherent scattering mean free path and the n
Our experiment using gravitationally trapped ultracold neutrons (UCN) to measure the neutron lifetime is reviewed. Ultracold neutrons were trapped in a material bottle covered with perfluoropolyether. The neutron lifetime was deduced from comparison
Spectra of ultracold neutrons that appeared in experiments on neutron diffraction by a moving grating were measured using the time-of-flight Fourier spectrometer. Diffraction lines of five orders were observed simultaneously. The obtained data are in