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Register a new userQuasi-specular albedo of cold neutrons from powder of nanoparticles
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We predicted and observed for the first time the quasi-specular albedo of cold neutrons at small incidence angles from a powder of nanoparticles. This albedo (reflection) is due to multiple neutron small-angle scattering. The reflection angle as well as the half-width of angular distribution of reflected neutrons is approximately equal to the incidence angle. The measured reflection probability was equal to ~30% within the detector angular size that corresponds to 40-50% total calculated probability of quasi-specular reflection.
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We study possibility of efficient reflection of very cold neutrons (VCN) from powders of nanoparticles. In particular, we measured the scattering of VCN at a powder of diamond nanoparticles as a function of powder sample thickness, neutron velocity and scattering angle. We observed extremely intense scattering of VCN even off thin powder samples. This agrees qualitatively with the model of independent nanoparticles at rest. We show that this intense scattering would allow us to use nanoparticle powders very efficiently as the very first reflectors for neutrons with energies within a complete VCN range up to $10^{-4}$ eV.
Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined by the Fermi potential in material bottles, are playing an increasing role in measurements of fundamental properties of the neutron. The ability to manipulate UCN with material guides and bottles, magnetic fields, and gravity can lead to experiments with lower systematic errors than have been obtained in experiments with cold neutron beams. The UCN densities provided by existing reactor sources limit these experiments. The promise of much higher densities from solid deuterium sources has led to proposed facilities coupled to both reactor and spallation neutron sources. In this paper we report on the performance of a prototype spallation neutron-driven solid deuterium source. This source produced bottled UCN densities of 145 +/-7 UCN/cm3, about three times greater than the largest bottled UCN densities previously reported. These results indicate that a production UCN source with substantially higher densities should be possible.
The investigation of the isospin dependence of multifragmentation reactions relies on precise reconstruction of the fragmenting source. The criteria used to assign free emitted neutrons, detected with the TAMU Neutron Ball, to the quasi-projectile source are investigated in the framework of two different simulation codes. Overall and source-specific detection efficiencies for multifragmentation events are found to be model independent. The equivalence of the two different methods used to assign experimentally detected charged particles and neutrons to the emitting source is shown. The method used experimentally to determine quasi-projectile emitted free neutron multiplicity is found to be reasonably accurate and sufficiently precise as to allow for the study of well-defined quasi-projectile sources.
We present the status of the development of a dedicated high density ultra-cold neutron (UCN) source dedicated to the gravitational spectrometer GRANIT. The source employs superthermal conversion of cold neutrons to UCN in superfluid helium. Tests have shown that UCN produced inside the liquid can be extracted into vacuum. Furthermore a dedicated neutron selection channel was tested to maintain high initial density and extract only neutrons with a vertical velocity component 20 cm/s for the spectrometer. This new source would have a phase-space density of 0.18 cm-3(m/s)-3 for the spectrometer.
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 experimental observation of small changes in energy of UCN upon their collisions with surface. The first hypothesis explaines the nature of the observed phenomenon by inelastic coherent scattering of UCN on nanoparticles weakly attached at surface, in a state of permanent thermal motion. It got experimental confirmed in ref. [Physics of Atomic Nuclei 65(11): 1996 (2002)]. The second hypothesis inverts the problem of neutron interaction with nanoparticles in the following sence. In all experiments with UCN, the trap-wall temperature was much higher than a temperature of about 1 mK, which corresponds to the UCN energy. Therefore, UCN preferentially increased their energy. The surface density of weakly attached nanoparticles was low. If, however, the nanoparticles temperature is lower than the neutron temperature and if the nanoparticles density is high, the problem of interaction of neutrons with nanoparticles is inverted. In this case, the neutrons can cool down, under certain conditions, owing tot heir scattering on ultracold-heavy-water, deuterium, and oxigen nanoparticles to their temperature of about 1 mK, with result that the UCN density increases by many orders of magnitude. In the present article we repeat the argumentation given in the first mentioned article and formulate in a very general way the research program in order to verify validity of this hypothesis. Both the theoretical and the experimental investigation of the problem are going to intensify in the near future.
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