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The process of ionization that is due to the Migdal effect and which occurs in the elastic scattering of a heavy neutral particle, including a weakly interacting massive particle (WIMP), on a noble-gas atom in the case of its small recoil energy is considered. The mean number of primary and secondary electrons emitted in an individual event of such ionization is estimated, and the energy distributions of primary electrons are obtained. The calculations were performed for various noble-gas atoms with allowance for experimental data on their ionization by photons. [ABSTRACT FROM AUTHOR]

A method for improving the production of the radioisotope 123I in proton cyclotrons, which makes it possible to increase its technological yield by 2–3 times, is reported. For this purpose, it is proposed to introduce hydrogen into a target with 124Xe, which makes it possible to extract from it the 123I formed over the irradiation time on decay of the accumulated 123Xe. [ABSTRACT FROM AUTHOR]

Free-electron emission by stopping recoil atoms arising from particle–atom collisions in a noble-gas medium is numerically investigated using argon as an example. We demonstrate that, during propagation through matter of recoil atoms with energies over a few keV, vacancies in their internal L-shells arise via the Pauli mechanism with a probability on the order of 100%. As a result, over 30 free electrons are released upon a single interaction act in liquid or gaseous noble gas as a working medium of a particle detector. Thereby, the sensitivity of an argon-filled particle detector is significantly enhanced. In a xenon-filled detector, Pauli ionization sets in at higher recoil-atom energies of ≳100−200 keV and, therefore, is unlikely to boost the detector sensitivity to light-dark-matter particles, which are generally expected to produce recoil atoms with energies ≲10 keV. [ABSTRACT FROM AUTHOR]

The process of atomic nucleus recoil under the elastic scattering of a neutral particle, a hypothetical dark matter particle (WIMP) in particular, is considered. In the case of a low-energy recoil of the nucleus, the relations between the probability of ionization of the recoil atom and the cross section of ionization of such an atom by a photon, as well as by an electron, are obtained. These expressions contain only one parameter, the values of which are calculated for different types of atoms, taking into account experimental data on ionization by photons and electrons. The probabilities of ionization of noble-gas recoil atoms are compared with the results of other theoretical studies, and it is emphasized that the proposed calculating model is quite reliable and its accuracy is determined by the error of the experimental cross sections that are used. [ABSTRACT FROM AUTHOR]

The radionuclide 99Mo was produced and separated in the process of irradiating powdered mixtures of molybdenum compounds and buffer particles by 30 MeV protons. The separation is based on the Szilard-Chalmers effect wherein 99Mo recoil particles are fixed in inert buffer particles. Two types of targets were investigated by using mixtures: soluble molybdenum compound-insoluble buffer and insoluble molybdenum compound-soluble buffer. 99Mo yield equal to 20% with enrichment coefficient 18.3 was obtained by using a target consisting of a mixture of submicron 100MoO3 and Al2O3 particles; the 99Mo yield was equal to 20% and the enrichment coefficient 18.3. For a target with the composition 100MoS2 + KCl, making it possible to separate 99Mo recoil atoms directly into solution, the 99Mo yield was equal to 8.7% and the enrichment coefficient 30.7. [ABSTRACT FROM AUTHOR]

The phenomenological vector model of water is used to clarify the nature of the percolation phase transition in hydration water films around the surface of immersed bodies, which is found in molecular dynamic calculations. The transition is explained by the emergence of ordering in the directions of projections of water dipole moments on the body surface at the lower critical temperature, i.e. by the formation of ferroelectric water film. The evaluation of this temperature is given, which is consistent with numerical calculations. [ABSTRACT FROM AUTHOR]

A phase transition is discussed that can occur in a plasma with substantially different transverse and longitudinal temperatures of electrons moving in a magnetic field, T⊥/T|| > 1. The Debye cloud surrounding an ion sharply contracts as T|| decreases or the magnetic field increases. The effect of larger radiative electron–ion recombination cross sections compared with their theoretical values is explained; this effect is observed in storage rings with electron cooling systems (coolers). The role played by the phase transition in the crystallization of ion beams is discussed. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]