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November 2018

14.11.2018 - FLNR Scientific Seminar "Determination of Fusion Barrier Distributions from Quasielastic Scattering Cross Sections towards Superheavy Nuclei Synthesis", 15-30, Flerov Lab Conference Hall.
Speaker: Taiki Tanaka (RIKEN, Kyushu University) for the collaboration

In order to study the nucleus-nucleus interaction for synthesis of superheavy nuclei, we have measured excitation functions for Quasielastic (QE) scattering cross section relative to the Rutherford cross section dσQE/dσR of 48Ca+208Pb, 50Ti+208Pb, 22Ne+248Cm, 26Mg+248Cm, 48Ca+238U and 48Ca+248Cm using gas-filled type recoil ion separator GARIS[1]. In contrast to previous QE barrier distribution studies[2-3], which measured the recoiled projectile nuclei at back side (θ ~ 170°), this work could measure the QE scattering cross section for angular momentum l = 0 by measurement of the target nuclei which recoiled at completely forward side with using the gas-filled-type recoil ion separator GARIS. The QE scattering events were clearly separated from deep-inelastic events by using GARIS and its focal plan detectors. The QE barrier distributions were successfully extracted, and compared with coupled-channels calculations[4]. The results of the calculations indicate that vibrational and rotational excitations of the colliding nuclei, deformation of the actinide target, as well as neutron transfers before contact, strongly affect the structure of the barrier distribution. For the reactions of 48Ca+208Pb and 50Ti+208Pb, a local maximum of the barrier distribution occurred at the same energy as the peak of the 2n evaporation (ER) cross section[5-8] of the system. On the other hand, for the hot fusion reactions of 22Ne+248Cm, 26Mg+248Cm, 48Ca+238U and 48Ca+248Cm, we found that the peaks of ER cross section[9-16] appear between the experimental average Coulomb barrier height B0 (the energy point at dσQE/dσR = 0.5) and the Coulomb barrier of side collision Bside. This indicates that the ER cross sections are largely determined by using the advantage of the compact collision. In the compound nucleus (CN) formation process, the probability of CN formation increases for side collision because of the shorter distance of the center of nuclei in the touching configuration[17]. Moreover, increasing the fusion hindrance, such as 48Ca+248Cm (Z1Z2 = 1920), the peak of the σER is close to the Coulomb barrier of side collision Bside. A few experimental groups will attempt (have attempted) to syntheses new elements Z > 118 by using the combinations of the 50Ti, 54Cr projectiles with 248Cm, 249Bk, 249-251Cf targets, in hot fusion reactions[18-20]. In that case, our study strongly implies that the incident energy of maximum σER will appear at the energy of Bside.

[1] T. Tanaka et. al., J. Phys. Soc. Jpn. 87, 014201 (2018).
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01.11.2018 - FLNR CAP and Sector N7 Scientific Seminar "Osmosis in negatively charged nanocapillaries and its enhancement by anionic surface-active agent", 11-00, Flerov Lab Conference Hall.

Speaker: Yu.Yamauchi

Osmotic flows through track membranes of 10-50 nm pore radius in water/membrane/salt solution system at the latter concentration order of several mmol/l are measured. It is found that water transport through the pores is intensive only if the solute dissociates into ions (KCl, K2SO4, sodium dodecyl sulfate). Molecules of low-molecular nonelectrolytes almost don't induce osmotic flow under given capillary radii which points out the essential role of double electric layer in the mechanism of osmotic transport.
It was shown that osmotic pressure transport through pores is of convectional nature: Poiseuille's law for viscous flow through cylindric capillary works.
Osmotic pressure values at different salt concentrations are determined and reflection coefficients are calculated. Sorption of anionic surface active agent increases membrane surface charge and enhances osmotic effect.

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