7 research outputs found
First application of mass measurement with the Rare-RI Ring reveals the solar r-process abundance trend at A=122 and A=123
The Rare-RI Ring (R3) is a recently commissioned cyclotron-like storage ring
mass spectrometer dedicated to mass measurements of exotic nuclei far from
stability at Radioactive Isotope Beam Factory (RIBF) in RIKEN. The first
application of mass measurement using the R3 mass spectrometer at RIBF is
reported. Rare isotopes produced at RIBF, Sn, In, Cd,
Ag, Pd, were injected in R3. Masses of In, Cd,
and Pd were measured whereby the mass uncertainty of Pd was
improved. This is the first reported measurement with a new storage ring mass
spectrometery technique realized at a heavy-ion cyclotron and employing
individual injection of the pre-identified rare nuclei. The latter is essential
for the future mass measurements of the rarest isotopes produced at RIBF. The
impact of the new Pd result on the solar -process abundances in a
neutron star merger event is investigated by performing reaction network
calculations of 20 trajectories with varying electron fraction . It is
found that the neutron capture cross section on Pd increases by a
factor of 2.2 and -delayed neutron emission probability,
, of Rh increases by 14\%. The neutron capture cross
section on Pd decreases by a factor of 2.6 leading to pileup of
material at , thus reproducing the trend of the solar -process
abundances. The trend of the two-neutron separation energies (S)
was investigated for the Pd isotopic chain. The new mass measurement with
improved uncertainty excludes large changes of the S value at
. Such large increase of the S values before was
proposed as an alternative to the quenching of the shell gap to
reproduce -process abundances in the mass region of
Energy dependence of total reaction cross sections for 17Ne on a proton target
We measured the energy dependence of the total reaction cross sections (sigma_R) for the proton drip-line nucleus of neon isotopes, 17Ne, with a solid hydrogen target. The sigma_R on a proton target in the low- and intermediate-energy regions were provided, where only a few values are available for unstable nuclei. The new data were compared with theoretical calculations using the Glauber model. In the low-energy region (∼100A MeV), the theoretical cross sections overestimate the experimental ones, whereas the theoretical ones significantly underestimate the experimental data in the intermediate energy region (∼300-500A MeV). We discuss several possibilities for solving this discrepancy. This work suggests the necessity of more careful investigations of the energy dependence of sigma_R for various nuclei on a proton target to determine the nuclear size properties precisely
Single Crystallization of Olivine Lithium Phosphate Nanowires using Oriented Attachments
Facultative commensalism of a free-burrowing urothoid amphipod with a deep burrow-dwelling callianassid shrimp in intertidal sand
Species of the free-burrowing amphipod genus, Urothoe, are common on open sandy beaches. On intertidal sandflats, some species are associated with burrows or tubes of large infauna. How this link is formed and persisting under sheltered conditions was examined. On an intertidal sandflat in mid-western Kyushu, Japan, U. carda co-occurred with the deep burrow-dwelling callianassid shrimp, Nihonotrypaea harmandi, along a 300-m transect between tide marks. Amphipods resided in the surface 5-cm sediment outside shrimp burrows, as confirmed by sediment coring and burrow casting. In summers 1980 and 1981, the shrimp and amphipod populations were confined to the upper shore at mean densities of 182 and 701 inds m?2, respectively. In winter to spring, when the sediment surface mixing was caused by seasonal wind-induced waves, the amphipod but not the shrimp expanded down to the lowest shore. Later, by 1983, the shrimp increased mean density by 2.5 times and now also ranged to the lowest shore. In the summers of 1984, 2010, and 2015, the amphipod expanded to the lowest shore as well, with small variations in population size. Three marked changes in substrate properties were associated with shrimp inhabitation: thicker oxidized layer (proxy for oxygenated layer) in the sediment column; looser surface sediment, as evaluated with vane shear strength; and coarser and better-sorted surface sediment with less mud content. At least the former two changes were attributable to shrimp bioturbation, which could provide the amphipod with more permeable and softer substrates, leading to the formation of facultative commensalism