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Register a new user$gamma$ ray spectroscopy of $^{19}$C via single neutron knock-out reaction
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The one neutron knock-out reaction $^1$H($^{20}$C,$^{19}$C$gamma$) was studied at RIKEN using the DALI2 array. A $gamma$ ray transition was observed at 198(10) keV. Based on the comparison between the experimental production cross section and theoretical predictions, the transition was assigned to the decay of the 3/2$_1^+$ state to the ground state.
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The low-lying unbound level structure of the halo nucleus $^{19}textrm{C}$ has been investigated using single-neutron knockout from $^{20}textrm{C}$ on a carbon target at 280 MeV/nucleon. The invariant mass spectrum, derived from the momenta of the forward going beam velocity $^{18}textrm{C}$ fragment and neutrons, was found to be dominated by a very narrow near threshold ($E_textrm{rel}$ = 0.036(1) MeV) peak. Two less strongly populated resonance-like features were also observed at $E_textrm{rel}$ = 0.84(4) and 2.31(3) MeV, both of which exhibit characteristics consistent with neutron $p$-shell hole states. Comparisons of the energies, measured cross sections and parallel momentum distributions to the results of shell-model and eikonal reaction calculations lead to spin-parity assignments of $5/2^+_1$ and $1/2^-_1$ for the levels at $E_x$ = 0.62(9) and 2.89(10) MeV with $S_n$ = 0.58(9) MeV. Spectroscopic factors were also deduced and found to be in reasonable accord with shell-model calculations. The valence neutron configuration of the $^{20}textrm{C}$ ground state is thus seen to include, in addition to the known $1s^2_{1/2}$ component, a significant $0d^2_{5/2}$ contribution. The level scheme of $^{19}textrm{C}$, including significantly the $1/2^-_1$ cross-shell state, is well accounted for by the YSOX shell-model interaction developed from the monopole-based universal interaction.
An extended investigation of the low-spin structure of the $^{65}$Ni nucleus was performed at the Institut Laue-Langevin, Grenoble, via the neutron capture reaction $^{64}$Ni(n,$gamma$)$^{65}$Ni, using the FIPPS HPGe array. The level scheme of $^{65}$Ni was significantly expanded, with 2 new levels and 87 newly found transitions. Angular correlation analyses were also performed, allowing us to assign spins and parities for a number of states, and to determine multipolarity mixing ratios for selected $gamma$ transitions. The low-energy part of the experimental level scheme (up to about 1.4 MeV) was compared with Monte Carlo Shell Model calculations, which predict spherical shapes for all states, apart from the 9/2$^+$ and the second excited 1/2$^-$ states of oblate deformation.
Understanding of $gamma$-ray production via neutron interactions on oxygen is essential for the study of neutrino neutral-current quasielastic interactions in water Cherenkov detectors. A measurement of $gamma$-ray production from such reactions was performed using a 77~MeV quasi-monoenergetic neutron beam. Several $gamma$-ray peaks, which are expected to come from neutron-${rm ^{16}O}$ reactions, are observed and production cross sections are measured for nine $gamma$-ray components of energies between 2 and 8~MeV. These are the first measurements at this neutron energy using a nearly monoenergitic beam.
We have investigated the heaviest one-neutron halo candidate C-19 nucleus. Few-body model calculations of cross section angular distributions for the C-19(p,d)C-18 reaction, together with the test calculations carried out for the C-17(p,d)C-16 reaction, at a low incident energy are presented for different possible halo-neutron configurations. We show that there is a clear distinction between in particular $ell_{n}=0$ and $ell_{n}=2$ halo transfers. The sensitivity of the cross sections to the assumed C-19 single neutron separation energy is discussed.
The $^{15}$O($alpha$,$gamma$)$^{19}$Ne reaction is responsible for breakout from the hot CNO cycle in Type I x-ray bursts. Understanding the properties of resonances between $E_x = 4$ and 5 MeV in $^{19}$Ne is crucial in the calculation of this reaction rate. The spins and parities of these states are well known, with the exception of the 4.14- and 4.20-MeV states, which have adopted spin-parities of 9/2$^-$ and 7/2$^-$, respectively. Gamma-ray transitions from these states were studied using triton-$gamma$-$gamma$ coincidences from the $^{19}$F($^{3}$He,$tgamma$)$^{19}$Ne reaction measured with GODDESS (Gammasphere ORRUBA Dual Detectors for Experimental Structure Studies) at Argonne National Laboratory. The observed transitions from the 4.14- and 4.20-MeV states provide strong evidence that the $J^pi$ values are actually 7/2$^-$ and 9/2$^-$, respectively. These assignments are consistent with the values in the $^{19}$F mirror nucleus and in contrast to previously accepted assignments.
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