arXiv subjects

S. Takeuchi

Publications and source records attributed to S. Takeuchi.

59 records · Page 4Linked to original sources

arXiv2007

Search for low lying dipole strength in the neutron rich nucleus $^{26}$Ne

Coulomb excitation of the exotic neutron-rich nucleus $^{26}$Ne on a $^{nat}$Pb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an $^{nat}$Al target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV $^{40}$Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the $^{25}$Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed $^{26}$Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B(E1)=0.49$\pm$0.16 $e^2fm^2$ is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.

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arXiv2006

Measurement of excited states in 40Si and evidence for weakening of the N=28 shell gap

Excited states in 40Si have been established by detecting gamma-rays coincident with inelastic scattering and nucleon removal reactions on a liquid hydrogen target. The low excitation energy, 986(5) keV, of the 2+[1] state provides evidence of a weakening in the N=28 shell closure in a neutron-rich nucleus devoid of deformation-driving proton collectivity.

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arXiv2003

Anomalously hindered E2 strength B(E2;2_1^+ -> 0^+) in 16C

The electric quadrupole transition from the first 2+ state to the ground 0+ state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured lifetime is 75 +- 23 ps, corresponding to a B(E2;2_1+ -> 0^+) value of 0.63 +- 0.19 e2fm4, or 0.26 +- 0.08 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.

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arXiv1995

Up-Down Quark Mass Difference Effect in Nuclear Many-Body Systems

A charge-symmetry-breaking nucleon-nucleon force due to the up-down quark mass difference is evaluated in the quark cluster model. It is applied to the shell-model calculation for the isovector mass shifts of isospin multiplets and the isospin-mixing matrix elements in 1s0d-shell nuclei. We find that the contribution of the quark mass difference effect is large and agrees with experiment. This contribution may explain the Okamoto-Nolen-Schiffer anomaly, alternatively to the meson-mixing contribution, which is recently predicted to be reduced by the large off-shell correction.

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arXiv1993

On the Spectacular Large Asymmetry in $\pbarppipi$ and $\pbarpKK$ Reactions}

An illustrative analysis is presented to show the origin of the energy-independent maximal asymmetry observed for wide ranges of angles in the reactions $\pbarppipi$ and $\pbarpKK$. % The general nature of our simple relation between helicity -flip and -nonflip partial wave amplitudes enforces the notion that % these features of the asymmetry for these two annihilation reactions are likely to persist within the hadronic regime. % At higher energies these features of the asymmetry will probably be modified significantly, signaling the onset of perturbative QCD. % Our study supports the arguments that the final $\KbarK$ state originates from a more central reaction than the $\pipi$ final state.

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