Y. Shimbara

Complete electric dipole response and the neutron skin in 208Pb

A benchmark experiment on (208)Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in (208)Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

High resolution beam line for the Grand Raiden spectrometer.

Abstract We have designed and constructed a new beam line which can accomplish both lateral and angular dispersion matching with the Grand Raiden spectrometer. In dispersive mode, lateral and angular dispersions of the beam line are b 16 =37.1 m and b 26 =−20.0 rad , respectively, to satisfy matching conditions for Grand Raiden. In achromatic mode, the beam line satisfies the double achromatic condition of b16=b26=0. The magnifications of the beam line are (Mx,My)=(−0.98,0.89) and (−1.00,−0.99) for dispersive and achromatic modes, respectively. In the commissioning experiments, we have succeeded to separate the first excited 2+ state of 168Er with E x =79.8 keV clearly from the ground state in the (p,p′) reaction. We achieved energy resolutions of ΔE=13.0±0.3 and 16.7±0.3 keV in full width at half-maximum for 295 and 392 MeV protons, respectively. These energy resolutions agree with the resolving power of Grand Raiden for an object size of about 1 mm .

Realization of matching conditions for high-resolution spectrometers

For precise measurements of nuclear-reaction spectra using a beam from an accelerator, a high-resolution magnetic spectrometer is a powerful tool. The full capability of a magnetic spectrometer, however, can be achieved only if the characteristics of the beam coming from the accelerator are matched to those required by the spectrometer by properly adjusting the beam line conditions. The matching methods, lateral dispersion matching, focus matching and also the kinematic correction compensate the spectrum line-broadening effects caused by the beam momentum spread and reaction kinematics. In addition, angular dispersion matching should be performed if good resolution of the scattering angle is important. Diagnostic methods developed to realize these matching conditions for the spectrometers K600 at IUCF and Grand Raiden at RCNP are presented.

Pygmy dipole resonance in 208Pb

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208 Pb shows that, at very forward angles, J π = 1 − states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.

Resonance states in 22Mg for reaction rates in the rp-process

Abstract Motivated by the need of spectroscopic data to better understand the astrophysical rp-process, we developed a new experimental method using the Grand Raiden magnet spectrometer to study protin rich nuclei with α and 3 He induced reactions. First results of the 24 Mg( 4 He, 6 He) 22 Mg reaction at 206 MeV and 0° are presented, showing states relevant for resonant reaction rate calculations of the proton capture 21 Na(p,γ) 22 Mg and the 18 Ne(α,p) 21 Na reaction which controls the break-out of the hot CNO cycles at X-ray burst conditions.

Thin ice target for 16O(p,p′) experiment

Abstract A windowless and self-supporting ice target is described. An ice sheet with a thickness of 29.7 mg / cm 2 cooled by liquid nitrogen was placed at the target position of a magnetic spectrometer and worked stably in the 16 O(p,p′) experiment at E p =392 MeV . Background-free spectra were obtained.

M 1 and Gamow-Teller transitions in T = 1 / 2 nuclei 23 Na and 23 Mg

The magnetic dipole

Suppression of Gamow-Teller and M1 transitions in deformed mirror nuclei Mg-25 and Al-25 - Direct observation of K selection rules

(M1)

High resolution study of the Gamow–Teller strength distribution starting from the ground state of 14N in the β− and β+ directions

operator consists not only of the usually dominant isovector (IV) spin

Calibration of the effective analyzing power for a polarimeter at

(\ensuremath{\sigma}\ensuremath{\tau})