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Adam GorbErik SatieHK Grube

(HE-3,T) CHARGE-EXCHANGE REACTIONS AT E(HE-3)=450 MEV, THETA=0-DEGREES

Spin-isospin excitations in nuclei have been studied by means of the (He-3,t) reactions at 450 MeV on the targets Be-9, (nat)C, Si-28, Ni-58, Ni-62, Zr-90, Sn-118, Sn-120, 124Sn, and Sm-154. The new spectrometer ''Grand Raiden'' was employed for the (He-3,t) study for the first time. Observed (He-3,t) spectra at 0-degrees show remarkable similarity with those from the (p,n) results at intermediate energies, suggesting a simple direct reaction mechanism for the (He-3,t) reaction at 450 MeV. The Gamow-Teller (GT) resonances and the spin-flip DELTAL = 1 resonances are excited very strongly. A fine structure of the GT resonances in medium-heavy nuclei is observed with an energy resolution of 210 keV. It is demonstrated that the (He-3,t) reaction at 450 MeV is a powerful tool to study the spin-isospin excitations in nuclei

DIRECT PROTON DECAY FROM THE GAMOW-TELLER RESONANCE IN BI-208

Spin-isospin excitations in Bi-208 have been investigated using the Pb-208(He-3,t)Bi-208 reaction at and near theta approximate to 0 degrees at E(He-3)=450 MeV. The microscopic structure of the Gamow-Teller resonance (GTR), the isobaric analog state (IAS), and the spin-flip dipole (Delta L = 1) resonance (SDR) in Bi-208 has been studied by observing their direct proton decays to the low-lying neutron-hole states in Pb-207. Decay protons were measured at backward angles in coincidence with tritons detected at and near 0 degrees. The total branching ratio for proton decay from the GTR is determined to be only 4.9+/-1.3%. The total branching ratio for proton decay from the SDR amounts to 14.1+/-4.2%. The deduced total widths as well as the total and partial proton escape widths of the GTR and IAS are found to be in reasonable agreement with recent theoretical estimates obtained in the framework of the continuum Tamm-Dancoff approximation

MICROSCOPIC STRUCTURE OF THE GAMOW-TELLER RESONANCE IN BI-208

The (Pb(He,t)Bi)-Pb-208-He-3-Bi-208 reaction has been studied with the RCNP ring cyclotron at E(He-3) = 450 MeV using the magnetic spectrometer Grand Raiden at theta = 0-degrees. The Gamow-Teller resonance is strongly excited at this bombarding energy. Its microscopic structure has been investigated by measuring the direct proton decay to the neutron-hole states in Pb-207. The branching ratio for proton emission of a few % is much smaller than that for the decay of the isobaric analog state. The total width of the Gamow-Teller resonance as well as its total and partial escape widths have been determined. Several recent theoretical estimates for the escape width differ from the measured values by factors of approximately 2.5

The reaction: A means to study the microscopic structure of spin-isospin modes

The microscopic structure of both the Gamow-Teller resonance (GTR) at E[chi] = 15.6 MeV and the spin-flip [Delta]L=1 resonances at higher excitation energies in 208Bi has been investigated by observing their direct proton decay to the , , , and neutron-hole states in 207Pb, following their excitation via the 208Pb (3He,t) reaction at E(3He) = 450 MeV. Decay protons were measured at backward angles in coincidence with tritons detected at very forward angles including [theta] = 0[deg]. The total widths of the resonances as well as total and partial proton escape widths were determined and compared to theoretical estimates for the GTR. Using the same experimental set-up and conditions proton decay of the spin-flip [Delta]L=1 resonances in 12C was also measured.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31323/1/0000232.pd

Collective and single-particle states at high excitation energy

Damping of high-lying single-particle states was investigated by the study of decay by proton emission from high-lying states in Nb-91, populated by the Zr-90(alpha, t) reaction at E-alpha = 180 MeV. In addition to decay to the ground state of Zr-90, semi-direct decay was observed to the low-lying (2(+)/5(-) and 3(-)) phonon states, confirming the conclusion from other experiments that phonon states play an important role in the damping process of the single-particle states. Furthermore, the population and decay of isobaric analogue states of Zr-91, which are located at an excitation energy of about 10 - 12 MeV in Nb-91, has been studied in the same reaction