J. Meissburger

Proton particle-hole states in 208Pb

Abstract Differential cross sections for the 209Bi(d, 3He)208Pb transitions to the proton particle-proton hole states in 208Pb were obtained with the 45 MeV analyzed deuteron beam from the JULIC cyclotron and the high resolution spectrograph BIG KARL. 72 states up to 6.6 MeV were studied with an overall resolution of 12 to 15keV. Spectroscopic factors were extracted relative to the simultaneously measured calibration reaction 208Pb(d, 3He)207Tl. For 26 states new parity assignments were possible on the basis of the measured angular distributions. The deduced inclusion into one of the four multiplets put limits on the possible spins of the states in question. With the help of sum rule arguments the spins of 12 states were assigned. The comparison with shell model calculations give only rough agreement as they predict the energies of the respective states about 300 keV too high. The magnetic dipole state at 5.846 MeV was observed with a Spectroscopic factor C2S = 0.17. From this, together with the transition probability B(M1↑) = (1.6 ± 0.5) μN2 from a ( γ , γ′) experiment we derived size and relative sign of the dominant neutron and proton spin-flip amplitudes. The result gives clear evidence for the isoscalar character of this state in accordance wtih TDA and RPA predictions. The matrix elements of the two-body residual interaction were derived unambiguously for the h 9 2 ∗ s 1 2 and h 9 2 ∗ d 3 2 multiplets. For the h 9 2 ∗ h 11 2 and h 9 2 ∗ d 5 2 multiplets uncertainties are larger because of assumptions of some of the spins for the states of high excitation energy. The four monopole terms are found close to the average of −308 keV. They are dominated by the Coulomb contributions of ≈ − 216 keV. The deduced J-dependence of the matrix elements differs from those found in other systematic investigations indicating more complicated underlying nuclear forces must contribute.

Spectroscopy of 142Nd and 143Nd via inelastic proton scattering at Ep = 25 MeV

Abstract The nuclei 142 Nd and 142 Nd have been studied by means of high-resolution inelastic proton scattering at E p = 25 MeV. Angular distributions have been measured from θ lab = 20° to 50°. Transitions to 24 levels in 142 Nd and 39 levels in 143 Nd up to an excitation energy of 3.8 MeV were observed. Multipolarities L and transition strengths G L were determined using distorted-wave Born approximation analysis. Particle-core coupled configurations were identified in 143 Nd. In particular, the identification of all members of the octupole multiplet ( 3 − · νf 7 2 ) provides insights on the particle-vibration coupling in this region of nuclei. Coupling to other excitation modes is discussed, and comparison with unified model calculations is made.

Identification of a complete particle-octupole multiplet in 143Nd

Abstract In a high resolution (p,p′) experiment at E =25.5MeV, the complete particle-core coupled multiplet (3 − · f 7 2 ) J in the N =83 143 Nd nucleus has been identified and the spins of its members assigned. The experimental results are discussed in connection with the observed large energy splitting of about 650 keV. The comparison with the corresponding multiplet observed in 146 Gd is a new strong indication for the shell closure at Z =64.

The role of 4H transfer in the 11B(3He, 7Li)7Be reaction at 71.8 MeV

Abstract Angular distributions of the 11 B( 3 He, 7 Li) 7 Be reaction were measured in the entire angular region at 71.8 MeV beam energy yielding information on the 4 H-like cluster transfer in the forward direction and α-cluster transfer in the backward region. A DWBA analysis including processes up to the second order indicates a rather small yield of 4 H transfer and a dominant two-step transfer mechanism in the ( 3 He, 7 Li) reaction.

Highly excited 8Be core in the configuration of the 12C and 11B ground states

Abstract Angular distributions of the 12 C(d, 6 Li) 8 Be reaction at E lab = 78.0 MeV and the 11 B( 3 He, 6 Li) 8 Be reaction at E lab = 71.8 MeV were measured. Transitions leading to 8 Be in the ground state and the 3.04, 16.63, 16.92, 17.64 and 18.15 MeV excited states were observed. A DWBA analysis was performed regarding the (d, 6 Li) and ( 3 He, 6 Li) reactions as direct α particle or triton transfers, respectively.

The new focal plane detector for the magnet spectrometer Big Karl

Two delay-line readout drift chambers with an active area of 90 cm by 7 cm are now in use as focal plane detectors at the high resolution spectrometer Big Karl. The position resolution is better than 0.2 mm fwhm with detector efficiencies exceeding 99.5% for 45 MeV deuterons. Light ions such as protons, deuterons, alphas and others up to 6He have been measured at energies between 15 and 45 Mev per nucleon. The new detector offers a significantly higher focal plane acceptance with improved background suppression and correction capabilities.

The ground state mass of147Gd from single-neutron-transfer reactions and its impact on derived mass values

Using a148Gd radioactive target and the (p,d), (d,t), and (3He,α) single neutron pick-up reactions we have measured the147Gd mass excess as — 75,366(4) keV, which differs by 139(24) keV from the adopted value of the 1983 mass table. From this result, and from recently reported first transfer-reaction mass determinations for145Eu and146Eu, we have recalculated the masses of nuclei above146Gd from a previous shell model analysis of high-spin states.

On the mechanism of the144Nd(p, α)141Pr reaction

Experimental evidence is presented that the144Nd(p, α)141Pr reaction excites residual nucleus levels with a dominant single proton configuration, suggesting a contribution from knock-on mechanism.The angular distributions of theα-particles populating these levels have been analysed by means of one step pick-up (both in finite and zero range approximation) and knock-on theories, assuming that the spectroscopic amplitudes for the two processes are proportional to the spectroscopic amplitudes for proton transfer in pick-up and stripping reactions, respectively. The results obtained suggest the importance of knock-on contributions to some of the transitions.

Excitation of single proton states in (p, α) reactions

A high resolution experiment, using the BIG KARL spectrometer has been made to identify the levels of141Pr excited in the144Nd(p,α) reaction at 25 MeV. It has been found that only levels with a dominant single proton component are populated with appreciable intensity.