W. Grüebler

Global optical-model analysis of the elastic deuteron scattering from medium heavy target nuclei

Abstract Angular distributions for the cross section and the analyzing powers iT 11 , T 20 , T 21 and T 22 in the angular range 20°–175° (lab) have been measured for 12 MeV deuterons scattered elastically from several medium-heavy, spin-zero target nuclei. The data have been analysed using an optical model including complex spin-orbit and tensor terms. With a few exceptions, excellent fits have been obtained to all the measured quantities, yielding a set of global parameters. The depths of the central part of the optical potentials are correlated and depend on the structure of the target nuclei. Contrary to the results for selenium, which exhibit clear shell-closure effects that are well reproduced by optical-model calculations, the data for N = 28 nuclei were found to be very difficult to describe. Irregularities in the optical-model parameters and problems in fitting the measurements are discussed. Possible ways of improving the theoretical description of deuteron scattering are suggested.

Investigation of the nucleon-nucleon tensor force in the three-nucleon system

Abstract Proton-deuteron elastic scattering has been investigated at E p =22.7 MeV by comparison of rigorous Faddeev calculations with experimental results. The observable most sensitive to the tensor force is the nucleon-nucleon polarization transfer coefficient K y y ′ . The new angular distribution of K y y ′ clearly favours the tensor force of the Bonn A potential, which is weaker than the one of the Paris potential.

Analyzing power measurements in deuteron-proton elastic scattering

Abstract The vector and tensor analyzing powers for deuteron-proton elastic scattering have been measured at 3.0, 5.0, 7.0, 10.0 and 13.0 MeV deuteron energy for c.m. angles from 22.6° to 165°. Additional results to 9° c.m. have been obtained for T 20 and show a marked negative minimum near 20° c.m. Proton analyzing powers have also been measured at 2.5, 3.5, 5.0 and 6.5 MeV proton energy from 15° to 170° c.m.

Spin-parity combinations in 28Al

Abstract The tensor analyzing powers T20 and the cross sections for the reaction 30 Si ( d , α) 28 Al to levels in 28Al with excitation energies up to 5.3 MeV have been measured at θlab = 175° for bombarding energies from 8.0 to 12.0 MeV in steps of 0.5 MeV. Comparison of the measured T20 values with theoretical predictions has led to assignments of natural or unnatural parity to some forty levels in 28Al. In a number of cases unique spin-parity assignments could be deduced by combining the present information with published spectroscopic data. A (probable) assignment of Jπ = 0+ could be made to three levels in 28Al on the basis of a very low observed cross section. No states with Jπ = 0− have been observed for Ex

Spin-parity combinations in 30P determined with A t20 polarized deuteron beam

Abstract The tensor analysing power T20 around θ = 180° has been measured of the 32 S( d , α 30 P reaction to final levels with excitation energies up to 7 MeV. This has been done for six bombarding energies between Ed = 8 and 12 MeV. Comparison of the measured T20 values with the theoretical value for the case that the final state has natural parity [T20 (0° or 180°) = 0.707 for (-)J = π] has led to certain assignments of unnatural parity and probable assignments of natural parity for some forty levels in 30P. In a similar way some probable assignments of Jπ = 0− and Jπ = 0+ could be made. The distribution of T20 values measured in cases where the final state has unnatural parity has been found to be in agreement with the predictions of the statistical theory for nuclear reactions.

Kinematically complete measurement of cross sections and vector and tensor analyzing powers of 4He(d, pα)n at Ed = 10 MeV

Abstract Differential cross sections and vector and tensor analyzing powers have been measured in the breakup reaction 4 He( d , pα)n at E d = 10 MeV , for θ α = 46°, θ p = 46° complete coincidence experiment. The kinematics allow for np final-state interaction (FSI) ( E np = 0). A comparison with theoretical predictions based on Faddeev equations is presented. Phenomenologically it appears that there are large interference effects between the different FSI and the importance of Coulomb interaction emerges clearly.

New constraints on D-state contributions to the trinucleon wave functions

Abstract Cross-section and polarization data of the 4 He(d, 3 He) 3 H reaction measured at 5 energies have been analysed. The vertex constants for the neutron transfer G n , the proton transfer G p and the asymptotic normalization constant C s 2 , for the S-state of the 3 H wave function have been determined. New constraints on the D- to S-state asymptotic normalization ratio η t , and η 3 He for the triton and 3 He wave functions are obtained from the tensor analyzing powers. The method of the analytic extrapolation in the angular variable to the transfer poles was used. Implications of this method and its application are discussed. Criteria for the reliability of the results are presented. The result of the analysis is C s 2 = 2.95 ±0.15, η t = 0.050 ± 0.006 and η 3 He = 0.035 ± 0.006. The ratio η t / η 3 He shows a significant deviation from unity suggesting a substantial isospin breaking effect.

Nuclear spectroscopy of 26Al

Abstract The tensor analyzing powers T20 and the cross sections for the reaction 28 Si ( d , α) 26 Al to levels in 26Al with excitation energies up to 6 MeV have been measured at θlab = 175°. The bombarding energy was varied in steps of 0.5 MeV from 10.0 to 12.5 MeV. Comparison of the measured T20 values with theoretical predictions, taking into account the finite-angle effect, has led to assignments of natural or unnatural parity to some fifty levels in 26Al. Two levels with Jπ = 0− could be identified on the basis of such a comparison. A (probable) assignment of Jπ = 0+ could be made to two levels in 26Al on the basis of a very low observed cross section. The information on spin-parity combinations found in this work was combined with spectroscopic data from other reactions to deduce new unambiguous Jπ assignments for 33 levels and Jπ restrictions for another three levels.

Barshay-Temmer test for the 4He(d, 3He)3H reaction

Abstract The mechanisms of isospin violation in the reaction 4 He ( d , 3 He ) 3 H is studied, in the framework of a microscopic model. To describe realistically the intermediate 6Li nucleus and the fragment states we use the refined resonating group model (RRGM). A detailed analysis of the matrix elements responsible for the asymmetry of cross sections and vector analyzing powers is presented. The isospin violation is found typically of the order of 5–10% and arises mainly from coupling to intermediate “5 + 1” structures in a two-step mechanism. The agreement with the experimental data is fair.

Polarization transfer observables in πd elastic scattering

Polarization transfer measurements in π+ elastic scattering have been performed at two incident pion energies, one below and one at the Δ(3, 3)-resonance. Using a vector polarized deuteron target four polarization transfer observables are determined. The results are compared to predictions from Faddeev calculations.