G. Rosner

Investigation of the level schemes of 73,75,77As via the (3He, d) reaction

Abstract The reactions 72, 74, 76 Ge( 3 He, d) were investigated at E lab = 23 MeV with a multigap and a Q3D magnetic spectrograph. Some 30 new levels up to E ∗ ≈ 4 MeV have been found. The level schemes of the odd As isotopes 73, 75, 77 As up to E ∗ ≈ 4 MeV seem to be rather independent of the neutron number. The good agreement of the low-lying level structure with the Coriolis-coupling model including a pairing force was verified and the vacancies of low-lying shell model states were extracted and compared with the simple pairing theory.

Prediction of the high-spin selectivity of compound reactions induced by heavy ions

Abstract Two procedures are described to predict the selectivity of heavy-ion (HI) compound reactions for excitation of high spins. The applicability of statistical-model calculations in respect to yrast line effects is discussed. Contour diagrams of the total cross sections σ(E ∗ , I), dσ(E ∗ , I)/ d E ∗ and d σ(E ∗ )/ d E ∗ are derived, yielding the gradient d σ(E ∗ , I)/ d I and the p to “background” ratio of high-spin states as well as the “optimum Q -value” for any given HI compound reaction. The dependence of both the optimum Q -value and the shape of d σ(E ∗ )/ d E ∗ on the critical L -value at high bombarding energies can be used to determine L crit . This is demonstrated for the reaction 12 C + 14 N → 26 AI . A rougher estimate of the selectivity is given by the “grazing-collision picture” which is based on a consideration of the angular momentum balance. Using the reactions 10 B( 12 C, d), 12 C( 12 C, d), 12 C( 14 N, d), 11 B( 14 N, p), 13 C( 14 N, p), 10 B ( 14 N , α) and 12 C( 14 N, 6 Li) as examples, the theoretical predictions are shown to be in excellent agreement with experiment, for bombarding energies ranging between 40 and 120 MeV. The possibility to predict the high-spin selectivity is the precondition for an application of HI compound reactions for investigations of yrast lines and converts this class of reactions into an outstanding means for spectroscopy of high-spin states in light nuclei.

Determination of critical angular momenta and spectroscopy of high-spin states by heavy-ion compound reactions

Abstract A method is presented that allows the determination of critical angular momenta Jcrit in light nuclei (A ⪅ 40) with high accuracy. The method is based on a statistical model analysis of ratios of cross sections for discrete states of known spin, which are excited in a high-spin selective decay channel of the compound nucleus. Extensive tests regarding the influence of level density and optical model parameters on the calculations show that the determination of Jcrit can be performed independently of the choice of these parameters. In addition, it is shown that after Jcrit has been determined, level density parameters a (averaged over shell effects) can be extracted very accurately from absolute cross sections. Furthermore, it turns out that high-spin selective heavy-ion compound reactions are a powerful means for spectroscopy of high-spin states. As a first application, these procedures are applied to the reaction 10B(12C, d) measured at Elab = 45 MeV (corresponding to E ∗ = 37.7 MeV excitation energy in 22Na). The value Jcrit = 14 ± 1 obtained is discussed in the frame of the existing models. Spin assignments have been suggested for hitherto unknown high-spin states in 20Ne, ranging up to 17.4 MeV in excitation energy. As a result, the hypothesis of the existence of superbands in 20Ne is shown to be wrong.

Complete and incomplete fusion in 19F+40Ca and 32S+27Al

Abstract Velocity distributions and excitation functions of fusionlike evaporation residues (ER) were measured for 41–216 MeV 19 F + 40 Ca and 142–393 MeV 32 S + 27 Al . The ER cross sections for 19 F + 40 Ca exceed those of 32 S + 27 Al by up to 44%, mainly due to an earlier onset of incomplete fusion of about 3.7 MeV/nucleon above the interaction barrier in 19 F + 40 Ca , compared to 5.6–7.7 MeV/nucleon in 32 S + 27 Al .

Complete and incomplete fusion in 19 F + 40 Ca and 32 S + 27 Al

Abstract Velocity distributions and excitation functions of fusionlike evaporation residues (ER) were measured for 41–216 MeV 19 F + 40 Ca and 142–393 MeV 32 S + 27 Al . The ER cross sections for 19 F + 40 Ca exceed those of 32 S + 27 Al by up to 44%, mainly due to an earlier onset of incomplete fusion of about 3.7 MeV/nucleon above the interaction barrier in 19 F + 40 Ca , compared to 5.6–7.7 MeV/nucleon in 32 S + 27 Al .

Spectroscopy with high spin selective compound reactions induced by heavy ions

Abstract A spectroscopic method for selective excitation and quantitative analysis of high-spin states in sd-shell nuclei is presented and tested in several heavy-ion reactions. The hypothesis of a “superband” in 20 Ne is tested by means of the reaction 10 B( 12 C, d) 20 Ne.

Yrast states in 24Mg up to 24 MeV excitation energy

Abstract The yrast line in 24 Mg has been studied by the high-spin selective reaction 10 B( 16 O, d) at E lab = 60 MeV. First for the 10 + yrast level in 24 Mg is obtained. The critical angular momentum for the compound nucleus formation is found to be J max = 15.

A method to determine critical angular momenta in light nuclei

A method is presented to determine with high accuracy critical angular momenta in light nuclei (A⪷40) from the statistical model analysis of relative experimental cross sections in high-spin selective heavy-ion compound reactions. The critical angular momentum in the reaction 10B(12C, d)22Na at Elab = 45 MeV is determined to be Jcrit = 14 ± 1.

Possible contribution of low-l waves to the deep inelastic collisions of 32S with 27Al

Abstract The deep inelastic reactions of 32S with 27A1 have been studied at incident energies of 152.6 and 175 MeV by measuring inclusive fragment distributions, fragment-fragment and fragment-light particle coincidences. The observed Q-value distributions of the primary deep inelastic process range down to large negative Q-values as predicted by time-dependent Hartree-Fock calculations in the presence of low partial waves. No distinct low-l window for deep inelastic reactions can, however, be inferred from the data.

Statistical model description of the system 12C+14N in agreement with experiment for ELab=20−120 MeV

Abstract Statistical model calculations for the two experimentally best known channels 6 Li+ 20 Ne and d+ 24 Mg of the reaction 12 C+ 14 N→x+y are in excellent agreement with experiment over a range of 100 MeV in bombarding energy. The method for prediction of the high spin selectivity of heavy ion compound reactions [1] has been refined by taking into account the Q -value dependence of the total cross section. At high bombarding energies the “optimum Q -value” is very sensitive to the critical L -value of the compound nucleus.