M. Schrader

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.

The γ-decay of the g92 analogue state in 59Cu

Abstract An investigation of the γ-decay of the 1 g 9 2 analogue state in 59Cu has been performed using the 58Ni(p, γ)59Cu reaction. The (p, γ) excitation function has been taken in the range Ep = 3450–3650 keV. The decay schemes of the (p, γ) resonances at Ep = 3483, 3532 and 3547 keV, measured with Ge(Li) detectors, lead to eight new levels in 59Cu with excitation energies between 1.8 and 4.7 MeV and to spin assignments of several states. The spins of the first two resonances are found to be ( 1 2 , 3 2 ) and ( 5 2 ). The spin of the Ep = 3547 keV resonan is, from angular distributions, uniquely determined to be J π = 9 2 + and this state is found to be the unfragmented analogue state of the E ∗ = 3.062 MeV , J π = 9 2 + parent state in 59Ni. The measured complete decay scheme of this resonance shows that its isovector M1 decay is in disagreement with all existing theoretical predictions.

Systematics of analogue-to-antianalogue M1 transitions up to g92 and d52 analogue states in As isotopes

Abstract The investigation of analogue-to-antianalogue M1 γ-transitions has been extended to g 9 2 and d 5 2 analogue states in As isotopes. The strongly hindered transitions in 73,75As do not seem to fit into the general systematics.

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.

The M1 strength distribution in the γ-decay of the gcase92 analogue state in 61Cu

Abstract The γ-decay of 26 resonances in the reaction 60Ni(p, γ)61Cu in the range Ep = 3690–3790 keV has been investigated. The g 9 2 isobaric analogue state (IAS) corresponding to the parent state at E ∗ = 2114 keV in 61Mi has been resolved into several fine structure components. The absolute strength for the transition to the antianalogue state is found to be Γγ = 0.24 ± 0.07 W.u. The measured M1 strength distribution for the decay of the g 9 2 . IAS is compared to theoretical predictions.

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.

High-spin states in 24Mg and upper limits for particle spectroscopy of high spins by heavy-ion compound reactions

Abstract High-spin states in 24Mg have been investigated by the reaction 10B(16O, d)24Mg up to E ∗ ≈ 24 MeV . High-spin states with I ≧ 9 have been identified at E ∗ = 19.20, 20.26, 20.8, 21.6, 23.1, and 23.5 MeV . The 10+ yrast state in 24Mg is probably located at 20.26 MeV. The upper limits with respect to spin and excitation energy of the applicability of heavy-ion compound reactions for particle spectroscopy of high-spin states are discussed. The main limitations result from the increasing continuum and from a decrease of the high-spin selectivity when the final spins approach the critical angular momentum for compound-nucleus formation. It will be shown that the difficulty in the analysis of the experiments arising from the decreasing probability of finding isolated yrast states at high excitation energies, i.e. from the increasing level density, can be overcome in such experiments. The decrease in the high-spin selectivity of the total cross section is compensated for spins up to Jmax by the fact that the shape of the angular distributions depends on the final spin for states with I ∼ Jmax. This is caused by the decreasing alignment of the final nucleus with decreasing values of |I − Jmax| and can be used for high-spin spectroscopy.

Yrast and high-spin states in 22Ne

Abstract High-spin states in 22 Ne have been investigated by the reactions 11 B( 13 C, d) 22 Ne and 13 ( 11 B, d) 22 Ne up to E ∗ ∼- 19 MeV . Yrast states were observed at 11.02 MeV (8 + ) and 15.46 MeV (10 + ) excitation energy. A backbending in 22 Ne is observed around spin 8 + . The location of high-spin states I ≦ 10 is discussed in terms of the rotational band structure, Strutinsky-type calculations, and pure shell-model predictions.

Structure of the neutron-deficient nuclide 121I

The distribution of the single-particle strength in 121I has been investigated by the reaction 120Te(3He,d) using a Q3D magnetic spectrograph and is interpreted within the framework of the three-particle-cluster-vibrational-core coupling model.