L. Cleemann

High spin states in 67Ga

Abstract The nucleus 67Ga has been studied through the reaction 57Fe(12C, pnγ)67Ga at E12c = 40 MeV. New levels above 4 MeV excitation energy have been found and nuclear properties of these states are proposed from investigations of prompt γ-rays using in-beam γ-spectroscopic techniques. Comparison between the ground state sequence in 66Zn and the favoured states of positive parity up to J π = 25 2 + in 67Ga suggests that the latter can be explained in terms of coupling a g 9 2 proton to the 66Zn core. A second collective band of positive parity is proposed to be based on a configuration [( f 5 2 ) J≠O 2 π g 9 2 ] 15 2 + . Results on magnetic substate populations of nuclear states formed in different heavy-ion induced reactions compiled. The α2, α4 combinations are consistent with the assumption of Gaussian distributed substate populations within the experimental errors.

In-beam γ-ray spectroscopy of 66Ge

The nucleus 66Ge has been studied through the reaction 54Fe(14N, pnγ)66Ge at E14N = 42 MeV. Eleven new levels above 2 MeV excitation energy have been found and nuclear properties of these states have been assigned from investigations of prompt γ-rays using in-beam γ-spectroscopic techniques such as angular distributions, γγ-coincidences, yield function, lifetime measurements and linear polarization. As in the neighbouring even Ge and Zn isotopes, negative parity states 5−, 7−, (9−) have been observed. In the framework of the cluster-vibration coupling model these states can be explained in terms of mixing of seniority-two clusters [(p32, p12, f52) ⊗ g92]j ≠ 0 coupled to zero, one and higher phonon excitations. B(E2) values are reproduced in good agreement with experiment.

On the structure of negative-parity states in 66Zn and 70Ge

Abstract Mean lifetimes of negative-parity states in 66Zn and 70Ge have been measured using the recoil distance Doppler shift technique. The states in 66Zn have been studied through the reaction 55Mn(14N, 2pnγ)66Zn at E = 47 MeV, those in 70Ge through the reaction 56Fe(16O, 2pγ)70Ge at E = 46 MeV. The measurements were performed with a plunger apparatus with a piezo-electric distance regulation. The mean lifetimes in 66Zn were measured to be 66 ± 4ps (5− state), 43 ± 2 ps (6− state), 192 ± 15 ps (7− state), and 2.7 ± 1.2 ps (9− state), those of 70Ge 19.7 ± 2 ps (5− state), 51 ± 4 ps (6− state), and 25.2 ± 1.4 ps (7− state). Deduced B (Ml) and B(E2) values are compared with theoretical predictions of a two-proton cluster-vibration coupling model (CVM) which describes these states as couplings of g 9 2 ⊗ (fp shell) proton clusters to zero, one and higher phonon excitations of the corresponding Ni and Zn cores. Good overall agreement between the theoretical values and the experimental data was found.

Gamma-spectroscopic investigations on 67Ge

Abstract By γ-γ coincidence measurements following the 57 Fe( 12 C, 2nγ) reaction at E 12C = 40 MeV several new states above 1.5 MeV excitation energy in 67 Ge have been established. Spin and parity assignments on the basis of the angular distribution, linear polarization and γ-ray yield function indicate very similar structures in 67, 69 Ge. The positive-parity states can be followed up to the 17 2 + state at E x = 3.07 MeV followed by a sequence of negative-parity high-spin states at nearly the same excitation energy relative to the 9 2 + single-particle state as in the neighbouring nucleus 69 Ge where these states were found to have strong single-particle admixtures. A reinvestigation of the spin of the E x = 2.75 MeV level in 69 Ge resulting in a change of its spin from 15 2 + to 17 2 + and for all spins above, removed the discrepancy concerning the spin assignments of corresponding levels in 67, 69 Ge. The excitation pattern of the Ge isotopes with 34 ≦ N ≦ 39 clearly indicate same structures probably due to the strong competition between collective and single-particle excitations along the whole chain similar to the results for the Zn isotopes.

Details of conversion electron spectroscopy with mini-orange spectrometers

Abstract Two mini-orange spectrometers for in-beam measurements of conversion electrons have been built and employed for spin and parity assignments of nuclear states by measuring absolute conversion coefficients. A detailed description of the experimental procedure and data analysis is given. Numerical calculations of transmission curves have been performed in order to achieve precise predictions of the optimal measuring geometry and to design new versions of mini-orange spectrometers. The methods were applied to 70 Ge, where spins and parities of 6 − and 7 − were assigned to the levels at 3666.1 and 3954.5 keV, respectively, including the influences of the electron and γ angular distributions.

The shape of magnetic substate distributions in fusion-evaporation reactions

Abstract Nuclear alignment attenuation factors α K of high spin states in nuclei around A = 70 excited in heavy-ion induced fusion-evaporation reactions have been measured. The data indicate a definite correlation between α 2 and α 4 . On the basic assumption of highly aligned entry states in the residual nucleus, the influence of γ-ray transitions on the nuclear alignment is investigated leading to an upper boundary for α 4 -values near the curves representing magnetic substrate distributions of Gaussion shape if it is guaranteed that there is no β-feeding to the level, the particular level is not preceded by an isometric state, and the lifetime is long enough. A review is given on effects resulting from problems in the data analysis, e.g., Doppler broadening due to short lifetimes which may cause α 4 -values above the ALY-curve.

A plunger device with a piezoelectric fine adjustment and a PLL distance regulation

Abstract A plunger device with a piezoelectric fine adjustment and a phase locked loop (PLL) distance regulation is described. The linear motion for the adjustment of the target-stopper distance is provided by two independent sources: a micrometer for distances above 15 μm and a piezocrystal for distances below that value. During measurement the distance is regulated by a phase comparison of the oscillator frequency determined by the target-stopper capacity with the frequency of a reference source. The performance of the plunger device and the regulation is demonstrated by measuring the life-times of some levels in 41 K and 41 Ca with the reaction 27 Al( 16 O, npγ) 41 Ca at 34 MeV.

Spin and parity assignments in Ge 70

Proposed spin and parity of the states 2450.9, 2561.33, and 3415.7 keV in /sup 70/Ge could be confirmed by ..gamma.. angular distribution and linear polarization measurements. The assignments of the states 3666.1 and 3954.5 keV could be corrected to 6/sup -/ and 7/sup -/.

Spin and parity assignments in /sup 70/Ge

Proposed spin and parity of the states 2450.9, 2561.33, and 3415.7 keV in /sup 70/Ge could be confirmed by ..gamma.. angular distribution and linear polarization measurements. The assignments of the states 3666.1 and 3954.5 keV could be corrected to 6/sup -/ and 7/sup -/.

Energy and projectile dependence of nuclear alignment in fusion-evaporation reactions

Nuclear alignment attenuation coefficients of excited levels in 67Ga have been measured via the reactions 64Zn + α and57Fe + 12C for incident energies between 9 and 22 MeV and 32 and 48 MeV, respectively. The data were deduced from angular distributions of four pure electric quadrupole transitions in 67Ga. For the heavy-ion induced reaction a slight decrease of alignment with incident energy has been observed while there is a strong energy dependence of nuclear alignment for the α-induced reaction due to the feeding mechanism. The attenuation coefficients are consistent with the Gaussian magnetic substate population hypothesis except where direct and cascade feeding compete with comparable intersities.