V. Lopac

A simple explanation of the sign and magnitude of quadrupole moments in even-A Fe, Zn, Cd, Te and Hg isotopes

Abstract Coupling valence-shell protons (cluster) to the vibrational field gives the sign and magnitude of quadrupole moments in Fe, Zn, Cd, Te and Hg as a consequence of the shell structure. Competition of contributions of the available valence proton configurations determines the sign and magnitude of the quadrupole moment of two-proton clusters. The field-induced polarization effect always leads to an enhancement of the cluster quadrupole moment.

Nuclear structure of 198Au studied with (n, γ) and (d, p) reactions and interpreted with the IBFFM

Abstract The 197 Au(d, p) 198 Au reaction was measured with the high-resolution Q3D spectrograph at the Munich Tandem Accelerator at θ lab = 35°, using 20 MeV deuterons. Average resonance neutron capture gamma rays were measured with a filtered neutron beam at the Brookhaven National Laboratory. Using also secondary (n, γ) data a level scheme of 198 Au was established with 66 levels up to an excitation energy of 1600 keV mostly with spin and parity assignments. The level energies, E2 and M1 branching ratios and (d, p) transfer data were compared with new model predictions of the interacting boson-fermion-fermion model (IBFFM). This model provides a basic understanding of 198 Au.

Even Zn isotopes in the cluster-vibration model

Abstract Even-A nuclear systems with two protons in the 28–50 valence shell (even Zn isotopes) are described in the cluster-vibration model. Energy spectra and electromagnetic properties are calculated and their qualitative features are discussed with emphasis on the coexistence between quasivibrational and quasirotational characteristics. The influence of possible cubic anharmonicities and of the presence of the g 9 2 configuration are investigated. For some states, pairing phonons are recognized as intrinsic building blocks created in the cluster-vibration model. The relation between this approach and recent shell-model calculations is discussed.

Structure of the energy levels of 53, 55, 57Mn from the (d, 3He) reaction on iron isotopes at 80 MeV

Abstract The 54, 56, 58 Fe(d, 3 He) 53, 55, 57 Mn reactions have been studied at a bombarding energy of 80 MeV. Angular distributions have been measured in the range of 6° to 30° lab. Energy levels up to excitation energies of 9.2 MeV, 7.2 MeV, and 7.4 MeV in 53 Mn, 55 Mn, and 57 Mn, respectively, have been studied. DWBA calculations were employed to extract spectroscopic factors. Shell-model, quasiparticle-core-coupling, and cluster-vibration-model calculations were performed. Theoretical spectroscopic factors compare favourably with experimental values.

Electromagnetic properties of some odd-odd nuclei in the A≈ 100 region and IBFFM description of 106Ag

Abstract Electromagnetic properties of odd-odd transitional nuclei with A ≈ 100 are investigated experimentally and theoretically. Nanosecond isomers are studied in-beam by means of delayed γγ-coincidences and the generalized centroid-shift method. The reactions 98 Mo+30MeV 7 Li and 92,94 Mo+ 50 MeV 12 C are utilized. Following half-lives are determined: T 1 2 (547.2 keV in 102 Rh) = 0.25±0.07ns, T 1 2 (243.1 keV in 102 Rh) = 0.30±0.10ns, T 1 2 (181.1 keV in 99 Tc) = 3.8 ± 0.3ns, T 1 2 (2902.0keV in 104 Cd) = 0.6±0.1 ns, T 1 2 (118.7keV in 103 Pd) =0.8±0.2 ns, T 1 2 (131.1 keV in 105 Cd) = 1.5 ±0.3 ns, T 1 2 (211.8 keV in 104 Ag) = 1.4±0.1 ns, T 1 2 (181.0 keV in 102 Ag) = 3.5±0.2 ns. Additionally, several upper limits of level lifetimes are derived. The systematics of E1, M1 and E2 transition rates in 100,102,104 Rh and 102,104,106 Ag is presented and discussed. Fast M1 transitions within the 2qp π g 9 2 ν h 1 2 band appear to be associated with the strong coupling of the π g 9 2 proton and the rotational alignment of the h 11 2 neutron. Extensive IBFFM calculations of level energies and electromagnetic properties of 106 Ag as a typical case demonstrate that this model could account for the complex structural pattern of this type of nuclei. NUCLEAR REACTIONS 98 Mo( 7 Li, 3n), ( 7 Li2nα), E =30 MeV; 92,94 Mo( 12 C, pn), 94 Mo( 12 C, 2n), ( 12 C, 2pn), E = 50 MeV; measured E γ , I γ , γγ ( t ). 102 Rh, 99 Tc, 102,104 Ag, 104 Cd,

Proton-hole states in 57Co studied with the 58Ni(d, 3He) 57Co reaction at 78 MeV

Abstract The 58 Ni(d, 3 He) 57 Co reaction was measured at a bombarding energy of 78 MeV. Energy levels up to 7.0 MeV excitation energy in 57 Co were studied. Angular distributions of the 3 He particles, corresponding to transitions to the ground state and to 42 excited states in 57 Co, were analyzed in the range of θ lab = 2.7° to 25°. Exact finite-range DWBA calculations were employed to extract l -values and spectroscopic factors. Shell-model calculations were carried out in an fp-shell model space. In addition, calculations of the energy levels in 57 Co were performed in the SU(6) particle-vibration model (PTQM). Satisfactory agreement is observed between the experimental results and both theoretical predictions.

Thermal-neutron-capture studies on 135Ba

Abstract The nucleus 135 Ba has been studied via primary, secondary γ-rays, γγ coincidences following thermal-neutron capture. A level scheme was established up to 3.7 MeV consisting of 41 levels including 114 γ-transitions. The neutron binding energy was determined to be 6971.78(17) keV. The total thermal cross section and isomer production of the 11 2 − state were determined to be σ(tot) = 1.4(4) and σ( 135 Ba) = 0.11(2) barn. The level energies, E2 and M1 transitions and electromagnetic moments were compared with model predictions of the interacting boson-fermion model (IBFM).

Nuclear structure and high-spin states of 137Pr

Abstract Levels in 137 Pr were populated in the 126 Te( 14 N, 3n) and 122 Sn( 19 F, 4n) reactions and the subsequent radiation was studied using in-beam γ-ray spectroscopy methods including γ-ray excitation-function, angular-distribution, γγ ( t ) coincidence and γ ( t ) measurements. A level scheme with new states up to spin 35 2 belonging to 137 Pr is given. The lifetime of the 11 21 state at 563.4 keV has been determined as T 1 2 = 2.66±0.07 μ s . The calculation of low-lying levels in 137 Pr performed in IBFM has been compared to experimental data.

Structure of low-lying levels in91Rb and93Rb

Life-times of low-lying levels in3791Rb54 and3793Rb56 have been determined fromβ−−γ coincidence measurements at the fission-product separator JOSEF. Values oft1/2=17.0(8) ns and 2.0(2) ns have been obtained for the levels at 1,134 keV in91Rb and 267 keV in93Rb, respectively, and upper limits could be deduced for several other states. Calculations in the frame of IBFM/PTQM have been performed for91Rb, the results of which allow an interpretation of the low-lying levels of this nucleus. For the 1,134 keV level the configuration [πg9/2⊗2+] 7/2+ is suggested which lies close to or even below the 9/21+ level. The calculated half-life of 14 ns for the 1,134 keV level reproduces well the experimental value. The half-life of the 267 keV level in93Rb favours the assignment ofIπ=1/2− to this state over the alternative 3/2−.

Quantum chaos forN=79 nuclei in the IBFM model

Spectral rigidityΔ3 (L) is calculated for the energy spectra of131Te,135Ba and137Ce, obtained in the IBFM calculation. Results reveal an intermediate situation between regularity and chaos, but remarkably closer to the chaotic limit. Influence of the model parameters on the fluctuation pattern is discussed.