The spectroscopic quadrupole moment of the T-1/2 = 9.4(5) ns isomer in Pb-193 at an excitation energy E-ex = (2585 + x) keV is measured by the time-differential perturbed angular distribution method as vertical bar Q(s)vertical bar = 2.6(3) e b. Spin and parity I-pi = 27/2(-) are assigned to it based on angular distribution measurements. This state is the band head of a magnetic-rotational band, described by the coupling of a neutron hole in the 1i(13/2) subshell with the (3s(1/2)(-2)1h(9/2)1i(13/2))(11-) proton excitation. The pairing-plus-quadrupole tilted-axis cranking calculations reproduce the measured quadrupole moment with a moderate oblate deformation epsilon(2) = -0.11, similar to that of the 11(-)proton intruder states, which occur in the even-even Pb nuclei in the region. This is the first direct measurement of a quadrupole moment and thus of the deformation of a magnetic-rotational band head.

The nucleus Ti-46 has been studied with the reaction Ca-42(Li-7,p2n)Ti-46 at a bombarding energy of 31 MeV. Thin target foils backed with a thick Au layer were used. Five new levels of negative parity were observed. Several lifetimes have been determined with the Doppler shift attenuation method. Low-lying experimental negative-parity levels are assigned to three bands with K-pi = 3, 0, and 4, which are interpreted in terms of the large-scale shell model, considering particle-hole excitations from d(3/2) and s(1/2) orbitals. Shell model calculations were performed using a few effective interactions. However, good agreement was not achieved in the description of either negative- or positive-parity low-lying levels.

The transition strenghts for the low-lying levels of Ba-122,Ba-124 have been determined analysing the Recoil Distance Doppler Shift data by the Differential Decay Curve Method. The trend of normalised B(E2) reveals a drop in correspondance of the 8(1)(+) state. This feature is also present in Ba-122: entering the backbending region the interplay between collective and quasiparticle degrees of freedom have to be carefully taken into account.

The g factors of the 12(+), 11(-), and 8(-) isomeric states in Pb-188 were measured using the time-differential perturbed angular distribution method as g(12(+)) = -0.179(6), g(11(-)) = +1.03(3), and g(8(-)) = -0.037(7). The g factor of the 12(+) state follows the observed slight down-sloping evolution of the g factors of the i(13/2)(2) neutron spherical states with decreasing N. The g factors of the 11(-) and 8(-) isomers proposed as oblate and prolate deformed states, respectively, were interpreted within the rotational model, using calculated and empirical g factor values for the involved single-particle orbitals.

In this paper we propose to perform the scintigraphy of small organ using a rotating-slit collimator and a bundle of scintillating glass fibers, put in parallel with the slit and rotating with it. An intensified CCD, coupled to the end of the fibers, acquires an integrated image of the events per each rotation angle. The final image is computed by a back-projection procedure. The advantages of this method, with respect to conventional scintigraphy, are the improvement of the detection efficiency of one-two order of magnitude without counting rate limitations, the improvement of the spatial resolution, the elimination of the parallax error and the rejection of the spurious events, without energy analysis. Simulations and first experimental results are showed.

The lifetimes of excited states of the Ba-122 ground-state band, populated via the Cd-108(O-16,2n)Ba-122 and the Sn-112(C-13,2n)Ba-122 reactions, have been measured using the Recoil Distance Doppler-Shift method. The level scheme of Ba-122 has also been revised.

The lifetimes of excited states of the 122Ba ground—state band, populated via the 108Cd(16O,2n)122Ba and the 112Sn(13C,2n)122Ba reactions, have been measured using the Recoil Distance Doppler—Shift method. The level scheme of 122Ba has also been revised.

The feasibility of the entire process of gamma-ray tracking is demonstrated experimentally for the first time. The accuracy of the results is verified by the capability to carry out a Doppler correction of gamma-rays emitted in flight. The resolution of the 846.8 keV transition detected with the MARS detector after Coulomb excitation of a 56 Fe beam could be improved from approximately 16 up to 4.6 keV (FWHM). This result corresponds to an obtained position resolution of about 6mm (FWHM). (C) 2007 Elsevier B.V. All rights reserved.

The precession of the lowest 3/2− and 5/2− states in107Ag and109Ag, recoiling in thin iron foils, have been measured employing the transient-field method. Theg-factors have been measured relative to that of the first 2+ state in106Pd and resulted to be $$\begin{gathered} g(\frac{3}{2}^ - ,{}^{107}Ag) = 0.70(9) g(\frac{5}{2}^ - ,{}^{107}Ag) = 0.45(6) \hfill g(\frac{3}{2}^ - ,{}^{107}Ag) = 0.79(12) g(\frac{5}{2}^ - ,{}^{109}Ag) = 0.36(6) \hfill \end{gathered} $$ (1) The values obtain have been compared with some theoretical predictions.

Excited states in the very neutron-deficient 122 La nucleus have been established for the first time using the 92 Mo( 40 Ca, 2α1 p 1 n ) reaction at beam energies of 190 and 200MeV. The observed transitions were grouped in three bands. Configurations have been assigned to the observed bands based on the properties extracted from the experimental data and on cranked shell model calculations.

High-spin states in Ar-35 and Cl-35 have been populated in the Mg-24(O-16, alpha n) and Mg-24(O-16, alpha p) reactions, respectively, at a beam energy of 70 MeV. The comparison between the level schemes of these mirror nuclei shows a striking asymmetry in the population yield of high-spin analog states of positive parity, which indicates different intensities of E1 transitions connecting positive- and negative-parity structures in both nuclei. Large energy differences are observed between analog states of negative parity with configurations of dominant pure single-particle character. This results from the comparison with large-scale shell-model calculations in the s(1/2)d(3/2)f(7/2)p(3/2) valence space. It is shown that important contributions to the energy differences arise from the multipole Coulomb and the relativistic electromagnetic spin-orbit interactions.

The spectroscopic quadrupole moments of the 11− and 12+ isomers in 192,194Pb, described by the 3s1/2−21h9/21i13/2 intruder two-proton and 1i13/22 two-quasineutron configurations, respectively, have been determined by the method of time-differential observation of the γ-ray perturbed angular distribution. The derived values are |Qs|(12+,192Pb) = 0.32(4) eb, |Qs|(11−,192Pb) = 2.9(3) eb and |Qs|(11−,194Pb) = 3.6(4) eb. The 8+ 2304 keV and 9− 2514 keV states in 192Pb have been identified as isomers, with half-lives of 3.9(3) and 3.3(2) ns, respectively. The experimental spectroscopic quadrupole moments for the 11− and 12+ isomers in neutron deficient Pb nuclei have been described in the framework of the pairing plus quadrupole model. The intrinsic quadrupole moments and deformation of the 11− isomers are compared with the predictions of mean-field and interacting boson models.

The nucleus P-31 has been studied in the Mg-24(O-16,2 alpha p) reaction with a 70-MeV O-16 beam. A complex level scheme extended up to spins 17/2(+) and 15/2(-), on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd-fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T=0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of P-31.

The nucleus Cr-49 has been studied by analyzing gamma-gamma coincidences in the reaction Ti-46(alpha,n)Cr-49 at the bombarding energy of 12 MeV. The level scheme has been greatly extended at low excitation energy, and several lifetimes have been determined by means of the Doppler shift attenuation method. Shell model calculations in the full pf configuration space reproduce well the negative parity levels. Satisfactory agreement is obtained for positive parity levels by extending the configuration space to include a nucleon-hole in either the 1d(3/2) or 2s(1/2) orbitals. A nearly one-to-one correspondence is found between experimental and theoretical levels up to an excitation energy of 4 MeV. Experimental data and shell model calculations are interpreted in terms of the Nilsson diagram and the particle-rotor model, showing the strongly coupled nature of the bands in this prolate nucleus. Nine values of K-pi are proposed for the levels observed in this experiment. As a secondary result, it is shown that the values of the experimental magnetic moments in 1f(7/2) nuclei are well reproduced without quenching the nucleon g factors.

Received 3 November 2006DOI:https://doi.org/10.1103/PhysRevLett.97.199901©2006 American Physical Society

Gamma decays from excited states up to Jpi=6+ in the N=Z-2 nucleus 54Ni have been identified for the first time. Level energies are compared with those of the isobars 54Co and 54Fe and of the cross-conjugate nuclei of mass A=42. The good but puzzling f7/ cross-conjugate symmetry in mirror and triplet energy differences is analyzed. Shell model calculations reproduce the new data but the necessary nuclear charge-dependent phenomenology is not fully explained by modern nucleon-nucleon potentials.

Spectroscopic quadrupole moment measurements for high-spin isomeric states in Pb-192,Pb-193,Pb-194 nuclei have been performed by the time-differential perturbed gamma-ray angular distribution method. The quadrupole moments of the isomers described by quasineutron configurations in neutron-deficient Ph nuclei are well reproduced by the pairing plus quadrupole model, which predicts for these states a very small prolate deformation beta approximate to 0.02. The quadrupole moment of the I I isomeric state in 192 Ph involving the pi(3s(1/2)(-2)1h(9/2)1i(13/2)) configuration corresponds to a deformation beta(2)=-0.11(1). The quadrupole moments of the proton intruder states in Pb nuclei are compared with theoretical predictions of tilted-axis cranking, mean-field and interacting boson models.

Gamma decays from excited states up to J(pi)=6(+) in the N=Z-2 nucleus Ni-54 have been identified for the first time. Level energies are compared with those of the isobars Co-54 and Fe-54 and of the cross-conjugate nuclei of mass A=42. The good but puzzling f(7/2) cross-conjugate symmetry in mirror and triplet energy differences is analyzed. Shell model calculations reproduce the new data but the necessary nuclear charge-dependent phenomenology is not fully explained by modern nucleon-nucleon potentials.