L. Hasselgren

Quadrupole collective properties of 114Cd

Abstract The nucleus 114 Cd has been Coulomb excited using beams of 16 O, 40 Ca, 58 Ni and 208 Pb. Several new states have been observed and an almost complete set of reduced E2 matrix elements for the lowest-lying positive-parity states in 114 Cd have been measured. In total, about 40 E2 matrix elements have been determined in a model-independent way, including the static quadrupole moments of the 4 + 1 , 6 + 1 , 2 + 2 and 2 + 3 states. Large negative static quadrupole moments were found for the 4 + 1 and 6 + 1 states and a large positive quadrupole moment for the 2 + 2 state. All E2 matrix elements involved in the deexcitation of the quintuplet of states at an energy of about 1.2 Me V were determined. The data are compared with predictions by various models, including a configuration mixing calculation within the framework of the IBA model, the harmonic vibrator and a model in which the states of a near-harmonic vibrator are mixed with those of a rotational intruder band with a large deformation. Although no perfect match is obtained, the data favour a vibration-like structure involving levels up to the four-quadrupole phonon multiplet.

Multiphonon vibrational states in 106,108Pd

Abstract The nuclei 106 Pd and 108 Pd have been Coulomb excited using beams of 16 O, 58 Ni and 208 Pb. The data determined 25 and 31 E2 matrix elements in 106 Pd and 108 Pd, respectively. The experimental data are qualitatively in agreement with the spherical-harmonic quadrupole vibrational model, but quantitatively there are large discrepancies, even for the states generally accepted to be the two-phonon vibrational states. A sum-rule method was applied to the data, the result of which implies that the vibrational quadrupole strengths of the 0 + and 4 + two-phonon states are fragmented and shared between several E2 matrix elements. The E2 matrix elements imply appreciable quadrupole triaxiality with a γ-centroid of about 20°. A systematic comparison is made with neighbouring Pd-isotopes and with 114 Cd.

Reorientation precession measurements on 108, 110Pd and the quadrupole moments of their first 2+ states

Abstract The reorientation precession technique, REPREC, for measurements of quadrupole moments is described. The application of REPREC to the measurement of the static electric quadropole moments of the first excited 2 + states in 108, 110 Pd is presented. The possibility to measure the sign of the matrix product P 4 = M 02 M 22′ M 02′ M 22 is also discussed. Such measurements are presented for 108, 110 Pd. The results of these measurements are P 4 108 Pd and 110 Pd. For 108 Pd the quadrupole moment of the first excited 2 + state was found to be −0.66±0.18 e ·b and for 110 Pd, −0.72±0.14 e ·b. Intrinsic nuclear properties for 106−110 Pd are derived using the sum rules suggested by Kumar.

Heavy-ion Coulomb excitation of 72Ge

Abstract The nucleus 72Ge has been Coulomb excited using 16O, 58Ni and 208Pb. Seventeen E2 matrix elements coupling the low-lying states have been determined. Based on these data, an interpretation of the structure of 72Ge has been proposed that includes an “intruder” 0+ state perturbing what the present work shows to be a triaxial quadrupole-deformed collective rotational structure.

The Quadrupole Moments of the First Excited 2+ States in 96 100 104Ru

The quadrupole moments of the first excited 2+ states in 96,100,104Ru have been measured using the reorientation precession technique. In 104Ru the sign of the Coulomb interference term P4 = M0+12+1 M0+12+2 M2+22+1 × M2+12+1 was determined and found to be P4 < 0. The quadrupole moment in 104Ru was determined to be -0.76 ± 0.19 eb. In 96Ru and 100Ru the measurements revealed quadrupole moments of -0.15 ± 0.27 eb and -0.40 ± 0.12 eb, respectively, independent of the sign of P4. The experimentally determined values are compared with theoretical calculations.

Internal conversion studies of transitions populating and depopulating the 161 keV level in 133Cs

Abstract Four transitions in 133 Cs have been studied by measurements of relative conversion electron intensities and electron-gamma directional correlations. The transitions studied, 276, 223, 161 and 80 keV respectively, all feed and de-excite the 161 keV level in 133 Cs. In addition the L-subshell ratios for the 81 keV transition have been measured and analysed. The 161 and 223 keV transitions show penetration effects in the internal conversion process. The penetration effects in the 223 keV transition are reported for the first time.

studies in the decay of 131Ba revealing nuclear penetration effects in the 92 keV transition in 131cs

Abstract The γ-ray and internal conversion spectra of the decay of 131 Ba to levels in 131 Cs were investigated using a Ge(Li) detector and a double-focussing β-ray spectrometer. Accurate transition energies and internal conversion coefficients were deduced using the internal conversion data of Horen et al . 1 ) in conjunction with the results obtained here. Gamma-gamma and electron-γ directional correlation measurements were performed. Unique spin-parity assignments were obtained for all levels in a compiled level scheme using the deduced conversion coefficients, the results from angular correlation measurements and the deduced log ft values. Nuclear penetration effects were found to be present in the 92 keV transition characterized by λ = 23 −11 +7 .

A determination of the sign of P3 = M01+21+M21+22+M22+01+ for 194Pt

Abstract The sign of the matrix product P 3 = M 0 1 + 2 1 + M 2 1 + 2 1 + M 2 2 + 0 1 + is determined for 194 Pt and found to be negative. A suggestion is made that single particle degrees of freedom in the wavefunctions will be important for the sign of P 3

K, L and M electron directional correlations in 123Te

Abstract Directional correlations of the cascade in 123 Te involving K, L and M electrons from the 89 keV M4 transition have been measured in order to determine the δ (E2/M1) value for the 159 keV transition. The result agrees with that from older correlation measurements, but is in conflict with values derived from Coulomb excitation and lifetime measurements as well as from L subshell ratios.

ELECTRON--GAMMA DIRECTIONAL CORRELATIONS IN

Transitions in the decay of 168Tm to 168Er have been studied by measurements of electron-gamma directional correlations. The M1-contributions of the 632-, 731- and 816-keV transitions between the gamma-vibrational band and the ground state rotational band have been determined to amount to less than 0.8%. The 99-, 198- and 830-keV transitions depopulating the 1094-keV state have been determined to be of predominantly E1-character. A pure E1-multipolarity for the 99-keV transition is however possible only if a penetration effect is present in the internal conversion process characterized by a nuclear current parameter ? = 303-8+7 or ? = -12.2-2.0+2.0