The $g$ factor of the ${2}_{1}^{+}$ state of ${}^{168}$Hf was measured using the perturbed angular correlation technique in a static external magnetic field. The result, $g({2}_{1}^{+})=0.17(3)$, is discussed in relation to the systematics of the previously reported $g$ factors in the Hf isotopes and compared to the predictions of several models. An interesting outcome of the analysis presented in this paper has to do with the relatively small result for the $g$ factor. This indicates that in the Hf isotopes, a minimum in the $g$(${2}_{1}^{+}$) dependence on $N$ occurs at $N\ensuremath{\le}98$ and not at midshell, as expected from IBA-2 or large-scale shell-model calculations. The pairing plus quadrupole model of Kumar and Baranger predicts a minimum at $N=98$ and gives the best description of the experimental data. The present result clearly shows the importance of $g$-factor measurements in ``fine-tuning'' among different models.

The $g$ factor of the ${2}_{1}^{+}$ state of $^{172}\mathrm{Hf}$ was measured using the perturbed angular correlation technique in a static external magnetic field. The result, $g({2}_{1}^{+})=0.25(5)$, is discussed in relation to the systematics of the previously reported $g$ factors in the Hf isotopes and compared with the predictions of several models. An interesting outcome of the analysis presented in this paper is the agreement between the calculated $g$ factors within the interacting boson approximation (IBA) and the results of a large-scale shell model calculation. This agreement supports the emphasis in the IBA on the valence space. The undershooting of the empirical $g$ factors near midshell in both models suggests that they underestimate the role of the saturation of collectivity, which is explicitly incorporated into a phenomenological model that agrees better with the data.

The g factor of the 2(1)(+) state of Hf-172 was measured using the perturbed angular correlation technique in a static external magnetic field. The result, g(2(1)(+))=0.25(5), is discussed in relation to the systematics of the previously reported g factors in the Hf isotopes and compared with the predictions of several models. An interesting outcome of the analysis presented in this paper is the agreement between the calculated g factors within the interacting boson approximation (IBA) and the results of a large-scale shell model calculation. This agreement supports the emphasis in the IBA on the valence space. The undershooting of the empirical g factors near midshell in both models suggests that they underestimate the role of the saturation of collectivity, which is explicitly incorporated into a phenomenological model that agrees better with the data.

Excited low-spin, nonyrast states in {sup 170,172,174}Hf were populated in {beta}{sup +}/{epsilon} decay and studied through off-beam {gamma}-ray spectroscopy. New coincidence data allowed for a substantial revision of the level schemes of {sup 170,172}Hf and a confirmation of the level scheme of {sup 174}Hf. The Hf isotopes represent a unique situation in which a crossing of collective intrinsic excitations occurs, enhancing significantly the effects of mixing. Using branching ratios from excited 2{sup +} states, this mixing is followed and studied. The resulting mixing matrix elements are found to be {approx}30 keV - an order of magnitude larger than estimated previously for nearby nuclei. In the case of {sup 170}Hf, the 2{sub {beta}}{sup +} and 2{sub {gamma}}{sup +} level are shown to be completely mixed.

Internal conversion coefficients have been measured for transitions in both normal deformed and triaxial strongly deformed bands in Lu-167 using the Gammasphere and ICE Ball spectrometers. The results for all in-band transitions are consistent with E2 multipolarity. Upper limits are determined for the internal conversion coefficients for linking transitions between TSD Band 2 and TSD Band 1, the n(w)=1 and n(w)=0 wobbling bands, respectively.

A. Wolf,1,2 Z. Berant,1,2 A. Heinz,2 V. Werner,2 E. A. McCutchan,2 G. Gürdal,2,3 R. B. Cakirli,2,4 Y. Oktem,2,4 J. Ai,2 L. Amon,2,4 C. W. Beausang,5 D. S. Brenner,3 R. F. Casten,2 R. J. Casperson,2 K. Dusling,6 C. R. Fitzpatrick,2,7 A. B. Gransworthy,2,7 N. Pietralla,6,8 J. Qian,2 P. H. Regan,7 N. J. Thompson,2,7 E. Williams,2 and R. Winkler2 1Nuclear Research Center Negev, Beer-Sheva 84190, Israel 2Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520, USA 3Chemistry Department, Clark University, Worcester, Massachusetts 01610, USA 4Department of Physics, University of Istanbul, Istanbul, Turkey 5University of Richmond, Richmond, Virginia 23173, USA 6Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794, USA 7Department of Physics, University of Surrey, Guilford GU2 7XH, United Kingdom, 8Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany (Received 21 August 2007; published 29 October 2007)

A. Wolf,1,2 Z. Berant,1,2 A. Heinz,2 V. Werner,2 E. A. McCutchan,2 G. Gürdal,2,3 R. B. Cakirli,2,4 Y. Oktem,2,4 J. Ai,2 L. Amon,2,4 C. W. Beausang,5 D. S. Brenner,3 R. F. Casten,2 R. J. Casperson,2 K. Dusling,6 C. R. Fitzpatrick,2,7 A. B. Gransworthy,2,7 N. Pietralla,6,8 J. Qian,2 P. H. Regan,7 N. J. Thompson,2,7 E. Williams,2 and R. Winkler2 1Nuclear Research Center Negev, Beer-Sheva 84190, Israel 2Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520, USA 3Chemistry Department, Clark University, Worcester, Massachusetts 01610, USA 4Department of Physics, University of Istanbul, Istanbul, Turkey 5University of Richmond, Richmond, Virginia 23173, USA 6Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, New York 11794, USA 7Department of Physics, University of Surrey, Guilford GU2 7XH, United Kingdom, 8Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany (Received 21 August 2007; published 29 October 2007)

The surrogate ratio technique is described. New results for neutron induced fission cross sections on actinide nuclei, obtained using this technique are presented. The results benchmark the surrogate ratio technique and indicate that the method is accurate to within 5% over a wide energy range. New results for internal conversion coefficients in triaxial strongly deformed bands in Lu-167 are also presented.

The g factor of the 2(1)(+) state of Hf-170 was measured by perturbed gamma-gamma angular correlation in a static external magnetic field. The result, g(2(1)(+))=0.28(5), extends the systematics of g factors of even-even Hf isotopes to N = 98 and enables a better test of theoretical models. The g(2(1)(+)) experimental values of these isotopes exhibit a remarkable constancy as a function of neutron number. This phenomenon, which was also observed for other isotopic chains in the Gd-W range, is explained in terms of a recently proposed empirical model.

Empirical average proton-neutron interaction energies, delta V-pn, between the last nucleons can be isolated using double differences of masses. We have examined the systematic behavior of delta V-pn throughout the mass surface using the 2003 mass table that includes many new and improved experimental masses. The results are especially revealing for self-conjugate nuclei and in regions of strong shell closures in heavy nuclei. In the former the large p-n interaction strength can be interpreted as a consequence of the T=0 interaction between protons and neutrons in spatially similar orbitals. In the latter, the bifurcated systematic can be understood in terms of the evolution of proton and neutron orbital overlaps in regions surrounding a shell closure. In regions between shells, anomalies are sometimes encountered that are not fully understood. They might reflect structural effects or could arise from one or more erroneously measured masses. A scheme based on fractional shell filling is presented that may serve as a signature of shell structure in exotic nuclei. A link between empirical p-n interactions and growth rates of collectivity is pointed out. Finally, our analysis is used to identify candidates for future mass measurements and their needed levels of accuracy, many of which will require new exotic beam facilities.

The rare earth nuclei from N=92 to N=108 display a very regular pattern of empirically extracted interactions of the last protons with the last neutrons. The simplicity of the empirical systematics suggests that a simple interpretation should be possible. We discuss calculations of these proton-neutron (p-n) interactions with a zero-range delta force.

Lifetime measurements of yrast levels in 162 Yb and 166 Hf were performed using the recoil distance Doppler-shift method in coincidence mode. Excited states in 162 Yb and 166 Hf were populated via the reactions 116 Cd( 50 Ti, 4 n ) and 122 Sn( 48 Ti, 4 n ), respectively. The resulting B ( E 2) values are compared with the X(5) critical point model predictions and interacting boson approximation (IBA) model calculations. The X(5) model provides a reasonable description of the yrast B ( E 2) values in 166 Hf, whereas the IBA fails to reproduce the transition strengths from the higher spin levels. In 162 Yb, some transitions agree with the X(5) predictions while others are more consistent with the predictions of the IBA or a deformed symmetric rotor.