J. N. Orce, 2, ∗ J. D. Holt, 3, 4 A. Linnemann, C. J. McKay, C. Fransen, J. Jolie, T.T.S. Kuo, S. R. Lesher, 7 M. T. McEllistrem, N. Pietralla, 8 N. Warr, V. Werner, 9 and S. W. Yates 10 Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA Institut für Kernphysik, Universität zu Köln, 50937 Köln, Germany Nuclear Structure Laboratory, Department of Physics and Astronomy, SUNY, Stony Brook, NY 11794-3800, USA Department of Physics, University of Wisconsin La Crosse, 1725 State Street, La Crosse, WI 54601, USA Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520-8120, USA Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA (Dated: December 6, 2021)

Excited states in Pd-106 were studied with the (n, n gamma.) reaction, and comprehensive information for excitations with spin <= 6h was obtained. The data include level lifetimes in the femtosecond regime, spins and parities, transition multipolarities, and multipole mixing ratios, which allow the determination of reduced transition probabilities. The E2 decay strength to the low-lying states is mapped up to approximate to 2.4 MeV in excitation energy. The structures associated with quadrupole collectivity are elucidated and organized into bands.

Level lifetimes in 106Pd were measured with the Doppler-shift attenuation method following inelastic neutron scattering, and electric monopole transition strengths between low-lying 2+ states were deduced. The large \( \rho^{2}\)(E0) values obtained provide evidence for shape coexistence, extending observation of such structures in the N = 60 isotones. Included in these results is the first determination of the E0 transition strength in the Pd nuclei between levels with K = 2 .

Excited states in 106Pd and 106Cd have been studied using the (n,n′γ) reaction. The data include level lifetimes, spins, branching ratios, and multipole mixing ratios, and give a comprehensive view of excitations with spin ≤6ħ. The determined E2 strengths show serious discrepancies with the quadrupole phonon structure expected in these nuclei.

A. Chakraborty, F.M. Prados-Estevez, E.E. Peters, M.G. Mynk, D. Bandyopadhyay, N. Boukharouba, S.N. Choudry, B.P. Crider, P.E. Garrett, S.F. Hicks, A. Kumar, S.R. Lesher, C.J. McKay, M.T. McEllistrem, S. Mukhopadhyay, J.N. Orce, M. Scheck, J.R. Vanhoy, J.L. Wood, and S.W. Yates Department of Physics, Krishnath College, Berhampore, Murshidabad, West Bengal-742101, INDIA Department of Physics & Astronomy and Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA Department of Physics, University of Guelph, Guelph, Ontario, N1G2W1, Canada Department of Physics, University of Dallas, Irving, TX 75062, USA Department of Physics, University of the Western Cape, P/B X17, Bellville, ZA-7535, South Africa Department of Physics, United States Naval Academy, Annapolis, MD 21402, USA and Department of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA

A comprehensive decay scheme of $^{93}$Nb below 2 MeV has been constructed from information obtained with the $^{93}$Nb(n,n$^\prime$$\gamma$) and $^{94}$Zr(p,2n$\gamma$$\gamma$)$^{93}$Nb reactions. Branching ratios, lifetimes, transition multipolarities and spin assignments have been determined. From $M1$ and $E2$ strengths, fermionic-bosonic excitations of isoscalar and isovector character have been identified from the weak coupling $\pi1g_{9/2}$$\otimes$$^{92}_{40}$Zr and $\pi2p_{1/2}^{-1}$$\otimes$$^{94}_{42}$Mo configurations. A microscopic interpretation of such excitations is attained from shell-model calculations using low-momentum effective interactions.

A comprehensive level scheme of Nb-93 below 2 MeV has been constructed from information obtained with the Nb-93(n,n'gamma) and the Zr-94(p,2n gamma gamma)Nb-93 reactions. Branching ratios, lifetimes, transition multipolarities, and spin assignments have been determined. From M1 and E2 strengths, fermionic-bosonic excitations of isoscalar and isovector characters have been identified from the weak couplings of the pi 1g(9/2) circle times Zr-92(40) and pi 2p(1/2)(-1) circle times Mo-94(42) configurations. A microscopic interpretation of such excitations is obtained from shell-model calculations, which use low-momentum effective interactions.

Understanding the nuclear structure of Sm-152, along with other N = 90 isotones, has long posed a challenge. A rapid transition in shape between the spherical N = 88 Sm-150 and well-deformed N = 92 Sm-154 is observed, along with strong evidence for shape coexistence. Competing ideas have been put forward over the decades, with the most recent being that N = 90 is at the critical point of a shape phase transition. Until recently, the lack of high-precision data has not allowed the competing models to be extensively tested. In a coordinated program of investigation, a series of complementary experiments, which include high-statistics beta decay, multi-step Coulomb excitation, the Nd-150(alpha,2n) reaction, and the (n,n'gamma) reaction, have been performed for Sm-152. These experiments have revealed the existence of a pairing-isomer band, a hexadecapole band, the lack of multi-phonon beta vibrational bands, and the repetition of structures built on the first excited K-pi=0(+) as built on the ground state. The status of these coordinated studies is examined.

The 685 keV excitation energy of the first excited 0(+) state in Sm-152 makes it an attractive candidate to explore expected two-phonon excitations at low energy. Multiple-step Coulomb excitation and inelastic neutron scattering studies of Sm-152 are used to probe the E2 collectivity of excited 0(+) states in this "soft" nucleus and the results are compared with model predictions. No candidates for two-phonon K-pi = 0(+)quadrupole vibrational states are found. A 2(+), K = 2 state with strong E2 decay to the first excited K-pi = 0(+) band and a probable 3(+) band member are established.

Experimental studies of 152Sm using multiple-step Coulomb excitation and inelastic neutron scattering provide key data that clarify the low-energy collective structure of this nucleus. No candidates for two-phonon beta-vibrational states are found. Experimental level energies of the ground-state and first excited (0+ state) rotational bands, electric monopole transition rates, reduced quadrupole transition rates, and the isomer shift of the first excited 2+ state are all described within ~10% precision using two-band mixing calculations. The basic collective structure of 152Sm is described using strong mixing of near-degenerate coexisting quasi-rotational bands with different deformations.

The low-spin structure of Nb-93 has been studied using the Nb-93(gamma,gamma(')), Nb-93(n,n(')gamma) and Zr-94(p,2n gamma gamma)Nb-93 reactions. Lifetimes were determined from both Nb-93(gamma,gamma(')) and Nb-93(n,n(')gamma) measurements. Branching ratios were measured, and multipolarities and spin assignments were determined from the Zr-94(p,2n gamma gamma)Nb-93 angular correlation experiment. From M1 and E2 strengths, the J(pi)=9/2(+) and 7/2(+) states at 1297.1 keV and 1483.6 keV, respectively, are proposed as members of the quintet of mixed-symmetry states associated with the pi 1g(9/2)circle times(2(1,MS)(+),Zr-92) configuration. The large B(M1) values determined in Nb-93 cannot be explained within the weak coupling limit of the interacting boson fermion model.

Extensive studies of the low-spin excited states in ${}_{42}^{96}{\mathrm{Mo}}_{54}$ with the ($n,{n}^{\ensuremath{'}}\ensuremath{\gamma}$) reaction have clarified the level scheme below 3.7 MeV excitation energy and determined detailed information about $^{96}\mathrm{Mo}$, including lifetimes from the Doppler-shift attenuation method, branching ratios, and multipole mixing ratios. Also, $B(E2)$ and $B(M1)$ values were determined for many transitions, multiphonon states were identified, and several low-spin states were characterized in terms of collective, mixed-symmetry states.

Extensive studies of the low-spin excited states in Mo-96(42)54 with the (n,n(')gamma) reaction have clarified the level scheme below 3.7 MeV excitation energy and determined detailed information about Mo-96, including lifetimes from the Doppler-shift attenuation method, branching ratios, and multipole mixing ratios. Also, B(E2) and B(M1) values were determined for many transitions, multiphonon states were identified, and several low-spin states were characterized in terms of collective, mixed-symmetry states.

A careful determination of the lifetime and measurement of the branching ratio for decay of the first 2(T)(=1)(+) state in Sc-42 has allowed an accurate experimental test of charge independence in the A = 42 isobaric triplet. A lifetime of 69(17) fs was measured at the University of Kentucky, while relative intensities for the 975 keV and 1586 keV transitions depopulating the first 2(T)(=1)(+) 1 state have been determined at the University of Cologne as 100(1) and 8(1), respectively. Both measurements give an isoscalar matrix element, M-0, of 6.4(9) (W.u.) 1/2. This result confirms charge independence for the A=42 isobaric triplet. Shell model calculations have been carried out for understanding the global trend of Mo values for A = 4n + 2 isobaric triplets ranging from A = 18 to A = 42. The 2(1)((T=1))(+)-> 0(1)((T=1))(+) transition energies, reduced transition probabilities and M-0 values are reproduced to a high degree of accuracy. The trend of MO strength along the sd shell is interpreted in terms of the shell structure. Certain discrepancies arise at the extremes of the sd shell, for the A = 18 and A = 38 isobaric triplets, which might be explained in terms of the low valence space at the extremes of the sd shell.