Enhanced decay of the 31-yr isomer of ${}^{178}\mathrm{Hf}$ induced by x-ray irradiation has been reported previously. Here we describe an attempt to reproduce this result with an intense “white” x-ray beam from the Advanced Photon Source. No induced decay was observed. The upper limits for the energy-integrated cross sections for such a process, over the range of energies of 20–60 keV x rays, are less than $2\times {10}^{-27\mathrm{}}{\mathrm{cm}}^2\mathrm{keV}$, below the previously reported values by more than 5 orders of magnitude; at 8 keV the limit is $5\times {10}^{-26\mathrm{}}{\mathrm{cm}}^2\mathrm{keV}$.

The energetic proton emission has been investigated as a function of the reaction centrality for the system ${}^{58}\mathrm{Ni}{+}^{58}\mathrm{Ni}$ at 30A MeV. Extremely energetic protons $(E_p^{\mathrm{NN}}\ge 130\mathrm{MeV})$ were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.

Excited states in ${}^{216}\mathrm{Th}$ were investigated via prompt and delayed $\gamma$ decays and the recoil-decay tagging method. The decay schemes of the $I^{\pi }=\left(8^{+}\right)$, $t_{1/2}=128\mathrm{}\left(8\right)\mu \mathrm{s}$, the $I^{\pi }=\left({11}^{-}\right)$, $t_{1/2}=615\mathrm{}\left(55\right)\mathrm{ns}$, and the $I^{\pi }=\left({14}^{+}\right)$, $t_{1/2}\ge 130\mathrm{ns}$ isomers were established. The configuration $\pi h_{9/2}{f}_{7/2}$ is assigned to the $I^{\pi }=\left(8^{+}\right)$ isomer, which implies that the $h_{9/2}$ and $f_{7/2}$ states are nearly degenerate. This is ascribed to increased binding of the $f_{7/2}$ orbital by its coupling to a low-lying $I^{\pi }=\left(3^{-}\right)$ state at $E_x=1687\mathrm{}\mathrm{keV}$. The role of octupole and pairing correlations for a $Z=92\mathrm{}$ shell closure prediction is discussed on the basis of shell model calculations.

Using the fact that pseudospin is an approximate symmetry of the Dirac Hamiltonian with realistic scalar and vector mean fields, we derive the wave functions of the pseudospin partners of eigenstates of a realistic Dirac Hamiltonian and compare these wave functions with the wave functions of the Dirac eigenstates.

The nuclear quadrupole moment (NQM) of the $I^{\pi }{=3/2\mathrm{}}^{-}$ excited nuclear state of ${}^{57}\mathrm{Fe}$ at 14.41 keV, important in Mössbauer spectroscopy, is determined from the large-scale nuclear shell-model calculations for ${}^{54}\mathrm{Fe}$, ${}^{57}\mathrm{Fe}$, and also from the electronic ab initio and density functional theory calculations including solid state and electron correlation effects for the molecules $\mathrm{Fe}(\mathrm{CO}{)}_5$ and $\mathrm{Fe}({\mathrm{C}}_5{\mathrm{H}}_5{)}_2$. Both independent methods yield very similar results. The recommended value is 0.15(2) e b. The NQM of the isomeric $10+$ in ${}^{54}\mathrm{Fe}$ has also been calculated. The new NQM values for ${}^{54}\mathrm{Fe}$ and ${}^{57}\mathrm{Fe}$ are consistent with the perturbed angular distribution data.

Prompt and delayed $\gamma$-ray cascades in doubly magic ${}^{132}\mathrm{Sn}$ and its neighbor ${}^{131}\mathrm{Sn}$ have been studied at Gammasphere using a ${}^{248}\mathrm{Cm}$ fission source. Isotopic assignments of unknown $\gamma$ rays were based on coincidences with known transitions in $A=112\mathrm{}–116\mathrm{Pd}$ fission partners. The yrast level spectra of both tin nuclei are interpreted using empirical nucleon-nucleon interactions from the ${}^{132}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ regions. Results include identification of the $\left(\nu f_{7/2}{h}_{11/2}^{-1\mathrm{}}\right)9^{+}$ aligned state in ${}^{132}\mathrm{Sn}$ and of extensive $\left(\nu f_{7/2}{h}_{11/2}^{-2\mathrm{}}\right)$, $\left(\nu f_{7/2}{d}_{3/2}^{-1\mathrm{}}{h}_{11/2}^{-1\mathrm{}}\right)$ and $(\nu h_{11/2}^{-1\mathrm{}}\times 3^{-})$ multiplets in ${}^{131}\mathrm{Sn}$. The previously reported ${\beta }^{-}$ decay of an unusual ${}^{131}\mathrm{In}$ high-spin isomer to levels in ${}^{131}\mathrm{Sn}$ is also elucidated.

We compare the shell-model results for realistic interactions with those obtained for various ensembles of random matrix elements. We show that, although the quantum numbers of the ground states in the even-even nuclei have a high probability ( $\sim 60\%$) to be $J^{\pi }{T=0\mathrm{}}^{+}0$, the overlap of those states with the realistic wave functions is very small in average. The transition probabilities $B\left(E2\mathrm{}\right)$ predicted with random interactions are also too small. The presence of the regular pairing is shown to be a significant element of realistic physics not reproduced by random interactions.

The first measurement of energy produced transverse to the beam direction at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory is presented. The midrapidity transverse energy density per participating nucleon rises steadily with the number of participants, closely paralleling the rise in charged-particle density, such that $〈E_T〉/〈N_{\mathrm{ch}}〉$ remains relatively constant as a function of centrality. The energy density calculated via Bjorken’s prescription for the $2\%$ most central $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=130\mathrm{}\mathrm{GeV}$ is at least ${\epsilon }_{\mathrm{Bj}}=4.6\mathrm{}\mathrm{GeV}/{\mathrm{fm}}^3$, which is a factor of 1.6 larger than found at $\sqrt{s_{\mathrm{NN}}}=17.2\mathrm{}\mathrm{GeV}$ ( $\mathrm{Pb}+\mathrm{Pb}$ at CERN).

An extended mean-field model is presented that describes states of different isospin in odd-odd and even-even nuclei. Excitation energies of the $T=1\mathrm{}$ states in even-even as well as $T=0\mathrm{}$ and $T=1\mathrm{}$ states in odd-odd $N=Z$ nuclei are calculated. It is shown that the structure of these states can be determined in a consistent manner when both isoscalar and isovector pairing collectivity as well as isospin projection (treated here within the isocranking approximation) are taken into account. In particular, in odd-odd $N=Z$ nuclei, the interplay between quasiparticle excitations (relevant for the case of $T=0\mathrm{}$ states) and isorotations (relevant for the case of $T=1\mathrm{}$ states) explains the near degeneracy of these states.

An approximate solution at the critical point of the spherical to axially deformed shape phase transition in nuclei is presented. The eigenvalues of the Hamiltonian are expressed in terms of zeros of Bessel functions of irrational order.

It is shown that ${}^{152}\mathrm{Sm}$ and other $N=90\mathrm{}$ isotones are the first empirical manifestation of the newly predicted analytic description of nuclei at the critical point of a vibrator to axial rotor phase transition.

Within the impulse approximation, the response of a many-body system at large momentum transfer can be directly related to ground state properties. Although the physics assumptions underlying impulse approximation are well defined, their implementation involves ambiguities that may cause significant differences in the calculated responses. We show that, while minimal use of the impulse approximation assumptions naturally leads to write the response in terms of the spectral function, the alternative definition in terms of the momentum distribution involves a more extended use of the same assumptions.

Two components in the $M_{\gamma }\left(M\right)$ distribution were established in detailed measurements of mean $\gamma$-ray multiplicities from fission fragments of ${}^{226}\mathrm{Th}$. For the first time in the $M_{\gamma }\left(M\right)$ dependencies we were able to distinguish two components associated with primary and the final (after the neutron evaporation) fission fragments, and show that at the scission point $M_{\gamma }$ is extremely sensitive to symmetric and asymmetric modes of fission. Theoretical calculations of the pre-scission shapes of the fissioning nuclei confirm our conclusions.

Radiative capture of protons is investigated as a probe of clustering in nuclei far from stability. The first such measurement on a halo nucleus is reported here for the reaction ${}^6\mathrm{He}(p,\gamma )$ at 40 MeV. Capture into ${}^7\mathrm{Li}$ is observed as the strongest channel. In addition, events have been recorded that may be described by quasifree capture on a halo neutron, the $\alpha$ core, and ${}^5\mathrm{He}$. The possibility of describing such events by capture into the continuum of ${}^7\mathrm{Li}$ is also discussed.

The heat capacity of iron isotopes is calculated within the interacting shell model using the complete $\left({pf+0g}_{9/2}\right)$ shell. We identify a signature of the pairing transition in the heat capacity that is correlated with the suppression of the number of spin-zero neutron pairs as the temperature increases. Our results are obtained by a novel method that significantly reduces the statistical errors in the heat capacity calculated by the shell model Monte Carlo approach. The Monte Carlo results are compared with finite-temperature Fermi gas and BCS calculations.

A new superdeformed rotational band has been observed in ${}^{154}\mathrm{Er}$ using the Euroball Ge detector array. The new band and the one previously observed can be understood as based on coexisting superdeformed structures at prolate and triaxial shapes, respectively. The observation resolves long-standing difficulties in the theoretical interpretation of superdeformed states in ${}^{154}\mathrm{Er}$.

A series of measurements have been performed at KVI to obtain the vector analyzing power $A_y$ of the ${}^2\mathrm{H}(\overrightarrow{p},pd)$ reaction as a function of incident beam energy at energies of 120, 135, 150, and 170 MeV. For all these measurements, a range of ${\vartheta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}$ from $30°$ to $170°$ has been covered. The purpose of these investigations is to observe possible spin-dependent effects beyond two-nucleon forces. When compared to the predictions of Faddeev calculations, based on two-nucleon forces only, significant deviations are observed at all energies and at center-of-mass angles between $70°$ and $130°$. The addition of present-day three-nucleon forces does not improve the description of the data, demonstrating the still insufficient understanding of the properties of three-nucleon systems.

The nucleus ${}^{163}\mathrm{Lu}$ has been populated through the fusion-evaporation reaction ${}^{139}\mathrm{La}{(}^{29}\mathrm{Si},5n{)}^{163}\mathrm{Lu}$ with a beam energy of 152 MeV. The electromagnetic properties of several connecting transitions between two presumably triaxial, strongly deformed (TSD) bands have been studied. Evidence is presented for the assignment of the excited TSD band as a wobbling mode built on the yrast TSD band, based on comparisons to new calculations in which an aligned particle is coupled to a strongly deformed triaxial rotor. The wobbling mode is uniquely related to triaxiality in nuclei.

$K^{+}$-meson production in $\mathrm{pA}$ ( $A=\mathrm{C},\mathrm{Cu},\mathrm{Au}$) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Jülich accelerator. The complete momentum spectrum of kaons emitted at forward angles, $\vartheta \le 12°$, has been measured for a beam energy of $T_p=1.0\mathrm{}\mathrm{GeV}$, far below the free $\mathrm{NN}$ threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.

The production of nuclear bremsstrahlung photons ( $E_{\gamma }>30\mathrm{}\mathrm{MeV}$) has been studied in inclusive and exclusive measurements in four heavy-ion reactions at $60A\mathrm{MeV}$. The measured photon spectra, angular distributions, and multiplicities indicate that a significant fraction of the hard photons is emitted in secondary nucleon-nucleon collisions from a thermally equilibrated system. The observation of the thermal component in multifragment ${}^{36}\mathrm{Ar}{+}^{197}\mathrm{Au}$ reactions suggests that the breakup of the thermalized source produced in this system occurs on a rather long time scale.