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The spallation neutron source at the Los Alamos Neutron Science Center Weapons Neutron Research facility was used to populate excited states in $^{186}\mathrm{Re}$ via $(n,2n\ensuremath{\gamma})$ reactions on an enriched $^{187}\mathrm{Re}$ target. Gamma rays were detected with the GErmanium Array for Neutron Induced Excitations spectrometer, a Compton-suppressed array of 18 HPGe detectors. Incident neutron energies were determined by the time-of-flight technique and used to obtain $\ensuremath{\gamma}$-ray excitation functions for the purpose of identifying $\ensuremath{\gamma}$ rays by reaction channel. Analysis of the singles $\ensuremath{\gamma}$-ray spectrum gated on the neutron energy range $10\ensuremath{\le}{E}_{n}\ensuremath{\le}25\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ resulted in five transitions and one level added to the $^{186}\mathrm{Re}$ level scheme. The additions include the placement of three $\ensuremath{\gamma}$ rays at 266.7, 381.2, and 647.7 keV which have been identified as feeding the $2.0\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{4pt}{0ex}}\mathrm{yr}$, ${J}^{\ensuremath{\pi}}=({8}^{+})$ isomer and yield an improved value of $148.2(5)\phantom{\rule{4pt}{0ex}}\mathrm{keV}$ for the isomer energy. These transitions may have astrophysical implications related to the use of the Re-Os cosmochronometer.

A sample of $6.3\ifmmode\times\else\texttimes\fi{}{10}^{14}$ nuclei of the 4-quasiparticle isomer of ${}^{178}\mathrm{Hf}$ having a half-life of 31 yr and excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device typically used in dental medicine. It was operated at 15 mA to produce bremsstrahlung radiation with an end point energy set to be 70 or 90 keV. Spectra of the isomeric target were taken with a high purity Ge detector. Intensities of selected transitions in the normal decay cascade of the ${}^{178}\mathrm{Hf}$ isomer were found to increase by about $4%$. Such an accelerated decay is consistent with an integrated cross section of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\mathrm{cm}{}^{2}\mathrm{keV}$ for the resonant absorption of x rays to induce gamma decay.

Storage-ring mass spectrometry was applied to neutron-rich ${}^{197}$Au projectile fragments. Masses of ${}^{181,183}$Lu, ${}^{185,186}$Hf, ${}^{187,188}$Ta, ${}^{191}$W, and ${}^{192,193}$Re nuclei were measured for the first time. The uncertainty of previously known masses of ${}^{189,190}$W and ${}^{195}$Os nuclei was improved. Observed irregularities on the smooth two-neutron separation energies for Hf and W isotopes are linked to the collectivity phenomena in the corresponding nuclei.

The scattering of thermal neutrons from isomeric nuclei may include events in which the outgoing neutrons have increased kinetic energy. This process has been called inelastic neutron acceleration, or INNA, and occurs when the final nucleus, after emission of the neutron, is left in a state with lower energy than that of the isomer. The result, therefore, is an induced depletion of the isomer to the ground state. A cascade of several $\ensuremath{\gamma}$'s must accompany the neutron emission to release the high angular momentum of the initial isomeric state. INNA was previously observed in a few cases, and the measured cross sections were only in modest agreement with theoretical estimates. The most recent measurement of an INNA cross section was ${\ensuremath{\sigma}}_{\mathrm{INNA}}=258\ifmmode\pm\else\textpm\fi{}58 \mathrm{b}$ for neutron scattering by $^{177}\mathrm{Lu}$${}^{m}$. In the present work, an INNA cross section of ${\ensuremath{\sigma}}_{\mathrm{INNA}}=168 \ifmmode\pm\else\textpm\fi{} 33 \mathrm{b}$ was deduced from measurements of the total burnup of the high-spin, four-quasiparticle isomer $^{178}\mathrm{Hf}$${}^{m2}$ during irradiation by thermal neutrons. Statistical estimates for the probability of different reaction channels past neutron absorption were used in the analysis, and the deduced ${\ensuremath{\sigma}}_{\mathrm{INNA}}$ was compared to the theoretically predicted cross section.

A study of cooled Au-197 projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides Hf-183,Hf-184,Hf-186 and Ta-186,Ta-187. The results support the prediction of a strongly favored isomer region near neutron number 116.

Photoexcitations of the short-lived isomers {sup 167}Er{sup {ital m}}, {ital T}{sub 1/2}=2.28 s, {sup 179}Hf{sup {ital m}}, {ital T}{sub 1/2}=18.68 s, {sup 191}Ir{sup {ital m}}, {ital T}{sub 1/2}=4.94 s, and {sup 197}Au{sup {ital m}}, {ital T}{sub 1/2}=7.8 s, were produced with bremsstrahlung from the superconducting Darmstadt linear accelerator. Excitation functions were measured for the population of these isomers by ({gamma},{gamma}{prime}) reactions between 2 and 7 MeV. They indicated that the isomers were excited by resonant absorption through isolated intermediate states having integrated cross sections in excess of 10{sup {minus}26} cm{sup 2} keV, i.e., values about 1000 times larger than most ({gamma},{gamma}{prime}) activation reactions reported previously although they were comparable to those reported earlier for the depopulating reaction {sup 180}Ta{sup {ital m}}({gamma},{gamma}{prime}){sup 180}Ta. In all four nuclei a common onset was observed near 2.5 MeV for intermediate states with strengths much larger than those occurring at lower energies. The summed cross sections exhibit a clear correlation with the ground state deformations.

Time-resolved Schottky mass spectrometry has been applied to uranium projectile fragments which yielded the mass value for the Hg-208 (Z=80, N=128) isotope. The mass excess value of ME=-13 265(31) keV has been obtained, which has been used to determine the proton-neutron interaction strength in Pb-210, as a double difference of atomic masses. The results show a dramatic variation of the strength for lead isotopes when crossing the N=126 neutron shell closure, thus confirming the empirical predictions that this interaction strength is sensitive to the overlap of the wave functions of the last valence neutrons and protons.

Photoexcitation of the isomers of 19 nuclides was examined in this work. Four accelerators were used as sources of bremsstrahlung to expose the samples and end-point energies covered the range from 0.5 to 11 MeV. No evidence was found for nonresonant processes of excitation. However, more than half the cases showed enhanced channels for the resonant photoexcitation of isomers with integrated cross sections approaching ${10}^{\mathrm{\ensuremath{-}}21}$ ${\mathrm{cm}}^{2}$ keV. These results are three to four orders of magnitude larger than values usually characterizing (\ensuremath{\gamma},\ensuremath{\gamma}') reactions.

Photoexcitation of the long-lived isomers {sup 123}Te{sup {ital m}}, {ital T}{sub 1/2}=119.7 d, and {sup 125}Te{sup {ital m}}, {ital T}{sub 1/2}=58 d, was produced with bremsstrahlung from the superconducting Darmstadt linear accelerator. The excitation function for the reaction {sup 123}Te({gamma},{gamma}{prime}){sup 123}Te{sup {ital m}} was measured between 2 and 6 MeV. It indicated that the isomer was populated by resonant absorption through isolated intermediate states having integrated cross sections in excess of 10{sup {minus}26} cm{sup 2} keV, i.e., values about 100 times larger than most ({gamma},{gamma}{prime}) activation reactions reported previously. An excitation function was also obtained for the reaction {sup 125}Te({gamma},{gamma}{prime}){sup 125}Te{sup {ital m}} in this energy range.

A previously unreported isomer has been identified in Mo-99 at an excitation energy of E-x = 3010 keV, decaying with a half-life of T-1/2 = 8(2) ns. The nucleus of interest was produced following fusion-fission reactions between a thick Al-27 target frame and a Hf-178 beam at a laboratory energy of 1150 MeV. This isomeric state is interpreted as an energetically favored, maximally aligned configuration of nu h (11/2) circle times pi(g (9/2))(2).

An experiment has been performed to detect the $\ensuremath{\alpha}$ emission mode in ${}^{178}\mathrm{Hf}{}^{m2}$ isomer decay and a partial half-life of $(2.5\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{10}$y was measured. It was concluded that $\ensuremath{\alpha}$ decay is strongly retarded by the centrifugal barrier arising due to the high spin of this isomeric state. Additional analysis shows, however, that the $K$-hindrance in this $\ensuremath{\alpha}$ decay is relatively weak, despite the strong manifestation of spin-hindrance.

The quasistable odd-odd-mass nucleus {sup 176}Lu is of special interest in nuclear structure physics and, above all, in nuclear astrophysics. Systematic photon scattering experiments have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator with bremsstrahlung end-point energies of 2.3 and 3.1 MeV to determine the low-energy dipole strength distribution in the s-only isotope {sup 176}Lu. The main goal was to pin down possible intermediate states (IS) for the photoactivation of the short-lived 123-keV isomer, which is the key process determining the effective lifetime of {sup 176}Lu in a stellar photon bath and hence for the use of this isotope as a stellar chronometer. Using an enriched sample, 29 transitions ascribed to {sup 176}Lu were detected below 2.9-MeV excitation energy. The corresponding excitation strengths were determined. For the previously proposed lowest IS at 839 keV, an upper limit for the excitation strength corresponding to a lifetime of {tau}{>=} 1.5 ps can be given. Astrophysical consequences, also in view of new Stuttgart photoactivation experiments, are discussed. The fragmentation of the dipole strength is compared to those in neighboring even-even and odd-even nuclei.

The low-lying dipole strength distribution in the rare isotope ${}^{176}\mathrm{Hf}$ was studied in nuclear resonance fluorescence experiments performed at the Stuttgart Dynamitron facility using bremsstrahlung beams with end- point energies of 4.1 and 2.4 MeV. In total, about 55 excited spin-1 states, unknown so far, were observed in the excitation energy range up to 4 MeV. Detailed spectroscopic information has been obtained on excitation energies, spins, decay widths, decay branchings, and transition probabilities. Ascribing a positive parity to all observed $K=1$ states, the detected total $B(M1)\ensuremath{\uparrow}$ strength in the energy range of the scissors mode amounts to $2.56(6){\ensuremath{\mu}}_{N}^{2},$ nearly as much as for well-deformed midshell rare-earth nuclei. The total strength is higher than in the heavier Hf isotopes ${}^{178,180}\mathrm{Hf},$ but fits well into the systematics. The observed low-lying $\ensuremath{\Delta}K=0$ transitions (with probable $E1$ character) lie in the energy range around 2 MeV, as expected from the systematics. The excitation probabilities correspond to values which are characteristic for nuclei in the transitional region from deformed rotors to more $\ensuremath{\gamma}$-soft nuclei.

The photo-induced depopulation of the quasistable isomer ${(t}_{1/2}g~1.2\ifmmode\times\else\texttimes\fi{}{10}^{15} \mathrm{yr})$ in ${}^{180}\mathrm{Ta}$ with angular momentum and parity ${J}^{\ensuremath{\pi}}{=9}^{\ensuremath{-}}$ at an excitation energy ${E}_{x}=75 \mathrm{keV}$ was studied at the new bremsstrahlung irradiation facility installed at the Stuttgart 4.3 MV DYNAMITRON accelerator in the energy range of bremsstrahlung end point energies between ${E}_{0}=0.8--3.1 \mathrm{MeV}.$ The onset of the isomer depopulation could be observed starting at an end point energy of ${E}_{0}\ensuremath{\approx}1 \mathrm{MeV},$ i.e., at an intermediate state of ${}^{180}\mathrm{Ta}$ at or below that energy. Higher-lying intermediate states were found at 1.22, 1.43, 1.55, 1.85, 2.16, 2.40, 2.64, and 2.80 MeV. The extracted integrated cross sections show a remarkably strong depopulation of the ${}^{180}{\mathrm{Ta}}^{m}$ isomer by photoexcitation. The results are compared with previous experiments and recent quasiparticle-phonon model calculations. Implications of the results for a possible nucleosynthesis of ${}^{180}\mathrm{Ta}$ in the s process and the neutrino process are discussed.

Fission-fragment mass distributions in the ${}^{232}\mathrm{Th}(\ensuremath{\gamma},f)$ reaction have been measured from the cumulative yields of radionuclides following activation at bremsstrahlung endpoint energies ${E}_{e}=7.5,$ 12.0, and 24.0 MeV. The yields of the light nuclei ${}^{24}\mathrm{Na}$ and ${}^{28}\mathrm{Mg}$ were detected following activation at ${E}_{e}=16.5$ and 24.0 MeV. Energy dependences of the symmetric mode and light nuclide yields are discussed. Fine-structure manifestations near asymmetric and symmetric masses were observed.