The first excited $0^{+}$ state of ${}_{}{}^{82}{}_{}{}^{}\mathrm{Kr}$ appears to have a noncollective nature, in contrast to the $0_3^{+}$ and other low-spin states in this nucleus. This is corroborated by a conversion-electron measurement of the $0_2^{+}$→$0_1^{+}$ and the $0_3^{+}$→$0_1^{+}$ transitions in ${}_{}{}^{82}{}_{}{}^{}\mathrm{Kr}$, following the decay of ${}_{}{}^{82}{}_{}{}^{}\mathrm{Rb}_{}^{\mathrm{g}}{}_{}{}^{}$. The values B(E${0;0}_2^{+}$→$0_1^{+}$)=3.1 (5) $e^2$${\mathrm{fm}}^4$ and $X_{311}$=B(E${0;0}_3^{+}$→$0_1^{+}$ $2_1^{+}$)=0 .097(24) have been deduced from the intensities of the conversion lines, observed with a mini-orange spectrometer. Previous eviewed.

The ${\beta }^{+}$ decay of ${}_{}{}^{47}{}_{}{}^{}\mathrm{Cr}$ ($J^{\pi }$,T${=(3/2)\mathrm{}}^{\mathrm{-}}$,(1/2)) has been studied following its production by the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$${(}^{40}$Ca, 2n${)}^{47}$Cr reaction at E${(\mathrm{}}^{40}$Ca)≊90 MeV. In addition to the previously reported superallowed decay to the mirror state (i.e., the ${}_{}{}^{47}{}_{}{}^{}\mathrm{V}$ ground state), we observe a (3.7±1.2)% allowed ${\beta }^{+}$ branch to the ${\mathrm{}(5/2)\mathrm{}}^{\mathrm{-}}$ state at 87 keV in ${}_{}{}^{47}{}_{}{}^{}\mathrm{V}$. These two branches appear to dominate the decay of ${}_{}{}^{47}{}_{}{}^{}\mathrm{Cr}$; an upper limit of less than 0.5% is set on possible γ rays, other than the 87-keV γ ray, in the range of 15 to 2800 keV. Measurement of the time decay of the 87-keV γ ray establishes a value of $T_{1/2}$=508±10 ms for the ${}_{}{}^{47}{}_{}{}^{}\mathrm{Cr}$ half-life which is in significant disagreement with two previously reported values. The present work utilized Ge spectroscopy and a He-jet system for transport of the beam-induced radioactivity, as opposed to previous measurements which used a plastic scintillator to detect positrons and either a He-jet chopper or a slow beam-pulsing system. A summary of decay data for the complete $f_{7/2}$ shell series of mirror nuclei is also presented.

A sample of ${\mathrm{Ta}}_2$${\mathrm{O}}_5$ containing 151 mg of Ta enriched to 5.47% in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}_{}^{\mathrm{m}}{}_{}{}^{}$ was counted in a well-type high-purity Ge detector. This was enclosed in a large NaI(Tl) detector operated in anticoincidence to reduce the cosmic-ray continuum background. Several runs of ∼100 days each were made under different conditions to search for γ-ray singles or summing peaks that would follow the electron capture decay of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}_{}^{\mathrm{m}}{}_{}{}^{}$ to ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}$ or the ${\beta }^{\mathrm{-}}$ decay to ${}_{}{}^{180}{}_{}{}^{}\mathrm{W}$. Lower limits derived were $T_{1/2}$>3.0×${10}^{15}$ yr, log$f_0$t>22.9 for electron capture decay and $T_{1/2}$>1.9×${10}^{15}$ yr, log$f_0$t>21.3 for ${\beta }^{\mathrm{-}}$ decay. The total half-life of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}_{}^{\mathrm{m}}{}_{}{}^{}$ is therefore $T_{1/2}$>1.2×${10}^{15}$yr.

The weak nonanalog Fermi branch to the 1.837 MeV level of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$ and several weak branches in ${}_{}{}^{35}{}_{}{}^{}\mathrm{Ar}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$ ${\beta }^{+}$ decay have been remeasured in order to reduce statistical uncertainties and reconcile discrepancies in the literature. The weak branches were detected by measuring subsequent cascade gamma rays with a Ge detector surrounded by a NaI anti-Compton shield. Fast transport of thin, self-supporting targets was provided by a magnetically driven rabbit system. For ${}_{}{}^{42}{}_{}{}^{}\mathrm{Sc}$ the ratio of the weak branch relative to the superallowed ground state to ground state transition was found to have a value of (7.0±1.2)×${10}^{\mathrm{-}5}$. This value is in good agreement with two of the three earlier, less precise, measurements. It is at the low end of theoretical estimates. The new results for the weak branches in ${}_{}{}^{35}{}_{}{}^{}\mathrm{Ar}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$ have reduced uncertainties and agree well with a previous determination.

A new γ ray with an energy of 100.7 keV has been observed in the decay of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. This line is interpreted as the transition between the $I^{\pi }$${=8\mathrm{}}^{+}$ level at 174 keV and the $9^{\mathrm{-}}$ isomeric state in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ following the 113-keV endpoint β decay of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. The laboratory branching ratio is 2.3×${10}^{\mathrm{-}4}$ compared to the electromagnetic decay mode of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}_{}^{\mathrm{m}}{}_{}{}^{}$. A possible second branch to a proposed $7^{\mathrm{-}}$ level in ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}$ is not seen. Even when the enhancement due to bound state β decay in a stellar environment is included, the observed branch is not sufficient to explain the abundance of ${}_{}{}^{180}{}_{}{}^{}\mathrm{Ta}_{}^{\mathrm{m}}{}_{}{}^{}$ in the universe.

The ${\beta }^{\mathrm{-}}$ decay energy of ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$ has been &=929±16 keV. The beta shape is treated within the modified $B_{\mathrm{ij}}$ approximation. & has been combined with atomic mass differences known from mass spectroscopy to infer the electron capture decay energy of the nucleus ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$, $Q_{\mathrm{EC}=1221\mathrm{}\pm 17}$ keV. When additional information from similarly decaying rotational nuclei is used, the recent suggestion that ${}_{}{}^{158}{}_{}{}^{}\mathrm{Tb}$ may allow one to measure effects of a finite neutrino mass seems improbable.

In rotating nuclei, localized stable surface excitations might develop. Experimental signatures of this effect may be linked with hot spots created in peripheral heavy ion collisions.

The use of physical boson basis states is stressed for the calculations in the boson space. The explicit form of physical boson basis states in terms of bosons is derived for the nonunitary boson mapping of Dyson. The ambiguity in the normalization introduced due to the use of bi-orthonormal basis states is satisfactorily resolved, resulting in a Hermitian matrix. This Hermitian matrix is found to coincide with the Hamiltonian matrix in the fermion space. The model cases where the use of a boson basis is justified are shown to be consistent with our view of using physical boson basis states.

The ground state and the first excited state of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ are investigated in harmonic oscillator shell-model bases including all the configurations up to 10ħω excitation energy. The Gogny et al. potential and versions I/III and V of the Malfliet-Tjon potential are used in the calculation. The difficulties in describing these states in a consistent manner are not overcome by substantially enlarging the shell-model bases. The lowest eigenvalue with a 1ħω center-of-mass wave function is also extracted from the energy matrices, providing the absolute energy of the first $J^{\Pi }$${=1\mathrm{}}^{\mathrm{-}}$, T=0 level. It is found that the agreement with experiment for this level is significantly improved when the model space is enlarged.

A variational trial wave function is used to develop a perturbation expansion for the effective shell model interaction in the case of a degenerate zero-order basis. The form of this trial function is suggested by the Brillouin-Wigner perturbation procedure, and the Moszkowski-Scott separation method. Application is made to the low lying levels of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$. The absolute binding energies obtained are 4 to 5 MeV short of experimental values. Acceptable agreement with experiment is found for the energy level spacing.

We show that the S-D subspaces, which are used in the Otsuka-Arima-Iachello microscopic derivation of the interacting-boson model, form a particle-hole-symmetric family. Consequently, there exist particle-hole-symmetric prescriptions for determining the structure of the S and D pairs. This result holds independently of whether the Hamiltonian conserves generalized seniority. Nevertheless, there are deviations from particle-hole symmetry when boson matrix elements involving more than two d bosons are calculated in lowest order using the boson mapping procedure of Otsuka, Arima, and Iachello. These deviations are used to estimate the inaccuracies introduced by the lowest-order mapping.

The numerically generated SU(3) basis used by Casten, Warner, and Aprahamian in the interacting-boson model is shown to deviate from the standard Vergados basis. We give the transformation between the two bases and study under which conditions the deviation becomes insignificant. Some properties of the β- and γ-band E2 matrix elements are pointed out.

Recent data for the most probable total kinetic energy release in fission $〈E_K〉$, have been combined with earlier results in order to reevaluate the systematic dependence of these values on the Coulomb parameter $\frac{Z^2}{A^{\frac{1}{3}}}$. A least-squares analysis of the current data base yields $〈E_K〉=0.1189\mathrm{}\frac{Z^2}{A^{\frac{1}{3}}}+7.3\mathrm{}$ MeV, where $\frac{Z^2}{A^{\frac{1}{3}}}$ refers to the fissioning nucleus. This expression exhibits a somewhat steeper slope than previous fits.

Elastic scattering of monochromatic photons ($\Delta E\sim 25$ eV) at 8999, 10 055, and 11 388 keV was used to probe the microstructure of known bumps in the low-energy tail of the giant dipole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The scattered radiation is found to be predominantly dipole. The results set an upper limit to the widths of the 10.06 and 11.3 MeV bumps.

Experimental results for the fragment production in 1 GeV proton collisions on various nuclei are presented. It is shown that the observed depletion of the light cluster production which is also found in other experiments can be explained by a Pauli quenching mechanism.

The existence of the higher nodal states of the $\alpha$+${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ cluster structure in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ is discussed through the analysis of the backward angle anomaly in alpha-particle scattering from ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ at $E_{\alpha }=22, 24, \mathrm{and} 28$ MeV.

The reactions ${}_{}{}^2{}_{}{}^{}\mathrm{H}({\pi }^{-}, {\pi }^{-}\mathrm{p})\mathrm{n}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{H}({\pi }^{-}, {\pi }^{-}\mathrm{n})\mathrm{p}$ have been observed in a kinematically complete experiment at 150 MeV for two pairs of pion and nucleon angles corresponding to quasifree scattering. The general features of the pion energy spectrum are reproduced by the simple impulse approximation. However, both the ratio of neutron to proton production and the lower energy side of the pion energy spectra show significant departures from this model.

Spin-$\frac{9}{2}$ resonances have been observed in proton capture by ${}_{}{}^{50}{}_{}{}^{}\mathrm{Cr}$ at $E_{\mathrm{p}}=2.397\mathrm{}$ MeV and by ${}_{}{}^{52}{}_{}{}^{}\mathrm{Cr}$ at $E_{\mathrm{p}}=2.680\mathrm{} \mathrm{and} 2.686$ MeV, 0.80, and 1.45 MeV below the respective $g_{\frac{9}{2}}$ analog resonances.

It has been suggested that the discrepancy between data for large-angle proton-nucleus elastic scattering at 200 MeV and standard optical model interpretations can be explained by the formation of intermediate $\Delta$ isobars. To test this hypothesis we have carried out a measurement of the elastic scattering cross section for 300 MeV protons from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ for momentum transfers up to 6.8 ${\mathrm{fm}}^{-1\mathrm{}}$. Although the energy was chosen to match the resonance energy for $\Delta$ production, no need for corrections to a simple optical model, and thus no experimental evidence for intermediate $\Delta$ isobars, was found.

The back-angle yields of the oxygen and carbon particles from the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ reaction have been measured at $E_{\mathrm{lab}}\left({}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}\right)=79.5\mathrm{}$ MeV by using reverse kinematics. Comparison with data for the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ reaction forming the same compound nucleus at the same excitation energy and with very similar spin distribution, demonstrates a strong entrance channel effect which is favorin the breakup into the entrance channel with large excitation energy. This result qualitatively supports the picture of the formation of a long-lived orbiting complex whose structure and decay is dependent on the entrance channel. The compound nucleus contribution is inferred to be less than 15% of the measured oxygen cross section.