A theoretical study of the ${}^{99}\mathrm{Zr}$ nucleus is presented. Energy levels, wave functions, and electromagnetic rates were calculated in the framework of the interacting boson-fermion model and are compared to the available data for low-lying states. In particular, we discuss the sensitivity of the $g$ factor of the ${3/2}_1^{+}$ state to the quenching of the spin gyromagnetic ratio and to the structure of the respective wave function.

Double-differential cross sections and analyzing powers $A_y$ for the $(\overrightarrow{p},n)$ reactions on ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ were measured at 200 MeV between ${\theta }_{\mathrm{lab}}=0\mathrm{}°$ and $44°.$ The neutron spectra from ${}^3\mathrm{He}(\overrightarrow{p},n)$ are dominated by the quasifree scattering peak and show no evidence for resonances in the three-proton system. The spectra from ${}^4\mathrm{He}(\overrightarrow{p},n)$ exhibit strong resonance behavior in the $p^3\mathrm{He}$ system at low relative $p^3\mathrm{He}$ energies owing to the excitation of known $L=1\mathrm{}$ resonances in ${}^4\mathrm{Li},$ but there is no distinct quasifree peak in the measured spectra. The experimental $A_y$ for ${}^3\mathrm{He}(\overrightarrow{p},n),$ averaged over the experimental range of neutron energies, are similar to those for free nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ scattering, whereas for ${}^4\mathrm{He}(\overrightarrow{p},n)$ the $A_y$ are generally larger than the free values. The cross sections at far forward angles for both ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ appear to be suppressed relative to the free NN cross sections by Pauli blocking. At most angles, the shapes of the cross section spectra from both ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ are reproduced by distorted-wave impulse approximation (DWIA) calculations using a quasifree scattering model. Specifically for ${}^4\mathrm{He}(\overrightarrow{p},n),$ the model requires the use of an optical potential which has a strong $L=1\mathrm{}$ potential resonance corresponding to the low-lying $L=1\mathrm{}$ states in ${}^4\mathrm{Li}.$

Measurements of $\mathrm{pp}$ spin correlation coefficients $A_{\mathrm{xx}},$ $A_{\mathrm{yy}},$ and $A_{\mathrm{xz}}$ and analyzing power $A_y$ for $\mathrm{pp}$ elastic scattering at 197.4 MeV over the laboratory angular range 3.5 °–43.5 ° $({\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=7\mathrm{}°–90°)$ have been carried out. The typical statistical accuracy per 1$°$ angle bin is better than 0.02 for the $A_{\mathrm{mn}}$ and better than 0.005 for $A_y.$ Systematic errors are negligible except for an overall normalization uncertainty of 2.5% for $A_{\mathrm{mn}}$ and 1.3% for $A_y.$ The experiment makes use of a polarized hydrogen gas target internal to a proton storage ring (IUCF Cooler) and a circulating beam of polarized protons. The target polarization is switched in sign and direction $(x,y,z)$ every 2 s by reversing a weak guide field $(\approx 0.3$ mT). Scattered and recoil protons are detected in coincidence by two sets of wire chambers, by scintillators, and by silicon-strip recoil detectors placed 5 cm from the proton beam. Analysis methods and comparison to recent $\mathrm{pp}$ partial-wave analyses and $\mathrm{NN}$ potential models are described.

The nucleon-deuteron analyzing power $A_y$ in elastic nucleon-deuteron scattering poses a longstanding puzzle. At energies $E_{\mathrm{lab}}$ below approximately 30 MeV $A_y$ cannot be described by any realistic nucleon-nucleon (NN) force. The inclusion of existing three-nucleon forces does not improve the situation. Because of recent questions about the ${}^3{P}_J$ NN phases, we examine whether reasonable changes in the NN force can resolve the puzzle. In order to do this we investigate the effect on the ${}^3{P}_J$ waves produced by changes in different parts of the potential (viz., the central force, tensor force, etc.), as well as on the two-body observables and on $A_y.$ We find that it is not possible with reasonable changes in the NN potential to increase the three-body $A_y$ and at the same time to keep the two-body observables unchanged. We therefore conclude that the $A_y$ puzzle is likely to be solved by new three-nucleon forces, such as those of the spin-orbit type, which have not yet been taken into account.

The contributions from meson exchange and isobar excitation currents to proton-proton bremsstrahlung are discussed within the framework of a relativistic $\mathrm{NN}$ interaction. Below the pion-production threshold the Δ isobar is shown to give the dominant contribution to the two-body currents. The nonrelativistic and static limits to these current operators are discussed, and are shown to give a good approximation to the full relativistic meson-exchange current in the considered kinematic region. For the Δ isobar the static limit is a poor approximation. Including, however, also the energy dependence of the Δ propagation yields a reasonable representation of the isobar excitation current.

Mean lifetimes of 20 out of 31 bound levels in ${}^{32}\mathrm{S}$ below an excitation energy of 8.0 MeV are deduced from the Doppler-broadened $\gamma$-ray line shapes produced in the reactions ${}^2\mathrm{H}{(}^{31}\mathrm{P},n\gamma {)}^{32}\mathrm{S},\hspace{0.5em}{\hspace{0.5em}}^{28}\mathrm{Si}{(}^6\mathrm{Li},pn\gamma {)}^{32}\mathrm{S},$ and ${}^{31}\mathrm{P}(p,\gamma {)}^{32}\mathrm{S}.$ Of the 20 levels, lifetimes for 4 are reported here for the first time. For the remaining 16 levels, the lifetime values obtained in this work are considered to be more reliable and accurate than those reported in the literature. Compared to lifetime measurements reported in the literature, significant procedural improvements have been made by (i) using the entire line shape in the data analysis, (ii) making measurements with targets implanted in high-stopping-power media, and (iii) simulating with the Monte-Carlo method the slowing-down process, experimental conditions, and the delayed feeding from higher levels to the level being analyzed. The low-lying portion of the level scheme, level lifetimes, $\gamma$-ray branchings, $E2/M1\mathrm{}$ mixing ratios, and reduced transition probabilities are compared with shell-model calculations. The reduced $B\left(E2\mathrm{}\right)\mathrm{}$ values for 16 out of 18 transitions and $B\left(M1\mathrm{}\right)\mathrm{}$ values for 5 out of 10 transitions are reproduced to within a factor of 5. A one-to-one correspondence between 33 experimental and predicted states is established up to 8.2 MeV for both positive- and negative-parity states.

We analyze for the first time the full γγ directional correlations from oriented states (DCO) in an experiment performed with the GASP detector array. Our analysis is based on a transformation of the directional information into expansion coefficients of an orthogonal basis. With this method, which we call SpeeDCO (spectral expansion of DCO), the complete DCO information is concentrated in 12 γγ coincidence spectra. The analysis is applicable to all detector arrays which uniformly cover the solid angle. We show that the complete DCO information can be used for a reliable and unique determination of spins and multipolarity mixing ratios in weakly populated bands. We were able to establish the spins and the positive parity of the $\Delta I=1\mathrm{}$ “$M1\mathrm{}$ band” in ${}^{128}\mathrm{Ba}$ and multipolarity mixing ratios of nine $M1/E2\mathrm{}$ in-band transitions were derived as well. The measured values are in good agreement with those expected for a high-$K$ rotational band.

Parity nonconserving asymmetries have been measured in $p$-wave resonances of ${}^{106}\mathrm{Pd}$ and ${}^{108}\mathrm{Pd}$. The data analysis requires knowledge of the neutron resonance parameters. Transmission and capture $\gamma$-ray yields were measured for $E_n=20\mathrm{}$–2000 eV with the time-of-flight method at the Los Alamos Neutron Science Center (LANSCE). A total of 28 resonances in ${}^{106}\mathrm{Pd}$ and 32 resonances in ${}^{108}\mathrm{Pd}$ were studied. The resonance parameters for ${}^{106}\mathrm{Pd}$ are new for all except one resonance. In ${}^{108}\mathrm{Pd}$ six new resonances were observed and the precision improved for many of the resonance parameters. A Bayesian analysis was used to assign orbital angular momentum for the resonances studied.

Excited states of ${}^{42}\mathrm{K}$ and ${}^{43}\mathrm{K}$ were investigated using the reactions ${}^9\mathrm{Be}{(}^{36}\mathrm{S}{,2np)}^{42}\mathrm{K}$ and ${}^9\mathrm{Be}{(}^{36}\mathrm{S}{,np)}^{43}\mathrm{K}$. Three methods of selective $\gamma$-ray spectroscopy were employed: recoil-nuclei-$\gamma$, proton-$\gamma$, and $\gamma$-$\gamma$ coincidence measurements. Thirty-eight electromagnetic transitions were observed originally, 22 belonging to ${}^{42}\mathrm{K}$ and 16 belonging to ${}^{43}\mathrm{K}$. Eight new levels are suggested for ${}^{42}\mathrm{K}$ and four for ${}^{43}\mathrm{K}$. Shell-model calculations were performed in the ${\mathrm{}\left(\mathrm{sd}\right)\mathrm{}}^{-1}{\mathrm{}\left(\mathrm{fp}\right)\mathrm{}}^3$ space to obtain negative-parity states of ${}^{42}\mathrm{K}$ and ${\mathrm{}\left(\mathrm{sd}\right)\mathrm{}}^{-1}{\mathrm{}\left(\mathrm{fp}\right)\mathrm{}}^4$ space for positive-parity states of ${}^{43}\mathrm{K}$. The calculated energies are in good agreement with the experimental values, but some systematic differences indicate that the collectivity of the actual levels is not completely accounted for by the configuration space used in the calculations.

β-ray end-point energies for the decay of ${}^{150}\mathrm{Er}$ and ${}^{151}\mathrm{Er}$ were measured using a plastic scintillator-Ge, ${\beta }^{+}-\gamma$ coincidence spectrometer. Mass excess values are reported for these nuclides and for members of the α-decay chain which terminates at ${}^{151}\mathrm{Er}.$ Our results are compared with predictions of mass formulas and with extrapolations based on systematic properties for other nuclei.

Levels in ${}^{200,202}\mathrm{Po}$ were studied via the ${\beta }^{+}$ and electron-capture decay of mass-separated At isotopes. Multiscaled singles γ, x, and conversion-electron spectra as well as γ-γ-t, $\gamma -{\mathrm{e}}^{-}$-t, and ${\mathrm{x}-\mathrm{e}}^{-}$-t coincidences were measured. These isotopes contain key information for the presence of π(4p-2h) intruder configurations in the light Po isotopes.

The strength distribution of low-lying dipole excitations in the heavy odd-mass nucleus ${}^{181}\mathrm{Ta}$ was studied in nuclear resonance fluorescence experiments performed at the bremsstrahlung beam of the Stuttgart 4.3 MV Dynamitron accelerator. To increase the detection sensitivity in the whole range of excitation energies between 1.8 and 4 MeV two measurements were carried out at different bremsstrahlung end-point energies of 2.7 and 4.1 MeV using two large-volume HPGe detectors of a relative efficiency of 100%. Detailed information on excitation energies, decay widths, transition probabilities, and branching ratios of 37 new low-lying states in the energy range 1.8–3.5 MeV have been obtained. The observed dipole strength is rather fragmented, apart from a strong excitation at 2.297 MeV. The total strength in the investigated range of excitation energies (1.8–4 MeV) is reduced by a factor of $\approx 3.5$ as compared to the neighboring even-even nucleus ${}^{180}\mathrm{Hf}$.

The decays of ${}^{187}$Hg (2.2 min; $J^{\pi }$=13/2${}^{+})$ and ${}^{187}$Hg (2.4 min; $J^{\pi }$=3/2${}^{-})$ have been studied with mass-separated sources at the UNISOR facility. Multiscaled spectra of $\gamma$ rays, x rays, and conversion electrons, as well as $\gamma \gamma t$, $\gamma \mathrm{xt}$, $e\gamma t$, and $\mathrm{ext}$ coincidences were obtained. Decay schemes have been constructed incorporating $>$99$\%$ of the decay intensities assigned to the high-spin and low-spin decays. The $\gamma$-ray gated conversion-electron spectra permitted determination of 367 conversion coefficients. A variety of coexisting band structures are established in ${}^{187}$Au. Some of these have near-identical analogs in the heavier odd-mass Au isotopes. The remaining bands reveal new degrees of freedom at low excitation energy in ${}^{187}$Au. Nine electric monopole $(E$0) transitions are observed to deexcite members of these new bands. The work represents an undertaking to achieve a benchmark in complete spectroscopy following radioactive decay. The most notable band structure in ${}^{187}$Au has two bands with identical spins, nearly identical relative energies, and electric monopole transitions connecting the favored members. These bands can be understood as $\pi h_{9/2}$ and $\pi f_{7/2}$ intruder configurations coupled to coexisting prolate or near-prolate $(\gamma$ $<~$ 20$°)$ cores having diabatic configurations that differ only in the number of protons occupying the $N$=5 intruder configurations.

Photon scattering experiments have been performed on the nucleus ${}^{136}$Ba with photon energies of $E_{\gamma }<~4.1$ MeV and $E_{\gamma }<~2.8$ MeV. At 2.1 MeV clear evidence for the $2_{\mathrm{ms}}^{+}$ state has been found. From the measured lifetime we extract signatures for the isovector quadrupole excitation in the valence shell: a weakly collective $E2\mathrm{}$ decay to the ground state and a strong $M1\mathrm{}$ decay to the $2_1^{+}$ state. As the resonant photon scattering with bremsstrahlung is a complete reaction, we can conclude that the $2^{+}$ state at 2129 keV is a rather pure $2_{\mathrm{ms}}^{+}$ state with little fragmentation. This is in contrast to the $1^{+}$ scissors state. A comparison with an IBM-2 calculation is given.

Excited states have been identified in neutron-deficient ${}_{\hspace{0.5em}58}^{125}{\mathrm{Ce}}_{67}$ using the ${}^{58}\mathrm{Ni}{(}^{70}\mathrm{Ge}{,2pn)}^{125}\mathrm{Ce}$ reaction at 280 and 310 MeV. The experiment was performed at the Holifield Radioactive Ion Beam Facility, Oak Ridge National Laboratory. A $\gamma$-ray array of six clover plus four single-crystal HPGe detectors was used in conjunction with the Recoil Mass Spectrometer, which had a position sensitive avalanche counter (mass $A$ identification) at its focal plane, together with an ionization chamber (charge $Z$ identification). Two band structures assigned to ${}^{125}\mathrm{Ce}$ are interpreted as based on the $\nu h_{11/2}\left[523\right]{7/2}^{-}$ and $\nu d_{5/2}\left[402\right]{5/2}^{+}$ Nilsson orbitals, respectively.

High-spin states in the cross-conjugate pairs of nuclei ${}^{46}{\mathrm{Ti}–}^{50}\mathrm{Cr}$ and ${}^{47}{\mathrm{V}–}^{49}\mathrm{Cr}$ have been investigated using the reaction ${}^{28}{\mathrm{S}\mathrm{i}+}^{\mathrm{nat}}\mathrm{Si}$ at a laboratory energy of 125 MeV. Coincidence spectra, in some cases gated by charged particle detection, allow the yrast level schemes of all four nuclei to be extended, up to the $f_{7/2}$-shell band termination at ${14}^{+}$ and ${\frac{31}{2}}^{-}$ in ${}^{46}\mathrm{Ti}$ and ${}^{49}\mathrm{Cr},$ and beyond to ${17}^{+}$ and ${\frac{35}{2}}^{-}$ in ${}^{50}\mathrm{Cr}$ and ${}^{47}\mathrm{V}.$ Opposite-parity bands in ${}^{46}\mathrm{Ti}$ and ${}^{47}\mathrm{V}$ were observed up to ${11}^{-}$ and ${\frac{31}{2}}^{+},$ respectively. Lifetimes derived from DSAM measurements provide $B\left(E2\mathrm{}\right)\mathrm{}$ and $B\left(M1\mathrm{}\right)\mathrm{}$ values for transitions among the higher levels of each of the nuclei. These are compared with earlier measurements and with $f_{7/2}$- and $\mathrm{fp}$-shell model calculations. No model calculations have been published for the opposite-parity bands, but their level spacing and reduced transition rates support a spectator nature of the $\mathrm{sd}$ hole.

The threshold energy of the ${}^{38}\mathrm{Ar}{\mathrm{}(p,n)\mathrm{}}^{38}{\mathrm{K}}^m$ reaction has been measured using solid ${}^{38}\mathrm{Ar}$ targets and has been found to be 7008.52(12) keV, with a 1 V standard as reference. This is in agreement with, but more precise than, the accepted value. The average gives a $Q$ value for the ${}^{38}{\mathrm{K}}^m$ superallowed positron decay of 6044.34(12) keV and an ft value of 3049.4(21) s. To improve this last, the discord in the measured ${}^{38}{\mathrm{K}}^m$ halflives should be resolved.