A shell-model calculation for $A=27,28, \mathrm{and} 29$ nuclei has been carried out in a truncated $0d_{\frac{5}{2}}-1\mathrm{}{s}_{\frac{1}{2}}-0\mathrm{}{d}_{\frac{3}{2}}$ basis space with a modified-surface-$\delta$-interaction Hamiltonian. A comparison of the calculated results for level energies, single-nucleon spectroscopic factors and $E2\mathrm{}$ and $M1\mathrm{}$ transition strengths in ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ with the corresponding experimental values indicates that a unified and quantitive explanation of nuclear structure around $A=28\mathrm{}$ can be obtained via shell-model techniques.

A method is described for determining the 0-1.5-MeV part of the energy spectra of neutrons from ($p,n$) reactions. It utilizes measurements of energy spectra of protons from ($p,np$) reactions and corrections obtained by various measurements including neutron-proton coincidence studies. When the shapes of the neutron spectra are analyzed with the statistical theory, it is found that the cross section for the "inverse reaction" (capture of a low-energy neutron by a highly excited nucleus) exhibits a giant-resonance behavior as a function of mass number, peaking sharply near $A=91\mathrm{}$. This peak is at least as sharp as is predicted by usual optical-model calculations.

$\gamma$-ray mixing ratios have been measured for four transitions in ${}_{}{}^{154}{}_{}{}^{}\mathrm{Gd}$. The mixing ratios were obtained through the analysis of $\gamma$-ray angular correlations involving the transitions in question. All cascades had the $2^{-}$ octupole level at 1719.6 keV as the initial emitting state. A Ge(Li)-NaI(Tl) detector array was used to measure correlations for the following cascades: 592-1005 keV ($2^{-}-3_{\gamma }^{+}-2_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}$); 723-996 keV ($2^{-}-2_{\gamma }^{+}-0_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}$); 723-873 keV ($2^{-}-2_{\gamma }^{+}-2_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}$). A two-parameter [$\delta \left({\gamma }_1\right),\delta \left({\gamma }_2\right)$] search routine was developed for the analysis of the correlations involving two mixed-multipole transitions. Results for the mixing ratios are: $\delta \mathrm{}\left(592\right)={0.08|}_{-0.22\mathrm{}}^{+0.14\mathrm{}}$; $\delta \mathrm{}\left(723\right)={0.04}_{-0.04\mathrm{}}^{+0.02\mathrm{}}$; $\delta \mathrm{}\left(873\right)=-{10.0}_{-4.0\mathrm{}}^{+2.0\mathrm{}}$; $\delta \mathrm{}\left(1005\right)=-{9.5}_{-4\mathrm{}}^{+7\mathrm{}}$.

The $\gamma$ decay of 11 states in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$ populated in the ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}\mathrm{}(d,t)\mathrm{}{}_{}{}^{208}{}_{}{}^{}\mathrm{Bi}$ reaction has been measured in a particle-$\gamma$ coincidence experiment. The resulting decay scheme allows probable $J^{\pi }$ assignments to be made which are consistent with those obtained in earlier ($d,t$) and (${}_{}{}^3{}_{}{}^{}\mathrm{He},d$) studies. The experimental decay scheme is compared with that calculated with the wave functions of Kim and Rassmussen and of Kuo, and is found to be in reasonable agreement with both.

It is pointed out that the chances for the involvement of two close levels in the nuclear-resonance-scattering process are, for certain cases, as high as 20%. It is shown that when the angular distribution of a two-level scattering process is interpreted in terms of a single level only, the result can show an apparent $M2\mathrm{}-E1\mathrm{}$ mixing. An experiment is suggested which will uniquely clear up this question.

The ${}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}\mathrm{}(p,t)\mathrm{}{}_{}{}^{92}{}_{}{}^{}\mathrm{Mo}$ and ${}_{}{}^{96}{}_{}{}^{}\mathrm{Mo}\mathrm{}(p,t)\mathrm{}{}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}$ reactions have been studied at an incident proton energy of 31 MeV. The triton spectra were obtained with a magnetic spectrograph with overall resolution of about 20 keV. Experimental angular distributions are compared with two-nucleon-transfer distorted-wave Born-approximation calculations to extract spin-parity assignments and enhancement factors. Particular emphasis is placed on the study of the $L=0\mathrm{}$ transitions near the closed shell at 50 neutrons.

A detailed study of the 0.962-MeV $\beta$ transition from the decay of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ is performed. A complete description of the theoretical formalism employed is given. Two sets of nuclear matrix elements have been extracted from the experimental data. In one of them the $\beta$ moment of multipolarity $\lambda =2\mathrm{}$ is of the same order of magnitude as those of multipolarities $\lambda =0\mathrm{}$ and $\lambda =1\mathrm{}$ and the ratio $\Lambda (=\frac{〈\overrightarrow{\alpha }〉}{\xi 〈i\overrightarrow{\mathrm{r}}〉})$ is consistent with the Fujita-Eichler estimate [$\Lambda \left(\mathrm{FE}\right)=2.4\mathrm{}$]. In the second case the $\beta$ moment of $\lambda =2\mathrm{}$ is negligible and the ratio $\Lambda$ is strongly reduced with respect to $\Lambda \left(\mathrm{FE}\right)$. A possible mechanism for the reduction of the $\beta$ moments from their single-particle values is discussed on the basis of a particle-plus-phonon coupling model. It is concluded that the state $2f_{\frac{5}{2}}$ is the dominant neutron single-particle configuration in the ground state of ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$.

The $\beta$ moments of the ${\frac{7}{2}}^{-}\left(\beta \right){\frac{5}{2}}^{+}$ transition from the decay of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Ce}$, have been extracted from the experimental data. We have obtained the following results. $〈i\overrightarrow{\mathrm{r}}〉=0.98\mathrm{}\pm 0.20$ fm, $〈\overrightarrow{\sigma }\times \overrightarrow{\mathrm{r}}〉=-1.11\mathrm{}\pm 0.35$ fm, $〈i{B}_{\mathrm{ij}}〉=1.30\mathrm{}\pm 0.50$ fm, and $\frac{〈i\overrightarrow{\alpha }〉}{\xi }=2.16\mathrm{}\pm 0.45$ fm. These results are consistent with the analysis of the ${\frac{7}{2}}^{-}\left(\beta \right){\frac{5}{2}}^{+}$ transition in ${}_{}{}^{139}{}_{}{}^{}\mathrm{Ba}$ and with the measurement of the $\gamma$ moment $〈i\overrightarrow{\mathrm{r}}〉$ from the isobaric analog state of the ground state in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Ce}$ to the ground state in ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$. We present here a discussion concerning the polarizability effects due to the charge-exchange excitation modes.

$\gamma$-ray singles and coincidence measurements following the decay of 2.41-min ${}_{}{}^{108}{}_{}{}^{}\mathrm{Ag}$ have been performed with Ge(Li) and NaI(Tl) detectors. A total of 13 $\gamma$ rays have been assigned to ${}_{}{}^{108}{}_{}{}^{}\mathrm{Ag}$ decay and their energies and intensities have been measured accurately. From the coincidence measurements and energy-sum relationships 12 $\gamma$ rays have been fitted into six excited states of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Pd}$ with the following energies in keV and spins: 433.96, $2^{+}$; 931.09, $2^{+}$; 1052.82, $0^{+}$; 1314.22, $0^{+}$; 1441.16, $2^{+}$; and 1539.97, 1, 2. The first excited $2^{+}$ state of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Cd}$ at 632.98 keV is also populated by the $\beta$ decay of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Ag}$. The spins of the 1052.82- and 1314.22-keV levels were determined uniquely as 0 from the NaI(Tl)-Ge(Li) directional-correlation measurements. These data also yield a spin of 2 for the 1441.16-keV level and $E2+\le 2\% M1\mathrm{}$ multipolarity for the 1007.22-keV transition. A discussion of the ${}_{}{}^{108}{}_{}{}^{}\mathrm{Pd}$ levels within the vibrational framework is presented.

$\gamma$-ray spectra and total capture yields were measured for resonant neutron capture in an enriched ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ sample for neutron energies less than 2.3 keV. The experiment utilized the 40-m flight path of the Oak Ridge electron linear accelerator and a nonhydrogenous liquid-scintillator $\gamma$-ray detector. A total of 162 resonances were observed in this interval, and the resonance energies and neutron widths deduced. Approximately 14% of the resonances are assigned to $p$-wave capture on the basis of the $\gamma$-ray spectral measurements while an additional 23% are assigned to $s$-wave capture on the basis of their large neutron widths. The parity of the remainder is undetermined. A lower limit of 0.9 × ${10}^{-4\mathrm{}}$ is observed for the $p$-wave neutron strength function [$\Sigma \frac{g\Gamma _n^{}{}_{}{}^1}{\mathrm{}(2l+1)\mathrm{}\Delta E}$] while the $s$-wave neutron strength function [$\Sigma \frac{g\Gamma _n^{}{}_{}{}^0}{\Delta E}$] is 0.15 × ${10}^{-4\mathrm{}}$.

The quadrupole interaction of ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ ions following the decay of ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ implanted by ($\alpha ,2n$) reactions into a cubic (fcc) Ag lattice has been measured with the time-differential perturbed-angular-correlation method. A nonvanishing quadrupole interaction corresponding to a distribution of electric field gradients was observed. The "smeared out" quadrupole interaction frequency has a centroid $\overline{\omega }$ from 2.04 to 1.50 MHz depending on the temperature and the time the irradiated Ag was allowed to "heal." In addition, about 3% of the ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$-${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ ions experience a quadrupole interaction with a sharp frequency ${\omega }_Q=157\mathrm{}\pm 2$ MHz. The temperature dependence of the healing process was investigated. At room temperature no further healing occurs after 6 days once the $\overline{\omega }=1.50\mathrm{}$ MHz was reached. Annealing for 12 hours at 600°C causes the quadrupole interaction to vanish conpletely. Various quadrupole-perturbation and "healing" mechanisms are discussed. The most likely cause of the quadrupole perturbation in the cubic Ag lattice are vacancies and/or Ag interstitials.

Inelastic electron scattering from ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ in the momentum transfer range $q=150-300\mathrm{} \frac{\mathrm{MeV}}{c}$ induces a broad, strong excitation at about 20 MeV which cannot be explained by shell-model quasielastic knockout calculations. The excitation form factor exhibits a diffraction pattern whose dependence on $q$ is consistent with preliminary predictions for previously unobserved $E0\mathrm{}$ or $E2\mathrm{}$ giant collective modes in the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ region.

Available experimental data on fission-isomer excitation functions have been reanalyzed using an improved statistical model to determine values for the energies relative to the ground state of the secondary minimum and second maximum in the fission barrier for a series of plutonium, americium, and curium isotopes. The statistical model incorporates realistic decay-width calculations for neutron emission, fission, and $\gamma$-ray emission which are based on nuclear level densities derived from appropriate single-particle-level spectra. Values for the curvature $\hslash {\omega }_B$ of the second barrier are also estimated from the observed fission-isomer half-lives. The fission-barrier shapes determined from the analysis of experimental results are compared to theoretical calculations of barriers performed by several groups. The experimental barrier parameters agree with a variety of theoretical calculations to an accuracy of about 1 MeV. Systematic deviations between the experimental and theoretical results suggest that the surface asymmetry constant $\kappa$ in the liquid-drop mass formula should be substantially larger than the value of 1.7826 used in the second mass formula of Myers and Swiatecki.

Neutron time-of-flight resonance spectroscopy results, using the Nevis synchrocyclotron, for the separated Yb isotopes (170, 171, 172, 173, 174, 176) are given. Transmission and self-indication measurements were made for several sample thicknesses of each isotope. Resonance parameters, ${\Gamma }_n^0$ (or $g{\Gamma }_n^0$), are given to ∼1.8 keV for 171 and 173, and to ∼10 keV for 172, 174, and 176. Levels in 170 were those seen in the natural element, but not in the 171-176 isotopes. Many resonance ${\Gamma }_{\gamma }$ and $J$ values were also obtained for 171 and 173, and a few ${\Gamma }_{\gamma }$ values for 172 and 174. The $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}$ values are 2.25± 1.0, 1.86± 0.16, 1.68± 0.20, 1.60 ± 0.28, 1.62± 0.21, and 2.29± 0.32 for 170, 171, 172, 173, 174, and 176, respectively. $〈{\Gamma }_{\gamma }〉=76.5\mathrm{}$ meV (37 levels), 72.3 meV (3 levels), and 73.8 meV (33 levels) for 171, 172, and 173, respectively. A shape fit to the asymmetric level in 174 at 342.7 eV gave $R^{\prime }=(7.9\mathrm{}\pm 0.5)$ fm. The increasing $\sigma$ below ∼100 eV for 174 and natural Yb, and the known thermal 174 partial cross sections, were fitted assuming a bound 174 level at $E_0=-25\mathrm{}$ eV, ${\Gamma }_n^0=160\mathrm{}$ meV. Comparison of the ${\left(g{\Gamma }_n^0\right)}^{\frac{1}{2}}$ distributions with Porter-Thomas theory and the nearest-neighbor energy spacings with the Wigner theory gave best agreement for 172, as did other statistical orthogonal ensemble (O.E.) tests. There were missing weak $s$ levels for 171 and 173 and extra $p$ levels for 176. The 174 and 176 results were also compatible with O.E. theory but provided poorer test cases than 172.

It is well known that the nuclear single-particle level density $g_{\mathrm{obs}}$, obtained from statistical nuclear reactions, does not follow the behavior of a free Fermi gas; previous attempts to reproduce $g_{\mathrm{obs}}$ have largely been empirical. We have used the properties of our renormalized gas model (RGM) to deduce an approximate analytic expression for our model density $g_{\mathrm{RGM}}$ We study the consequence of the concept of momentum anisotropy in the phase space of the RGM system relative to the isotropic distribution of the free Fermi gas. We find that our model is a very suitable one to fit in with this concept. With fair accuracy, we find that $g_{\mathrm{RGM}}=g_{\mathrm{obs}}$ throughout the range of stable nuclei, $50\le A\le 250$. The effects of specific model interaction energies (the single-particle combinatorial effects, the pairing, deformation, and Coulomb effects) are all observed in appropriate regions in desired strengths. All these effects are strongly dominated by the prescribed shell structure and its state-mixing and occupation dependence.

$\gamma$ rays following the $\beta$ decay of ${}_{}{}^{37}{}_{}{}^{}\mathrm{S}$ have been observed with a Ge(Li) detector during the course of a study of the decay modes of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Cl}$. These two isotopes have been produced simultaneously through the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}(n,\alpha )$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}\mathrm{}(n,p)\mathrm{}$ reactions. The energies and relative intensities of the two lines (3103.3 ± 0.3 keV, 99.7% and 3741.8 ± 0.4 keV, 0.3%) measured earlier in this laboratory using the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}\mathrm{}(n,p)\mathrm{}{}_{}{}^{37}{}_{}{}^{}\mathrm{S}$ reaction, are confirmed. No transition with the energy of 3706 ± 2 keV and the decay rate of ${}_{}{}^{37}{}_{}{}^{}\mathrm{S}$ has been found. Nevertheless, a $\gamma$ ray of 3704.6 ± 0.8 keV is shown clearly to arise from the deexcitation of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$.

It is shown that separable potentials including repulsion and tensor components with Yamaguchi form factors are unable to give a reasonable fit simultaneously to ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ phase shifts and the following deuteron data: the binding energy, the quadrupole moment, and the electric form factor. It is also found that a good phase-shift fit cannot be obtained from potentials of this type if the $D$-state probability of the deuteron desired is higher than 4%.

This paper reports new results on the yield of photoneutrons from thick targets bombarded with electron beams. Yields have been calculated for incident electron energies from 20 MeV down to the photonuclear cross section threshold, for tantalum and tungsten targets with thicknesses up to 12.5 g ${\mathrm{cm}}^{-2\mathrm{}}$. The increased yield from composite tungsten-beryllium targets has been explored.

Small admixtures of doorways $|d^{\prime }〉$ in with the dominant doorway $|d〉$ are shown to account for the possibility of $\gamma$ decay from the neutron fine structure associated with the doorway $|d〉$. The example of low-lying ${\frac{1}{2}}^{+}$ resonances in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}$ is investigated via the particle-vibration model with the important doorway $|d^{\prime }〉$ for $E1\mathrm{}\gamma$ decay found to be that based on the $1^{-}$ giant dipole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$.

An expression is derived for the cross section of the process $A+d\to B+p\to C+c+p$ in which $C$ and $c$ are not observed. The result is proportional to ${\Gamma }_n$ (the partial width of $B$ for $n$ emission) and does not depend on the fact that $B$ may decay into channels other than $A+n$.