The threshold photodisintegration of ${\mathrm{Pb}}^{208}$ and the thermal-neutron capture by ${\mathrm{Pb}}^{207}$ is considered. It is shown that the magnitude of the thermal capture cross section and the asymmetry of the resonance observed in the ($\gamma ,n$) reaction at 41 ke V above threshold may be explained by extrapolating the giant resonance amplitude and the amplitude of a subthreshold resonance into the appropriate energy domains. It is found that the direct (optical) processes are small compared with the effects of the "resonance tails."

The predictions of asymmetric collective models with pure quadrupole, pure octupole, and mixed quadrupole-plus-octupole shapes are developed for negative-parity states in deformed even nuclei in an effort to determine the usefulness of the asymmetric model as a tool to distinguish surface shapes. The models are applied to the data for ${}_{}{}^{228}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, and the comparison indicates that the energy and electric quadrupole branching-ratio predictions are independent of surface-shape multipolarity.

Differential cross sections for elastic and inelastic proton scattering on ${}_{}{}^{94}{}_{}{}^{}\mathrm{Zr}$ were measured between 6.0- and 8.5-MeV bombarding energy. The decay of analogs of states in ${}_{}{}^{95}{}_{}{}^{}\mathrm{Zr}$ to the ground state and the 0.92 MeV ($2^{+}$), 1.30 MeV ($0^{+}$), 1.66 MeV ($2^{+}$), and 2.06 MeV ($3^{-}$) states in ${}_{}{}^{94}{}_{}{}^{}\mathrm{Zr}$ was investigated. In the analysis of the inelastic proton groups, the enhancement of the Hauser-Feshbach background, as well as the interference of the resonance amplitude with direct nuclear excitation were taken into account. Spins, spectroscopic factors, and possible weak-coupling configurations in the parent system are derived and compared with results previously obtained for ${}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}$ and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Zr}$.

Four $\alpha$-decay chains initiated by ${}_{}{}^{225}{}_{}{}^{}\mathrm{Pa}$, ${}_{}{}^{224}{}_{}{}^{}\mathrm{Pa}$, ${}_{}{}^{223}{}_{}{}^{}\mathrm{Pa}$, and ${}_{}{}^{222}{}_{}{}^{}\mathrm{Pa}$ were produced by the bombardment of thallium, lead, and bismuth targets with beams of ${}_{}{}^{22}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ at the Berkeley heavy-ion linear accelerator. The reaction products were transported from the reaction cell by the helium-jet technique and their decay was measured with a semiconductor detector. Energy values, excitation functions, half-lives, and genetic relationships of individual peaks were determined. Two new techniques based on the use of a time-to-amplitude converter were developed for the measurement of μsec half-lives of daughter products, and five half-lives in the μsec range were measured.

These new $\alpha$ data help to determine the trends in $\alpha$-decay energies for isotopes of odd-$Z$ elements, particularly in the poorly defined region just above the 126-neutron shell. This allows more accurate predictions of $\alpha$-decay properties of many unknown nuclei. Some anomalous behavior of the apparent $\alpha$-decay energies for nuclei with 133 and 135 neutrons is pointed out.

The difference in the total neutron cross section due to nuclear orientation, $\Delta {\sigma }_{\mathrm{def}}$, has been measured for ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ over the energy range of 2 to 135 MeV. The results show that $\Delta {\sigma }_{\mathrm{def}}$ oscillates as well as changing sign, contrary to our classical concept of the interaction. The data, both ${\sigma }_{\mathrm{t}}$ and $\Delta {\sigma }_{\mathrm{def}}$, are successfully fitted by adiabatic coupled-channel calculations using the optical model. The parameters for the optical model were determined by fitting ${\sigma }_{\mathrm{t}}$ and ${\sigma }_{\mathrm{R}}$ data (over approximately the same energy range as in the present work) for the two spherical nuclei Cd and Pb. The only additional quantity introduced was the quadrupole deformation parameter for ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ which is known to be 0.33. The data for $\Delta {\sigma }_{\mathrm{def}}$ can also be explained quite well by a simple semiempirical model which makes use of the black-nucleus model, the nuclear Ramsauer effect, and the experimental ${\sigma }_{\mathrm{t}}$ data. The temperature dependence of $\Delta {\sigma }_{\mathrm{def}}$ agrees very well with our calculated values for the degree of nuclear orientation, which is consistent with ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ being almost a pure quadrupole-shaped nucleus.

A 10-cc coaxial Ge(Li) detector and a 2-in.×2-in. NaI(Tl) detector were used in conjunction with a multichannel coincidence configuration to investigate the following $\gamma -\gamma$ directional correlations in the decay of 11.1-day ${\mathrm{Nd}}^{147}$: 319-91, 398-91, 440-91, 121-319, and 276-319 keV. Using the well-established values of $\frac{7}{2}$ and $\frac{5}{2}$ for the ground and 91-keV levels, respectively, and an admixture of $(1.6\mathrm{}\pm 0.4)\% E2\mathrm{}$ for the 91-keV transition, this experiment favored the following spin assignments to the various levels: 410 ($\frac{3}{2}$), 489 ($\frac{5}{2}$), 531 ($\frac{5}{2}$), and 686 keV ($\frac{5}{2}$). The $M1+E2\mathrm{}$ multipolarity mixtures obtained, which are in agreement with nuclear-orientation and internal-conversion measurements reported by previous investigators, for each of the respective $\gamma$ transitions are: $121 (1.5\mathrm{}\pm 0.5)\% E2\mathrm{}$, $276 \left(\sim 1\right)\% E2\mathrm{}$, $319 (11\mathrm{}\pm 2)\% E2\mathrm{}$, $398 (3\mathrm{}\pm 2)\% E2\mathrm{}$, and 440 keV $(27\mathrm{}\pm 7)\% E2\mathrm{}$. A 310-keV $\gamma$ ray proposed by several investigators was directly observed in the Ge(Li) spectrum; measurements indicate that this peak decays with the half-life of ${\mathrm{Nd}}^{147}$.

Excitation functions for ($\alpha ,xn$), ($\alpha ,\alpha n$), and ($\alpha ,2p$) reactions upon niobium targets have been measured for incident $\alpha$-particle energies from 15 to 41 MeV Excited states in ${\mathrm{Mo}}^{95}$ have been studied by observing the decay of the 61-day isotope ${\mathrm{Tc}}^{95m}$, which was produced by the ${\mathrm{Nb}}^{93}(\alpha ,2n)$ reaction. The energies and the intensities of the $\gamma$ rays resulting from this decay have been measured. The angular-correlation coefficients of the two strongest cascades in ${\mathrm{Mo}}^{95}$ have been found to be $A_{22}=-0.292\mathrm{}\pm 0.005$ and $A_{44}=-0.001\mathrm{}\pm 0.006$ for the 582-204-keV cascade, and $A_{22}=-0.196\mathrm{}\pm 0.006$ and $A_{44}=-0.003\mathrm{}\pm 0.008$ for the 835-204-keV cascade. The mean life of the 204-keV state has been measured by the delayed-coincidence technique and found to be 1.09 ± 0.02 nsec. The $g$ factor of the 204-keV state has been measured to be -0.26 ± 0.02. A summary of a number of calculations concerning the nuclear structure of ${\mathrm{Mo}}^{95}$ is given, and some predictions of the Kisslinger-Kumar model of near-spherical nuclei for ${\mathrm{Mo}}^{95}$ are presented. The technique of perturbed angular correlations has been used to measure the hyperfine fields at the molybdenum nucleus in iron and nickel hosts. These fields have been found to be ${\mathrm{B}}_{\mathrm{e}\mathrm{f}\mathrm{f}}\left(\mathrm{Mo}\mathrm{in}\mathrm{Fe}\right)=-236\mathrm{}\pm 19$ kG and ${\mathrm{B}}_{\mathrm{e}\mathrm{f}\mathrm{f}}\left(\mathrm{Mo}\mathrm{in}\mathrm{Ni}\right)=-29.9\mathrm{}\pm 5.1$ kG at 55°C.

States up to 5.6 MeV in excitation energy in ${\mathrm{Pb}}^{207}$ were studied by the ${\mathrm{Pb}}^{208}\mathrm{}(d,t)\mathrm{}$, ${\mathrm{Pb}}^{206}\mathrm{}(d,p)\mathrm{}$, and ${\mathrm{Pb}}^{207}(d,d^{\prime })$ reactions at a deuteron bombarding energy of 17 MeV. Over 100 states were observed and 70 angular distributions were measured and compared with distorted-wave Born approximation calculations for the ($d,p$), and ($d,t$) reactions. Special emphasis was placed on obtaining accurate excitation energies to compare those states excited in more than one reaction. In ${\mathrm{Pb}}^{206}\mathrm{}(d,p)\mathrm{}$, some of the two-hole-one-particle (2h-1p) states are found to be fragmented. The $i_{\frac{11}{2}}$ and $j_{\frac{15}{2}}$ 2h-1p states are tentatively identified. Many of the weaker (less than 5 μb/sr) transitions in ($d,t$) have angular distributions which do not follow DWBA - possibly indicating other than one-step reaction mechanisms. Observation of the 2h-1p states in ($d,t$) indicate that the ${\mathrm{Pb}}^{208}$ closed shell contains about $4.7\% {\left(2\mathrm{}{g}_{\frac{9}{2}}\right)}^2$, $\lesssim 4.7\% {\left(3\mathrm{}{d}_{\frac{5}{2}}\right)}^2$, and $\lesssim 1.2\% {\left(4\mathrm{}{s}_{\frac{1}{2}}\right)}^2$ particle-${\mathrm{Pb}}^{206}$ core admixture.

The cross sections of ($p,2p$), ($p,pn$), and ($p,2n$) reactions at 400 MeV on the separated isotopes of cadmium were determined. The ($p,pn$) cross sections exhibit abrupt variations within a narrow target mass range. The data are examined in terms of the currently accepted mechanisms for high-energy ($p,2\mathrm{}$ nucleon) reactions. An estimate is made of the relative contribution of direct knockout processes versus the two-step inelastic scattering and neutron evaporation mechanism. There does not appear to be any obvious explanation for the abrupt cross-section variations. The cross section of the cadmium ($p,2p$) reactions is inversely proportional to the neutron skin thickness. This is consistent with the conclusion that these reactions take place predominantly by direct knockout processes and in the peripheral region of the nucleus.

The cross sections of ($p,2p$), ($p,pn$), and ($p,2n$) reactions at 300 MeV on the separated isotopes of tellurium were determined. The total ($p,pn$) cross sections, for those cases in which it was only possible to measure one of the isomeric states in the product, was calculated by assuming that the direct knockout mechanism was predominant. Both the total ($p,pn$) cross sections and the ($p,2n$) cross sections are directly proportional to the neutron skin thickness. This is consistent with the assumption that these reactions take place by direct knockout processes in the diffuse or peripheral region of the nucleus. The tellurium ($p,2p$) reactions were observed to be inversely proportional to the neutron skin thickness.

The $N=81\mathrm{}$ isomer ${\mathrm{Gd}}^{145m}$ is characterized as having a half-life of 85 ± 3 sec and an $M4\mathrm{}$ isomeric transition of 721.4 ± 0.4 keV. It also has a direct $\frac{{\beta }^{+}}{\epsilon }$ branch to the $h_{\frac{11}{2}}$ state at 716.1 keV in ${\mathrm{Eu}}^{145}$. The intensity of this branch is 4.7% of the decay, implying a $log\mathrm{ft}$ of 6.2. The $M4\mathrm{}$ transition probability is calculated and compared with the trends among other isomeric transitions in this region.

Calculation of electric monopole $X$ ratios in deformed nuclei using the higher-order shape deformations $Y_4$ and $Y_6$ yields much better agreement with measured values than is obtained when only pure quadrupole surfaces are assumed. Use was made of recently measured values of ${\beta }_4$, and ${\beta }_6$.

Elastic and inelastic scattering of monochromatic photons were used for studying nuclear energy levels in ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$; the photons were produced by thermal-neutron capture in titanium and iron. Two independent resonance lines at 6418 and 6760 keV were excited with the titanium $\gamma$ source, and three independent resonances at 6018, 7279, and 7632 keV were excited with the iron $\gamma$ source. Some 18 known low-lying levels were populated by deexcitation of these resonance levels. The angular distribution of some intense elastic and inelastic lines were measured and the following spin and parity determinations (keV, $J^{\pi }$) were made: 166, $\frac{5}{2}$; 1220, $\frac{5}{2}$, ($\frac{9}{2}$); 1384, $\frac{7}{2}$; 1419, $\frac{7}{2}$, ($\frac{11}{2}$); 1536, $\frac{7}{2}$; 1580, $\frac{9}{2}$; 2232, ($\frac{7}{2},\frac{11}{2}$); 6018, ${\frac{7}{2}}^{-}$; 6418, ${\frac{9}{2}}^{-}$; and 6760, $\frac{7}{2}$, where parentheses denote uncertainties. The parities of the 6018- and 6418-keV levels were directly determined using a Compton polarimeter. The total radiative widths of the 6018- and 6418-keV levels were measured and found to be ${\Gamma }_{\gamma }=0.051\mathrm{} \mathrm{and} 0.081$ eV, respectively. The ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ levels are compared with recent theoretical calculations.

Two new isotopes of californium have been identified through bombardments of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{233}{}_{}{}^{}\mathrm{U}$ with ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions from the Oak Ridge isochronous cyclotron. They decay with half-lives of 3.78 ± 0.70 and 1.06 ± 0.15 min and with the emission of $\alpha$ particles of 7.335 ± 0.005 and 7.590 ± 0.010 MeV, respectively. Analysis of the excitation functions for these $\alpha$ emitters favors the assignment of mass 241 to the former and mass 240 to the latter; also, the 7.335-MeV activity was shown to be chemically similar to californium. New values for the $\alpha$-particle energies of ${}_{}{}^{242}{}_{}{}^{}\mathrm{Cf}$ were obtained: 7.385 ± 0.004 and 7.351 ± 0.006 MeV, assigned, respectively, to $\alpha$-decay transitions to the ground and first excited states of ${}_{}{}^{238}{}_{}{}^{}\mathrm{Cm}$.

The average-resonance method of neutron-capture $\gamma$-ray spectroscopy is critically examined by means of measurements on stable isotopes of palladium, gadolinium, holmium, and erbium. A mathematical model of the capture process is developed. This model shows that the intensities of the lines in average-resonance-capture spectra can yield the parities and set narrow limits on the spins of states in almost all nuclides with $A>\mathrm{}100\mathrm{}$ if the $\gamma$-ray strength function is a smooth function of $\gamma$-ray energy and if the random fluctuations in intensity result only from the Porter-Thomas distribution of partial radiation widths. The measurements give extensive data for ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$, ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{166}{}_{}{}^{}\mathrm{Ho}$, and ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$, and some for ${}_{}{}^{103}{}_{}{}^{}\mathrm{Pd}$, ${}_{}{}^{105}{}_{}{}^{}\mathrm{Pd}$, ${}_{}{}^{155}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{157}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{165}{}_{}{}^{}\mathrm{Er}$, ${}_{}{}^{167}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{169}{}_{}{}^{}\mathrm{Er}$. These data are examined for information relating to the mechanisms of radiative capture. All of the data are consistent with the hypothesis that the radiation widths are a smooth function of $\gamma$-ray energy and that the random fluctuations in intensity are well described by the Porter-Thomas distribution. The intensities of $E1\mathrm{}$ transitions vary with $\gamma$-ray energy more rapidly than $E_{\gamma }^{}{}_{}{}^3$, as expected from a giant-resonance description of the radiative process. The intensity of $M1\mathrm{}$ radiation was measured over a 2-MeV range for ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$ and ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$, and the reduced $M1\mathrm{}$ widths for ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$ form a giant-resonance-like curve that peaks at ∼7.8 MeV. Ratios of widths for $E1\mathrm{}$ and $M1\mathrm{}$ radiation and for $E1\mathrm{}$ and $E2\mathrm{}$ radiation are obtained for several nuclides. These properties of radiative capture are used to obtain spectroscopic information about final states. The most complete results are for ${}_{}{}^{166}{}_{}{}^{}\mathrm{Ho}$, for which 16 rotational bands are identified and interpreted in terms of the collective model. Similar but less extensive data are obtained for ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$, ${}_{}{}^{158}{}_{}{}^{}\mathrm{Gd}$, and ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}$. The measurements on ${}_{}{}^{106}{}_{}{}^{}\mathrm{Pd}$ show that the shapes of the observed $\gamma$-ray lines may be used to determine the parities of final states.

The radiation widths of bound nuclear levels excited by ($\gamma ,{\gamma }^{\prime }$) reactions in nuclei ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, ${}_{}{}^{130}{}_{}{}^{}\mathrm{Te}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}$ have been measured. The present results together with results published by other authors using ($\gamma ,{\gamma }^{\prime }$) reactions are summarized and compared with similar results obtained in capture reactions of thermal and resonance neutrons. The expected properties of the nuclear levels obtained by extrapolation of the giant-dipole resonance to lower energies are compared with the present experimental data. The fluctuation in partial radiative widths from these bound levels is shown to be compatible with the Porter-Thomas distribution.

The 536-keV ($2^{+}$) first excited state of ${\mathrm{Xe}}^{130}$ has been investigated by means of nuclear-resonance-fluorescence scattering experiments. The use of a Ge(Li) detector allowed a good determination of the Rayleigh scattering contribution which amounted to about 30% of the resonant peak. The level width was found to be (5.2 ± 0.9) × ${10}^{-5\mathrm{}}$ eV, corresponding to a mean life of (1.3 ± 0.3) × ${10}^{-11\mathrm{}}$ sec and a ${B\left(E2\mathrm{}\right)\mathrm{}}_{\uparrow }$ of $(0.69\mathrm{}\pm 0.15)e^2\times {10}^{-48\mathrm{}}$ ${\mathrm{cm}}^4$. From this result and the relative transition probabilities determined previously in a Coulomb-excitation experiment by Pieper, Anderson, and Heydenburg, the absolute $B\left(E2\mathrm{}\right)\mathrm{}$ values for the first excited states of ${\mathrm{Xe}}^{128}$ and ${\mathrm{Xe}}^{132}$ were obtained.

Measurements of the relative thick-target yields of $\gamma$ rays deexciting the 2+ first excited states in ${}_{}{}^{112,116,118,120,122,124}{}_{}{}^{}\mathrm{Sn}$, following Coulomb excitation by $\alpha$ particles and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions, have been interpreted in terms of the relative static quadrupole moments of these states. The absolute static quadrupole moment of the 2+ state in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ was determined to be +(0.09 ± 0.10) b. With this value it was then possible to obtain the absolute static quadrupole moments for the 2+ state in the other even tin nuclei. The resulting values are closer to the vibrational-model prediction (static quadrupole moment of zero) than to values predicted by the rotational model. A set of absolute $B(E2,0\mathrm{}\to 2)$ values was also obtained with assigned errors between 2 and 3%.

A charge-exchange threshold cusp is observed in the summed 160° excitation curve for ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}\mathrm{}(d,p)\mathrm{}{}_{}{}^{94}{}_{}{}^{}\mathrm{Nb}(6^{+},\mathrm{g}.\mathrm{s}.-2^{+},0.31\mathrm{} \mathrm{MeV})$ at ∼7.1 MeV, the threshold of the analogous ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}\mathrm{}(d,n)\mathrm{}{}_{}{}^{94}{}_{}{}^{}\mathrm{Mo}_{}^A{}_{}{}^{}(6^{+},13.2\mathrm{} \mathrm{M}\mathrm{e}\mathrm{V}-2^{+},13.5\mathrm{} \mathrm{MeV})$ reaction. As predicted by theory, it is essentially identical in shape to the excitation curve previously measured for ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}\mathrm{}(d,p)\mathrm{}{}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}(d_{\frac{5}{2}},\mathrm{g}.\mathrm{s}.\mathrm{})$ in the same energy region.

Using new information concerning the decay modes of the 460-, 557-, and 559-keV levels in ${\mathrm{Ir}}^{193}$, previous resonance-fluorescence data have been reevaluated in terms of the mean lives of these levels.