Some relative and absolute $\gamma$-ray transition probabilities have been measured for the low-lying levels in ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ by observing the Coulomb excitation and subsequent decay of the states. Thick bismuth targets were bombarded with 19-MeV $\alpha$ particles, and $\gamma$-ray yields at 0°, 30°, 45°, 60°, and 90° were observed with a 25-${\mathrm{cm}}^3$ LiGe detector. Determinations have been made of the transition strengths to the $f_{\frac{7}{2}}$ (0.897-MeV), the $i_{\frac{13}{2}}$ (1.608-MeV), and the $f_{\frac{5}{2}}$ (2.822-MeV), and the septuplet of levels near 2.6 MeV, formed by coupling an $h_{\frac{9}{2}}$ particle to the $3^{-}$ octupole state in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, excited by $E2\mathrm{}$, $E3\mathrm{}$, $E2\mathrm{}$, and $E3\mathrm{}$ Coulomb excitation, respectively, Approximate $E1\mathrm{}$ transition strengths for ground-state decays of the 2.563-, 2.581-, and 2.598-MeV levels have been determined from the Doppler broadening of the $\gamma$ peaks. Branches are observed corresponding to decays from the 2.741- and 2.600-MeV states to the 1.608 (${\frac{13}{2}}^{+}$) level, and from the 2.822-, 2.615-, and 2.581-MeV levels to the 0.897 (${\frac{7}{2}}^{-}$) state. The $\gamma$-ray strengths and relative transition rates are compared with the predictions of a particle-vibration coupling model.

Multiple Coulomb excitation of the ground-state rotational band of ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}$, ${}_{}{}^{166}{}_{}{}^{}\mathrm{Er}$, and ${}_{}{}^{172,174,176}{}_{}{}^{}\mathrm{Yb}$ was measured in order to test the predicted ratios of the $B\left(\mathrm{E}2\right)$ values for a rotational sequence of states. The deexcitation $\gamma$ rays from the rotational levels were observed in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-$\gamma$ and $\alpha -\gamma$ conicidence spectra with a Ge(Li) detector. Experimental excitation probabilities are compared to the probabilities calculated with the de Boer-Winther Coulomb-excitation computer program. The $B(E2, 2\to 4)$ and $B(E2, 4\to 6)$ values were determined to accuracies of 6-10%. The $B(E2, 6\to 8)$ values were determined to accuracies of 15-25%. For the poor-rotor ${}_{}{}^{152}{}_{}{}^{}\mathrm{Sm}$, the results indicate some increase in the $B\left(\mathrm{E}2\right)$ values over the rigid-rotor predictions for the higher transitions. The observed increase is less than that predicted by "centrifugal stretching" based on the level positions. However, the results for the four good-rotor nuclei show smaller $B\left(E2\mathrm{}\right)\mathrm{}$ values between higher rotational states than those given by the rigid-rotor values, rather than the larger values predicted by centrifugal stretching.

The ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(d, p){}_{}{}^{209}{}_{}{}^{}\mathrm{Pb}$ ground-state reaction is analyzed using the method of Butler, Hewitt, McKellar, and May. Using proton parameters fitted to elastic scattering data and Rosen's neutron parameters, good agreement with the proton angular distribution is obtained when the energy of the incident deuteron is above the Coulomb barrier. The spectroscopic factor extracted from the data is 0.65±0.1.

The even cerium isotopes 130 through 140 have been investigated by $\mathrm{Ba}(\alpha , \mathrm{xn}\gamma )\mathrm{Ce}$. The energies, relative intensities, angular distributions, and time distributions of the $\gamma$ rays relative to the cyclotron beam bunch have been measured. The results show transitions from states up to $8^{+}$ in ${}_{}{}^{130}{}_{}{}^{}\mathrm{Ce}$ (253.2, 456.4, 613.9, and 729.0 keV ±1 keV), up to ${10}^{+}$ in ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ce}$ (325.6, 533.5, 684.5, 789.0, and 875 keV), and up to $8^{+}$ in ${}_{}{}^{134}{}_{}{}^{}\mathrm{Ce}$ (409.4, 639.9, 814.8, and 947 keV). Several transitions from states not in the ground-state band have been assigned in the three heaviest isotopes. The most prominent transitions (ground-state band; others) are for ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ce}$: 551.7, 761.7, 898.8; 328.6, 623.6, 664.3, and 1051.9 keV; for ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ce}$: 787.9, 1037.4; 302.1, 390.7, 402.8, 417.5, 430.1, and 815.0 keV; and for ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}$: 1596.7, 486.7, 202.0, 222.0, 1317.5, and 1404.1 keV. A 22-nsec level is found in ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}$. Significant long-lived (≳200 nsec) feeding of the ground-state band has been observed in each Ce isotope.

Cross sections have been measured for the production of Po nuclides with mass numbers 194 to 200 in bombardments of a 92.7% ${}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$ target with ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ions in the ion-energy range 160-280 MeV. The maximum cross sections were 0.5, 2.1, 8.0, 35, 50, 70, and 20 mb for the production of mass numbers 194, 195, 197, 198, 199, and 200, respectively. Isomer ratios for the odd-$A$ nuclides were obtained. A good fit is obtained between the shapes of calculated and experimental excitation-function curves. The fit involved (a) calculation of the compound-nucleus cross section by the use of the parabolic approximation to the real part of the optical-model potential with the parameters $V_0=-70\mathrm{}$ MeV, $r_0=1.26\mathrm{}$ F, and $d=0.44\mathrm{}$ F; (b) modification of Jackson's formula for the probability for neutron emission to include angular-momentum effects using $T=1.2\mathrm{}$ MeV and $\frac{\mathfrak{J}}{{\mathfrak{J}}^0}=1.4\mathrm{}$; and (c) assumption of an energy independence for the average partial level width for neutron emission. In the fitting process, experimental values for the latter quantity are obtained to which an empirical formula is fitted. Fission is the main competing mode of decay.

The spectroscopic quadrupole moments of the first $2^{+}$ states of ${\mathrm{Os}}^{188,190,192}$ were determined by means of Coulomb-excitation experiments. The results are compared with recent-model calculations and found to be in rather good agreement with these predictions.

The proton-neutron hole states of ${\mathrm{Tl}}^{206}$ have been studied by the direct ${\mathrm{Pb}}^{208}(d, \alpha ){\mathrm{Tl}}^{206}$ reaction with 17-MeV deuterons. Experimental resolutions of 12-15 keV for about 28-MeV $\alpha$ particles permitted the investigation of many two-hole states previously unknown. For most levels, $L$ values could be extracted from the comparison of microscopic two-nucleon transfer distorted-wave Born-approximation (DWBA) calculations with experimental angular distributions. The experimental level energies and $J^{\pi }$ assignments (or limits) were compared where possible to recent ($n, \gamma$) and ($t, \alpha$) data for ${\mathrm{Tl}}^{206}$ and to structure calculations by Kuo. It was possible to correlate about 20 low-lying levels ($E_x\lesssim 2.2$ MeV) with calculated shell-model states. In addition, Kuo's wave functions were used to derive detailed ($d, \alpha$) cross-section intensity distributions, and to check the dependence of the absolute normalization constant $N(d, \alpha )$ on various DWBA parameters. Constructive coherence in the transition amplitudes predicted by the wave functions for the lowest states of a given $J^{\pi }$ was varified experimentally. Ten enhanced ($d, \alpha$) cross sections are observed, in good qualitative agreement with theoretical predictions. The predicted enhancement for the population of some of these states was occasionally in excess of the observed enhancement.

Excitation functions have been measured for elastic and inelastic scattering of protons from ${}_{}{}^{110}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$, and ${}_{}{}^{114}{}_{}{}^{}\mathrm{Cd}$ at proton energies from 6.0 to 11.0 MeV. The isobaric-analog resonances observed in ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$, ${}_{}{}^{113}{}_{}{}^{}\mathrm{In}$, and ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ nuclei were analyzed by fitting the elastic excitation functions using a shell-model approach to reaction theory to extract quantitative nuclear-structure information for the parent analog states in ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{113}{}_{}{}^{}\mathrm{Cd}$, and ${}_{}{}^{115}{}_{}{}^{}\mathrm{Cd}$. Spectroscopic factors have been evaluated, and their dependence on the choice of optical and bound-state potentials has been studied. Coulomb displacement energies were also obtained from these data. Comparisons have been made with existing ($d, p$) work on ${}_{}{}^{110}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$, and ${}_{}{}^{114}{}_{}{}^{}\mathrm{Cd}$. In general, there is reasonable agreement between the ($p, p_0$) and ($d, p$) spectroscopic factors, excitation energies, orbital angular momenta, and total angular momenta.

The $\beta$-decay modes of ${\mathrm{Na}}^{25}$ and ${\mathrm{Al}}^{29}$ have been studied by observation of delayed $\gamma$ rays with a Ge(Li) $\gamma$-ray spectrometer system. The nuclei were produced via the ${\mathrm{Na}}^{23}(t, p){\mathrm{Na}}^{25}$ and ${\mathrm{Al}}^{27}(t, p){\mathrm{Al}}^{29}$ reactions, respectively, at the incident triton energy of 2.7 MeV. For ${\mathrm{Na}}^{25}$, the previously reported $\beta$ branches to the 0.975- and 1.612-MeV states of ${\mathrm{Mg}}^{25}$ are confirmed, while new branches were found to the states at 1.965 and 2.801 MeV. Decay modes (labeled by the final-state energy in ${\mathrm{Mg}}^{25}$) and their relative intensities, assuming a ground-state branch of 65%, are 0.975 MeV, 25.5%; 1.612 MeV, 8.8%; 1.965 MeV, 0.4%; and 2.801 MeV, 0.3%. Accurate excitation energies in ${\mathrm{Mg}}^{25}$ deduced from the $\gamma$-ray pulse-height distribution are (in keV) 585.9±0.4, 975.3±0.3, 1612.0±0.4, 1965.2±0.9, and 2801.0±0.7. In the decay of ${\mathrm{Al}}^{29}$, previously reported branches to the 1.273- and 2.427-MeV states of ${\mathrm{Si}}^{29}$ were confirmed, while a new branch is reported to the state at 2.028 MeV. Assuming zero ground-state branching, the decay modes with their relative intensities are 1.273 MeV, 89.1%; 2.028 MeV, 4.1%; and 2.426 MeV, 6.8%. The state at 3.069 MeV is populated with an intensity ≤0.1%. Excitation energies in keV of 1273.2±0.8, 2028.2±0.8, and 2426.3±0.8 have been obtained for these states in ${\mathrm{Si}}^{29}$. For both nuclei, experimentally observed $log\mathrm{ft}$ values have been compared with nuclear-model predictions. An adequate description of the ${\mathrm{Na}}^{25}$ $\beta$ decay in terms of the Nilsson model is obtained by introducing mixing of the two $K=\frac{1}{2}$ bands based on neutrons in orbits 9 and 11 in ${\mathrm{Mg}}^{25}$. The $J^{\pi }={\frac{1}{2}}^{+}$ states of these bands are at 0.586 and 2.562 MeV, respectively. The collective-model interpretation of ${\mathrm{Si}}^{29}$ is strengthened by the observation of a $\beta$ branch to the 2.028 MeV level in ${\mathrm{Si}}^{29}$; quantitative agreement, however, with the ${\mathrm{Al}}^{29}$ $\beta$-decay modes could not readily be obtained using the Nilsson-model wave functions. Possible spherical-shell-model configurations to explain the decay modes are suggested. The $\beta$-decay strengths deduced from these observations for ${\mathrm{Na}}^{25}$ and ${\mathrm{Al}}^{29}$ are compared with analogous $\gamma$-ray strengths observed in ${\mathrm{Al}}^{25}$ and ${\mathrm{P}}^{29}$, respectively.

Level energies, $\gamma$-ray transition rates, and proton spectroscopic factors are calculated for the nuclei with $N=28\mathrm{}$ and $20<Z\le 28$ from simple mixed-configuration shell models. First, the effective-interaction method is used to calculate wave functions in which the pure ($1{f_{\frac{7}{2}}}^n$) configuration and the ($1{f_{\frac{7}{2}}}^{n-1\mathrm{}}2p_{\frac{3}{2}}$) configuration are included. The results are compared with experimental values for 43 levels. The calculated and measured energies and spectroscopic factors agree well, but $M1\mathrm{}$ transition rates are too slow. The model is then extended to include the configuration ($1{f_{\frac{7}{2}}}^{n-1\mathrm{}}1f_{\frac{5}{2}}$). The wave functions are recalculated using additional two-body matrix elements calculated with a modified surface $\delta$ interaction (MSDI) fitted to the effective interactions of the first calculation. The expanded model provides a good fit to energies, spectroscopic factors, and transition rates. For comparison, the calculation is repeated using the reaction matrix elements of Kuo and Brown. The results are less satisfactory than those with the MSDI.

A search was made for double-photon decay occurring in the $0^{+}$→$0^{+}$ transition in ${\mathrm{Zr}}^{90}$, with the aid of a "fast-slow" coincidence spectrometer which permitted two-dimensional pulse-height analysis, and which was modified to suppress higher-order accidental coincidences and to accumulate prompt and delayed coincidences sumultaneously. Coincident $\gamma$ rays were observed; however, neither the energy spectra nor the angular correlation corresponds to two-photon decay. Analysis of the observed spectrum yields an upper limit to the probability of double-photon decay of $\frac{W_{\gamma \gamma }}{(W_{\mathrm{pair}}+W_e)}\le 1.2\times {10}^{-4\mathrm{}}$. The significance of the negative result is discussed in this paper, while the process that accounts for the observed twofold coincidence spectrum is the subject of the following two articles.

The continuous coincidence $\gamma$-ray spectrum discovered in the process of searching for two-photon decay in ${\mathrm{Zr}}^{90}$ is found to be double inner bremsstrahlung originating in the 2.26-MeV $\beta$ decay of ${\mathrm{Y}}^{90}$ to the ${\mathrm{Zr}}^{90}$ ground state. The angular correlation, energy dependence, and total transition intensity of the coincidence spectra are compared with recent theoretical calculations.

Two Feynman diagrams for double internal bremsstrahlung are evaluated for an allowed $\beta$ decay. The nucleons are treated nonrelativistically, and Coulomb effects are not considered.

Independent yields of ${}_{}{}^{112}{}_{}{}^{}\mathrm{Ag}$, ${}_{}{}^{134}{}_{}{}^{}\mathrm{I}$, and ${}_{}{}^{138}{}_{}{}^{}\mathrm{Cs}$ from the spontaneous fission of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ have been measured. These nuclides were separated from metal foils which were used as collectors for fission fragments recoiling from a one-microgram ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ source and purified radiochemically. Independent yields were calculated from a knowledge of the activities of the nuclides as a function of separation time. The yields, expressed as fractional independent yields are 0.009±0.004, 0.26±0.03, and 0.11±0.03, for ${}_{}{}^{112}{}_{}{}^{}\mathrm{Ag}$, ${}_{}{}^{134}{}_{}{}^{}\mathrm{I}$, and ${}_{}{}^{139}{}_{}{}^{}\mathrm{Cs}$, respectively. Corresponding values of $Z_p$ are 45.18, 52.14, and 53.82. These values differ from unchanged charge distribution by ∼0.45 charge units in agreement with previously measured fractional cumulative yields from ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ fission.

The level scheme of the ${}_{58}{}^{}{}_{}{}^{}\mathrm{Ce}_{83}^{141}{}_{}{}^{}$ nucleus was studied by observing the $\gamma$ rays from the ${\mathrm{Ce}}^{140}(n_{\mathrm{th}}, \gamma )$ reaction at the Brookhaven high flux beam reactor. $\gamma$-ray singles and coincidence spectra were obtained with a 20-${\mathrm{cm}}^3$ Ge(Li) detector and a Ge(Li)-Ge(Li) detector combination. Thirty-two $\gamma$ rays were assigned to ${\mathrm{Ce}}^{141}$ and all but three of these $\gamma$ rays were included in the ${\mathrm{Ce}}^{141}$ level scheme. We have identified nine of these transitions as primary transitions from the neutron capture state to low-lying levels in ${\mathrm{Ce}}^{141}$. These primary transitions have the following energies (in keV) and relative intensities [I(662) = 100]; 4766.6±0.5(48.0), 4291.4±0.6(22.1), 3619.7±0.6(4.0), 3435.0±0.6(2.0), 3239.0±1.5(2.7), 3092.5±0.5(2.8), 3017.1±0.7(4.7), 3003.3±0.6(3.9), and 2905.9±0.5(3.0). Our data, together with the information available from earlier charged particle reaction and radioactive decay studies, establish levels in ${\mathrm{Ce}}^{141}$ with energies 662.0±0.1, 1137.0±0.3, 1497.3±0.4, 1808.7±0.5, 1994.0±0.6, 2189.6±0.5, 2336.3±1.0, 2410.8±0.6, 2425.6±0.8, and 2522.9±0.6 keV. The measured neutron separation energy is 5428.6±0.6 keV. All of these levels may be identified with levels observed earlier with lower accuracy in the ${\mathrm{Ce}}^{140}(d, p){\mathrm{Ce}}^{141}$ reaction. As in the neighboring $N=83\mathrm{}$ nuclei ${\mathrm{Ba}}^{139}$ and ${\mathrm{Nd}}^{143}$, there appears to be a correlation between the strengths of excitation of the $p_{\frac{3}{2}}$ and $p_{\frac{1}{2}}$ levels in the ($n, \gamma$) and ($d, p$) reactions. The 1808.7-keV state, shown here to have $\frac{3}{2}$— spin and parity and not $\frac{5}{2}$— as previously believed, exhibits properties typical of a core excitation state formed from the coupling of an $f_{\frac{7}{2}}$ neutron to the first excited 2+ state of the semimagic ${\mathrm{Ce}}^{140}$ core. In particular, an $E2\mathrm{}$ transition proceeds from this state to the $\frac{7}{2}$— ground state in competition with $M1\mathrm{}$ transitions to the $\frac{3}{2}$— and ½— first and second excited states. Accordingly, a calculation of the properties of the low-lying excited states in ${\mathrm{Ce}}^{141}$ was carried out on the basis of the weak-coupling model. The results obtained are in reasonable agreement with the measured properties of the levels of ${\mathrm{Ce}}^{141}$. In particular, it is shown that the measured branching ratios of the transitions from the 1497.3- and 1808.7-keV levels are correctly predicted by this model. The level scheme of ${\mathrm{Ce}}^{141}$ is compared with the level schemes of the other even-$Z$, $N=83\mathrm{}$ nuclei.

Measurements of the $\gamma$ spectra, time distributions, angular distributions, and excitation functions of $\gamma$ rays from ($\alpha , 2n$) and ($\alpha , 4n$) reactions producing the vibrators ${}_{}{}^{114-126}{}_{}{}^{}\mathrm{Te}$ reveal that the most prominent $\gamma$ rays are in $8^{+}$→$6^{+}$→$4^{+}$→$2^{+}$→$0^{+}$ cascades. The energies and intensities exhibit remarkably regular systematics.

The $\gamma -\gamma$, $e_K-\gamma$, and $\gamma -e_K$ directional correlations have been measured for the 276-161-keV cascade in ${\mathrm{Cs}}^{133}$. The $\gamma -\gamma$ correlation was measured using two NaI(Tl) detectors, and also using NaI(Tl) to detect the 161-keV $\gamma$-ray and a cylindrical Ge(Li) to detect the 276-keV $\gamma$ ray. The results of the measurements are $A_2(\gamma -\gamma )=-0.450\mathrm{}\pm 0.011$, $A_4(\gamma -\gamma )=-0.014\mathrm{}\pm 0.012$, for the first method, and $A_2(\gamma -\gamma )=-0.432\mathrm{}\pm 0.022$, $A_4(\gamma -\gamma )=-0.038\mathrm{}\pm 0.025$ for the second. The directional correlations involving conversion electrons were made using a surface-barrier detector and a NaI(Tl) detector. The results of these measurements are $A_2(e_K-\gamma )=-0.740\mathrm{}\pm 0.047$, $A_4(e_K-\gamma )=0.047\mathrm{}\pm 0.042$, $A_2(\gamma -e_K)=-0.244\mathrm{}\pm 0.023$, and $A_4(\gamma -e_K)=0.071\mathrm{}\pm 0.038$. In addition, the $\frac{K}{(L+M+\cdots )}$ ratio of the 161-keV transition has been measured with the result $\frac{K}{(L+M+\cdots )}=4.0\mathrm{}\pm 0.3$. The $\gamma -\gamma$ directional correlation agrees quite well with other measurements which are consistent with a spin sequence of ${\frac{1}{2}}^{+}-{\frac{5}{2}}^{+}-{\frac{7}{2}}^{+}$. The $e_K-\gamma$ directional correlation is also in agreement with this spin sequence. The $\gamma -e_K$ directional correlation is consistent with the $\gamma -\gamma$ and $e_K-\gamma$ measurements only if we use a theory which includes nuclear structure effects. The combination of $A_2(\gamma -e_K)$ and $\frac{K}{(L+K+\cdots )}$, when compared with nuclear-structure-dependent particle parameters and conversion coefficients, gives the most probable value of the ratio of the penetration matrix element to the normal $\gamma$-ray matrix element, $\lambda =40\mathrm{}\pm 15$, for the 161-keV transition.

The deexcitation of the $h_{\frac{11}{2}}$ isomeric 164-keV level in ${\mathrm{Xe}}^{131m}$ has been reinvestigated for the possible simultaneous emission of two $K$-conversion electrons. The double-decay process was searched for by observing the x-ray coincidence spectrum with Ge(Li)-NaI(Tl) and Ge(Li)-Si(Li) coincidence spectrometers. Although the characteristic x ray of xenon was actually observed in the coincidence spectrum, it was found that this was not primarily due to the simultaneous emission of two $K$ electrons. Our experiment places an upper limit on the possible occurrence of double $K$-electron emission per single-photon decay: $\frac{W_{e_K{e}_K}}{W_{\gamma }}<1.4\mathrm{}\times {10}^{-3\mathrm{}}$. From the observed photon spectrum in coincidence with $K$ x rays, an upper limit of 2×${10}^{-2\mathrm{}}$ is obtained for the probability of $e_K-\gamma$ transitions per single-photon decay.

Thirty-six excited states of ${}_{}{}^{136}{}_{}{}^{}\mathrm{Xe}$ at excitation energies up to 6.3 MeV have been observed in proton inelastic-scattering excitation-function measurements at proton energies from 9.77 to 12.89 MeV. The $2^{+}$ first excited state at 1.30 MeV and the second excited state at 1.68 MeV resonate strongly at all of the lowest isobaric analog resonances, indicative of a collective nature for these states. Excitation functions for many of the remaining states exhibit resonant behavior characteristic of neutron-particle-neutron-hole excited states. Proton inelastic angular distributions have been measured at the lowest five analog resonances. Angular distributions for the particle-hole states at the first ($f_{\frac{7}{2}}$), second ($p_{\frac{3}{2}}$), and fourth ($f_{\frac{5}{2}}$) analog resonances have been fitted to determine the hole structure of the particle-hole configurations. Using the results of this analysis in conjunction with the resonant behavior of the corresponding inelastic excitation functions, it has been possible to determine particle-hole configurations and spin assignments for a number of excited states of ${}_{}{}^{135}{}_{}{}^{}\mathrm{Xe}$.