Carbon widths have been determined for resonances found in the total reaction cross section of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ reaction. A comparison of reduced carbon widths and single particle widths shows that a few resonance states in the energy range 7-12 MeV (c.m.) are possible candidates for a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ nuclear molecule.

NUCLEAR STRUCTURE $A=24\mathrm{}$ system; calculated carbon widths ${\Gamma }_{\mathrm{C}}$ for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ resonances.

The neutron total cross section of ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$ + n was measured from 0.2 to 1400 keV and the data were analyzed to obtain resonance parameters. Two $s$-wave resonances corresponding to ${\mathrm{½}}^{+}$ states in ${}_{}{}^{31}{}_{}{}^{}\mathrm{Si}$ predicted from shell model calculations were found. Contrary to earlier (d,p) measurements, the present measurement indicates a fairly uniform fragmentation of $p$-wave strength, in agreement with earlier weak coupling shell model calculations of negative parity states for ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$.

NUCLEAR REACTIONS ${}_{}{}^{30}{}_{}{}^{}\mathrm{Si}$(n,n), deduced $E_0$, ${\Gamma }_{\mathrm{n}}$, strength functions, level densities.

NUCLEAR STRUCTURE ${}_{}{}^{31}{}_{}{}^{}\mathrm{Si}$, shell model calculations, MSDI.

In order to study the gross effects of particle collisions, we formulate a model to include particle collisions in the time-dependent mean-field theory. The model consists of the time-dependent Hartree-Fock equation for the single-particle states and a linearized but truncated equation for the occupation numbers, with the $H$-theorem and the conservation laws properly satisfied. Numerical calculations are performed with a "conventional" set of basis states in which the occupied and the unoccupied static Hartree-Fock states are boosted in the same way. They are carried out for the head-on collisions of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ on ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ at 100 MeV per nucleon. It is found that the dynamics of the reaction is affected in only a minor way when particle collisions are included. The projectile and the target nuclear matter appear to interpenetrate each other, with only a 20% reduction in the center-of-mass kinetic energies, just as in mean-field calculations with no particle collisions. This result reinforces the idea that the conventional basis states do not include some important degrees of freedom. It is suggested that in future work one should modify the basis in order to allow for ample wave propagation in the direction normal to the collision axis.

NUCLEAR REACTIONS Extended time-dependent Hartree-Fock theory. Particle collision models. Numerical calculations for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ at $E_{\mathrm{lab}}=100\mathrm{}$ MeV per nucleon.

The neutron emission from fusionlike reactions leading to evaporation residues and fission fragments was measured in the reaction ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}$ + ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ at 220, 292, and 402 MeV ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ bombarding energies. Preequilibrium high-energy neutrons having up to twice the beam velocity were observed. The multiplicity of these neutrons increases with the bombarding energy from 0.4 to 2.3. This corresponds to 5 to 15% of the total number of neutrons emitted per fusionlike event. The measured energy spectra of the highly energetic neutrons cannot be described with the Fermi-jet mechanism (one body promptly emitted particles), especially at angles larger than 35°. Reasonable agreement with the modified Harp-Miller-Berne model can be obtained. In that case, however, it is necessary to treat the initial degree of freedom as a parameter which increases with bombarding energy from 20 to 28. The evaporative component in the energy spectra of fusion-fission events was used to deduce that the number of prefission neutrons is 5.6±0.5, 5.8±0.5, and 5.3±1.0 at bombarding energies of 220, 292, and 402 MeV, respectively, whereas the statistical model predicts a maximum number of 1.6 to 2.0 prefission neutrons. Although no conclusive explanation can be given for the unexpectedly large multiple chance fission probability, it is suggested that most of the additional prefission neutrons are emitted during the transition from saddle to scission.

NUCLEAR REACTIONS ${}_{}{}^{165}{}_{}{}^{}\mathrm{Ho}+{}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}\to A+n$, $E_{\mathrm{l}\mathrm{a}\mathrm{b}-\mathrm{N}\mathrm{e}}=220, 292, \mathrm{and} 402$ MeV; $A=\mathrm{e}\mathrm{v}\mathrm{a}\mathrm{p}\mathrm{o}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{i}\mathrm{d}\mathrm{u}\mathrm{e}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{f}\mathrm{u}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}-\mathrm{f}\mathrm{i}\mathrm{s}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{f}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{m}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{s}$; measured $\sigma (E_A, {\theta }_A, E_n, {\theta }_n)$ for $7.5°\le {\theta }_n\le 160°$, $6.5\le {\theta }_A\le 60°$; deduced neutron multiplicities and energy spectra; prefission neutron multiplicities and temperatures.

Trajectory calculations have been performed with an improved model to derive information on the scission-point configuration for ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$(sf). The technique used permits a full and uniform coverage of the phase space of the three particles without any a priori assumptions on the shape of the initial probability distribution. Results are presented for the equatorial as well as the polar emission of alpha particles. It is observed that the effects due to approximations in the point-charge model are significant in the determination of the scissionpoint configuration.

NUCLEAR REACTIONS Long-range alpha fission ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$, trajectory calculations, scission configuration.

Proton-induced fission ($E_{\mathrm{p}}=190\mathrm{}$ MeV) has been studied for uranium and selected nuclei, $140\lesssim A\lesssim 200$. Analysis of coincident-fragment energies suggests highly asymmetric fission near $A=140\mathrm{}$, even in the presence of relatively high fission barriers. The data have been compared with statistical-model fission calculations modified to include precompound nucleon emission. The data can be reproduced using standard fission-barrier and level-density parameters.

NUCLEAR REACTIONS Fission, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$, ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Ce}(\mathrm{p}, f)$. $E=190\mathrm{}$ MeV; measured ${\sigma }_f$ (90°), angular correlations, coincident fragment energies. Deduced mass division, total kinetic energy release, fission cross sections; compared with statistical-model fission calculations.

Nucleon charge exchange reactions are explored as prospective probes of isovector giant monopole resonances. Using charge exchange transition densities based on random-phase approximation sum rules, distorted wave impulse approximation calculations are made for the (p,n) and (n,p) reactions exciting the isovector giant monopole resonances in several nuclei at bombarding energies of 120 and 800 MeV. Based on our calculations, the charge exchange reactions at 800 MeV appear more promising.

NUCLEAR STRUCTURE, NUCLEAR REACTIONS Estimates of nucleon charge exchange cross sections for isovector monopole resonances.

The differential cross section for the reactions $\gamma \mathrm{d}\to \mathrm{pn}$, $\gamma d\to {\pi }^0\mathrm{d}$, and $\gamma \mathrm{d}\to \mathrm{p}X$ has been measured by using a tagged photon beam in the energy range of dibaryon resonances. The most characteristic feature of the data for $\gamma \mathrm{d}\to \mathrm{pn}$ is a forward nonpeaking angular distribution. This behavior is in complete disagreement with the existing predictions which take into account the dibaryon resonances. A phenomenological analysis is made by slightly modifying the model of the Tokyo group, but no satisfactory result is obtained. The data for $\gamma \mathrm{d}\to {\pi }^0\mathrm{d}$ at large angles show that the differential cross section decreases exponentially as a function of pion angle. A comparison is made with a Glauber model calculation. The result seems to be rather in favor of the existence of dibaryon resonances, but a clear conclusion is not possible because of a lack of more accurate data. In the process $\gamma \mathrm{d}\to \mathrm{p}X$, a broad peak due to quasifree pion production is observed, but the limitation of experimental sensitivity does not allow us to have a definite conclusion for the dibaryon resonance of mass 2.23 GeV conjectured by the Saclay group.

NUCLEAR REACTIONS ${}_{}{}^2{}_{}{}^{}\mathrm{H}(\gamma , \mathrm{p})$, ($\gamma , {\pi }^0$), $(\gamma , \mathrm{p})X$, $E=180-600\mathrm{}$ MeV; measured $\sigma (E, \theta )$; tagged photons. Dibaryon resonance effect.

The ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${\mathrm{}(\mathrm{p},\mathrm{p}\mathrm{p})\mathrm{}}^2$H and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${\mathrm{}(\mathrm{p},\mathrm{p}\mathrm{p})\mathrm{}}^2$${\mathrm{H}}^{*}$ reactions were investigated in a kinematically complete experiment at $E_{\mathrm{p}}=136\mathrm{}$ MeV for three angle pairs. The cross sections as a function of relative n-p energy were analyzed and compared to plane-wave impulse approximation predictions using one-boson exchange and Reid soft-core potentials to obtain detailed information about the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ wave function. No clear preference was established for one potential over the other, but limits were established on the mixed symmetry component of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ wave function.

NUCLEAR REACTIONS ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${\mathrm{}(\mathrm{p},\mathrm{p}\mathrm{p})\mathrm{}}^2$H, ${}_{}{}^3{}_{}{}^{}\mathrm{He}$${\mathrm{}(\mathrm{p},\mathrm{p}\mathrm{p})\mathrm{}}^2$${\mathrm{H}}^{*}$, $E_p=136\mathrm{}$ MeV, measured $\sigma (E_1, E_2, {\theta }_1, {\theta }_2)$; PWIA OBE and RCS analysis, d/pn ratio.

We have analyzed recent 0.8 GeV proton inelastic scattering cross sections for eight low-lying states in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ using the distorted wave impulse approximation and transition densities from a large basis shell model calculation. The shell model basis consists of the configurations of 12 valence protons in the $2p_{\frac{1}{2}}$, $2p_{\frac{3}{2}}$, $1f_{\frac{5}{2}}$, and $1g_{\frac{9}{2}}$ orbits. In general the shapes of the cross sections are well reproduced, but the calculated transition amplitudes must be multiplied by factors of 2.2 to 4.6 to fit the magnitudes. These enhancement factors are larger than those required for the $B\left(E\lambda \right)$ values derived from electron scattering, indicating large neutron components in these states. We argue that transitions to the $3_1^{-}$ and $2_3^{+}$ states cannot be described adequately in the chosen shell model basis. From the proton and electromagnetic enhancement factors we are able to obtain estimates of the missing "core" neutron and proton matrix elements.

NUCLEAR REACTIONS ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$(p,p′) at 0.8 GeV, analyzed with DWIA and shell model theory. $B\left(E\lambda \right)$ values calculated. Neutron and proton core matrix elements deduced.

Proton spectra of ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}({\pi }^{\pm }, \mathrm{p})$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}({\pi }^{\pm }, \mathrm{p})$ have been measured at ${\theta }_{\mathrm{p}}=20\mathrm{}°$ for $T_{\pi }=50, 100, 150, 200, \mathrm{and}, 250$ MeV, and at ${\theta }_{\mathrm{p}}=20\mathrm{}° \mathrm{and} 40°$ for $T_{\pi }=295\mathrm{}$ MeV. A small contributor to these spectra is the exclusive pion absorption reaction for which the cross section of ${}_{}{}^4{}_{}{}^{}\mathrm{He}({\pi }^{+}, \mathrm{p}){}_{}{}^3{}_{}{}^{}\mathrm{He}$ is reported. Major contributions are identified to come from quasifree $\pi \mathrm{N}\to \pi \mathrm{p}$ scattering and $\pi \mathrm{NN}\to \mathrm{Np}$ absorption for which cross sections are also reported. The quasifree cross sections are compared with those of the free reactions $\pi \mathrm{N}\to \pi \mathrm{p}$ and $\pi \mathrm{d}\to \mathrm{pp}$. We use these results to assess the contribution of quasifree reactions to the total reaction cross section. The comparison of the quasifree $\pi \mathrm{NN}\to \mathrm{Np}$ reaction relative to $\pi \mathrm{d}\to \mathrm{pp}$ is discussed in terms of differences in the attenuation and the dynamics of the reactions. This information is of interest for the phenomenological interpretation of complex reactions such as the two-nucleon absorption model of ${}_{}{}^3{}_{}{}^{}\mathrm{He}({\pi }^{-}, \mathrm{n}){}_{}{}^2{}_{}{}^{}\mathrm{H}$, ${}_{}{}^4{}_{}{}^{}\mathrm{He}({\pi }^{-}, \mathrm{n}){}_{}{}^3{}_{}{}^{}\mathrm{H}$, and ${}_{}{}^4{}_{}{}^{}\mathrm{He}({\pi }^{+}, \mathrm{p}){}_{}{}^3{}_{}{}^{}\mathrm{He}$ in which $\pi \mathrm{d}\to \mathrm{pp}$ is assumed to be an elementary process. This experiment also provides information on the cross section of ${\pi }^{-}\mathrm{pp}\to \mathrm{pn}$ from which we determine the dependence of pion absorption on the isospin of the initial NN state.

NUCLEAR REACTIONS ${}_{}{}^{3,4}{}_{}{}^{}\mathrm{He}({\pi }^{\pm }, \mathrm{p})$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}({\pi }^{\pm }, \mathrm{p})$ $E=50-295\mathrm{}$ MeV; measured $\sigma (E; E_{\mathrm{p}})$; $\theta =20, 40°$.

The leading contribution of threshold double-pion production to inelastic electron scattering from nuclei through a given angle and with a given energy loss is calculated in a Fermi gas model of the nuclear spectrum. The isobar model characterized by the threshold creation of a $\pi -\Delta$ pair constitutes the one-body input with the contact term providing the dominant contribution. The cross sections are found to have an ${\eta }^5$ dependence near threshold, where $\eta =\frac{({\epsilon }_1-{\epsilon }_2-2\mathrm{}{m}_{\pi })}{m_{\pi }}$ for initial and final electron energies, ${\epsilon }_1$ and ${\epsilon }_2$. The technique utilized of Fermi averaging near threshold is shown to reproduce the threshold behaviors of the various components of the analogous incoherent electroproduction cross section found earlier by Czyz and Walecka.

NUCLEAR REACTIONS Threshold double-pion electroproduction cross section $\frac{d^2\sigma }{d{\Omega }_{e^{\prime }}d{\epsilon }_{e^{\prime }}}$ calculated, Fermi gas model of nucleus, $\pi -\Delta$ production mechanism.

A systematic study of inclusive pion scattering from targets of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ has been performed at incident ${\pi }^{+}$ kinetic energies of $T_{{\pi }^{+}}=100, 160, 220, \mathrm{and} 300$ MeV. Particular attention was paid to the kinematic region where energy losses were greater than typical single-particle binding energies. The spectra of scattered pions were integrated to yield angular distributions and total inelastic-scattering cross sections. The spectra for all targets are similar, showing a peak near that expected for a single-step quasifree scattering process.

NUCLEAR REACTIONS ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, (${\pi }^{+}, {{\pi }^{+}}^{\prime }$), $T_{{\pi }^{+}}=100, 160, 220, 300$ MeV; measured $\frac{d^2\sigma }{d{\Omega }_{{{\pi }^{+}}^{\prime }}d{E}_{{{\pi }^{+}}^{\prime }}}$.

The inner bremsstrahlung spectrum accompanying first forbidden beta decay in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$-${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$ has been measured in the energy region from 80 to 600 keV with a 4.5×5.1 cm NaI(Tl) scintillation spectrometer. The magnetic deflection technique was employed in conjunction with a good geometry setup. After making all the corrections, viz., background, energy resolution, Compton electron distribution, detection efficiency (including geometry factor), and can absorption, the measured pulse height distribution is compared with (1) the allowed theory of Knipp and Uhlenbeck and Bloch, (2) the Coulomb-corrected theory of Lewis and Ford, and (3) the detour theory of Ford and Martin summing the contributions from ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$ in the investigated energy region. The measured pulse height distribution was found not to show agreement with any one of the theories. However, limited proximity exists between the measurements and different theories at different energy ranges.

RADIOACTIVITY $\beta$ decay, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Sr}$-${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$, measured IB, magnetic deflection, NaI(Tl).

In a continuing effort to explore electron-capture decay properties of ${}_{}{}^{163}{}_{}{}^{}\mathrm{Ho}$ as a means of measuring the mass of the neutrino, we measured a half-life of 4570±50 yr (95% confidence level) for ${}_{}{}^{163}{}_{}{}^{}\mathrm{Ho}$ using isotope-dilution mass spectrometry. From this value of the half-life we infer an electron-capture $Q$ value of approximately 2.65 keV using known atomic physics factors and an estimate of the nuclear matrix element based on the systematics of electron-capture $\mathrm{ft}$ values of other Ho isotopes.

RADIOACTIVITY ${}_{}{}^{163}{}_{}{}^{}\mathrm{Ho}$, electron capture decay, measured $T_{\frac{1}{2}}$, deduced $Q$ value.

We calculate the simulation of $T$-violating correlations induced by final state electromagnetic interactions in nuclear beta decay.

RADIOACTIVITY Nuclear beta decay, calculated final state Coulomb simulation of $T$ violation.

The asymmetry parameter, $A_{\beta }$, in the positron decay of polarized ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$ has been measured to be +0.341±0.013. Assuming the standard $T$-invariant $V-A$ weak interaction theory, the Fermi to Gamow-Teller mixing ratio, $y=\frac{C_V{M}_{\mathrm{F}}}{C_A{M}_{\mathrm{GT}}}$, was determined to be -0.005±0.008. The vanishing value of $y$ is consistent with the isospin selection rule for the Fermi matrix element.

RADIOACTIVITY ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$; measured $\beta \left(\theta \right)$, $\gamma \left(\theta \right)$; deduced source $P$, $\beta$ asymmetry coefficient, Fermi to Gamow-Teller mixing ratio.

Gamma-gamma angular correlations for several cascades in ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ were measured using a four-detector system. In a recent publication the level at 1219 keV was assigned $2_2^{+}$ in contradiction to a previous assignment of $4_1^{+}$. This makes ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ completely different from any known nucleus in the same region. It is shown, however, that this level is, in fact, completely consistent with $4^{+}$ and is in agreement with systematics.

RADIOACTIVITY ${}_{}{}^{142}{}_{}{}^{}\mathrm{La}$ [from ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}(\mathrm{n}, f)$)]; measured $\gamma -\gamma \left(\theta \right)$; deduced $J^{\pi }$, $\delta$; mass-separated ${}_{}{}^{142}{}_{}{}^{}\mathrm{La}$ activity; Ge detectors.

Fluctuations of the nuclear surface about the Hartree-Fock configuration can have a significant influence on ground state charge densities. We present simple formulas to describe the effects of zero-point motions of the surface due to random phase approximation vibrations. We use a collective treatment, justifying it with a solvable model. We find that the main correction to the densities comes from low-lying collective states, whereas giant resonances are of minor importance.

NUCLEAR STRUCTURE Charge density in the correlated ground state obtained from Hartree-Fock theory and the RPA response.

The experimental strengths extracted from several one neutron pickup and stripping reactions on the Pt isotopes are compared to predictions derived in the framework of the multi-$j$ supersymmetry model. It appears that the model describes quite reasonably the experimental results for the reactions involving ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$. However, due to a clear change of structure between ${}_{}{}^{195}{}_{}{}^{}\mathrm{Pt}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Pt}$, an appreciable breaking is observed for the reactions involving ${}_{}{}^{197}{}_{}{}^{}\mathrm{Pt}$.

NUCLEAR STRUCTURE ${}_{}{}^{194,195,196,197,198}{}_{}{}^{}\mathrm{Pt}$. Multi-$j$ supersymmetry model; calculation of $S$ for one nucleon transfer reactions; comparison with experimental results.