A systematic study of the decay properties of ${}^{164}$Yb compound nuclei with excitation energies of 100–300 MeV was performed. The emission patterns of light charged particles detected in coincidence with evaporation residues produced in ${}^{64}$Ni+${}^{100}$Mo and ${}^{16}$O+${}^{148}$Sm reactions have been measured and compared to statistical model predictions. There is found to be significant disagreement between the experiment and the model calculations in the magnitude of the multiplicities and the peak position in the energy spectra. For deuterons and tritons, significant nonstatistical components were present at all excitation energies. The proton energy spectrum did not exhibit any entrance-channel dependence at an excitation energy of $\sim 170$ MeV. However for $\alpha$ particles, there is an enhancement in the spectrum at the lowest kinetic energies for the more symmetric reaction. It is suggested that the emission and subsequent decay of ${}^5$He fragments, can account for a large fraction of the apparent, and often reported, decrease in the Coulomb barrier for $\alpha$ particle emission.

Fragment velocity, kinetic energy, mass yield, and element yield distributions in the fission of neutron-deficient Pa isotopes produced in the reactions of ${}^{16}$O and ${}^{18}$O on ${}^{209}$Bi have been measured at incident beam energies near and above the Coulomb barriers by the time-of-flight and radiochemical methods. An asymmetric mass-division component has been observed. Measured fission cross sections were compared with the results of statistical model calculations which take into account two fission barrier heights for symmetric and asymmetric yields. The fission barrier height deduced for the asymmetric fission is found slightly lower than that for the symmetric one. The difference between the two barrier heights in the fission of the present protactinium nuclides $\left(N\sim 135\right)$ is considerably smaller than that in the neutron-rich nuclide of ${}^{233}$Pa $\left(N\sim 142\right)$, indicating that the difference sensitively depends on the neutron number of the fissioning nuclide.

Quasielastic $\mathrm{}(p,n)\mathrm{}$ reactions on $\mathrm{sd}$- and $f$-shell nuclei were studied at an incident proton energy of 35 MeV. Differential cross sections for isobaric analog $\Delta J^{\pi }{=0\mathrm{}}^{+}$ (Fermi-type) transitions and their angular distributions were measured in 13 $N>Z$ target nuclei ranging $17<~A<~48,$ ${}^{17,18}\mathrm{O},$ ${}^{22}\mathrm{Ne},$ ${}^{25,26}\mathrm{Mg},$ ${}^{27}\mathrm{Al},$ ${}^{30}\mathrm{Si},$ ${}^{34}\mathrm{S},$ ${}^{38,40}\mathrm{Ar},$ and ${}^{42,44,48}\mathrm{Ca}.$ Pure $\Delta J^{\pi }{=0\mathrm{}}^{+}$ Fermi-type transitions were observed in six of them. As for the other seven nuclei, contributions from mixed $\Delta J^{\pi }\ne 0^{+}$ components or those from unresolved transitions were evaluated by microscopic distorted-wave Born approximation (DWBA) calculations to subtract them from the raw data and extract pure Fermi-type transition strengths. Thus a total of 13 $\Delta J^{\pi }{=0\mathrm{}}^{+}$ angular distributions was fitted by macroscopic DWBA calculations with a Lane-model optical potential to derive systematically the isovector part of the potential. The best-fit parameters for each target are presented. $A$-dependent global parameters were obtained from these best-fit parameters by a least-squares fit.

Light-charged particles were measured in coincidence with evaporation residues for ${}^{12}$C+${}^{144}$Sm, ${}^{35}$Cl+${}^{121}$Sb, and ${}^{60}$Ni+${}^{96}$Zr reactions which populate the compound nucleus ${}^{156}$Er at the same excitation energy. The particle spectral shape for ${}^{12}$C+${}^{144}$Sm is harder than the other two reactions. A one-body dissipation model predicts that the fusion times for the ${}^{35}$Cl- and ${}^{60}$Ni-induced reactions are similar and are about twice as long as that of the ${}^{12}$C-induced reaction. Statistical model calculations considering particle evaporation during compound nucleus formation successfully reproduce the particle spectra for all the reactions.

The isomeric cross section ratio ${\sigma }_m/{\sigma }_g$ for the reaction ${}^{45}$Sc$\mathrm{}(n,2n)\mathrm{}$ ${}^{44}$Sc${}^{m,g}$ was measured in the neutron energy range of 13.6–14.9 MeV for six different neutron energies. The neutrons were produced by the ${}^3$H${\mathrm{}(d,n)\mathrm{}}^4$He reaction utilizing a SAMES T-400 neutron generator. Isomeric cross section ratios were determined by applying the method of least squares to the time behavior of the ground-state decay of isomeric pair. The absolute cross section for the formation of the metastable state was measured by the usual activation technique. The ground-state cross section was then obtained by using the absolute cross section of the metastable state and isomeric cross section ratio for each neutron energy. Experimental cross section values and isomeric cross section ratios were compared with those obtained by a statistical model calculation.

The absolute $\gamma$-ray yields from $\alpha$-particle-induced reactions on thick targets of Be, BN, NaF, Mg, Al, and Si for incident energies between 5.6 and 10 MeV are presented. The excitation distributions of several nuclei have been deduced from the experimental $\gamma$-ray yields and are compared to theoretical predictions based on a statistical model of nuclear reactions.

Multinucleon transfer reactions in ${}^{48}$Ca+${}^{124}$Sn have been studied at 174 MeV with a time-of-flight magnetic spectrometer. The pickup and stripping of several protons and neutrons have been observed. The experimental isotope yields for the $-2p$ and $+2p$ channels cannot be reproduced with calculations that incorporate only independent single-nucleon transfer modes. The discrepancies can be accounted for by explicitly including nucleon pair and $\alpha$-cluster degrees of freedom.

We point out that to any order of the hole line expansion simple graph theoretical arguments yield an upper bound on the number of hole lines contained in the diagrams. The derivation of this upper bound suggests a procedure which could be useful in the actual enumeration of the hole line expansion diagrams. The cases of the binding energy and of the mass operator are treated in sufficient detail to make obvious the extension of our results to other quantities.

The effects of the real potential on the absorption of lighter heavy ions are discussed. The effects are illustrated with “effective potentials” reproducing the elastic scattering phase shifts in the eikonal approximation.

A generalized version of density dependence has been introduced into the M3Y effective nucleon-nucleon $\mathrm{}\left(\mathrm{NN}\right)\mathrm{}$ interaction that was based on the $G$-matrix elements of the Paris $\mathrm{NN}$ potential. The density dependent parameters have been chosen to reproduce the saturation binding energy and density of normal nuclear matter within a Hartree-Fock scheme, but with various values for the corresponding nuclear incompressibility $K$ ranging from 176 to 270 MeV. We use these new density dependent interactions in the folding model to calculate the real parts of $\alpha$-nucleus and nucleus-nucleus optical potentials for those systems where strongly refractive scattering patterns have been observed. These provide some information on the potentials at short distances, where there is a strong overlap of the projectile and target density distributions, and hence where the density dependence of the interaction plays an important role. We try to infer, from careful optical model (OM) analyses, the sensitivity of the scattering data to different $K$ values. Results obtained for elastic $\alpha$ scattering on targets ranging from ${}^{12}$C to ${}^{208}$Pb allow us to determine unambiguously that the $K$ value favored in this approach is within the range of 240 to 270 MeV. Similar OM analyses have also been done on measurements of the elastic scattering of ${}^{12}$C+${}^{12}$C, ${}^{16}$O+${}^{12}$C, and ${}^{16}$O+${}^{16}$O at incident energies up to 94 MeV/nucleon. These data were found to be much less sensitive over such a narrow range of $K$ values. This lack of sensitivity is due mainly to the smaller maximum overlap density which occurs for these systems, compared to that which is formed in an $\alpha$-nucleus collision. This makes the effects of density dependence less substantial. Another reason is that a small difference between two folded heavy ion potentials can often be compensated for, in part, by a small overall renormalization of one of them. This renormalization is often allowed in optical model analyses, and interpreted, for example, as accounting for a contribution from a higher-order dynamic polarization potential. In an attempt to avoid this ambiguity, some OM analyses of the extensive and accurate data for ${}^{16}$O+${}^{16}$O scattering were done using the unrenormalized folded potentials, together with the explicit addition of a correction term, expressed in terms of cubic splines. This correction term can be interpreted as representing a contribution to the real potential from the dynamic polarization potential. The results of such a “folding+spline” analysis suggest a tendency to favor the same $K$ value range that was found in the OM analyses of $\alpha$-nucleus scattering.

We present a multistep direct reaction theory for analyzing nucleon-induced reactions to the continuum for incident energies up to 200 MeV. Two principal advances in multistep direct theory are studied. (1) A microscopical approach is given for calculating distorted-wave Born approximation (DWBA) transitions to the continuum, where transitions to all accessible 1$p$1$h$ shell model states are explicitly determined. These states, obtained from a simple noninteracting Nilsson model, are assumed to be spread according to Gaussian distributions. In this approach, therefore, state densities are not used. We also provide a link with more conventional methods that utilize particle-hole state densities, and present a more accurate technique for sampling the DWBA strength. (2) A two-component formulation of multistep direct reactions is given, where neutron and proton excitations are explicitly accounted for in the evolution of the reaction, for all orders of scattering. We show that the attractive convolution structure for multistep processes persists within a two-component formalism, and conveniently automatically generates the many reaction pathways that can occur in the Feshbach-Kerman-Koonin expansion of the multistep cross section when neutron and proton excitations are followed. This formalism is particularly important for the simultaneous analyses of neutron and proton emission spectra. The multistep direct theory is applied, along with theories for multistep compound, compound, and collective reactions, to analyze experimental emission spectra for a range of targets and energies. Particular attention is paid to a complete and comprehensive analysis of all important decay channels and reaction mechanisms. We show that the theory correctly accounts for measured neutron and proton emission angle-integrated spectra, as well as angular distributions. Additionally, we note that these microscopic and two-component developments facilitate more fundamental studies into effective nucleon-nucleon interactions in multistep calculations.

We investigate the properties of three methods of fragment recognition in microscopic simulations of molecular dynamics. They are (a) the early cluster recognition algorithm (ECRA) which looks for the most bound partitions in phase space, (b) the minimum spanning tree in two particle energy space (MSTE) which looks for those simply connected partitions in which each particle is bound to, at least, one other member of the cluster to which it belongs, and (c) the standard minimum spanning tree (MST) in configuration space. It is found that, if the objective of a given calculation is to study the time evolution of properties related to the fragment distribution, the MST should be discarded, MSTE results will be valid for not too short times, and ECRA results will give the most complete description of such properties.

Excited states in the $T_z=\frac{1}{2}$ nucleus ${}^{75}\mathrm{Rb}$ were observed for the first time using the ${}^{40}\mathrm{Ca}{(}^{40}\mathrm{Ca},\alpha p$) reaction at 128 MeV. Identification was achieved using events detected by the Daresbury recoil separator in coincidence with $\gamma$ rays detected in the 45 element EUROGAM I Ge-detector array. Threefold events were used to build a decay scheme which consists of two rotational bands observed to $I^{\pi }=\left({\frac{45}{2}}^{+}\right)$ and $I^{\pi }=\left({\frac{33}{2}}^{-}\right).\mathrm{}$ The positive parity band in ${}^{75}\mathrm{Rb}$ behaves similarly to a negative-parity band in ${}^{74}\mathrm{Kr}$ and contains a region of alignment at $ħ\omega \approx 0.75$ MeV. These data, and those of ${}^{77}\mathrm{Sr},$ can be interpreted by treating protons and neutrons separately in a cranked shell model approach despite a recent suggestion for the presence of $T=1\mathrm{}$ neutron-proton pairing correlations in the neighboring self-conjugate, odd-odd ${}^{74}\mathrm{Rb}$ ground state band. Our study suggests that some experimental observables such as the energy levels and moments of inertia, may not be able to differentiate between different $T=1\mathrm{}$ pairing phases in these $T_z=\frac{1}{2}$ nuclei.

The excitation function of positive pions produced at 90° by protons on Copper has been studied to get information on the long-standing problem of the existence of a narrow resonance near 350 MeV incident energy. Momentum spectra of ${\pi }^{+}$ were measured by the CLAMSUD magnetic spectrometer. A narrow resonance has been indeed observed, in agreement with previous results obtained in different laboratories during the past years.

The high-spin normally deformed and superdeformed states of ${}^{194}\mathrm{Hg}$ have been populated in an exit channel of the ${}^{16}{\mathrm{O}+}^{186}\mathrm{W}$ reaction at 110 MeV bombarding energy. The Doppler shift analysis of the energies of the γ transitions de-exciting both normally deformed and superdeformed states in ${}^{194}\mathrm{Hg}$ indicates a lower recoil velocity of the ${}^{194}\mathrm{Hg}$ nucleus compared to that of the ${}^{196}\mathrm{Pb}$ nucleus obtained from the $6n$ exit channel of the complete-fusion compound nucleus. This suggests that incomplete fusion plays the main role in the population of normally deformed and superdeformed states of ${}^{194}\mathrm{Hg}$ in this reaction.

The $E1\mathrm{}$ transitional rates between the double giant dipole resonance (DGDR) states and giant dipole resonance (GDR) ones are studied using the wave functions, which include one-, two-, and many-phonon components. It is shown that there is a possibility for the enhancement of the $E1\mathrm{}$ transition rates from the DGDR states to the GDR ones as compared to the harmonic limit. This enhancement arises from the matrix elements for the $E1\mathrm{}$ transitions between many-phonon terms of the wave functions, which differ by one $E1\mathrm{}$ phonon.

We investigate the origin of subthreshold $K^{+}$ production in heavy ion collisions at intermediate energies. In particular we study the influence of the pion induced $K^{+}$ creation processes. We find that this channel shows a strong dependence on the size of the system, i.e., the number of participating nucleons as well as on the incident energy of the reaction. In an energy region between 1 and 2 GeV/nucleon the pion induced processes essentially contribute to the total yield and can even become dominant in reactions with a large number of participating nucleons. Thus we are able to reproduce recent measurements of the KaoS Collaboration for 1 GeV/nucleon Au on Au reactions adopting a realistic momentum dependent nuclear mean field.

In heavy ion collisions resonances can create strong non-Gaussian effects in the two-pion correlation function. Hence, the commonly used Gaussian fit parameters do not fully characterize these correlators. We suggest a different set of HBT parameters which does not presuppose a particular shape of the correlator and allows one to extract additional information not contained in the Gaussian fit parameters. Within a simple model for an expanding source including resonance decays it is shown that this additional information provides a clean distinction between scenarios with and without transverse flow.

For a set of $N$ identical massive boson wave packets with optimal initial quantum mechanical localization, we calculate the Hanbury-Brown–Twiss (HBT) two-particle correlation function. Our result provides an algorithm for calculating one-particle spectra and two-particle correlations from an arbitrary phase space occupation $({\mathbf{q}}_i,{\mathbf{p}}_i{,t}_i{)}_{i=1,N}$ as, e.g., returned by event generators. It is a microscopic derivation of the result of the coherent state formalism, providing explicit finite multiplicity corrections. Both the one- and two-particle spectra depend explicitly on the initial wave packet width $\sigma$ which parametrizes the quantum mechanical wave packet localization. They provide upper and lower bounds which suggest that a realistic value for $\sigma$ has the order of the Compton wavelength.

The energies and intensities of 58 γ rays emitted in thermal-neutron capture by nitrogen (99.63% ${}^{14}\mathrm{N}$) have been measured accurately. A major reason was to establish this reaction as a standard for similar measurements on other nuclides. These γ rays have been placed between 19 known levels (including the ground state and the capturing state) in ${}^{15}\mathrm{N}.$ The primary γ rays of both electric dipole $\mathrm{}\left(E1\mathrm{}\right)\mathrm{}$ and magnetic dipole $\mathrm{}\left(M1\mathrm{}\right)\mathrm{}$ types have been analyzed with existing theories of slow-neutron capture. Unlike many other light nuclides, the cross sections for $E1\mathrm{}$ transitions in ${}^{15}\mathrm{N}$ differ drastically from the calculations of pure direct-capture theory. The role of the resonance-capture contribution from the proton-unbound, neutron-bound level at $29\pm 2\mathrm{keV}$ below the neutron separation energy was considered. Some of the properties of this level are quite well known from the ${}^{14}\mathrm{C}(p,\gamma )$ reaction, and others can be derived from an R-matrix analysis of the total cross section as a function of neutron energy. The thermal-neutron capture γ-ray spectrum is different from the proton-capture γ-ray spectrum, but if proper account is taken of the interference among the compound-nuclear processes, the valence-neutron mechanism, and potential capture, the data can be satisfactorily explained. In the thermal-neutron reaction, compound-nuclear $E1\mathrm{}$ and direct-capture $E1\mathrm{}$ contributions are of comparable magnitude. Valence-neutron capture forms a significant component of capture by the neutron-bound level at $-29\mathrm{keV}.$ Largely destructive interference between compound-nuclear and valence processes in a few transitions in thermal-neutron capture gives rise to a much smaller total cross section than would be obtained from the compound-nuclear process alone. The $M1\mathrm{}$ transitions also show some evidence of a direct process but not a dominant one. The magnitudes of the compound-nuclear transitions, both $E1\mathrm{}$ and $M1,$ are largely consistent with the values implied by giant resonance theories. The resonance parameters deduced for the $-29-\mathrm{keV}$ level are: total radiation $\mathrm{w}\mathrm{i}\mathrm{d}\mathrm{t}\mathrm{h}=565\mathrm{}\pm 24\mathrm{}\mathrm{meV},$ $\mathrm{reduced}\mathrm{}\mathrm{neutron}\mathrm{}\mathrm{w}\mathrm{i}\mathrm{d}\mathrm{t}\mathrm{h}=51.6\mathrm{}\pm 0.3\mathrm{}\mathrm{keV}$ (for a channel radius of 3.5 fm), and proton $\mathrm{w}\mathrm{i}\mathrm{d}\mathrm{t}\mathrm{h}=160\mathrm{}\pm 30\mathrm{}\mathrm{meV}.$