We present results of a long-term search for cluster (neon) decay and spontaneous fission of ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$ performed at Gran Sasso Underground Laboratory with nuclear track detectors. We found a lower limit for the partial half-life for ${}_{}{}^{24\mathrm{-}26}{}_{}{}^{}\mathrm{Ne}$ decay, ${\mathit{T}}_{1/2}$>1.57×${10}^{29}$ s and a partial half-life for spontaneous fission ${\mathit{T}}_{1/2}$=3.84×${10}^{28}$ s=1.22×${10}^{21}$ yr. These results are compared with the available theoretical predictions and the experimental systematics for cluster decay and spontaneous fission.

We have measured differential cross sections for the elastic scattering of charged pions from ${}_{}{}^3{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ into the backward hemisphere. Near the peak of the delta resonance, at ${\mathit{T}}_{\mathrm{\pi }}$=180 MeV, an angular distribution covering 114° to 168° in the laboratory extends our earlier measurements. At ${\mathit{T}}_{\mathrm{\pi }}$=142, 180, 220, and 256 MeV, we have measured an excitation function at angles approaching 170°. The cross sections for the reactions ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$${)}^3$He, ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{\mathrm{-}}$${)}^3$H show a rise at back angles which is not seen for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{\mathrm{-}}$${)}^3$He and ${}_{}{}^3{}_{}{}^{}\mathrm{H}$(${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{+}$${)}^3$H. There is a dip in the cross sections near 130° for ${\mathit{T}}_{\mathrm{\pi }}$=180 MeV.

Systematic measurements of ${\mathrm{\pi }}^{\mathrm{-}}$ elastic scattering on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ above the Δ-resonance region are reported. The differential cross sections were measured at 610, 710, 790, and 895 MeV/c over an angular range from 5° to 50°. The obtained data were compared with the first-order optical potential model. In the forward region, agreement with the calculation increases with the incident momentum. In the backward region, however, the calculation underestimates the data. The total cross section was extracted, and its energy dependence shows that the effect of Fermi averaging is important.

Measurements of the reaction ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(γ,n), made with tagged photons at ${\mathit{E}}_{\gamma }$∼58 MeV, are presented. Neutron energy determination was by time of flight, giving a resolution of ∼2 MeV which enabled the ground-state excitation in ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ to be resolved from states at 5.2 and 6.2 MeV. Differential cross sections were measured in the angular range 30°–110° and are compared with the predictions of a microscopic, self-consistent Hartree-Fock, random phase approximation model of (γ,N) reactions. The implications for the theoretical description are discussed, notably the dependence of the (γ,n) cross section on meson exchange currents and final-state rescattering.

The charge and mass of the projectilelike fragments produced in the 12-MeV/nucleon ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$${+}^{165}$Ho reaction were measured at a laboratory scattering angle of 16°. The mass and charge distributions of the projectilelike fragments were generated as a function of total kinetic energy loss (TKEL), and characterized by their neutron and proton centroids and variances, and correlation factors. A weak drift of the system towards mass asymmetry, opposite to the direction which minimizes the potential energy of the composite system, was observed. The increase in the variances with energy loss is consistent with a nucleon exchange mechanism as a means for energy dissipation. Predictions of two nucleon exchange models, Randrup’s and Tassan-Got’s models, are compared to the experimental results of the 672-MeV ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$${+}^{165}$Ho reaction and to other Fe-induced reactions. The proton and neutron centroids were found to be generally better reproduced by Tassan-Got’s model than by Randrup’s model. The variances and correlation factor are well reproduced for asymmetric systems by both models.

The vector analyzing power ${\mathit{iT}}_{11}$ and the composite observable ${\mathrm{\tau }}_{22}$=${\mathit{T}}_{22}$+${\mathit{T}}_{20}$/ √6 were measured at 10 incident pion energies between 100 and 294 MeV, in an angular range between 50° and 120°. Two different techniques were applied, the detection of the pion with a magnet spectrometer, and the πd coincidence method with scintillation counters. In the case of the first technique also two different target materials were used. Consistency among all data was obtained. The experimental data are compared to Faddeev calculations from one of us (H.G.). The discrepancies between theory and experiment are discussed, and an outlook for further research is given.

The population of evaporation residue entry states in the decay of the compound nucleus ${}_{}{}^{160}{}_{}{}^{}\mathrm{Er}_{}^{\mathrm{*}}{}_{}{}^{}$(54 MeV) is investigated in a cross-bombardment employing the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{144}$Nd and ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$${+}^{96}$Zr. Evaporation residue cross sections and entry state γ-ray fold distributions of the dominant exit channels were obtained for each reaction, using a 4π γ-ray detection system. An entrance-channel dependence of the γ-ray fold distributions of the xn products is observed. This effect is described successfully by the statistical model making use of compound nucleus angular momentum distributions obtained with a fusion model that provides a good description of the bombarding energy dependence of fusion data for both reactions. In accordance with recent findings on the decay of ${}_{}{}^{164}{}_{}{}^{}\mathrm{Yb}_{}^{\mathrm{*}}{}_{}{}^{}$, it is suggested that the observed differences in the population of the dominant exit channels originate from the primary spin distributions rather than a possible dependence of the compound nucleus decay on the formation mode.

The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,pn${)}^{12}$C reaction was studied at ${\mathit{E}}_{\mathit{p}}$=35 MeV with an experimental arrangement which favored detection of p-n pairs in the ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$ state. Measured cross section angular distributions were compared with those for the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$(p,d${)}^{12}$C reaction at the same incident energy. The two reactions show different angular distribution shapes, those for (p,pn) being more slowly decreasing at large angles. Coupled channel calculations which include continuum states of the p-n system reproduce angular distribution shapes and cross section magnitudes of both the (p,pn) and (p,d) data.

A rapid increase with energy has been observed in the emission of prescission giant dipole resonance (GDR) γ rays in excited Th and Cf nuclei formed in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{208}$Pb and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$${+}^{\mathrm{nat}}$W${,}^{208}$Pb reactions, which is not explained by the normal reaction dynamics near the barrier. This increase occurs over a narrow excitation energy range of ${\mathit{E}}_{\mathrm{exc}}$=40–60 MeV for the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{208}$Pb reaction and ${\mathit{E}}_{\mathrm{exc}}$=70–90 MeV for the ${}_{}{}^{32}{}_{}{}^{}\mathrm{induced}$ reactions. Below the transition energy the γ-ray spectra can be described by the standard statistical model, whereas inclusion of an increasingly strong nuclear dissipation is required to account for the data at higher excitation energies. For the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{208}$Pb reaction a fit to the GDR γ-ray spectra and evaporation residue cross sections is used to extact the temperature dependence of the linear dissipation parameter.

The breakup of ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ nuclei into ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$${+}^{12}$C and of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ nuclei into ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C has been studied using the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{23}$Na${,}^{11}$${\mathrm{B}}^{12}$C${)}^{12}$C and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{23}$Na${,}^{12}$${\mathrm{C}}^{12}$C${)}^{11}$B. Clear evidence was found for the breakup of the ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ and ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ nuclei into the ground states of both fragments. The yieldrotect from the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{23}$Na${,}^{11}$${\mathrm{B}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{12}$${\mathrm{C}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$${)}^{12}$${\mathrm{C}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ reaction was concentrated in the region of excitationrotect energy in ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ between 24 and 28 MeV and fragmented among a number of states. Therotect ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{23}$Na${,}^{12}$${\mathrm{C}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{\mathrm{g}.\mathrm{s}.)}^{11}{}_{}{}^{}$${\mathrm{B}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ reaction was found to proceed chiefly via broad states at 22.1 and 23.9 MeV in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$.

The ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,${\mathit{p}}_{0+1}$${)}^{11}$B differential cross section has been measured for tagged-photon energies of ${\mathit{E}}_{\gamma }$=44–98 MeV, at laboratory angles of 30°, 45°, 65°, and 90°. Comparison has been made with four different types of calculation. Results from similar calculations for the photoneutron channel have been compared to previously published ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(γ,${\mathit{n}}_{0+1}$${)}^{11}$C data.

We have recently developed a realistic model for studying cluster radioactivities from actinide nuclei. This model uses a cubic potential in the overlapping region connected by a Yukawa-plus-exponential potential in the post-scission region. In the present work we use this model to study ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ radioactivities in the region of nuclides with proton and neutron number in the range Z=56–64 and N=58–72, which has been recently identified by Poenaru et al. as a new island of such cluster emitters. It is found that charge equilibration is not needed in the study of these radioactivities and the half-lives obtained for these decays lie very close to those reported by Poenaru et al. using their analytical super asymmetric fission model.

Nuclei at the neutron-drip line are studied. The light neutron-halo nuclei are found to play an important role for both cold fusion reactions and exotic cluster decay studies of heavy nuclei at the neutron-drip line. For cold fusion reactions, beams of neutron-halo nuclei are shown to occur as natural extensions of the conventional lighter beams but with the corresponding target nuclei as the heavy neutron-rich radioactive nuclei. Thus, in synthesizing the various isotopes of a neutron-rich cool compound nucleus, both the target and projectile nuclei have to be richer in neutrons, with their proton numbers remaining the same. On the other hand, neutron-halo (cluster) decays are favored for a relatively less neutron-rich parent nucleus. Possible consequences of this work for the shell structure effects in neutron-rich heavy nuclei are also pointed out. This follows from the fact that the so far observed phenomena of both cold fusion and cluster radioactivity are associated with closed or nearly closed shell nuclei. Calculations are made for ${}_{}{}^{274,288}{}_{}{}^{}104$, using the quantum mechanical fragmentation theory for cold fusion reaction studies and a performed cluster model for cluster decay studies.

Statistical aspects of the dynamics of chaotic scattering in the classical model of α-cluster nuclei are studied. It is found that the dynamics governed by hyperbolic instabilities, characterized by the positive Lyapunov exponents and the fractal dimensions, which results in an exponential decay of the survival probability, evolves to a limiting energy distribution whose density develops the Boltzmann form. The angular distribution of the corresponding decay products shows symmetry with respect to the π/2 angle. The time estimated for the compound nucleus formation ranges within the order of ${10}^{\mathrm{-}21}$ s.

The evaporation residue cross sections ${\mathrm{\sigma }}_{\mathrm{ER}}$ in reactions between massive nuclei have been analyzed within different models of complete fusion. The calculations in the framework of the optical model, the surface friction model, and the macroscopic dynamic model can give the results which are by few orders of magnitude different from experimental data. This takes place due to neglect of the competition between complete fusion and quasifission. A possible mechanism of compound nucleus formation in heavy-ion-induced reactions has been suggested. The analysis of the complete fusion of nuclei on the basis of dinuclear system approach has allowed one to reveal an important feature of the fusion process of massive nuclei, that is, the appearance of the fusion barrier during dinuclear system evolution to a compound nucleus. As a result, the competition between complete fusion and quasifission arises and strongly reduces the cross section of the compound nucleus formation. A model is proposed for calculation of this competition in a massive symmetric dinuclear system. This model is applied for collision energies above the Coulomb barrier. The ${\mathrm{\sigma }}_{\mathrm{ER}}$ values calculated in the framework of dinuclear system approach seem to be close to the experimental data. For illustration the reactions ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$${+}^{100}$Mo, ${}_{}{}^{110}{}_{}{}^{}\mathrm{Pd}$${+}^{110}$Pd, and ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$${+}^{96}$Zr have been considered.

Medium modifications of the properties of bound nucleons and mesons are investigated by means of intermediate energy quasifree proton knockout reactions with polarized incident protons, by comparison of quantities which are insensitive against wave distortions. The sensitivity of the spin observables of the quasifree proton-proton cross section to modifications of the nucleon and meson properties is studied using the Bonn one-boson exchange model of the nucleon-nucleon interaction. A method proposed to extract the pp analyzing power in medium from the (p→,2p) asymmetries indicates a reduction of this quantity compared to its free space value. This reduction is linked to modifications of masses and coupling constants of the nucleons and mesons in the nucleus. The implications of these modifications for another spin observable to be measured in the future are discussed.

The possibility of observing heavy Ξ-hypernuclei by (${\mathit{K}}^{\mathrm{-}}$,${\mathit{K}}^{+}$) reactions is investigated. Several narrow peaks are clearly seen in the ${\mathit{K}}^{+}$ spectrum of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$(${\mathit{K}}^{\mathrm{-}}$,${\mathit{K}}^{+}$${)}_{\mathrm{\Xi }}^{\mathrm{-}208}$Hg reaction calculated by the Green’s function method. They correspond to ${\mathrm{\Xi }}^{\mathrm{-}}$ bound states with spin-stretched high angular momentum. The excitation of the ${\mathrm{\Xi }}^{\mathrm{-}}$ bound states amounts to about 0.4 μb/sr MeV for the ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target in the case of 2 MeV detector resolution, which is considerably larger than that for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ target. It is discussed whether or not the mass-number dependence of nucleus-Ξ potential depths is observed between A=12 and 208.

The longitudinal and transverse structure functions are calculated for inclusive electron scattering from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ in the quasielastic and dip region. The microscopic model presented here incorporates two-body currents derived from one-pion exchange and intermediate Δ excitation. The reaction mechanism involves both one-nucleon and two-nucleon knockout processes. It is demonstrated that, even for quasielastic kinematics, two-body currents give a substantial contribution to the transverse structure function. Furthermore, the observed excess of transverse strength in the dip region between the quasielastic and delta peak can be partially ascribed to direct two-nucleon knockout following photoabsorption on a two-body current.

In this article we investigate the influence of the expansion on the properties and the dynamical evolution of a piece of unstable nuclear matter. We discuss how the expansion modifies the spinodal decomposition of the system by deriving analytical results, which are confirmed and illustrated by numerical simulations in two dimensions. Moreover, the expansion is introducing a short freeze-out time which allows to unambiguously define the formed fragments. An important result of this study is that for a wide range of expansion velocities the fragmentation is dominated by the same unstable wave lengths, which happen to be weakly dependent on density and temperature provided that the system is lying well inside the spinodal instability region.

The elastic scattering of heavy ions at energies where the eikonal approximation is valid is discussed in detail. The nuclear phase shift and deflection functions for a complex Woods-Saxon interaction are evaluated in closed form. The resulting functions represent extremely well the numerically generated ones, even in cases involving the scattering of loosely bound nuclei. The elastic amplitude is evaluated in closed form, and found to be a reasonable approximation to the optical model one. Applications to the scattering of ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ are made.