No abstract

A new approach to the production and detection of bound neutron clusters is presented. The technique is based on the breakup of beams of very neutron-rich nuclei and the subsequent detection of the recoiling proton in a liquid scintillator. The method has been tested in the breakup of 11 Li, 14 Be and 15 B beams by a C target. Some 6 events were observed that exhibit the characteristics of a multineutron cluster liberated in the breakup of 14 Be, most probably in the channel 10 Be+ 4 n. The various backgrounds that may mimic such a signal are discussed in detail.

The dynamical effects of the entrance channel on the formation of the evaporation residues are studied by analyzing the 40 Ar + 176 Hf, 86 Kr + 130,136 Xe, 124 Sn + 92 Zr, and 48 Ca + 174 Yb reactions leading to the 216 Th * and 222 Th * compound nuclei. We find that the difference between the evaporation residue cross sections for the reactions leading to the same compound nucleus is caused by the different angular momentum distributions of the partial fusion cross sections σ fus (E c.m. ). The strong dependence of the fusion angular momentum distribution on the mass (charge) asymmetry and shell structure of reactants is demonstrated. The effect of the A/Z ratio for the 86 Kr + 130,136 Xe reactions is discussed. The dynamical conditions of capture affect the competition between complete fusion and quasifission and, consequently, the shape of the angular momentum distribution of the compound nucleus. By this way the peculiarities of the entrance channel also affect the fission-evaporation competition of the excited intermediate nuclei along the deexcitation cascade of the compound nucleus and, consequently, the evaporation residue formation.

The experimental data on the capture and evaporation residue cross-sections obtained in the 48 Ca +208 Pb reaction were analyzed in the framework of the dynamical model based on the dinuclear system concept and advanced statistical method to clarify the reaction mechanism. The experimental excitation function of the capture reactions was decomposed into contributions of the fusion–fission, quasifission and fast-fission processes. Total evaporation residues and ones after neutron emission were only calculated and compared with the available experimental data.

We obtained the spectrum of probability of the bremsstrahlung emission accompanying the α-decay of 226 Ra (Eα=4.8 MeV) by measuring the α-γ coincidences and using the model presented in our previous study on the α−decay of 214 Po (Eα=7.7 MeV). We compare the experimental data with the quantum mechanical calculation and find a good agreement between theory and experiment. We discuss the differences between the photon spectra connected with the α-decay of the 226 Ra and 214 Po nuclei. For the two mentioned nuclei we analyze the bremsstrahlung emission contributions from the tunneling and external regions of the nucleus barrier into the total spectrum, and we find the destructive interference between these contributions. We also find that the emission of photons during tunneling of the α-particle gives an important contribution to the bremsstrahlung spectrum in the whole Eγ energy range of the studied 226 Ra nucleus.