We report the results of a theoretical description of the threshold anomaly in the reaction /sup 7/Li(t, /sup 9/Li)/sup 1/H on the basis of the S-matrix formalism in the framework of perturbation theory. Analytic expressions are obtained for the cross section for the /sup 7/Li(t, /sup 9/Li)/sup 1/H reaction in the region of the anomaly. On the assumption that a resonance state of the /sup 10/Be system with E/sub x/ = 21.156 MeV and T = 2 is manifested in the anomaly, an estimate of the neutron binding energy in the /sup 10/Li nucleus is given: S/sub n/ = -28 +- 60 keV.

The basic characteristics of the /sup 3/H nucleus, namely the binding energy, mean square radius and virtual /sup 3/H..-->..n+D decay coupling constant, are calculated for two different central potentials, using the interpolation approach to nuclear theory and accounting for the binary nD-decay channel explicitly. The effect of the ''cluster'' function in these calculations is studied, as is the role of the ''internal'' wave function describing the pure three-nucleon bound state, in calculations of the doublet phase shift in elastic nD scattering.

In an investigation into the α-α and α-nucleus interaction the former is studied employing for the effective interaction a potential with a repulsive core embedded into a long range attractive part. Calculations with this potential reproduce the energies and widths of the levels of the α-α system8Be and the phases for α-α scattering quite well thus pointing to an applicability of the model to α-α and α-nucleus scattering for light nuclei.

A statistical approach with all quantum-mechanical specificity preserved isdeveloped for systems with a great number of channels. Resonances of a new type which may arise in such systems are predicted.

Problems of the existence and properties of nuclei near the limits of nucleon stability and related problems of analog states are considered. A survey is given of available experimental data on boundary isotopes and the possibilities of predicting the mass of as yet unobserved nuclei, and other properties of these isotopes are examined in detail. The basic experimental methods of searching for new nuclei and for investigation of analog states are discussed. The possibilities for the detection of new forms of radioactive decay of nuclei near the limits of nucleon stability such as proton and two-proton radioactivity are analyzed. A theoretical examination was made of the possibility of the existence of strongly neutron-excess and purely neutron nuclei. (tr-auth)

It is argued, that nuclear multineutrons, if they exist at all, are rather heavy nuclei, which contain at least 100 neutrons.