Study of natural and induced radioactivity by heavy ion beams at Dubna

The search for the production of transuranium and superheavy nuclei is surveyed. The stages of the progress can be characterized by different methods: neutron capture reactions, the first intensive heavy-ion beams at Birmingham and Dubna, the cold fusion reactions, and recent attempts and plans for new heavy-ion reactions producing superheavy nuclei. The most interesting discoveries are described: the existence of nuclear isomeric states, new kinds of radioactivity (protonic decay, spontaneous fission), neutron-abundant nuclei. The problem of the 'island of stability', the probable existence of very heavy stable nuclei, and the possible method of producing such nuclei are discussed. New experiments with meteoric materials indicate the hypothesis that the observed extra signals of spontaneous fission are due to the presence of a new stable (i.e. long-living) superheavy element. The contribution of JINR, Dubna, in each of the above research fields is underlined. (D.Gy.)