[en] In the previous study of some stony meteorites and geothermal waters the multiple emission of neutrons was observed which might have arisen from spontaneous fission of superheavy elements (SHE). In this connection it is of interest to search for terrestrial samples in which an increase of concentration of the sought nuclide might have occurred in comparison with meteorites, which are the least differentiated substance in the solar system. The search can be carried out by means of a setup of weight 1 t. The detection of multiple emission of neutrons from samples of this weight permits observation of an admixture of SHE with a sensitivity 10^-15 g/g with a length of measurement 20 days. The development and operation of this setup will permit analysis of an additional approach to the experimental problem of nuclear decays due to nonconservation of baryon number (the decay of the nucleon and the annihilation nN resulting from the oscillation of a neutron bound in the nucleus)

[en] In the fusion reactions of ^20,22Ne with ²⁰⁵Tl, ²⁰⁸Pb, and ²⁰⁹Bi the absolute production cross sections of the ²²⁷Np, ^222-224Pa, ^222-224Th, and ²²¹Ac isotopes were measured and the products of the xn evaporation channels and the α-decay properties were investigated. The identified isotope is ²²⁷Np (7680±10 keV). A new α-line structure of ²²⁴Pa was established (7460±10 keV (25±3%) and 7555±10 keV (75±3%)). Four α-lines of ²²³Th were identified (7290±10 keV (41±5%), 7320±10 keV (29±5%), 7350±15 keV (20±5%), and 7390±15 keV (10±4%)). The half life of ²¹⁷Fr was measured to be 16±2 μs and that of ²²⁰Ra was found to be 17±2 ms. (orig.)

[en] Since the past 10 years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in heavy-ion-induced complete fusion reactions. In the course of experimental work in the region of the elements with 92≤Z≤94, 14 new isotopes have been identified by the parent-daughter correlations. For further experiments aimed at the synthesis of the superheavy element isotopes (Z≥110) with intensive ⁴⁸Ca extracted beams, improvements in the focal plane detector system have been made. As a result, energy and position resolutions of the detectors have been significantly improved, the detection efficiency for the α-particles, emitted from the implanted into the focal plane detector recoil nuclei, has been increased to 85%. The decay properties of the new isotope of element 112 and the isotope of the new element 114 with mass 287 have been measured in two-nuclei decays

[en] In the heavy-ion complete fusion reaction ²⁰⁸Pb+²⁶Mg at a beam energy of 135 MeV the new nuclide ²³⁰Pu was produced. The measured α-decay energy was found to be E_α=7050±15 keV. The new isotope was identified after in-flight separation with the kinematic separator VASSILISSA, followed by its implantation into a silicon surface-barrier detector and the observation of the genetic relationships of subsequent α-decays. The half-life of ²²⁶U was measured more accurately. (orig.)

[en] Isomeric states in ²⁵³No have been investigated by conversion electron and γ-ray spectroscopy with the GABRIELA detection system. The 31 μs isomer reported more than 30 years ago is found to decay to the ground state of ²⁵³No by the emission of a 167keV M2 transition. The spin and parity of this low-lying isomeric state are established to be 5/2⁺. The presence of another longer-lived isomeric state is also discussed. (orig.)

[en] Within the last five years the kinematic separator VASSILISSA [A.V. Yeremin et al., Nucl. Instr. and Meth. A 274 (1989) 528; and A.V. Yeremin et al., Preprint JINR E15-90-347, Dubna 1990] has been used for investigations of neutron deficient evaporation residues (ER) produced in heavy ion fusion reactions. In the course of this work optimization of the ion-optical and other systems of the separator including improvements of the focal plane detector system have been made. As a result, the separation efficiency values ranging from 3 to 30% were achieved for ERs produced in the reactions with heavy ions ranging from ¹⁶O to ⁴⁰Ar. The suppression factors>10¹⁹ for the full energy beam particles and >10⁴ for multinucleon transfer reaction products were achieved. The results of the performed experiments illuminating the separator performance are briefly presented. ((orig.))