S. Iliev

Feeding and lifetimes of yrast levels in Hf nuclei

Abstract Feeding intensities and times, as well as lifetimes of yrast levels in doubly even 166, 168, 170 Hf nuclei have been measured. The reactions 122, 124 Sn( 48, 50 Ti, 4n) 166–170 72 Hf have been investigated using the recoil-distance Doppler-shift method. The lifetimes, and hence the B ( E 2) values measured, show the same trends of rather small deviations from the rigid rotor as in the known 68 Er and 70 Yb cases. In addition to the fast feeding component, showing behaviour rather similar to that of the Yb nuclei, another type of slow feeding, related to the low spin yrast levels, is observed.

Synthesis of superheavy nuclei in 48Ca+244Pu interactions

This article reports the results of experiments aimed at producing hypothetical long-lived superheavy elements located near the spherical-shell closures with Z≥114 and N≥72. For the synthesis of superheavy nuclei, we used a combination of neutron-rich reaction partners, with a 244Pu target and a 48Ca projectile. The sensitivity of the present experiment exceeded by more than two orders of magnitude previous attempts at synthesizing superheavy nuclides in reactions of 48Ca projectiles with actinide targets. We observed new decay sequences of genetically linked alpha decays terminated by spontaneous fission. The high measured alpha-particle energies, together with the long decay times and spontaneous fission terminating the chains, offer evidence for the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive alpha decays originating from the parent nuclides 288,289114, produced in the 3n-and 4n-evaporation channels with cross sections of about a picobarn. The present observations can be considered experimental evidence for the existence of the “island of stability” of superheavy elements and are discussed in terms of modern theoretical approaches.

Synthesis of Superheavy Nuclei in 48Ca-Induced Reactions

neutron-rich isotopes 242,244 Pu, 243 Am, 245,248 Cm and 249 Cf with 48 Ca projectiles. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating in the decays of parent nuclides 286,287,288,289 114, 287,288 115, 290,291,293 116 and 294 118 produced in the 2n- to 5n-evaporation channels. The present observations can be considered to be experimental evidence of the existence of the “island of stability” of superheavy elements.

Synthesis of the isotopes of elements 118 and 116 in the {sup 249}Cf and {sup 245}Cm+{sup 48}Ca fusion reactions

The decay properties of {sup 290}116 and {sup 291}116, and the dependence of their production cross sections on the excitation energies of the compound nucleus, {sup 293}116, have been measured in the {sup 245}Cm ({sup 48}Ca, xn){sup 293-x}116 reaction. These isotopes of element 116 are the decay daughters of element 118 isotopes, which are produced via the {sup 249}Cf+{sup 48}Ca reaction. We performed the element 118 experiment at two projectile energies, corresponding to {sup 297}118 compound nucleus excitation energies of E*=29.2{+-}2.5 and 34.4{+-}2.3 MeV. During an irradiation with a total beam dose of 4.1x10{sup 19} {sup 48}Ca projectiles, three similar decay chains consisting of two or three consecutive {alpha} decays and terminated by a spontaneous fission (SF) with high total kinetic energy of about 230 MeV were observed. The three decay chains originated from the even-even isotope {sup 294}118 (E{sub {alpha}}=11.65{+-}0.06 MeV, T{sub {alpha}}=0.89{sub -0.31}{sup +1.07} ms) produced in the 3n-evaporation channel of the {sup 249}Cf+{sup 48}Ca reaction with a maximum cross section of 0.5{sub -0.3}{sup +1.6} pb.

Synthesis, Decay Properties, and Identification of Superheavy Nuclei Produced in 48Ca‐induced Reactions

Thirty‐four new nuclides with Z = 104–116, 118 and N = 161–177 have been synthesized in the complete‐fusion reactions of 238U, 237Np, 242,244Pu, 243Am, 245,248Cm, and 249Cf targets with 48Ca beams. The masses of evaporation residues were identified through measurements of the excitation functions of the xn‐evaporation channels and from cross bombardments. The decay properties of the new nuclei agree with those of previously known heavy nuclei and with predictions from different theoretical models. A discussion of self‐consistent interpretations of all observed decay chains originating from the parent isotopes 282,283112, 282113, 286–289114, 287,288115, 290–293116, and 294118 is presented. Decay energies and lifetimes of the neutron‐rich superheavy nuclei as well as their production cross sections indicate a considerable increase in the stability of nuclei with the approach to the theoretically predicted nuclear shells with N = 184 and Z = 114.

Superheavy Elements — Status of Research in Dubna

This paper presents results of experiments aimed at producing long-lived superheavy elements located near the spherical shell closures with Z ≥114 and N ≥172 in the reactions of neutron-rich isotopes 244Pu, 245,248Cm and 249Cf with 48Ca projectiles. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating in the decays of parent nuclides 289114, 290,291,293116 and 294118 produced in the 2n and 3n-evaporation channels. The present observations can be considered to be experimental evidence of the existence of the “island of stability” of superheavy elements.

Data acquisition system for the Dubna gas filled recoil separator

A PC-based data acquisition system for heavy element research is described. Some special electronic modules were designed for the mentioned system. The system was tested for heavy-ion reactions at the main FLNR cyclotron U400. The detection module design is also described. This system was successfully applied in experiments to discover the shell closure at N=162 and Z=108 as well as for the discovery of new elements (two isotopes). A specific point of real-time detection of short recoil-alpha energy-time-position correlations is also presented.