Synthesis of elements 115 and 113 in the reactionAm243+Ca48

Abstract

The results of two experiments designed to synthesize element 115 isotopes in the 243 Am + 48 Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV 48 Ca projectiles, we observed three similar decay chains consisting of five consecutive α decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV 48 Ca projectiles, we registered a different decay chain of consecutive α decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new αand SF-decaying nuclei are consistent with expectations for consecutive α decays originating from the parent isotopes 288 115 and 287 115, produced in the 3n-and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the 288 115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, 268 Db (15 events), was found to be chemically consistent with the fifth group of the periodic table. The odd-odd isotope 288 115 was observed with largest cross section of about 4 pb. In the SF decay of 268 Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z = 105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.

Fission half-lives of superheavy nuclei in a microscopic approach

“…Many experimental data coming from the "cold fusion" reactions are available in the region of isotopes with N 162 [9,107]. The agreement of the α-decay half-lives with the theoretical predictions is noticeable, although some discrepancies are observed.…”

“…In the last decades huge progress in the synthesis of new elements has been achieved in world-leading laboratories such as the GSI, Darmstadt [1][2][3][4][5][6][7][8], the Joint Institute for Nuclear Research (JINR), Dubna [9][10][11][12][13][14], and Rikagaku Kenkyusho (Institute of Physical and Chemical Research, Japan; RIKEN), Tokyo [15][16][17][18]. The first SHEs with Z 113 and N 165 were produced in cold fusion reactions.…”

Heavy into Stability

“…For 2 Ti foils to a thickness of 0:33 mg=cm 2 of 249 Bk. The targets were mounted on the perimeter of a disk 12 cm in diameter that was rotated at 1700 rpm perpendicular to the beam direction.…”

“…The stabilizing effect of the expected N ¼ 184 neutron shell closure found previously for even-Z nuclei [1] is supported by the experimental observation of a decrease of the decay constant for emission with increasing neutron number. This observation was found to apply to the decays of odd-Z isotopes created during the discovery of elements Z ¼ 115 and 117 [2][3][4][5]. Longer lifetimes of nuclei located closer to N ¼ 184 can facilitate the measurements of chemical properties when the heaviest atoms are produced in sufficient amounts.…”

Procedures for Db chemical characterization in off-line experiments

“…decay chain with a half-life of about 1 day [3,4]. This nuclide is sufficiently longlived that the dubnium can be chemically characterized.…”