The discovery of the heaviest elements

Abstract

The nuclear shell model predicts that the next doubly magic shell closure beyond 208 Pb is at a proton number between Zϭ114 and 126 and at a neutron number Nϭ184. The outstanding aim of experimental investigations is the exploration of this region of spherical superheavy elements (SHE's). This article describes the experimental methods that led to the identification of elements 107 to 112 at GSI, Darmstadt. Excitation functions were measured for the one-neutron evaporation channel of cold-fusion reactions using lead and bismuth targets. The maximum cross section was measured at beam energies well below a fusion barrier estimated in one dimension. These studies indicate that the transfer of nucleons is an important process for the initiation of fusion. The recent efforts at JINR, Dubna, to investigate the hot-fusion reaction for the production of SHE's using actinide targets are also presented. First results were obtained on the synthesis of neutron-rich isotopes of elements 112 and 114. However, the most surprising result was achieved in 1999 at LBNL, Berkeley. In a study of the reaction 86 Krϩ 208 Pb→ 294 118*, three decay chains were measured and assigned to the superheavy nucleus 293 118. The decay data reveal that, for the heaviest elements, the dominant decay mode is alpha emission, not fission. The results are discussed in the framework of theoretical models. This article also presents plans for the further development of the experimental setup and the application of new techniques. At a higher sensitivity, the exploration of the region of spherical SHE's now seems to be feasible, more than 30 years after its prediction.

Are MCDF calculations 101% correct in the super-heavy elements range?

“…Superheavy elements have been subject of an intense experimental activity over the past few decades [2][3][4]. Elements 108 (Hs) [5][6][7], 109 (Mt) [8][9][10], 110 (Ds) [11], 111 (Rg) [12], 112 [13][14][15], 113 [16], 114 [17][18][19][20], 115 [3], 116 [21][22][23], 117 [24] and 118 [25,23] have been observed in a series of experiments in Berkeley, GSI, Dubna and RIKEN.…”

Multinucleon exchange in quasifission reactions

“…Much experimental effort has been spent to synthesize super-heavy elements by fusion mechanism of heavy systems [1][2][3][4][5]. It is crucial to choose the right projectiletarget combinations in order to have the largest probability for forming a compound nucleus that leads to production of the desired super-heavy element.…”

Shape evolution and collective dynamics of quasifission in the time-dependent Hartree-Fock approach

“…The creation of new elements is one of the most novel and challenging research areas of nuclear physics [1][2][3][4]. The search for a region of the nuclear chart that can sustain the so called superheavy elements (SHE) has led to intense experimental activity resulting in the discovery and confirmation of elements with atomic numbers as large as Z = 118 [5][6][7].…”