Impact of nuclear structure on production and identification of new superheavy nuclei

Abstract

Abstract. Using the microscopic-macroscopic approach based on the modified two-center shell model, the low-lying quasiparticle spectra, ground-state shell corrections, mass excesses and Q α-values for even Z superheavy nuclei with 108 ≤ Z ≤ 126 are calculated and compared with available experimental data. The predicted properties of superheavy nuclei show that the next doubly magic nucleus beyond 208 Pb is at Z ≥ 120. The perspective of using the actinide-based complete fusion reactions for production of nuclei with Z = 120 is studied for supporting future experiments. Experiments on complete fusion reactions with48 Ca beam and various actinide targets were successfully carried out at FLNR (Dubna), GSI (Darmstadt), and LBNL (Berkeley) in order to synthesize superheavy elements (SHE) with Z = 112-118 [1][2][3][4][5][6][7][8][9][10][11]. The found experimental trend of nuclear properties (Q α -values and half-lives) and cross-sections of production of SHE reveals increasing stability of nuclei approaching the spherical closed neutron shell N = 184, and also indicates a relatively small effect of the proton shell at Z = 114 [3,4,[12][13][14][15] predicted with the microscopic-macroscopic models [16][17][18][19][20][21][22]. This experimental observation seems to be in accordance with the predictions of relativistic and nonrelativistic mean-field models [23][24][25][26] where the island of stability corresponds to Z = 120-126 and N = 184. If there is a strong shell effect at Z = 120-126, then there is hope to synthesize new SHE with Z ≥ 120 by using the present experimental set up and actinide-based reactions with neutron-rich stable projectiles heavier than 48 Ca. With the predictions of the microscopic-macroscopic models [16], where the proton shell at Z = 114 is expected, the reactions 50 Ti+ 249 Cf and 54 Cr+ 248 Cm would result in Z = 120 nuclei with maximum cross-sections of 1.2 and 0.2 fb, respectively, in a 4n evaporation channel [27]. If the predictions of the phenomenological model [28][29][30][31], where the proton shell is assumed at Z = 126, are correct, the reactions 50 Ti+ 249 Cf and 54 Cr+ 248 Cm would lead to the production of Z = 120 nuclei with cross-sections of 550 fb (3n evaporation channel) and 40 fb (4n evaporation channel), respectively [27]. So, the structure of SHE crucially influences the evaporation residue cross-sections in a e-mail: adamian@theor.jinr.ru actinide-based complete fusion reactions. Because nuclear models contain a number of parameters which are fixed for the best description of known nuclei, their predictive power could be smaller for nuclei far from the well-studied region of the nuclear chart. To improve the predictions, one can specially adjust the parameters for describing the known properties of shell-stabilized nuclei close to the region of interest.In refs. [32,33] we proposed a microscopic-macroscopic approach based on the modified two-center shell model (TCSM) [34]. The parameters were set so to describe the spins and parities of the ground state of known heavy nu...

Role of quasiparticle structure inαdecays of the heaviest nuclei

“…The obtained results expand our knowledge of the single-particle structure and of the location of the next proton shell closure beyond Z = 82. The microscopic-macroscopic approaches [9][10][11][12][13][14][15] supply the basis for the intensive calculations of the properties of heavy nuclei. These approaches differ by the parametrization of nuclear shape and by the single-particle potential used.…”

“…[12] we proposed the microscopicmacroscopic approach based on the two-center shell model (TCSM) [17]. The parameters depending on (N − Z) were set to obtain the best description of the spins and parities of the ground state of well-studied heavy nuclei and of the twoquasiparticle states of rear-earth nuclei [12,14]. In the TCSM we have only two parameters to describe the deformations of various even multipolarities.…”

“…[12] we treated [14] the trends in the shell effects and Q α values with Z > 110. These trends seem to be close to those obtained with the self-consistent microscopic calculations [18].…”

“…[19,20] based on the analysis of experimental Q α values and evaporation residue cross sections, respectively. Here we use the microscopic-macroscopic approach [14] to study the one-quasiparticle spectra in the even-odd nuclei as well as the two-quasiparticle states in the even-even nuclei.…”

Influence of proton shell closure on production of new superheavy nuclei

“…[23] we treated the isotopes of superheavy nuclei with even Z which can be reached in complete fusion reactions with available stable projectiles and targets. The results for odd Z nuclei are given in Ref.…”