Systematics on production of superheavy nuclei Z=119-122 in fusion-evaporation reactions

The fusion dynamics of the formation of super-heavy nuclei were investigated thoroughly within the din-uclear system model.The Monte Carlo approach was implemented in the nucleon transfer process to include all possible orientations,at which the dinuclear system is assumed to be formed at the touching configuration of dinuclear fragments.The production cross sections of superheavy nuclei Cn,Fl,Lv,Ts,and Og were calculated and compared with the available data from Dubna.The evaporation residue excitation functions in the channels of pure neutrons and charged particles were systematically analyzed.The combinations of 44 Sc,48;50 Ti,49;51 V,52;54 Cr,58;62 Fe,and 62;64 Ni bombarding the actinide nuclides 238 U,244 Pu,248 Cm,247;249 Bk,249;251 Cf,252 Es,and 243 Am were calculated to produce the superheavy elements with Z¼119?122.We obtained that the production cross sections sensitively depend on the neutron richness of the reaction system.The structure of the evaporation residue excitation function is related to the neutron separation energy and fission barrier of the compound nucleus.

High Spin Structure in ^(106)Pd

The high spin states of 106pd have been populated through the 100Mo（11B, lp4n）106Pd reaction using a beam energy of 60 MeV provided by the Beijing HI-13 tandem accel- erator at China Institute of Atomic Energy. By analyzing the V-3＇ coincidence relation and DCO raios of transitions, 3 rotational bands with 13 new states and 22 new 7 transitions belonging to 106pd were constructed. Bands 2 and 3 with negative parity were supposed to build on the vh1l/297/2 and vh11/2ds/2 configuration, respectively.

Structure change of ^(156)Yb at high-spin states

High-spin states of 156Yb have been studied via the 144Sm(16O,4n)156Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. The characteristics of the negative-parity sequence above the 25-state may related to the excitation from the nucleon in the Z =64, N =82 core. The E-GOS curve for the positiveparity yrast sequence in 156Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. The Cranked Woods-Saxon-Strutinsky calculations by means of Total-Routhian-Surface (TRS) methods has been made to understand this structure change.

α-decay study of ^(218)Ac and ^(221)Th in ^(40)Ar+^(186)W reaction

In this study,^(218)Ac and ^(221)Th nuclides were produced via the heavy-ion induced fusion evaporation reaction ^(40)Ar+^(186)W.Their decay properties were studied with the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system.The cross section ratio between ^(222)Pa and ^(218)Ac was extracted experimentally,withmeasured value 0.69(9).Two new possible α decay branches to ^(221)Th are suggested.The valence neutron configurations for the daughter ^(217)Ra are discussed in terms of the hindrance factors.

A statistical approach to describe highly excited heavy and superheavy nuclei

A statistical approach based on the Weisskopf evaporation theory has been developed to describe the deexcitation process of highly excited heavy and superheavy nuclei, in particular for the proton-rich nuclei. The excited nucleus is cooled by evaporating γ-rays, light particles（neutrons, protons, α etc） in competition with binary fission,in which the structure effects（shell correction, fission barrier, particle separation energy） contribute to the processes.The formation of residual nuclei is evaluated via sequential emission of possible particles above the separation energies.The available data of fusion-evaporation excitation functions in the ^28Si＋^198Pt reaction can be reproduced nicely within the approach.

Electric-dipole transitions in ^(165)Er

High-spin states of ^165Er were studied using the ^160Gd（^9Be, 4n）reaction at beam energies of 42 and 45 MeV. The previously known bands based on the ν5/2^-[523] and ν5/2^＋[642] configurations have been extended to high-spin states. Electric-dipole transitions linking these two opposite parity bands were observed. Relatively large B（E1） values have been extracted experimentally and were attributed to octupole softness.

Fine structure ofαdecay in^(222)Pa

With the help of the gas-filled recoil spectrometer SHANS and a digital data acquisition system,the fine structure of the α decay for^(222)Pa was studied.The nuclides were produced through the 1p3n evaporation channel via the heavy-ion induced fusion evaporation reaction ^(40)Ar+^(186)W.Based on the ER-α1-α2-α3 andα-γcorrelation measurement,three new α decays were observed in addition to the three branches known previously.The one with the largestαdecay energy was regarded as the ground state to ground state transition.The newly measuredαdecay properties of ^(222)Pa were examined in a framework of reduced width.

Doublet bands in ^(128)La and systematic features of energy separationof doublet bands observed in the A～130 mass region

High spin states of 128La have been studied through the fusion-evaporation reaction 118Sn（14N,4n） 128La at a beam energy of 69 MeV. A positive-parity side band with the same configuration as that of the yrast band has been identified. Moreover, it is noted that the energy separation △E（I） = E（I）side-E（I）yrast of all doublet bands reported in odd-odd nuclei in the A～130 mass region exhibit a staggering pattern systematically, and they stagger up at even-spin and stagger down at odd-spin.

New high spin level scheme of ^(87)Sr

High spin states of the odd-A STSr were populated by the fusion-evaporation reaction ^82Se（^9Be,4n） u. br at a beam energy of 46 MeV. Excited levels of SrSr have been extended up to an excitation energy of 7.4 MeV at spin 31/2h. The coupling of a g9/2 neutron hole to the yrast states of the SSSr core can account for the low-lying states in STSr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N=49 isotones and possible configurations are proposed.

Fusion reactions around the barrier for Be+^(238)U

Fusion-evaporation cross sections of^(238)U(^(9)Be,5n)^(242)Cm are measured over a wide energy range around the Coulomb barrier.These measured cross sections are compared with model calculations using two codes,namely HIVAP2 and KE WPIE2.HIVAP2 calculations overestimate the measured fusion-evaporation cross sections by a factor of approximately 3.In KEWPIE2 calculations,two approaches,namely the Wentzel-Kramers-Brillouin(WKB)approximation and the empirical barrier-distribution(EBD)method,are used for the capture probability;both of them properly describe the measured cross sections.Additionally,fusion cross sections of^(7.9)Be+^(238)Umeas-ured in two experiments are applied to constrain model calculations further through three codes,i.e,HIVAP2,KEWPIE2,and CCFULL.Parameters in these codes are also examined by comparison with measured fusion cross sections.AIll the comparisons indicate that the K EWPIE2 calculations using the WKB approximation agree well with the measured cross sections of both fusion reactions 7.9 Be+^(238)U and the fusion-evaporation reaction 238U(9 Be,5n)242 Cm.Calculations using the fusion code CCFULL are also in good agreement with the measured fusion cross sections of 7.9 Be+^(238)U.