Session SHE1 Heavy and Super Heavy Elements I

Room: Pecos

Chair: J. Äystö

2:00PM

Synthetic Paths to the Heaviest Elements, W. Loveland, Oregon State University − The cross section for producing a heavy reaction product in a complete fusion reaction can be written as

where σ_capture(E_cm, J) is the "capture" cross section at center of mass energy E_c._m. and spin J and P_cn is the probability that the projectile-target system will evolve inside the fission saddle point to form a completely fused system rather than re-separating (quasifission) and W_sur is the survival probability of the completely fused system.  I will present the results of experiments to characterize these quantities in heavy element synthesis reactions.

2:30PM

Study of super-heavy nuclei at IMP, X. H. Zhou, Institute of Modern Physics, CAS, Lanzhou 730000 − Since the prediction of island of super-heavy elements in 1960s, great efforts have been made both theoretically and in experimentally in order to synthesize the heavy nuclei beyond Uranium.  A batch of super-heavy nuclei were synthesized using heavy-ion induced fusion-evaporation reactions, and the heaviest Z=118 element was discovered recently. The study of super-heavy nuclei can shed light on a number of significant scientific problems, for example, how many elements exist?  How long is their lifetime?  What make them stable?  How can they be synthesized?  What are their chemical properties? etc.

From 2000, we started the research program concerning the synthesis of super-heavy nuclei.  A helium-jet system coupled with a fast rotating-wheel apparatus was established, and two new isotopes ²⁵⁹Db and ²⁶⁵Bh were identified using the ²²Ne(²⁴¹Am, 4n)²⁵⁹Db and ²⁶Mg(²⁴³Am, 4n)²⁶⁵Bh reactions.  With the helium-jet based device, it now becomes very difficult to observe super-heavy isotopes with charge number larger than 108 since the production cross sections and the transportation efficiency of the system are very low.  Therefore, a gas-filled recoil separator is constructed, and a detection system for single atom identification is built.  Now, we are able to carry out experiment aimed at identification of super-heavy nuclei with charge number around 110.  The status of investigation of super-heavy nuclei at Institute of Modern Physics will be reported, and the future research plan will be presented.

3:00PM

Design and Development of a Trochoidal Mass Analyzer for the Berkeley Gas-filled Separator, J. M. Gates, N. E. Esker, K. E. Gregorich, G. K. Pang, H. Nitsche, Lawrence Berkeley National Laboratory, Berkeley, California, USA − Several upgrades to the Berkeley Gas-filled Separator (BGS) at the Lawrence Berkeley National Laboratory (LBNL) are currently underway.  These upgrades will include a new mass analyzer coupled to the BGS to i) provide a M/ΔM separation of ~500 and ii) transport nuclear reaction products to a shielded detector station on the tens of milliseconds timescale.  These upgrades will allow for direct A and Z identification of ii) new actinide and transactinide isotopes with ambiguous decay signatures such as electron capture or spontaneous fission decay and i) superheavy nuclei such as those produced in the ⁴⁸Ca + actinide reactions.

In the proposed setup, nuclear reaction products recoil from the target and are separated from the beam and unwanted reaction products in the BGS.  There they pass through a window and into a radio-frequency gas catcher where they are thermalized and extracted into a radio-frequency quadrupole (RFQ) trap.  The nuclear reaction products are cooled and bunched in the RFQ trap, where they maintain a +1 or +2 charge, and are injected into the mass analyzer.  The proposed mass analyzer consists of crossed electric and magnetic fields such that the ions take trochoidal trajectories.  Simulations predict that high mass dispersion and M/ΔM separation of >500 is possible with a 50‑cm long, ≤1.5 T magnetic field and electric field of <500 V/cm.  Here we will present the design of and future plans for the mass analyzer.

Financial Support was provided by the Office of High Energy and Nuclear Physics, Nuclear Physics Division, and by the Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231.

3:20PM

Systematic calculations of alpha-decay half-lives of heavy and superheavy nuclei, Z. Ren, Department of Physics, Nanjing University, China − Alpha decay is a powerful way to identify new nuclides and new elements in heavy and superheavy region.  The different methods to calculate a-decay half-lives and branching ratios are discussed.  Emphasis is placed on the microscopic models of the coupled channel calculations on a-decay branching ratios of heavy nuclei [1-4].  Systematic calculations on the decay-half-lives and branching ratios are carried out by the coupled-channel calculations and good agreement with available data is reached.  This is the systematic calculation on the branching ratios and a-decay half-lives of heavy nuclei.  It is worth noting that the aim is not only to reproduce the experimental data well, but also to extend our understanding of a-decay refined structure [5].

[1] Dongdong Ni and Zhongzhou Ren, Phys. Rev.C 80, 014314 (2009).

[2] Dongdong Ni and Zhongzhou Ren, Phys. Rev.C 80, 051303(R) (2009).

[3] Dongdong Ni and Zhongzhou Ren, Phys. Rev.C  81, 024315 (2010).

[4] Dongdong Ni and Zhongzhou Ren, Phys. Rev.C  81, 064318 (2010).

[5] Dongdong Ni and Zhongzhou Ren, Phys. Rev.C  83, 067302 (2011).

PACS numbers: 21.10.Dr 21.10.Pc, 21.60.Jz

3:40PM

Production of radon and thorium isotopes near N = 126 shell in ⁴⁸Ca and ⁵⁴Cr induced fusion reactions on ¹⁶²Dy, D. A. Mayorov^1,2, T. A. Werke^1,2, M. C. Alfonso^1,2, M. E. Bennett¹, C. M. Folden III¹, ¹ Cyclotron Institute, Texas A&M University, College Station, TX 77843-3366, USA; ² Department of Chemistry, Texas A&M University, College Station, TX 77842-3012, USA − Investigation of spherical nuclei produced by heavy ion fusion reactions is of current interest due to the recent efforts to synthesize superheavy nuclei near the predicted closed nucleon shells at Z = 120, N = 184. Evaporation residues (EvRs) produced near the known N = 126 shell closure have previously revealed surprisingly low survival probabilities despite stabilization from shell effects. Production of spherical EvRs near the N = 126 shell in ⁴⁸Ca and ⁵⁴Cr induced reactions on a ¹⁶²Dy target was investigated at the Texas A&M University Cyclotron Institute using the vacuum spectrometer MARS. A factor of > 7100 separates the production cross sections of the 4n EvRs synthesized in these reactions. Enhancement of the fission channel in the de-excitation cascade of ²¹⁰Rn and ²¹⁶Th is observed in this work, and this result can be well modeled by the inclusion of collective effects into the statistical decay of excited nuclei calculations. Further systematic study of ⁴⁸Ca, ⁵⁰Ti, and ⁵⁴Cr induced fusion with select lanthanide targets is planned in the interest of quantifying the cross section dependence on projectile. The present results suggest that cross sections for production of superheavy nuclei near these Effects of Odd-Z Projectiles on Fusion-Evaporation Cross Sections.

4:00PM