Production mechanism of neutron-rich nuclei in 238 U+ 238 U at near-barrier energy Kai Zhao (China Institute of Atomic Energy) Collaborators: Zhuxia Li, Xizhen Wu, Ning Wang, Yingxun Zhang, Qingfeng Li, Yongjia Wang 2015 December Shanghai SINAP- CUSTIPEN

Outline Motivation Primary and residual fragments produced in 238 U+ 238 U at 7MeV/nucleon Production mechanism of primary fragments and residual fragments Summary

Multinucleon transfer reactions ： 238 U as projectile or target Multinucleon transfer reactions ： 238 U as projectile or target Neutron-rich, Stable, The heaviest element in the nature. More neutron-rich Island of stability 238 U fission

Prediction of new isotopes by grazing code and Langevin-type equations V. I. Zagrebaev and Walter Greiner Phys. Rev. C 87, (2013) R. Yanez and W. Loveland, Phys. Rev. C 91, (2015): 238 U+ 238 U, E lab =2059MeV Langevin-type equations Grazing code

Our method: Microscopic transport model + statistical evaporation model First stage (from the collision between projectile and target to the production of primary fragments) is described by Improved Quantum molecular dynamics (ImQMD) model: The description of reactions is based on the motion of nucleons. Composite system Re-separation of composite system and producing primary fragments Decay of primary fragments Second stage (decay of primary fragments) is described by statistical evaporation model (HIVAP code): The evaporation of γ, n, p, α and fission are considered.

All primary fragments 238 U+ 238 U (7 MeV/nucleon) The cross sections for primary fragments are denoted by black lines.

All primary fragments and residual fragments produced in 238 U+ 238 U (7 MeV/nucleon) The cross sections for primary fragments are denoted by black lines. The cross sections for residual fragments are denoted by rectangle symbols with different color.

All primary fragments and residual fragments produced in 238 U+ 238 U (7 MeV/nucleon) compared with known nuclei The cross sections for primary fragments are denoted by black lines. The cross sections for residual fragments are denoted by rectangle symbols with different color. Area of known nuclei is denoted by magenta line.

All primary fragments and residual fragments produced in 238 U+ 238 U (7 MeV/nucleon) compared with known nuclei New isotopes New isotopes can be produced in 238 U+ 238 U.

All primary fragments and residual fragments produced in 238 U+ 238 U (7 MeV/nucleon) compared with known nuclei Residual fragments tend to more neutron-rich area.

(114,184) is denoted by red cross symbol (i) Large nucleon transfer take place within the lower laboratory angles. (ii) Primary fragments near the center of island of stability are produced within the outgoing angles ≤ 40 o. The contribution of cross sections for primary fragments from different outgoing angles (lab. system)

The contribution of cross sections for residual fragments from different outgoing angles (lab. system) Z=103 is denoted by dot line

The contribution of cross sections for residual fragments from different outgoing angles (lab. system) Z=103 is denoted by dot line (i) transactinide residual fragments with Z>103 are produced within the outgoing angles 10 o -50 o.

The contribution of cross sections for residual fragments from different outgoing angles (lab. system) Z=103 is denoted by dot line (i) transactinide residual fragments with Z>103 are produced within the outgoing angles 10 o -50 o. √

The contribution of cross sections for residual fragments from different outgoing angles (lab. system) Z=103 is denoted by dot line (i) transactinide residual fragments with Z>103 are produced within the outgoing angles 10 o -50 o. (ii) New isotopes can be produced within the outgoing angles ≤ 60 o.

The contribution of cross sections for residual fragments from different outgoing angles (lab. system) Z=103 is denoted by dot line (i) transactinide residual fragments with Z>103 are produced within the outgoing angles 10 o -50 o. (ii) New isotopes can be produced within the outgoing angles ≤ 60 o. √ √ √

Isotope distribution of elements from Z=94 to 101 and compared with experimental data Kai Zhao,et. al., Phys. Rev. C 92, (2015) (i) The widths for residual fragments are smaller than those for primary fragments.

Isotope distribution of elements from Z=94 to 101 and compared with experimental data Kai Zhao,et. al., Phys. Rev. C 92, (2015) (i) The widths for residual fragments are smaller than those for primary fragments. (ii) The peaks for residual fragments shift to the less neutron-rich side.

Isotope distribution of elements from Z=94 to 101 and compared with experimental data Kai Zhao,et. al., Phys. Rev. C 92, (2015) (i) The widths for residual fragments are smaller than those for primary fragments. (ii) The peaks for residual fragments shift to the less neutron-rich side. (iii)The cross section decrease exponentially with the increase of charge number. (iv) The experimental data are generally reproduced.

Element yields and most probable mass number of primary fragments and residual fragments Kai Zhao,et. al., Phys. Rev. C 92, (2015) 238 U Lighter fragments (Z L ) Heavier fragments (Z H ) (i) For lighter fragments, the cross sections for residual fragments are closer to those for primary fragments. (ii) For transuranium nuclei, the cross sections for residual fragments are several orders of magnitude smaller than those for primary fragments as increasing the charge number. (iii) For most probable mass number, the differences between primary and residual fragments for transuranium nuclei are smaller than those for lighter fragments.

A large number of degrees of freedom are self-consistently included in ImQMD model: Deformation of two nuclei, Neck formation, Nucleon transfer, Nucleon emission, …… Different primary fragments, Different excitation energies, Different outgoing angles An example: new isotope of uranium primary fragments Different lifetime of composite system Different types of separation of composite system Production mechanism of primary fragments: The dynamical process plays an important role

Production mechanism of residual fragments J. V. Kratz, et al., Phys. Rev. C 88, (2013) 238 U Rn* Cf* Supposition: most probable final products come from most probable primary fragments ? Rn Cf Primary fragments Residual fragments The differences between the measured maxima and the most probable primary mass number is usually taken as a measure for the number of evaporated neutrons. Probable mass number of primary fragments of Rn Probable mass number of primary fragments of Cf

Different production mechanisms for most probable residues 214 Rn and 249 Cf 214 Rn comes from the probable primary fragment 222 Rn 249 Cf comes from the more neutron-rich primary fragments Cf Kai Zhao,et. al., Phys. Rev. C 92, (2015) Rn Cf decay The production of probable residual fragments are influenced by the isospin dependence of the fission barrier height besides the cross section and excitation energies of primary fragments. 214 Rn and 249 Cf are all located near the local peaks of the isospin distribution of fission barrier height. The cross section for 249 Cf is three orders of magnitude smaller than that for 214 Rn.

Production of more neutron-rich residues 254,255,256 Cf (i) The cross section for 254,255,256 Cf drop more than three orders of magnitude compared with 249 Cf (denoted by red arrows in the right figure) : (ii) The production of probable residual fragments 249 Cf mainly come from the competition between neutron evaporation and fission, but the production of more neutron rich nuclei come from the competition of evaporation of neutron, proton, α particles and fission. (iii) The isospin dependent fission barrier height also plays important roles for the production of more neutron-rich nuclei (reduce the cross section): (a) come from those primary fragments with lower fission barrier height;(b)experience a flat (but not a hillside) in the fission barrier height. Kai Zhao,et. al., Phys. Rev. C 92, (2015)

summary The dynamical process plays an important role in the production of primary fragments. Our calculation results (ImQMD+HIVAP) also show that new more neutron-rich isotopes can be produced in 238 U+ 238 U. Most probable residual fragments probably do not come from the probable primary fragments for transuranium nuclei, but from more neutron-rich primary fragments. The isospin dependent fission barrier height is important for the production of transuranium nuclei. And it should be carefully considered for the production of new neutron-rich nuclei or superheavy nuclei further.

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