Production of neutron-rich heavy nuclei in deep-inelastic ²⁰⁸Pb + ²⁰⁸Pb collisions within the stochastic mean-field theory

Journal Article · Wed Aug 20 00:00:00 EDT 2025 · Physical Review. C

DOI:https://doi.org/10.1103/g7yp-d6yq· OSTI ID:2584303

Sekizawa, K. ^[1]; Ayik, S. ^[2]; Karanfil, E. C. ^[3]; Arik, M. ^[4]; Yilmaz, O. ^[5]; Umar, A. S. ^[4]

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1. Institute of Science Tokyo (Japan); University of Tsukuba, Ibaraki (Japan); RIKEN Nishina Center, Saitama (Japan)
2. Tennessee Technological University, Cookeville, TN (United States)
3. Ankara University (Turkey)
4. Vanderbilt University, Nashville, TN (United States)
5. Middle East Technical University, Ankara (Turkey)

In deep-inelastic collisions of heavy nuclei, reaction products with a wide range of mass and charge are produced. Such collisions been considered as a possible way to produce superheavy nuclei, as an alternative to fusion reactions. To provide reliable theoretical predictions, it is desired to develop microscopic approaches that correctly and accurately describe nucleon transfer processes in dissipative collisions of heavy nuclei. The purpose of the present work is (1) to investigate the mechanism of nucleon transfers in dissipative collisions of two heavy nuclei, and (2) to explore possible pathways to produce neutron-rich heavy nuclei, through detailed theoretical analyses of fluctuations and correlations in nucleon transfers in ²⁰⁸Pb + ²⁰⁸Pb reactions. Three-dimensional time-dependent Hartree-Fock (TDHF) calculations are performed for the collisions of ²⁰⁸Pb + ²⁰⁸Pb at 𝐸_c.m. = 832, 936, and 1040 MeV, using the Skyrme SLy4d energy density functional. To calculate fluctuations and correlations in nucleon transfers, we employ the stochastic mean-field (SMF) theory, and the results are compared with another theoretical framework currently available, the time-dependent random phase approximation (TDRPA). Primary and secondary production cross sections are calculated with the SMF theory combined with a statistical model, GEMINI₊₊. Using information of nucleon flow across a neck of colliding nuclei in TDHF calculations, we solve quantal diffusion equations for fluctuations and correlations in nucleon transfers based on the SMF theory. From the SMF calculations, we obtain the time evolution of diffusion coefficients as well as fluctuations and correlations in nucleon transfers for a range of initial orbital angular momenta. We compare the results of the SMF calculations with those of TDRPA, showing that TDRPA tends to predict substantially larger fluctuations and correlations in strongly damped collisions of heavy nuclei, which exhibit complex initial angular momentum dependence, while the SMF results provide almost constant (stable) values. Using the obtained fluctuations and correlations, we calculate primary and secondary production cross sections for the ²⁰⁸Pb + ²⁰⁸Pb collisions. From the results, we find that both lighter and heavier reaction products as compared to ²⁰⁸Pb are produced for a wide region in the 𝑁−𝑍 plane as primary products, thanks to the quantal diffusion mechanism in the dissipative collisions. However, we show that cross sections for production of heavy nuclei with 𝑍 ≳ 90 or 𝑁 ≳ 135 are washed out due to secondary particle evaporation and/or fission processes. On the other hand, we find that there remain sizable cross sections for production of neutron-rich nuclei along 𝑁 = 126 with 𝑍< 82, even after secondary disintegration processes. We demonstrate that the secondary production cross sections depend weakly on incident energies, but lower (higher) energy is slightly preferred for production of nuclei with smaller (larger) atomic numbers as compared to 𝑍 = 82. Here, based on the microscopic SMF calculations, it has been shown that deep-inelastic collisions of heavy nuclei, such as ²⁰⁸Pb + ²⁰⁸Pb examined in this study, can be a promising means to produce neutron-rich heavy nuclei along 𝑁=126. Discrepancies between the SMF and TDRPA approaches are left unsolved for future investigations.

• Research Organization: Vanderbilt University, Nashville, TN (United States)
• Sponsoring Organization: TUBITAK; USDOE
• Grant/Contract Number: SC0013847
• OSTI ID: 2584303
• Journal Information: Physical Review. C, Journal Name: Physical Review. C Journal Issue: 2 Vol. 112; ISSN 2469-9985; ISSN 2469-9993
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
Low &amp; intermediate energy heavy-ion reactions
Neutron-rich nuclei
Nuclear reactions
Rare &amp; new isotopes
Stochastic mean-field
TDHF
TDRPA
Transfer reactions