Publication

Multi-Nucleon Transfer Reactions as a Tool for Spectroscopy of Heavy Nuclei

Nuclear physics

Journal of Physics G: Nuclear and Particle Physics, Volume 26, Issue 1, pp. 23-34 (2000)

Authors:

J. F. C. Cocks, P. A. Butler, K. J. Cann, K. J., P. T. Greenlees, G. D. Jones, J. F. Smith, P. M. Jones, R. Julin, S. Juutinen, D. Müller, M. Piiparinen, A. Savelius, R. Broda, B. Fornal, B, I. Ahmad, D. J. Blumenthal, M. P. Carpenter, B. Crowell, R. V. F. Janssens, T. L. Khoo, T. Lauritsen, D. Nisius, S. Asztalos, R. M. Clark, M. A. Deleplanque, R. M. Diamond, P. Fallon, I. Y. Lee, A. O. Macchiavelli, R. W. MacLeod, F. S. Stephens, P. Bhattacharyya, C. T. Zhang

Summary

The publication investigates high-spin states in neutron-rich Rn, Ra, and Th isotopes using multi-nucleon transfer (MNT) reactions induced by heavy-ion collisions. Experiments employed ⁵⁶Fe (25 MeV/A), ⁸⁶Kr (20 MeV/A), and ¹³⁶Xe (15 MeV/A) beams impinging on a ²³²Th target, with γ-ray spectroscopy performed using the EUROGAM II array.

Key findings include:

  • High-Spin States: Observation of rotational bands in ²²⁶Th, ²²⁸Th, and ²²²,²²⁴Rn up to spins of I ≈28ħ, revealing collective behavior near the N=134 neutron mid-shell. Enhanced E2 transition strengths (B(E2) ~0.3 e²b²) suggest stable quadrupole deformation (β₂ ≈0.25) in these nuclei.
  • Transfer Mechanisms: Yield distributions of projectile-like fragments (e.g., Pb, Hg) and target-like fragments (e.g., Ra, Th) show Q-value dependence for proton pickup/neutron stripping channels. Cross sections for multi-proton stripping (e.g., 6p-8p transfers) peak at ~1 mb, while neutron transfers dominate due to lower Coulomb barriers.
  • Fission Competition: Significant fission of target-like fragments (σ_fission ≈20–30% of total transfer cross section) limits yields of neutron-rich transuranium products, highlighting challenges for exotic nucleus production.
  • Model Comparisons: The GRAZING model reproduces isotopic distributions for light fragments but underestimates yields for heavy fragments (e.g., Th isotopes), suggesting unaccounted contributions from deep-inelastic processes and N/Z equilibration.

The study underscores MNT reactions as a viable spectroscopic tool for neutron-rich heavy nuclei, bridging gaps between macroscopic models and microscopic interactions in low-energy heavy-ion collisions.

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