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Complex Nuclear Structure Phenomena Revealed from Nuclide Production in Fragmentation Reactions

This article presents experimental data from the 1A GeV 238U -> Ti reaction, revealing complex structural effects in nuclear phenomena. The results are analyzed using a statistical evaporation model, considering the role of pairing and other potential effects. The even-odd staggering of residual nuclei is observed in its entirety for the first time in high-energy reactions. Theoretical models, such as nuclear superfluidity and dynamical cluster decay, provide limited agreement. The proposed explanation suggests that even-odd fluctuations are produced at the end of the evaporation cascade. The statistical evaporation code ABRABLA successfully reproduces the main characteristics of the staggered yields. The findings highlight the restoration of structural effects in the end products of hot decaying nuclei, regardless of the initial reaction mechanism. The even-odd staggering is attributed to the blocking effect of pairing, but more complex phenomena may also contribute. Yield measurements from highly excited nuclei offer valuable insights into nuclear structure.

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Complex Nuclear Structure Phenomena Revealed from Nuclide Production in Fragmentation Reactions

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  1. Complex nuclear-structure phenomena revealed from the nuclide production in fragmentation reactions M. V. Ricciardi1, A.V. Ignatyuk2, A. Kelić1, P. Napolitani1, F. Rejmund3, K.-H. Schmidt1, O. Yordanov1 1GSI, Darmstadt, 2IPPE, Obninsk, Russia, 3IPN, Orsay, France Nuclear Physic A 733 (2004) 299-318 • OUTLINE • Experimental data from 1 AGeV 238U  Ti at the FRS (GSI) • reveal complex structural effects • Analysis of the results with statistical evaporation model • The role of pairing and other possible effects • Conclusions

  2. Experimental data (measured at FRS) Production cross sections of residues 1 AGeV 238U Ti Sequences: N-Z=constant

  3. ● N=Z■ N=Z+2 ▲N=Z+4 N=Z+6 ● N=Z+1■ N=Z+3▲ N=Z+5

  4. IS THIS OBVIOUS? Experimentally First time that the even-odd staggering of the residual nuclei from high-energy reactions is observed in all its complexity Theoretically Nuclear superfluidity: it vanishes at about E*~10 MeV  valid only for low-energy-reaction residues Dynamical cluster decay model: the quantitative agreement is rather poor Our proposition: even-odd fluctuations are produced at the end of the evaporation cascade

  5. ANALYSIS WITH AN EVAPORATION CODE (ABRABLA)

  6. CONCLUSIONS         • Structural effects are restored in the end products of hot decaying nuclei, regardless of the first-stage of the reaction mechanism • A statistical evaporation code can reproduce the main characteristics of the staggering • The the main characteristics of the staggering are a manifestation of the blocking effect of pairing • more complex phenomena could be responsible for the strong even-odd structure observed in the yields of the N=Z residues • Yields from highly excited nuclei are a rich source of information on nuclear structure

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