De-excitation effects in multi-nucleon transfer reactions

This study quantifies the impact of nuclear de-excitation on correlations in multi-nucleon transfer (MNT) reactions. To bridge the gap between initial collision dynamics and final experimental observables, we introduce a hybrid TDCDFT+GEMINI approach, integrating time-dependent covariant density functional theory (TDCDFT) with the statistical de-excitation model GEMINI++. Applied to the $^{40}$Ca + $^{208}$Pb reaction, our method demonstrates that the de-excitation is essential for reconciling theoretical cross sections with experimental data. Analysis of the cross-section Shannon entropy reveals that new reaction channels open abruptly at a specific energy threshold. By employing mutual information, we show that the de-excitation process significantly degrades the initial quantum entanglement between the projectile-like and the target-like fragments, revealing a key mechanism through which fundamental quantum correlations are lost.

💡 Research Summary

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This paper addresses a long‑standing challenge in the theoretical description of multi‑nucleon transfer (MNT) reactions: the discrepancy between the primary fragments produced directly after the collision and the final products that are actually measured in experiments. The authors develop a hybrid framework, denoted TDCDFT+GEMINI, that couples time‑dependent covariant density functional theory (TDCDFT) with the statistical de‑excitation code GEMINI++. TDCDFT provides a fully microscopic, quantum‑mechanical treatment of the collision dynamics, solving the time‑dependent Dirac equation for all occupied single‑particle states with a relativistic energy density functional (PC‑PK1). After the two nuclei separate, the wave function is partitioned into a projectile‑like fragment (PLF) and a target‑like fragment (TLF). Using particle‑number projection operators, the authors extract the probability distribution P_{N,Z}(E,b) for each fragment to contain a given number of neutrons (N) and protons (Z) as a function of incident energy E and impact parameter b. From the same projected wave function they compute the total angular momentum J_{N,Z} and the internal excitation energy E^{*}{N,Z} = E{N,Z} – E_{gs}(N,Z).

These three quantities (N,Z,J,E^{*}) constitute the initial conditions for GEMINI++, which simulates the subsequent cascade of binary decays, light‑particle evaporation, and fission. The statistical nature of GEMINI++ is respected by performing 1 000 Monte‑Carlo trials for each primary fragment; the resulting secondary probability ˜P_{N’,Z’}(b,E) is then integrated over impact parameters to obtain the observable cross sections ˜σ_{N’,Z’}(E).

The method is applied to the benchmark reaction 40Ca + 208Pb at laboratory energies ranging from 235 to 270 MeV. The authors first reproduce the primary‑fragment cross sections obtained in a previous TDCDFT study, confirming that the maximum impact parameter for fusion is b≈4.63 fm and that nucleon transfer becomes negligible for b≥10 fm. When the de‑excitation stage is included, the secondary cross sections align closely with experimental data (Ref.