Role of pairing in generating fission-fragment spin

Determine how pairing correlations influence the formation of intrinsic angular momentum and high-$K$ components in primary fission fragments, particularly whether pairing survives until nuclear scission while becoming sufficiently attenuated to permit diabatic retention of high-$\Omega$ quasiparticle configurations as mutually compensating fragment-$K$ components.

Background

The paper studies the origin of intrinsic spin in fission fragments using finite-temperature pairing and a multidimensional scission analysis for 236^{236}U. Pairing normally couples time-reversed nucleons into K=0K=0 pairs, suppressing separate angular-momentum projections, whereas pair attenuation may expose near-Fermi high-Ω\Omega orbitals during rapid neck rupture. The authors identify spectroscopically available high-KK channels and argue that non-adiabatic scission could retain them as locally compensated fragment projections.

The unresolved issue is whether the pairing field remains sufficiently strong to be consistent with observed odd–even effects while becoming sufficiently attenuated near rupture to allow diabatic occupation of high-Ω\Omega configurations. The paper estimates spectroscopic capacities and proposes a microscopic mechanism, but it does not calculate the dynamical populations of the resulting configurations.

References

However, the role of pairing in this process remains an open question.

— From Superfluid Coherence to High-$K$ Fragment Channels at Nuclear Scission  (2609.11485 - Kowal et al., 10 Sep 2026) in Introduction, paragraph beginning “Microscopic calculations show that fragment deformation”