NUC In the literature: open

Distribution of the angle between the two fragment spins

In plain words

Even if the sizes of the two fragment spins are unrelated, their directions could still be linked, and different theories predict different answers. Measuring the angle between them would tell which spinning motions are at work.

Precise statement

Compute and measure the distribution $P(\operatorname{cos}\theta_{\mathrm{LH}})$ of the opening angle between the fragment spin vectors $J_{\mathrm{L}}$ and $J_{\mathrm{H}}$ in $252\mathrm{Cf}(\mathrm{sf})$ or $235\mathrm{U}(n_{\mathrm{th}},\mathrm{f})$. Bending modes favor antiparallel spins and wriggling modes favor parallel spins perpendicular to the fission axis, while statistical post-scission generation gives a nearly isotropic distribution; the answer is the measured distribution and which mode content it implies.

What would settle it

A measurement of the opening-angle distribution, for example from angular correlations of gamma rays from both fragments, compared with time-dependent density-functional predictions.

Status in the literature

Unverified note

Time-dependent density-functional and statistical (FREYA) predictions of $P(\operatorname{cos} \theta_{\mathrm{LH}})$ differ, with a 2024 analysis tracing part of the difference to quantal spin effects; no measurement of the opening-angle distribution was found as of 2026.