How fission fragments acquire their angular momentum · revision history
Revision 1
Accepted · first revision · record
- Title
- How fission fragments acquire their angular momentum
- Plain
- Fission fragments spin with several units of angular momentum even when the parent nucleus barely rotates. A 2021 experiment found that the spins of the two fragments are unrelated in size, which challenges the idea that they are set by shared motions before the split.
- Precise
- For $252\mathrm{Cf}(\mathrm{sf})$, $232\mathrm{Th}(\mathrm{n},\mathrm{f})$, $238\mathrm{U}(\mathrm{n},\mathrm{f})$ and $235\mathrm{U}(\mathrm{n}_{\mathrm{th}},\mathrm{f})$, determine when (before scission, at scission, or after, during shape relaxation of the deformed fragments) and through which collective modes (bending, wriggling, twisting, tilting) the fragment spins $J_{\mathrm{L}}$ and $J_{\mathrm{H}}$ of several $\hbar$ are generated. An answer is a dynamical calculation that reproduces the measured mean spins versus fragment mass, the observed lack of correlation between $\mid J_{\mathrm{L}}\mid$ and $\mid J_{\mathrm{H}}\mid$, and their dependence on total kinetic energy.
- Settled by
- A microscopic calculation of the joint distribution $P(J_{L}, J_{H})$ that matches gamma-spectroscopy data on spin magnitudes versus fragment mass and total kinetic energy, plus a direct measurement of spin orientation correlations.
- Kind
- phenomenon
- Answer type
- mechanism
- References
- (empty)
- Literature status
- contested
- Status note
- Since the 2021 measurement of uncorrelated spin magnitudes (Wilson et al., Nature), 2025-2026 microscopic calculations across all fragments and spin versus kinetic energy data have not settled when the spin is generated.
- Posed since
- (empty)