A standard method to detect thermal neutrons is the nuclear interaction ${}^3\mathrm{He}{(\mathrm{n},\mathrm{p})}^3\mathrm{H}$. The spin dependence of this interaction is also the basis of a neutron spin-polarization filter using nuclear polarized ${}^3\mathrm{He}$. We consider the corresponding interaction for neutrons placed in an intrinsic orbital angular momentum (OAM) state. We derive the relative polarization-dependent absorption cross sections for neutrons in an $L=1$ OAM state. The absorption of those neutrons results in compound states $J^{\pi }=0^{-}$, $1^{-}$, and $2^{-}$. Varying the three available polarizations tests that an OAM neutron has been absorbed and probes which decay states are physically possible. We describe the energetically likely excited states of ${}^4\mathrm{He}$ after absorption, taking account of the odd parity of the compound state. This provides a definitive method for detecting neutron OAM states and suggests that intrinsic OAM states offer the possibility to observe new physics, including anomalous cross sections and new channels of radioactive decay.

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• Neutron physics
• Nuclear spin & parity
• Nuclear structure & decays
• Polarization phenomena
• Quantum measurements
• Neutrons