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Polarized proton spin filter for epithermal neutron based on dynamic nuclear polarization using photo-excited triplet electron spins

For the polarization of neutrons with an energy level of \textcolor{black}{$>0.1$ eV}, we developed a novel polarized proton spin filter based on dynamic nuclear polarization using photo-excited triplet electron spins. The spin filter consists of a single crystal of naphthalene doped with deuterated pentacene and has a size of $\phi15\times4$ ${\rm mm}^3$, allowing it to cover a wide beam diameter. It was operated in 0.35 T and at 90 K. We succeeded in polarizing neutrons in the energy range $0.1-10$ eV using a RIKEN accelerator-driven compact neutron source. The averaged values of the proton and neutron polarization were $0.250\pm0.050$ and $0.076\pm0.015$, respectively.