Anisotropic response measurements of ZnWO₄scintillators to neutrons for developing the direction-sensitive dark matter detector

The scintillation yields of ZnWO₄crystals change depending on the incident direction of particles. This property can be used as a direction-sensitive dark matter detector. So, we investigated the ZnWO₄light yields ratio of neutron-induced nuclear recoils to gamma-ray induced electron recoils(quenching factor). Two surfaces almost perpendicular to the crystal axis of ZnWO₄were irradiated with a quasi-monochromatic neutron beam of 0.885MeV, and the quenching factors of both surfaces for the oxygen-nucleus recoil in the ZnWO₄crystal were measured. The obtained quenching factors of the two surfaces were 0.235 ± 0.026 and 0.199 ± 0.020, respectively confirming 15.3% of anisotropy.