Measurement of the Anisotropic Response of the ZnWO₄ Crystal for Developing the Direction-Sensitive Dark Matter Detector

Abstract

We measured the scintillation light yield of ZnWO 4 crystals using a quasi-monochromatic neutron beam energy of 865 keV. Irradiating the neutron beam on two surfaces, which are almost perpendicular to the crystal axis, the light yield of oxygen recoil was measured. The obtained light yield ratio of a neutron recoil to gamma-ray-induced electron recoil for two surfaces was 0.235 ± 0.026 and 0.199 ± 0.020, respectively, which corresponds to 15.3% of anisotropy for ∼200-keV nuclear recoils of this crystal. This property can be applied to a directionsensitive dark matter (DM) detector.

Precise measurement of the scintillation decay constant of ZnWO$_4$ crystal

“…The anisotropic scintillation responses of a ZnWO 4 crystal to heavy particles [11,12] were investigated by irradiating each surface of the cubic crystal with α-particles from 241 Am and obtaining the scintillation decay time constants. The main components of the time constants depended on the incident surface.…”

“…The crystal was produced at the Laboratory of Crystal Growth, Nikolaev Institute of Inorganic Chemistry in Russia and was cut by Crystal Manufacturing Lab. Ltd. (Russia) [12]. During cutting, the shape of the monoclinic unit cell was preserved as far as possible (see Fig.…”

“…With these crystals, the WIMPs' signal can be obtained by comparing the visible energy spectra measured for different orientations related to the WIMP wind. The anisotropic scintillation response of ZnWO 4 crystals was first reported in 2005 [6][7][8] and has since been measured under irradiation with α and neutron sources [11][12][13]. The radiopurity of ZnWO 4 is considered as an advantage in dark matter detectors [9,10].…”