  Direction sensitivity could provide robust evidence for the direct detection
of weakly interacting massive particles constituting dark matter. However, the
sensitivity of this method remains low due to the radioactive backgrounds. The
purpose of this study is to develop a low-background detector as a
two-dimensional imaging device for a gaseous time projection chamber. In
direction-sensitive dark matter experiments~(e.g. NEWAGE), $\alpha$-rays
emitted from the detector components often create substantial radioactive
backgrounds. Based on the study of the background of NEWAGE, a new detector
"low-$\alpha$ $\mu$-PIC" is developed. The produced $\mu$-PIC performs well as
a gas detector and the $\alpha$-ray emission rate from the $\mu$-PIC reduced by
a factor of 100.
