The topological information (averaged angle) of Cherenkov light was measured by UNI-ZICOS
detector. We have retuned the pulse shape discrimination for a selection of the photomultiplier
which receives Cherenkov light for Hamamatsu H3164-12, and have developed a method of the
vertex reconstruction. An averaged angle for fixed energy fixed direction electron generated by
Compton scattering from Y-88 was used for the validity checking of the selection of PMT, and the
obtained peak was found around 50 degree which was reproduced by Monte Carlo simulation. A
pseudo background events of simultaneous beta and Compton electron scattered by gamma from
the decay of Tl-208 was simulated by Co-60 β source. Obtained data indicated that the averaged
angle of simultaneous beta with E ≤ 1.48 MeV plus gamma events should have a peak around 60
degree, and the value is different from 48 degree for an usual electron. In conclusion, the averaged
angle will be able to use as a reduction method for Tl-208 beta decay backgrounds even though they
have an energy around 3.35 MeV which is Q-value of Zr-96 neutrinoless double beta decay.