  The best method of measuring CP violating effect in neutrino oscillation
experiments is to construct and use a neutrino beam made of an ideal mixture of
$\bar{\nu}_e$ and $\nu_e$ of monochromatic lines. The conceptual design of such
a beam is described, together with how to measure the CP-odd quantity. We
propose to exploit an accelerated unstable hydrogen-like heavy ion in a storage
ring, whose decay has both electron capture and bound beta decay with a
comparable fraction.
