We developed a simple small-scale detection method for beta decay
spectrum of 3H. This research is motivated to investigate the presence
of sterile neutrinos in keV region. In our experiment, tritium nuclei
are embedded in a 1x1x1 cm^3 LiF crystal from 6Li(n,3H)4He reaction.
The beta energy spectrum is measured with an MMC sensor, one of the
high-resolution microcalorimeters operating at mK temperatures. We
present the method for the sample preparation and the experiment
together with the physics result from the first measurement set.
Moreover, an expected sensitivity to search for the heavy neutrino is
discussed for one year measurement with the setup.