  Recent ideas suggest that the 18.6 keV antineutrino (nuebar) line from 2-body
decay of 3H in crystals is emitted with natural width, motionally narrowed by
lattice vibrations as in recoilless emission. It can be resonantly captured in
3He with geometrical cross section sigma ~10 ^ -17 cm2. A key technique solves
a basic obstacle for achieving resonance--the chemical difference of H and He
in metals. The low nue energy, the high sigma and the hypersharp sensitivity
DELTA E/E ~10^--29 make an extraordinary tool for bench scale tests of nue
theta13 oscillations and predicted Planck length limits on nuclear level widths
in models of quantum gravity.
