  A natural nuclear fission reactor with a power output of 3- 10 terawatt at
the center of the earth has been proposed as the energy source of the earth's
magnetic field. The proposal can be directly tested by a massive liquid
scintillation detector that can detect the signature spectrum of antineutrinos
from the geo-reactor as well as the direction of the antineutrino source. Such
detectors are now in operation or under construction in Japan/Europe. However,
the clarity of both types of measurements may be limited by background from
antineutrinos from surface power reactors. Future U. S. detectors, relatively
more remote from power reactors, may be more suitable for achieving unambiguous
spectral and directional evidence for a 3TW geo-reactor.
