If an antineutron hits a neutron, both turn into energy.
The neutron shot out of the picture undetected, but the antineutron hit a carbon atom in the propane and committed double suicide with one of its protons or neutrons.
It is the antimatter counterpart to the nucleus of deuterium (heavy hydrogen), consists of an antiproton and antineutron bound by a strong nuclear force, and has a negative .