<radiobiology> Activation occurs when a particle interacts with an atomic nucleus, shifting the nucleus into an unstable state, and causing it to become radioactive.

In fusion research, where deuterium-tritium is a common fuel mixture, the neutron released when (D + T) combine to form (4He + n) can activate the reactor structure. In this case the 4He is inert, the neutron sticks to another nucleus, and the neutron + nucleus reaction creates an actvation product. Sometimes called radioactivation.

See: activation product, activation analysis.

(09 Oct 1997)