va]ˈnalə̇n-, və] noun
Usage: usually capitalized V&A
Etymology: after James A. Van Allen b 1914 American physicist
: a belt of intense ionizing radiation that surrounds the earth in the outer atmosphere, has particles carrying energies of from approximately 20,000 electron volts to several million electron volts or more, and has an outer zone that extends into space to a distance of about 55,000 kilometers