Magnetic fields and radical reactions: recent developments and their role in nature.

Recombination of pairs of radicals is exceptional in being affected by magnetic fields. The mechanism has been known for some thirty years, but recently new applications have appeared and research has been extended to very high fields (up to 30 Tesla). Claims that low electromagnetic fields damage health have led to extensive medical, chemical and physical research: no firm evidence of hazards has emerged; on the other hand, migrating birds orient themselves in the earth's field (50 microT): radical pairs may provide the mechanism.