Cyclooctatetraene C8H8, although a very reactive compound, is remarkably resistant to gamma irradiation1. Liquid phase radiolysis at high dose1,2, 30–50 Mrad, yields hydrogen, acetylene, benzene and some polymeric material. Such radiation resistance is rather surprising since gaseous C8H8readily undergoes photoisomerisation to styrene and photodecomposition to give benzene and acetylene3,4. More recent photochemical studies at lower temperatures also report bicyclo-4.2. O-octa-2,4,7-triene5and semibullvalene6as reaction products.