Abstract G(Br -)-values have been evaluated in Ar- and N 2O-saturated 1,2-dibromoethane (DBE), bromobutane, propylbromide and bromopentane (BP) under a variety of experimental conditions in aqueous solutions. G(Br -) increases with increasing halogenated hydrocarbon concentration and with increasing pH. Free Ḃr atoms formed as a result of e - aq and ȮH radical reactions with bromohydrocarbons are considered to initiate a chain reaction. Another chain reaction has been invoked to explain the high G(Br -) at high pH. Ḃr radicals may form a reactive intermediate with OH - (BrOH ⨪), which decays to Br - and ȮH. The ȮH radicals have been found to interact with bromohydrocarbons and eventually yields Br - ions. The formation of Br - ions is accelerated both at acidic and alkaline pH in systems containing t-butanol. Dose rate studies in Ar- and N 2O-saturated 1,2-DBE and BP show an increase in G(Br -)-values at low dose rate and confirm the occurrence of a chain reaction initiated by Ḃr atoms. From these studies the rate constant for the reaction of Ḃr with 1,2-DBE has been calculated to be ∼ 1 × 10 6M -1s -1.