Signatures of Weapon-grade Plutonium from Dedicated Production Reactors

We report neutronics calculations for the most important natural uranium fueled reactor types historically used for weapons plutonium production. These include an early design of the \\Hanford-type\" graphite-moderated and light-water-cooled reactor used in the United States, the \\Calder-Hall-type\" graphite-moderated and gas-cooled reactor used in the United Kingdom, and the \\NRX-type\" heavy- water-moderated and light-water-cooled reactor, originally developed in Canada for civilian purposes, but later used in India and Pakistan for military plutonium production. We show it is possible in principle to distinguish with a high level of condence weapon-grade plutonium compositions produced in other types of reactors, e.g. light-water-cooled or fast neutron reactors, but that it is rather dicult to distinguish among plutonium compositions that were generated in dedicated production reactors fueled with natural uranium. This suggests that eorts to determine the origin of weapon-grade plutonium could well remain inconclusive without access to databases based on actual samples.