US Patent 7622709 Variable-ratio neutron-gamma ray source

A variable-ratio neutron-gamma ray source comprises a neutron generator, a shield, a collimator, and an external gamma target. The neutron generator generates neutrons and the shield reduces external radiation exposure. The collimator collimates the neutrons into a neutron beam that traverses the shield. The external gamma target generates a dual neutron-gamma ray beam from the neutron beam, wherein the dual neutron-gamma ray beam has a variable neutron-gamma ratio as a function of a thickness of the external gamma target.