Passive Gamma-Ray and Neutron Imaging Systems for National Security and Nuclear Non-Proliferation in Controlled and Uncontrolled Detection Areas: Review of Past and Current Status

Global concern for the illicit transportation and trafficking of nuclear materials and other radioactive sources is on the rise, with efficient and rapid security and non-proliferation technologies in more demand than ever. Many factors contribute to this issue, including the increasing number of terrorist cells, gaps in security networks, politically unstable states across the globe and the black-market trading of radioactive sources to unknown parties. The use of passive gamma-ray and neutron detection and imaging technologies in security-sensitive areas and ports has had more impact than most other techniques in detecting and deterring illicit transportation and trafficking of illegal radioactive materials. This work reviews and critically evaluates these techniques as currently utilised within national security and non-proliferation applications and proposes likely avenues of development.

THE KINETIC ENERGY OF Cs136 PRIMARY FRAGMENTS FROM FISSION OF U235

The ranges of Cs136, Cs137, and Ba140 fission fragments in aluminum have been measured using an anodizing technique to strip layers from the aluminum together with radiochemical methods to determine the fission products. The mean ranges are, in milligrams per square centimeter: Cs136, 2.64; Cs137, 2.91; and Ba140, 2.82. The range distributions were of near-Gaussian form with the following percentage full widths at half height; Cs136 17.7; Cs137, 17.0; and Ba140, 17.5. The range–energy relationship of Bohr, R = const. A1/2E1/2Z−2/3, was tested using the range data of Katcoff (7) and of Niday (2) together with the kinetic energy data of Milton and Fraser (15) and found to be accurate, within experimental error, over any limited range of fragment masses. Using this formula it then appears that the total kinetic energy in the fission mode leading to Cs136 is ∼21 Mev less than normal.