Detection of Illicit Nuclear Materials Masked with other Gamma-Ray Emitters
The purpose of this work was to experimentally determine the extent to which legal shipments of radioisotopes could be used to mask the presence of illicit nuclear materials and the means by which this can be accomplished.
Characteristics of prompt, delayed, and prompt-delayed radiation in monitoring strongly screened fissile substances by the pulsed photonuclear method
The purpose of the present work is to investigate numerically the energy-time characteristics of γ and neutron radiation emitted from strongly screened fissile substances irradiated by pulsed bremsstrahlung. It is shown that when fissile materials are screened by a metal with a small or medium atomic number (e.g., aluminum and iron) the prompt and delayed neutrons provide the greatest information for monitoring fissile substances. When fissile substances screened by hydrogen-containing materials are irradiated, γ rays delayed with respect to the probe radiation pulse are emitted and can be an indication of the presence of fissile substances. The time intervals for detecting prompt and delayed neutrons and delayed γ rays are evaluated.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.