Types of Nuclear Materials

Special Nuclear Material consists of plutonium, uranium-233 or uranium with U²³³ or U²³⁵ content greater than that found in nature (i.e., >0.71% U²³⁵)

Source Material is thorium or uranium with a U²³⁵ content equal to or less than that found in nature (i.e., ≤ 0.71% U²³⁵)

Byproduct Material, in general, is radioactive material other than source or special nuclear material.  Specifically, by-product material is (a) isotopes produced or created in a nuclear reactor; (b) the tailings and waste produced by extracting or concentrating uranium or thorium from an ore processed primarily for its source material content; (c) discrete sources of radium-226 and (d) discrete sources of naturally occurring or accelerator-produced isotopes that pose a threat equal to or greater than a discrete source of radium-226.

Radium is a radioactive substance found in nature. Radium is produced by the radioactive decay of uranium. The intensity of radiation from radioactive materials decreases over time. The time required for the intensity to decrease by one-half is referred to as the half-life. The half-life of radium is approximately 1,600 years.