Final answer:
The specific interval at which the USAF performs leak tests for radioactive material is not detailed in the reference material, but such tests could typically be conducted annually, with variations based on regulation or policy. The reference material discusses the impact of nuclear fallout and the international treaties aimed at limiting nuclear testing and its environmental effects.
Step-by-step explanation:
The question regarding leak tests for radioactive material permitted by the USAF is specific to their regulations and not directly addressed in the provided reference material. However, based on standard industry practices and safety protocols for monitoring and maintaining nuclear materials, testing intervals can vary. Typically, such intervals for checking the integrity of sealed radioactive sources or containers might be annually, but this can differ based on regulatory requirements or the specific policies of an organization.
The reference material discusses the environmental impact of nuclear fallout, mentioning that the fallout from atmospheric tests is mainly composed of isotopes such as 90Sr and 137Cs with specific half-lives. It also touches upon international efforts to limit nuclear testing and the attempt to mitigate environmental contamination. For instance, the Partial Test Ban Treaty of 1963 significantly changed the landscape of nuclear testing by restricting atmospheric tests, which in the past had increased environmental radiation levels and had measurable impacts far beyond the test sites themselves.