Historical background on the replacement of gaseous diffusion by gas centrifuges and diffusion-plant closures. The later webpage is not used to assign present-day plant counts to 2019.
Consolidated Guidance About Materials Licenses, Volume 12 by United States Nuclear Regulatory Commission Created 2026-10-20 Updated 2026-11-05
Appendix I, printed page I-2, distinguishes low-atomic-number beta shielding from an outer layer used to reduce secondary bremsstrahlung.