20世纪50年代的核武器弹芯多用纯鈾-235,或者与钚复合,但是纯钚弹芯的直径最小,并且20世纪60年代初以来被视为标准。 "Restricted Data Declassification Decisions from 1945 until Present" (页面存档备份,存于互联网档案馆) – "Fact that plutonium
Marais, Adele; Vieira, Elisabeth Meloni; Reed, Geoffrey M. Proposed declassification of disease categories related to sexual orientation in the (ICD-11)
to the Warfighters 互联网档案馆的存檔,存档日期2001-06-18." Out of the Black: The Declassification of the NRO. nsarchive2.gwu.edu. [2021-05-27]. (原始内容存档于2021-08-26).