Reinvestigation of the Yield of the Trinity Device*

The recent movie “Oppenheimer” has revived interest in the Manhattan Project and Trinity, the world’s first nuclear explosion. Trinitite is material that was formed from desert sand and rock that was melted and  mixed together with bomb debris in the fireball following the explosion.  The yield of the device can be estimated using measurements of plutonium and a long-lived fission product in samples of Trinitite.  Previously published^1,2 analyses of trinitite to determine the yield of the Trinity nuclear explosion did not directly measure the amount of plutonium contained in the samples studied.    Furthermore, these studies utilized nuclear data that has subsequently been revised.  We have utilized a planar germanium detector to directly measure the amounts of ²³⁹Pu and ¹³⁷Cs contained in four samples of trinitite.  Using the observed rates of 52- and 129-kev gamma rays emitted in the decay of ²³⁹Pu, that of the 662-keV gamma from ¹³⁷Cs decay and a simple analysis method based on current nuclear data and weapons debris studies, we find yields that range from 5.8 to 14.9 kilotons from our four samples.  While these results are substantially lower than the actual yield of 21 kilotons, they are of the correct order of magnitude.

1.  D. Atkatz and C. Bragg, Am. J. Phys. 63, 411 (1995).

2.  D. Schlauf et al., Am. J. Phys. 65, 1110 (1997).