  One hundred and one atmospheric nuclear weapon tests were conducted between
1945 and 1962 in the United States, resulting in widespread dispersion of
radioactive fallout, and leading to environmental contamination and population
exposures. Accurate assessment of the extent of fallout from nuclear weapon
tests has been challenging in the United States and elsewhere, due to limited
monitoring and data accessibility. Here we address this deficit by combining
U.S. government data, high-resolution reanalyzed historical weather fields, and
atmospheric transport modeling to reconstruct radionuclide deposition across
the contiguous United States, with 10-kilometer spatial and one-hour temporal
resolution for five days following detonation, from all 94 atmospheric tests
detonated in New Mexico and Nevada with fission yields sufficient to generate
mushroom clouds. Our analysis also includes deposition estimates for 10 days
following the detonation of Trinity, the first ever nuclear weapon test, on
July 16, 1945. We identify locations where radionuclide deposition
significantly exceeded levels in areas covered by the U.S. Radiation Exposure
Compensation Act (RECA). These findings include deposition in all 48 contiguous
U.S. states. They provide an opportunity for re-evaluating the public health
and environmental implications from atmospheric nuclear testing. Finally, our
findings also speak to debates about marking the beginning of the Anthropocene
with nuclear weapons fallout. Our deposition estimates indicate that direct
fallout from Trinity, a plutonium device, reached Crawford Lake in Canada, the
proposed "golden spike" site marking the beginning of the Anthropocene epoch,
starting on July 20, 1945.

Atmospheric and Oceanic Physics;Physics and Society