Reconstruction of fallout deposition from U.S. atmospheric nuclear tests conducted in New Mexico and Nevada.

Between 1945 and 1962, the United States conducted 101 atmospheric nuclear weapon tests in New Mexico and Nevada, dispersing radioactive fallout across the contiguous United States. We reconstruct the first 10 days of fission-product deposition from the 94 non-zero-yield tests using U.S. government test data, benchmarked particle-size distributions, and the HYSPLIT atmospheric transport model driven by high-resolution ERA5 reanalysis. Comparisons with county-level iodine-131 deposition estimates from the National Cancer Institute show good agreement for tower and surface tests and motivate refinement of the particle-size distribution parameters associated with airbursts. We aggregate per-test reconstructions into a cumulative deposition map that includes long-range fallout from the 1945 Trinity test. Trinity fallout alone reached 46 states within 10 days, consistent with contamination observed in Indiana and Iowa soon after the test. An ensemble analysis bounds meteorological uncertainty for Trinity, showing robust large-scale transport patterns despite relatively sparse 1945 observations.