Heavy Isotope Abundances in Mike Thermonuclear Device

The November 1, 1952 thermonuclear explosion ("Mike") produced all of the uranium isotopes ${\mathrm{U}}^{239}$, ${\mathrm{U}}^{240}$,...${\mathrm{U}}^{255}$ through multiple neutron capture by ${\mathrm{U}}^{238}$. The long-lived products of successive ${\beta }^{-}$ decays from these isotopes were measured mass spectrometrically and radiometrically. The logarithms of the abundances decline smoothly with increasing mass number; the even-mass abundances slightly exceed the geometric mean of adjacent odd-mass abundances. Some nuclear properties of neutron-rich heavy nuclides, not subject to ordinary investigation are inferred.