Search for Stable, Abnormal (Collapsed) Nuclei in Nature

Very tightly bound, abnormally-high-density states of nuclei, suggested as a possibility by Bodmer and by Lee and Wick, have been searched for as an anomalous isotope of radon. This was done by looking for high-energy $\gamma$ rays following thermal-neutron capture. The limit that may be set for the atomic concentration of such nuclides on Earth is ∼${10}^{-29\mathrm{}}$ atom of Si.