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 by set for the atomic concentration of such nuclides on Earth is approx.10$sup -29$ atom of Si. (AIP)