On the search for strange matter

We report on a search for supermassive nuclei in nature with masses up to 107 amu. Such exotic nuclei might consist, for example, of stable 'strange' matter, which comprises a mixture of up, down, and strange quarks. Supermassive nuclei are among the candidates of dark matter which is likely to constitute a major fraction of the mass of the Universe. Our experiments are based on Rutherford backscattering of heavy ions, preferably 238U, from various target samples. The scattering of 238U into the backward hemisphere would indicate the presence of more massive and possibly strange nuclei. In our experiments no clear indication of the presence of supermassive isotopes was observed. The resulting upper limits for the abundance of exotic nuclei with masses up to 107 amu were found to be in the range 10-11 to 10-17 relative to the number of nucleons. (orig.)