The spinner technique was used for a search for superheavy elements in chemical compounds, minerals, and in targets which were irradiated with 24-GeV protons. For minerals and chemical compounds upper limits for the concentration of eka-elements of ${10}^{-13\mathrm{}}$-${10}^{-14\mathrm{}}$ g per gram of the homolog element were obtained, assuming a half-life for spontaneous fission of ${10}^9$ yr. Production cross sections of the order of ${10}^{-39\mathrm{}}$ ${\mathrm{cm}}^2$ were established as upper limits for the formation of eka-elements and actinides in tungsten targets irradiated by high-energy protons, if half-lives of one year are assumed.

[RADIOACTIVITY Fission of superheavy elements ($Z=110-115\mathrm{}$) from natural samples, limits for $T_{\frac{1}{2}}$, measured with the spinner technique.

NUCLEAR REACTIONS $W$ ($p$, recoil) actinides, eka-elements ($Z=110-115\mathrm{}$), $E_p=24\mathrm{}$ GeV, measurement of spontaneous fission with spinner technique.]

• Received 2 August 1973

DOI:https://doi.org/10.1103/PhysRevC.9.48