The daughter x-ray identification technique has been applied to the identification of element 104. The characteristic $K$-series x rays from the $\alpha$-decay daughter isotope, nobelium ($Z=102\mathrm{}$), have been observed in coincidence with $\alpha$ particles from the decay of 4.5-sec ${}_{}{}^{257}{}_{}{}^{}104$, thus providing an unequivocal determination of the parent atomic number, $Z=104\mathrm{}$.

• Received 25 June 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.647