Two-neutron emission from electromagnetic dissociation ofCo59andAu197targets by relativistic heavy ions

Electromagnetic dissociation of ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ and ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ target nuclei and their subsequent deexcitation by two-neutron emission was observed. Beams of relativistic ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ ions were used. The measured electromagnetic dissociation cross sections become large for high-Z targets and projectiles, reaching 335 mb for the ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ ${(}^{139}$La,X${)}^{195}$Au reaction with 1.26 GeV/nucleon ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ projectiles. The experimental cross sections in excess of the estimated nuclear contributions are in reasonable agreement with a calculation of the electromagnetic dissociation contribution using the Weizsäcker-Williams method for estimating the virtual photon spectrum.