A tandem mass spectrometer of high sensitivity has been used to measure the relative yields of the six stable isotopes of tin (117Sn, 118Sn, 119Sn, 120Sn, 122Sn, and 124Sn) and the long-lived isotope 126Sn, produced in the thermal- and fast-neutron fission of 233U and in a reactor fuel rod of natural uranium. Samples of the order of 10−9 g of tin were extracted and analyzed to give a range of yields in the region of symmetric fission. The results show that the mass yield curves in the region of symmetric fission covered by the stable tin isotopes are almost identical for the three irradiations. Furthermore, a smooth curve can be drawn through the yield points for the seven isotopes of tin and there is no evidence of "fine structure" or sharp depression in the curves in this region as has been predicted.
From fission yield measurements to evaluation: status on statistical methodology for the covariance question