U235Fission Yields in the Rare Earth Region

Abstract

The ${\mathrm{U}}^{235}$ fission yield curve for uranium fuel rods from mass number 143 to 160 has been measured, utilizing mass spectrometric techniques. Eight percentage yields are assumed in this region, and on the basis of measurements of the neodymium, samarium, europium, and gadolinium fission isotopes, nine other yields are obtained. The resulting yield curve is smooth. Based on the same assumptions which give the smooth yield curve the following cross sections and half-lives are obtained: Cross sections, ${\mathrm{Sm}}^{149}$, 47,000 barns; ${\mathrm{Sm}}^{151}$, 7200 barns; ${\mathrm{Gd}}^{155}$, 41,000 barns; ${\mathrm{Gd}}^{157}$, 59,500 barns; half-lives, ${61}^{147}$, 2.26 yr.; ${\mathrm{Sm}}^{151}$, 122 yr.