Fission of U233 with 14.8-MeV Neutrons

We have measured the yields of 25 products in the mass range from 66 to 175 from fission of ${\mathrm{U}}^{233}$ with 14.8-MeV neutrons. Each fission yield was measured in an absolute way, the number of atoms formed of each product being measured by absolute $\ensuremath{\beta}$- and $\ensuremath{\gamma}$-counting techniques. The number of fissions occurring was calculated from the target mass, the fission cross section, and the total neutron fluence. The neutron fluence in the target was monitored by the ($n, 2n$) reaction on yttrium foils. Total chain yields were estimated by correcting for the effects of nuclear charge dispersion in fission. The contribution of target-impurity activation to the measured fission yields is generally small.The yields of products on the wings of the mass-yield distribution are consistent with a Gaussian function, which is similar to those found previously for ${\mathrm{U}}^{235}$ and ${\mathrm{U}}^{238}$ fission. The yields of a number of unmeasured products on the wings have been estimated and tabulated using the Gaussian curve.The yields of a sufficient number of products in the peak and valley regions were measured so that a rough outline of the high-yield portion of the mass distribution could be made. The area under each half of the mass-yield curve was about 1.08, or 8% high. This discrepancy may be due to insufficient knowledge of the mass-yield curve, the contribution of fission induced by non-14.8-MeV neutrons, and/or errors in the cross sections that were used for the monitor reaction and the ${\mathrm{U}}^{233}$ fission reaction.We observe a very low peak-to-valley ratio of about 3.1, which is smaller than found for fission of other nuclides with 14.8-MeV neutrons. Our yields in the valley region are about 70% higher than those measured previously by others. We feel that this is probably due to the contribution of low-energy neutron fission in the earlier work, coupled with their normalization to unit fragment yield. A thermal-neutron contaminant of 0.3% in the target region could have caused the observed discrepancy.The fission yield of the shielded product ${\mathrm{Tb}}^{160}$ was measured as (3.2\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$. Using the total chain yield for mass 160 calculated from our Gaussian distribution function, we obtain (4.3\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ for the independent fractional chain yield. This value was used to estimate the ${Z}_{p}$ function for ${\mathrm{U}}^{233}$ fission in order to calculate total chain yields from observed fission yields.