Mass and nuclear charge distributions from the spontaneous fission of 254Fm

The relative fission yields of 20 mass chains from ²⁵⁴Fm spontaneous fission were measured by direct high-resolution γ-ray spectroscopy of the gross fission products. Reflected yields were calculated based on a prompt-neutron fission yield of 3.94; the absolute yields were determined by requiring the sum of all yields to be 200%. A peak-to-valley ratio for the mass-yield curve of ≥18 was determined radiochemically by measuring the cumulative yields of ¹⁴⁰Ba and ¹²⁷Sb.²⁵⁴Fm was produced by irradiating ²⁵³Es in a high-flux reactor and then chemically separating the 3.24-h ²⁵⁴Fm from its 39.3-h ${}^{254}{Es}^m$ parent. An aluminum "catcher" foil was used to collect the ²⁵⁴Fm fission products. Nuclear charge distribution studies included measurements of the independent yields of ¹⁴⁰La, ¹³⁵Xe, ¹³⁴I, and ¹³²I relative to their cumulative yields from direct γ-ray-spectroscopy data.