Fission Product Studies with the SPIDER Instrument at LANSCE

In order to advance our understanding of the fission process we need to measure changes in fission product yields as a function of excitation energy of the fissioning system, as well as study the correlations between kinetic energy, mass and charge of the products. In addition, fission product yields are used for diagnostics in nuclear technology and there is therefore interest in reducing the uncertainties in their yield. The SPIDER instrument is based on the 2v-2E technique for measuring the mass of fission products, and has been used to study spontaneous fission of Cf-252, as well as thermal neutron-induced fission of U-233, U-235, and Pu-239. The current instrument has two spectrometer "arms", which provides sufficient detection efficiency for studying fission at thermal neutron energies. In order to study the change in fission yields at fast energies higher detection efficiency is needed, and a new version of SPIDER is therefore under construction. The new instrument will have a total of 16 individual arms, bringing the total solid angular coverage to about 1%.