Aspects of charge distribution measurement for Cf 252 (sf)

Measurements of charge distributions of fragments in the spontaneous fission of Cf252 have been performed using a unique detector setup consisting of a typical grid-ionization chamber coupled with a ΔE-E charged particle telescope. We find that the fragment mass dependency of the kinetic-energy-averaged width of the charge distribution shows a systematically decreasing trend with obvious fluctuations. The variation of the widths of the charge distribution with kinetic energy shows a pan-like shape. This is due to the large number of neutrons emitted at the high excitation energies and cold fragmentation at the low excitation energies. Deviation of the kinetic-energy-averaged most probable charge Zp from the unchanged charge distribution (UCD), ΔZ, as a function of the mass number of primary fragments, A∗, changes from negative for mass asymmetric fission to positive near the symmetric fissions. Concerning the kinetic energy dependence of Zp given primary mass number A∗, obvious increasing tendencies of Zp with increasing kinetic energy are observed.