Observation of near-scission “polar” and “equatorial” proton emission in heavy-ion induced fission

Abstract

Proton and α-particle energy spectra were measured in coincidence with fission fragments at different relative angles in 16O (96 MeV) + 232Th reaction. The multiplicity spectra were analyzed within the framework of a Moving Source Disentangling Analysis (MSDA) to determine contributions from different emission stages. The MSDA conclusively shows “Near Scission Emission (NSE)” as an essential component in the multiplicity spectra. In contrast to NSE α particles which emit mainly perpendicular (“equatorial emission”), the NSE protons are observed to be emitted perpendicular as well as parallel (“polar emission”) to the fission axis with similar intensities (~20% for each). Thus, around 40% of total pre-scission protons are emitted near the scission stage, whereas the same fraction for α particles is only around 10%. The inevitable presence of “polar” and “equatorial” NSE protons in a heavy-ion induced fission has been observed for the first time. Present results open up a new avenue to study the heavy-ion induced fission dynamics.