Pion-induced fission in tin and bismuth observed with makrofol detectors

Pion is the field particle of nuclear force. Its interaction with the nucleons may lead to complete absorption resulting in the full deposition of the rest mass and kinetic energy within the nucleus. Consequently the nucleus can be excited to very high energies. This situation gives rise to binary decay even in those nuclei which are not normally prone to fission due to their high fission barriers. We have studied the occurrence of binary fission induced by pions of energies 500, 672, 1068 and 1665 MeV in the targets of Sn and Bi. The exposures have been made at the Brookhaven National Laboratory (USA). The experimental set-up was based on 2π-geometry with targets in the form of thin foils placed in front of Makrofol detectors. The fission events were counted manually with an optical microscope. The incident beam was monitored with the help of a scintillator and local fluences were determined in-situ. The fission cross-sections were calculated by using the known values of target thickness and local frequencies of fission counts.