Effects of negative pions and neutrons on the growth of Vicia faba bean roots.

Abstract

Vicia faba bean roots have been irratiated with neutrons of various energies and with negative pi-mesons, and the effect on the ten-day growth of the roots has been determened. The neutron irratiations were made in beams of 400 and 600 MeV maximum energy, as well as with neutrons from a plutonium-beryllium source (mean energy 4.4 MeV) and from a 14 MeV neutron generator. The bean roots have also been irradiated at various points along the depth-dose curve of negative pi-mesons, including the gegion where the pions annihilate on coming to rest. The results show a maximum relative biological effectiveness (RBE) of 3.7 for 50% reduction in ten days growth for stopped negative pions and values up to 3.3 for high-energy neutrons, compared to 5.5 for 14 MeV neutrons. The biological effectiveness of high-energy neutrons and stopped pions shows a more pronounced dependence on dose than does the effect with lower-energy neutrons.