Effects of negative pions and neutrons on the growth ofVicia fababean roots

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Abstract
V. faba bean roots were irradiated with neutrons of various energies and with negative .pi.-mesons, and the effect on the 10-day growth of the roots was determined. The neutron irradiations were made in beams of 400 and 600 MeV maximum energy and with neutrons from a plutonium-beryllium source (mean energy 4.4 MeV) and from a 14 MeV neutron generator. The bean roots were also irradiated at various points along the depth-dose curve of negative .pi.-mesons, including the region where the pions annihilate on coming to rest. The results show a maximum relative biological effectiveness (RBE) of 3.7 for 50% reduction in 10 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.