RBE of californium-252 at low dose rate for growth inhibition in Vicia faba

RBE of 252Cf, at low dose rate, has been determined for growth inhibition in Vicia faba roots. Two different strains were used: the classical ''Sutton's seeds'' and a new ''BelB'' variety. Some characteristics of this new variety are presented. Two sets of linear 252Cf sources were used (linear activity 0.31 and 0.47 μg.cm-1) in somewhat different geometrical arrangements. The (n+ν) 252Cf dose rates at the level of the root tips were 0.11 and 0.13 Gy.h-1 respectively. The reference radiation was the ν emission of 192Ir, used in the same geometrical conditions and for similar irradiation times. For both irradiation conditions and both strains, similar RBE dose relationships were observed. For sub(n+ν) absorbed doses decreasing from 0.4 to 0.2 Gy, the RBEsub(n+ν) of the total 252Cf emission increases from 5.9 +- 0.4 to 6.6 +- 0.8 (Sutton's seeds, first source-geometry), from 5.1 +- 0.3 to 6.2 +- 0.7 (BelB seeds, first source-geometry) and from 5.6 +- 0.4 to 6.2 +- 0.4 (BelB seeds, second source-geometry). The relative contribution of the gamma component Dsub(ν) to the total absorbed dose Dsub(n+ν) at the level of the root tips was evaluated Dsub(ν)/Dsub(n+ν) = 0.35 and 0.42 for the first and second source-geometry respectively. The RBEsub(n) of the neutron emission of 252Cf increases then from 8.5 +- 0.6 to 9.7 +- 1.2 (Sutton's seeds, first source-geometry), from 7.4 +- 0.5 to 9.0 +- 1.0 (BelB seeds, first source-geometry) and from 8.9 +- 0.6 to 10.0 +- 0.6 (BelB seeds, second source-geometry) for neutron doses Dsub(n) decreasing from 0.25 to 0.12 Gy respectively