tokens: As a result , relative biological effects ( RBE ) of 2 . 3 - 2 . 7 was obtained from the straight line that was given by modifying by the method of least squares the curves of the frequency of anomalous fetuses in total implants and survived embryos irradiated from 20 to 120 rad by Cf - 252 and from 80 to 220 rad by Co - 60 on day 8 of pregnancy .