CHROMOSOME BREAKAGE IN TRADESCANTIA 

 Table III. — Relative biological effectiveness of various ionizing radiation': 



index, gives an unambiguous reference point for comparing the effects of 

 the various radiations. 



These studies indicate the type of rough quantitative radiobiology possible 

 with fast neutrons from a large internal target cyclotron source. Certain 

 physical difficulties continue pending installation of a beam deflector and 

 external target. Serious problems remain in precisely characterizing the 

 neutron spectrum particularly at the very low energy or epithermal range. 

 Owing to the very high values of the RBE for chromosomal breakage in the 

 material used, the unavoidable presence of the contaminating gamma rays 

 is not as serious an objection in the present work. The dose figures which 

 have been given in all cases in rep are probably accurate to better than 

 i 15-20 per cent. A more detailed discussion of the fast neutron dosimetry 

 in the cyclotron facility is scheduled for future publication. 



REFERENCES 



1 Kirby-Smith, J. S. and Daniels, D. S. 



2 Bishop, C. J. Stain Technol. 1949, 24 9. 



3 Conger, A. D. ibid, 1953, 28 289. 



Genetics, 1953, 38 375. 



264 



