Quantitative Relation of RBE in Tradescantia and Average LET of Gamma-Rays, X-Rays, and 1.3-, 2.5-, and 14.1-Mev Fast Neutrons
The relative effectiveness of Co⁶⁰ %gg-rays, x-rays, and 14-Mev D, T. 2.5-Mev D, D, and cyclotron 1-Mev average-energy fast neutrons in causing chromosomal aberrations in the plant Tradescantia have been compared. A conservative estimate of the over-all accuracy in these experiments is 15% for physical values. 20% for biological values. and 2% for average LET values as defined here: it is believed that actually the over-all accuracy for all three factors is considerably better than this. Track average and energy average LET's are derived for each radiation in order to make comparisons of RBE against LET. The assignment of proper LET values and subsequent comparisons are relatively simple and straightforward when the ionization generated in tissue is substantially homogeneous. When tissue ionization is not homogeneous, but is made up of components of quite different average LET, the comparison is more complex because each separate component contributes a different relative amount to total dose, total track length, and total biological effect. For these cases. the biological and physical role of each component should be considered separately. RBE was compared against average LET for the radiations used, and to higher LET of alpha -particles and the heavy particles from the D, T neutron irradiation. RBE increases smoothly and about sevenfold from gamma -rays to 1- Mev average-energy cyclotron neutrons (track average LET range from 0.27 to 27 kev/ mu ), peaks somewhere between 1-Mev fast neutrons and gamma -particles in the average LET range of 50 to 70 kev/ mu at an RBE of 8 to 11, and then falls toward the higher-LET alpha -particles and D. T heay particles. Within the fast- neutron energy range, from 14-Mev D. T to 1-Mev cyclotron to 2.5-Mev D, D. neutrons (track average LET of 12, 27, and 31 kev/ mu ), RBE increases threefold. The shape of the curve of RBE against LET for chromosomal aberrations, an effect that may be considered as cellular cytogenetic lethality, is very similar to the curve for a galaxy of mammalian effects including lethality. In absolute amount, chromosomal RBE's are greater than those for mammalian lethality. (auth)
- Research Organization:
- Oak Ridge National Lab., Tenn.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-13-001088
- OSTI ID:
- 4329291
- Journal Information:
- Radiation Research, Vol. 9, Issue 5; Other Information: Orig. Receipt Date: 31-DEC-59; ISSN 0033-7587
- Publisher:
- Radiation Research Society
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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