RELATIVE BIOLOGICAL EFFICIENCIES OF 220 kVp X-RAYS AND 14.1 MeV FAST NEUTRONS ON THE INDUCTION OF ABERRATIONS IN THE CHROMOSOMES OF TRADESCANTIA AT LOW TEMPERATURES
Interphase chromosomes of the microspores of Tradescantia paludosa were irradiated at 22 = 1 deg C and 2.5 plus or minus 0.5 deg C with 220 kvp x rays and monoenergetic 14.1 Mev fast neutrons. The dosage range employed was 100 to 600 roentgens for x ray and 50 to 800 rads for fast neutrons. While the dosage rate of x rays from a Mandtron machine operating at 220 kv, 15 ma with an added filter of 4 mm Cu was 20 r per minute that of fast neutrons. obtained from the nuclear reaction T (d,n) He/sup 4/ at the tritium target in the 250 kv Cockcroft- Walton accelerator of the Biology Division, Oak Ridge National Labonatory varied from 15.5 to 28.9 rads per minute. The fast neutrons were accompanied by a small contamination of gamma rays. The irradiated chromosomes were fixed 72 hours after irradiation and the polar view metaphases were analyzed for chromosome dicentrics, tricentrics, quadri and pentacentrics, acentric and centric chromosome rings, simple chromosome breaks and minutes. The number of microspores scored from each treatmeni varied from 200 to 500. The results indicate that like oxygen low temperature may have an appreciable effect in altering the RBE values, especially when the chromosomal aberrations are the biological effects examined. The RBE values for fast neutrons at 22 plus or minus 1 deg C for all types of chromosomal aberration and microspore damage ranged from 2.0 to 2.5. There is a substantial difference between the values of RBE for chromosome reunions and chromosome deletions. The lowest value of RBE has been shown by the microspore damage. The corresponding range of RBE values for fast neutrons at 2.5 plus or minus 0.5 deg C has been found to be 2.9 to 4.3. Here again, a considerable difference has been observed between the RBE values for chromosome reunions and minute deletions. Microspore damage has shown the lowest RBE value i.e., about 2.9. It has further been observed that the RBE value may be dependent on the dose of radiation. There is evidence to suggest that it tends to decrease when the dosage level passes a critical maximum and proceeds to a state of saturation where a considerable amount of energy is wasted and the processes of reunion, restitution and healing of broken chroraosome ends are very much disturbed. For instance while the RBE value of fast neutrons in inducing chromosome reunions of all types at 2.5 plus or minus 0.5 deg C is about 2 when the dosage is in the region of 800 rads it is about 4 when the dosage level is reduced to about 150 rads. It is suggested that there may be a fundamental difference in the action of these two radiations at low and high temperatures. (auth)
- Research Organization:
- Atomic Energy Establishment, Trombay, India
- NSA Number:
- NSA-13-006238
- OSTI ID:
- 4270569
- Report Number(s):
- A/CONF.15/P/1652
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-59
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
CHROMOSOMES
COCKCROFT-WALTON ACCELERATORS
CONTAMINATION
COPPER
ELECTRON TUBES
ENERGY RANGE
FAST NEUTRONS
FILTERS
GAMMA RADIATION
HELIUM
LOW TEMPERATURE
MITOSIS
MUTATIONS
NUCLEAR REACTIONS
OXYGEN
PLANTS
RADIATION DOSES
RADIATION EFFECTS
REGENERATION
SEEDS
TARGETS
THICKNESS
TRADESCANTIA
TRITIUM
X RADIATION