INFLUENCE OF THE DOSE RATE AND TIME FACTOR ON THE BACTERICIDAL EFFECT OF RADIATION,
FORT DETRICK FREDERICK MD
Pagination or Media Count:
The relationship between the biological action of ionizing radiation and the dose distribution in time has been established by numerous experimental and clinical observations. The effect of the dose rate of ionizing radiation on biological reactions has been studied in plants, insects, birds, and mammals. There are only scattered reports dealing with the effect of duration of exposure on bacteria. Experiments show that increasing the duration of gamma irradiation of the vegetative and spore forms of bacteria intensifies the bactericidal effect. This pattern is revealed by comparing the biological effect of radiation at dose rates ranging from 102 to 48,000 rmin. There is an optimum duration of exposure to achieve a bactericidal effect. A complete bactericidal effect was obtained by irradiating a 10 billion cell microbial suspension with 50,000 r at a dose rate of 111.5 rmin duration of exposure 7 hours 29 min. The same effect was produced by irradiating a one billion cell suspension with 100,000 r at a dose rate of 107 rmin duration of exposure 15 hours 35 min. A comparison of the two experiments shows that the bactericidal effect of radiation is achieved in the case of E. coli regardless of the dose delivered within these limits if the exposure is longer than 7 hours.