Dry T-1 bacteriophage in measurement of large doses of ionizing radiation.

The irradiation of T1 bacteriophage in dry films of nutrient broth in a vacuum at room temperature has been suggested as a biological radiation dosimeter (see, for example, 1) and has been so employed in work with minimum ionizing electrons (2, S). T1 phage is especially suitable for dosimetry within beams of particles from accelerators for these reasons: (1) under the conditions specified above it is sufficiently insensitive to match the high doses usually encountered in such beams; (2) in some contrast with other T phages, it is reasonably stable through drying and resuspension, and can give quite reproducible survival data after such treatment; (3) the dose-effect relation for T1 is dependably logarithmic (4, 5) and independent of LET (rate of energy loss per unit particle track) up to 1000 Mev gm-1 cm2 (6); and (4) the films are easily made thin enough (<0.5 mg/cm2 routine to 0.01 mg/cm2 ultimate) to indicate directly the derivative of the dose-depth relation, often a difficulty in work with accelerated particle beams. The purpose of this paper is to collect results bearing on physical calibration of T1 phage as a dosimeter and to specify appropriate physical and biological conditions. The best figure for T1 radiation sensitivity under such conditions appears to be 570 + 15 krads for survival ratio e-1.