Sensitive cross section of a bacterium, Escherichia coli, to fast neutrons
An experiment was performed to determine the sensitive area of a lyophilized bacterium, Escherichia coli, to fast (14Mev.) neutrons. The neutrons were obtained from the H³(d,n)He⁴ reaction produced in the Cockeroft-Walton accelerator at Virginia Polytechnic Institute. The reaction provides a neutron source which is almost monoenergetic, symmetrical, has a low level of associated gamma rays, and gives a large number of neutrons per unit time. To insure that the maximum number of neutrons per cm² per unit time pass through the samples, a special target holder, and sample holder were constructed to position the samples close to the target's center. Source strength was determined with a long counter. The flux at the site of irradiation was determined by numerical integration.
One half of the lyophilized culture tubes were held for controls, the others were irradiated. after the letter had been irradiated, all were opened aseptically, plated on agar, and colonies counted. Because of the extreme variation between colony counts of lyophilized samples, a weighted least squares analysis was performed to estimate the sensitive area.
The total flux to which the bacteria were subjected was approximately 1012 neutrons/cm2 and the sensitive area was estimated to be lO-l2 cm2. This agrees with values obtained by others for this bacterium irradiated in aqueous solution and on agar plates.
Since the average size of Escherichia coli is .5 x 1.5 microns, the sensitive area is approximately 0.01% or the total cell area.