Effects of Fast Neutrons on Chromosomes in Mitosis.

Abstract

The neutron source was a beryllium target bombarded by deuterons accelerated to 8 million volts in the cyclotron of Lawrence and Cooksey. The neutrons so obtained were collimated in a beam as described by Aebersold. The biological material to be treated was placed just outside the 10 × 10 cm port at the end of the collimation apparatus at a distance of 70 cm from the target. Ionization produced by the neutrons was measured in arbitrary “n” units, and “n” unit being that amount of ionization produced by neutrons which gives the same reading on a 100 r Victoreen thimble ionization chamber as does one roentgen of X-rays. Six-day-old seedlings of Vicia faba and Pisum sativum were mounted on an annular wooden holder and oriented so that the root tips lay in the center of the 3-inch aperture which was covered on either side by a sheet of wet filter paper and a sheet of celluloid 5.4 thousandths of an inch thick. The cotyledons and epicotyl of the seedlings lay outside the neutron beam, so that corrections for scattering may be neglected. The much smaller seedlings of Solanum lycopersicum were mounted between 4 sheets of wet filter paper 3 1/2 inches in diameter lying between 2 sheets of cellophane held on a round wooden embroidery hoop 6 inches in diameter. All seedlings were kept at 23°C before and after treatment. The mouse tumors were treated in vivo by placing the animal which was tied on a piece of cardboard so that the tumor was in the center of the neutron beam. To obtain the dose given the tumor an ionization chamber was left immediately behind the tumor during exposure. For examination of the chromosomes only the tumor tissue adjacent to the ionization chamber was used.