The use of CVD diamond to produce carbon K ultrasoft x-rays.

Carbon K ultrasoft x-rays (278 eV) interact with biological material producing random, isolated tracks of single electrons with a range < 7 nm (cf width of DNA helix approximately2 nm). The electron tracks produced by these ultrasoft x-rays are similar to the numerous secondary electrons and 'track ends' produced by essentially all ionizing radiations. They therefore provide a unique tool in the study of mechanisms of radiation action in the cell. Conventional carbon targets used with the Medical Research Councils cold-cathode discharge tubes have a limited lifetime of 40-50 min. We have investigated the use of thin, freestanding diamond films produced using chemical vapour deposition techniques as a new transmission target for a cold-cathode tube. We present here a novel use of diamond to produce CK ultrasoft x-rays for irradiation purposes. The system described produces an entrance absorbed dose rate to attached cells of approximately 0.2 Gy min(-1) which due to the long target lifetime is usable for low dose-rate CK x-ray studies.