X-Radiation from Van De Graaff Accelerator Ion Sources

The presence of a positive ion beam of the JN accelerator was necessary for the production of any significant radiation. Most of the bremsstrahlung produced is a result of electrons striking the focus electrode and the third electrode of the accelerator tube. For the operating conditions discussed above, this source of radiation was about five times as intense as a 1 millicurie co60 source placed at an equivalent distance from the JN spectrometer. A second source of radiation of less intensity was found to originate in the vicinity of the gas reservoir above the ion source. This could be due to bremsstrahlung being scattered at 900 by the reservoir bottles. From these results, it is recommended that the region around the focus electrode of the accelerator tube be shielded more effectively or that the material of the electrode be changed to a smaller Z material (e.g. beryllium) to reduce radiative loss of the electrons. The CN accelerator ion sources exhibit more structure in the intensity distribution measurements. This structure persists at 3, 4, and 5 million volts on the terminal, although the intensity of the x-radiation observed increases rapidly with terminal voltage. The most intense radiation observed with the d.c. beam R.F. ion source came from the base of the ion source glass bottle. Intense bremsstrahlung was also observed as originating at the upper focus electrode nozzle shoulder and at the base of the nozzle.