 An example of a three-stage operation has been built in Oxford Nuclear Laboratory during 1964 of a 10 MV single-ended "injector" and a 6 MV EN tandem.By the 1970s, as much as 14 million volts could be achieved at the terminal of a tandem that used a tank of high-pressure sulfur hexafluoride (SF6) gas to prevent sparking by trapping electrons.This allowed the generation of heavy ion beams of several tens of megaelectronvolts, sufficient to study light ion direct nuclear reactions.