Radioisotope Detection with Tandem Electrostatic Accelerators

The MP tandem Van de Graaff accelerator at the University of Rochester's Nuclear Structure Research Laboratory†has been employed in part since May 1977 as an ultrasensitive mass spectrometer to directly detect 14C and 36Cl from natural samples and to generally investigate many of the technical details involved in this new technique. The sensitivity that has been achieved for measuring the 14C/C ratio is 3×10-16 and for the 36Cl/Cl ratio is 3×10-15. Both the radioisotopes were detected for the first time by direct extraction methods at Rochester. Carbon sample sizes are 3 mg or less and for chlorine the compound AgCl was employed in amounts of 70 mg or less. Both the sensitivity and the sample size represent many orders of magnitude improvement over even the most advanced conventional mass spectrometric methods. In the case of 14C the carbon sample sizes required are at least a thousand times less than required by the conventional radiocarbon measuring technique. A brief summary of published results and the most recent results on both radioisotopes will be described and the use of the method for other isotopes and for other applications will be discussed.