Detection of radiocarbon in the cyclotrino

Abstract

A small low-energy cyclotron (the “cyclotrino”), which was proposed for direct detection of radiocarbon in 1981, has now detected radiocarbon at natural abundance. This device combines the suppression of background through the use of negative ions with the high intrinsic mass resolution of a cyclotron. A high-current cesium-sputter negative-ion source generates a beam of carbon ions which is preseparated with a Wien filter and is transported to the cyclotron via a series of electrostatic lenses. The beam is injected radially into the cyclotron using electrostatic deflectors and an electrostatic mirror. Axial focusing is entirely electrostatic. A microchannel plate detector is used with a phase-gated output. Data is presented showing resolution of radiocarbon at natural abundance. In its present form the system is capable of improving the sensitivity of detecting 14C in some biomedical experiments by a factor of 10 4. Modifications are discussed which could bring about an additional factor of 100 in sensitivity, which is important for archaeological and geological applications. Possibilities for measurements of other isotopes are discussed.