THE DESIGN OF A RADIOCARBON MICROPROBE FOR TRACER MAPPING IN BIOLOGICAL SPECIMENS

Biological scientists use radioisotopes to label and subsequently monitor specific molecules within living systems. We aim to improve on conventional methods of imaging C-14 tracers, in both sensitivity and resolution, by combining a new scanning-beam ion source generating C- secondary ions with our AMS system. Our measurements, including that of the generation of sufficient C- ions to the quantity of tissue sputtered, demonstrate that the radiocarbon microprobe is feasible, and we expect its sensitivity to be 1 C-14 label atom in 2000. We have employed the negative ion production enhancing effect of surface caesiation, investigating the potential of a Cs vapour spray for this purpose. As suitable Cs+ ion sources are unavailable, the microprobe will feature a Cs spray to compensate for the lack of primary beam surface caesiation, in conjunction with a 0.2-mu-m spot Ga+ beam.