A compact tritium AMS system

Abstract

Tritium ( 3H) is a radioisotope that is extensively utilized in biological and environmental research. For biological research, 3H is generally quantified by liquid scintillation counting requiring gram-sized samples and counting times of several hours. For environmental research, 3H is usually quantified by 3He in-growth which requires gram-sized samples and in-growth times of several months. In contrast, provisional studies at LLNL’s Center for Accelerator Mass Spectrometry have demonstrated that accelerator mass spectrometry (AMS) can be used to quantify 3H in milligram-sized biological samples with a 100 to 1000-fold improvement in detection limits when compared to scintillation counting. This increased sensitivity is expected to have great impact on the biological and environmental research community. However, in order to make the 3H AMS technique more broadly accessible, smaller, simpler, and less expensive AMS instrumentation must be developed. To meet this need, a compact, relatively low cost prototype 3H AMS system has been designed and built based on an LLNL ion source/sample changer and an AccSys Technology radio frequency quadrupole (RFQ) linac. With the prototype system, 3H/ 1H ratios ranging from 1×10 −10 to 1×10 −13 have be measured from milligram-sized samples. With improvements in system operation and sample preparation methodology, the sensitivity limit of the system is expected to increase to approximately 1×10 −15.