Chapter 4 - Atom Trap Trace Analysis of Rare Noble Gas Isotopes

Abstract

Abstract Ultrasensitive analysis of long-lived rare isotopes is performed in a broad range of scientific and technological fields. Based on the technologies of laser trapping and cooling, Atom Trap Trace Analysis (ATTA) is a method capable of analyzing trace isotopes with an isotopic abundance at and below the parts-per-trillion (10 −12 ) level. ATTA has enabled us to measure radiokrypton isotopes 81 Kr (half-life = 229,000 yr, atmospheric isotopic abundance =1×10 −12 ) and 85 Kr (10.8 yr, 10 −11 ) in environmental samples. The cosmogenic 81 Kr is the ideal tracer for dating water and ice in the age range of 10 5 -10 6 years, a range beyond the reach of radiocarbon dating. Using the current generation instrument (ATTA-2), 81 Kr-dating was performed to determine the ages of the old groundwater in the Nubian Aquifer located underneath the Sahara Desert. However, due to the low trap loading efficiency of 10 −4 , a sample of >1000 liters of water was required for each groundwater measurement, making the method cumbersome for routine scientific applications. Recent developments in our laboratory have made it possible to further improve both the counting rate and counting efficiency of the ATTA method. The more advanced ATTA instruments currently under development are expected to find applications in environmental science, earth science, nuclear waste management, nuclear non-proliferation, as well as basic research in nuclear and particle physics. Future development in pulsed VUV lasers may push the ATTA technique further towards perfection.