Noble gases in Genesis Collector material: New Measurement Capabilities

The difficult task of measuring heavy noble gas isotopes in collector materials returned by the Genesis Mission has stimulated the development of new noble gas mass spectrometers. A new 8 multiplier instrument was developed and refined in collaboration with Nu-Instruments. This mass spectrometer has demonstrated an inherent sensitivity of 1.8 mA/torr, about 3.3 times greater than previous instruments, and it can measure the entire Xe isotopic spectrum in only two steps, providing an effective sensitivity about 17 times greater than previously available. We have measured 10 individual samples, each containing 760,000 atoms of 132Xe, equivalent to that accumulated in 0.85 cm2 during the two year exposure time for the Genesis bulk solar wind collectors. The standard deviation from the mean (in percent) for the 10 individual measurements is 60:52:4.2:2.7:3.0:5.4:1.6 and 1.4 for 124Xe/132Xe: 126Xe/132Xe: 128Xe/132Xe: 129Xe/132Xe: 130Xe/132Xe: 131Xe/132Xe: 134Xe/132Xe: and 136Xe/132Xe, respectively. On the average, these closely conrrespond to the statistical uncertainties measured for each of the isotope ratios. The measured amount of 132Xe is reproducible to 1.6 percent. This new mass spectrometer can simultaneously measure Kr and Xe isotopes. While the spacing between isotopes varies with the element in a conventional magnetic sector mass spectrometer, this instrument uses a cluster of electrostatic lenses to achieve the same isotope spacing for each element, allowing Kr and Xe isotopes to be sequentially measured in the same sample. Xe requires two magnetic field settings and Kr only one. Therefore, complete isotope spectra of both Kr and Xe can be determined with only three steps of the magnetic field. Noble gases are extracted from the Genesis collectors by rastering a focused pulsed UV laser, removing only surface material where the solar wind is implanted. Blank levels of a few thousand atoms/cm2 have been obtained in aluminum. Once confirmed in actual flight material (presently loaded), measurements of bulk and regime-specific solar wind will commence and reported at this meeting.