Neon isotopic measurements using high-resolution, multicollector noble gas mass spectrometer: HELIX-MC

We describe a new high-resolution, multicollection, noble gas mass spectrometer, the HELIX-MC, developed by GV instruments. The instrument uses a collector housing that holds five "MiniDual'' detection systems, each detector containing two devices: a Faraday cup collector and channel electron multiplier. Each detector is 5.2 mm wide, which permits collecting adjacent beams separated by 1 atomic mass unit (amu) at mass 136. The HELIX-MC operates at high mass resolution (m/Delta m > 1500), which allows the interference of Ar-40(++) on Ne-20(+) to be resolved. We report the results of some tests on the "MiniDual'' collectors, in which we have achieved precise Ne abundance and isotopic measurements. After a correction for doubly ionized CO2 (0.37-1.5%), our results show that the HELIX-MC produces only very limited instrumental Ne isotopic mass fractionation (approximate to -0.5%. amu(-1)). The sensitivity of the HELIX-MC for neon measurement performed on 10 12 ohms collector is around 1.4 x 10(-3) A torr(-1) for quantities of Ne-20 analyzed comprised between 1.27 x 10(-15) and 4.71 x 10(-15) moles. Within this range, the reproducibility of the isotopic measurements of standard gas falls in the range between 0.5 and 0.8% (1 sigma) for Ne-20/Ne-22 and 1 and 1.5% for Ne-21/Ne-22 over a period of several days. The machine characteristics for measuring He are also reported.