HIGH SENSITIVITY MASS SPECTROMETRY OF THE RARE GASES
A 60 deg sector type of mass spectrometer and associated sample preparation system adapted for ultrasensitive analysis of rare gas isotopic abundances is described. The electron bombardment ion source was designed to be stable over long periods wtth a high efficiency for ion production. The spectrometer uses a Hall crystal as a rapid method of mass identdication when using magnetic scanning. The detector is a secondary electron multiplier. The isotope abundances are measured under static vacuum conditions and standardized by the introduction of known amounts of rare gases during the measurements. Accuracies of about plus or minus 5% are possible for the absolute amount of any particular isotope present. The mass spectrometer is capable of detecting 2 x 10/ sup 5/ atoms of helium or 10/sup 4/ atoms of an argon isotope. The limiting factor in the isotope abundance measurement is the amount of natural abundance rare gas contamination added during the sample preparation. Vacuum fusion of the sample in a crucible inside a glass vacuum jacket (low helium diffusion rate) followed by purification with hot calcium and copper-copper oxide leads to the following contamination levels in units of cc at NTP: 10/sup -10/ for He/sup 3/, 10/sup -9/ for He/sup 4/, 4 x 10/sup -9/ for Ne/sup 20/, and 3 x 10 /sup -7/ for Ar/sup 40/. The amounts for the other isotopes are in their natural abundance ratio. These sensitivities make it possible to measure nuclear reaction cross sections of the order of 1 mb when 10/sup 15/ particles strike a target several g/ cm/sup 2/ thick, in measuring the rare gases of a meteorite, or to method. (auth)
- Research Organization:
- Brookhaven National Lab., Upton, N.Y.
- NSA Number:
- NSA-14-006251
- OSTI ID:
- 4204858
- Report Number(s):
- BNL-581
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-60
- Country of Publication:
- United States
- Language:
- English
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