Impurity Characterization of Solar Wind Collectors for the Genesis Discovery Mission by Resonance Ionization Mass Spectrometry

Abstract

NASA's Genesis Discovery Mission is designed to collect solar matter and return it to earth for analysis. The mission consists of launching a spacecraft that carries high purity collector materials, inserting the spacecraft into a halo orbit about the L1 sun-earth libration point, exposing the collectors to the solar wind for two years, and then returning the collectors to earth. The collectors will then be made available for analysis by various methods to determine the elemental and isotopic abundance of the solar wind. In preparation for this mission, potential collector materials are being characterized to determine baseline impurity levels and to assess detection limits for various analysis techniques. As part of the effort, potential solar wind collector materials have been analyzed using resonance ionization mass spectrometry (RIMS). RIMS is a particularly sensitivity variation of secondary neutral mass spectrometry that employs resonantly enhanced multiphoton ionization (REMPI) to selectively postionize an element of interest, and thus discriminates between low levels of that element and the bulk material. The high sensitivity and selectivity of RIMS allow detection of very low concentrations while consuming only small amounts of sample. Thus, RIMS is well suited for detection of many heavy elements in the solar wind, since metals heavier than Fe are expected to range in concentrations from 1 ppm to 0.2 ppt. In addition, RIMS will be able to determine concentration profiles as a function of depth for these implanted solar wind elements effectively separating them from terrestrial contaminants. RIMS analyses to determine Ti concentrations in Si and Ge samples have been measured. Results indicate that the detection limit for RIMS analysis of Ti is below 100 ppt for 106 averages. Background analyses of the mass spectra indicate that detection limits for heavier elements will be similar. Furthermore, detection limits near 1 ppt are possible with higher repetition rate lasers where it will be possible to increase signal averaging to 108 laser shots.

Atomic Spectrometry Update. Environmental analysis

“…The high sensitivity and selectivity of RIMS makes it well suited for the detection of many heavy elements in solar material collected by NASA space missions. 601 A recently developed spark source mass spectrometric (SSMS) technique using multiple ion counting has been used to determine Nb, Y and Ta in carbonaceous chondrites 602 and Y, Zr and ultra-low concentrations of Nb in geological materials. 603 The latter application 603 had an analytical precision of 2±5% for concentrations down to 0.020 mg g 21 and 10% for lower concentrations.…”

Resonance‐enhanced multiphoton ionization/secondary neutral mass spectrometry and cesium attachment secondary ion mass spectrometry of bronze: a comparison

“…Usually, a negative potential is applied to the target in order to eliminate secondary ions from the neutral sputtered plume. 12 This is necessary when conducting elemental analyses at trace levels (<1 ppm) because the presence of secondary ions can produce uncertainty in the measured signal. Because SARISA was being employed in this work to analyze elements at the percent level, the suppression of secondary ions was not implemented.…”

Atomic Spectrometry Update. Atomic mass spectrometry

“…Becker and Dietze 189 investigated the oxide ion formation of long-lived radionuclides ( 241 Am, 237 Np, 239 Pu, 226 Ra, 230 Th and 239 U) in a mixed aqueous solution using double-focusing sector field ICP-MS (DF-ICP-MS) with a shielded torch under hot plasma conditions. The measurements of the relative oxide ion intensities by DF-ICP-MS were performed using concentric, microconcentric and direct injection high-efficiency (DIHEN) nebulizers for sample introduction.…”

“…Calaway et al 226 systematically investigated the sources of noise in the TOFMS with resonant or resonantly enhanced multiphoton ionization (REMPI) of the neutrals generated by primary ion bombardment. Modified pulsing schemes for the primary ion beam and the lasers decreased the noise level by a factor of 100 to less than 5610 25 counts per pulse.…”