Direct measurement of 3He/4He in the LISM with the COLLISA experiment

Details Direct measurement of 3He/4He in the LISM with the COLLISA experiment Direct measurement of 3He/4He in the LISM with the COLLISA experiment

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aipc..598..275s&link_type=abstract

SOLAR AND GALACTIC COMPOSITION: A Joint SOHO/ACE Workshop. AIP Conference Proceedings, Volume 598, pp. 275-280 (2001).

Physics

3

Solar Neighborhood, Physical Properties, Remote Observing Techniques

Scientific paper

Results from direct measurements of the helium isotopic ratio in the closest regions of the Local Intersteller Medium (LISM) are presented. Neutral 3He and 4He atoms coming from the LISM were captured in space by means of the foil collection technique, a method already successfully used during the Apollo missions to determine the noble gas isotopic ratios in the solar wind. In the framework of the Swiss-Russian project COLLISA (COLLection of InterStellar Atoms), beryllium-copper foils were placed on the outer surface of the space station Mir and directly exposed to the flux of interstellar neutrals. The neutral particles of the LISM cross the heliopause and reach, almost unaltered, the Mir orbit at 400 km height above the Earth. Here, the kinetic energy of the interstellar flux ramming against the foils is sufficient to trap the particles into the atomic structure of the metal. After an exposure of ~60 hours, the foils were recovered by the cosmonauts and brought back to Earth by the American space shuttle Atlantis. The particles were then extracted with a stepwise heating procedure and their abundances were measured in the mass spectrometric laboratories of the University of Bern. The analysis performed so far allowed the detection of 3He and 4He atoms of interstellar origin. The measured interstellar ratio 3He/4He={1.70-0.42+0.50}×10-4 is consistent with protosolar values obtained from meteorites and Jupiter's atmosphere. Such a result seems to confirm the hypothesis that no significant change of the 3He abundance occurred in the LISM during the last 4.6 Gy. .

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