ACE News #5: 11/24/97

Isotope Measurements from the 11/6/97 Solar Particle Event

There were two large solar energetic particle (SEP) events on 11/4/97 and 11/6/97 that apparently mark the beginning of the transition to the next solar maximum. The event of 11/6/97, in particular, accelerated heavy nuclei up to energies of hundreds of MeV/nucleon, permitting the Solar Isotope Spectrometer (SIS) on ACE to measure directly the composition of a sample of material that originated in the solar corona. SIS is designed to measure both the elemental and isotopic composition of heavy nuclei in large solar events such as these, which requires that it make precise measurements of rare, heavy nuclei in the presence of intense fluxes of low energy protons.

The above figure illustrates charge histograms from the November 6 SEP event for data collected by SIS of elements from Sulfur to Calcium (Z = 16 to 20). For S, Ar, and Ca, peaks due to two individual isotopes are clearly resolved, marking the first time that the isotopes 34S, 38Ar, and 44Ca have been resolved in a solar energetic particle event. These data will be used to measure the isotope abundance ratios 34S/32S, 38Ar/36Ar, and 44Ca/40Ca as part of an effort to determine the isotopic composition of the solar corona. SIS will also be able to measure the abundances of the isotopes of C, O, Ne, Mg, Si, Fe, and Ni in this event. Note that the data only includes ranges 4 through 7 in the two SIS telescopes; additional data from the shorter ranges will also be available.

SIS was designed by Caltech, the Jet Propulsion Laboratory, and the Goddard Space Flight Center.

....contributed by Dr. Richard Leske, Caltech

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Last modified 20 November 1997, mrt
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