ACE News #6: Early Data from the Ultra-Low Energy Isotope Spectrometer (ULEIS)

The Ultra Low Energy Isotope Spectrometer (ULEIS) on the ACE spacecraft is a high resolution mass spectrometer designed to measure particle composition and energy spectra of elements He - Ni with energies from ~45 keV/nucleon to a few MeV/nucleon. The instrument measures particle mass and energy using the time-of-flight vs. residual energy method. ULEIS will investigate particles accelerated in solar energetic particle events, interplanetary shocks, and at the solar wind termination shock. ULEIS began operating with full high voltage on September 25, 1997.

Two sizable solar energetic particle events commenced on November 4 and November 6. The figure shows preliminary mass histograms from ULEIS for November 4 through November 9. This histogram shows the mass spectrum obtained using one of the three large solid state detectors, for particle energies of ~0.4-3 MeV/nucleon (including approximately 1/3 of the available data in this energy range). In addition to the major elements labeled in the figure, the data indicates the presence of less abundant species including S, Ar, and Ca. For this figure, a rough consistency check was made of the two time-of-flight measurements for each particle; however, information from the position sensing system has not been included. Incorporating this information, along with other refinements in the instrument calibration, should result in improved mass resolution and the separation of major isotopes.

ULEIS was developed by the University of Maryland and Johns Hopkins University Applied Physics Laboratory.

....contributed by Glenn Mason and Joe Dwyer, University of Maryland

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Last modified 4 December 1997, mrt
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