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5.2.6 Helium Over the Solar Poles

It is interesting to see the Cm source signature in the PHA matrix plot for days 94178 - 94311 (Figure 5.26), the period when Ulysses was at heliolatitudes over the south solar pole. During this period there was little natural H or He measured, and no cover-close calibrations took place. Of course the sources in the covers continue to emit alpha-particles, even when the covers are open, and in the neighborhood of the south solar pole at this time, the HISCALE radioactive sources appear to be a significant source of interplanetary helium. The total number of counts in this peak is less than 1 count/day. A similar signature is seen over the north solar pole (95133-95271).

Figure 5.26 PHA matrix plot during polar pass

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