Helium in near Earth orbit

Abstract

The helium spectrum from 0.1 to /100 GeV/nucleon was measured by the Alpha Magnetic Spectrometer (AMS) during space shuttle flight STS-91 at altitudes near 380 km. Above the geomagnetic cutoff the spectrum is parameterized by a power law. Below the geomagnetic cutoff a second helium spectrum was observed. In the second helium spectra over the energy range 0.1 to /1.2 GeV/nucleon the flux was measured to be (6.3+/-0.9)×10$^-3$(m$^2$ secsr)$^-1$ and more than ninety percent of the helium was determined to be $^3$He (at the 90% CL). Tracing helium from the second spectrum shows that about half of the $^3$He travel for an extended period of time in the geomagnetic field and that they originate from restricted geographic regions similar to protons and positrons.

Publication
Physics Letters B