Trapped Particles

NINA is accomodated on Resurs so as to point always to the zenith. The spacecraft makes about 14 revolutions per day, and when the orbit crosses the South Atlantic Anomaly (about 7 times per day) NINA can measure particles trapped in the inner radiation belt. At L-shell <= 1.2 the local pitch-angle loc distribution for particles detected by NINA is peaked at 90 degrees, that corresponds to an average equatorial angle 0 of about 75 degrees.

Figure 1

The period of observation taken under consideration ranges from November 1998 to April 1999. Figure 1 (left) presents the mass distribution for 3He and 4He in the SAA region. It is possible to see the good isotope separation, and the higher abundance of 3He with respect to 4He, in agreement with previous observations. Figure 1 (right) shows the mass distribution for hydrogen isotopes.

Figure 2

The energy spectra of 3He and 4He obtained by NINA at L-shell 1.18--1.22 and B < 0.22 G are presented in Figure 2, together with the data of MAST on SAMPEX at L-shell=1.2. Fluxes are averaged over local pitch angles at about 800 km and about 600 km of altitude for NINA and MAST respectively. The NINA and MAST data have been gathered during quite different periods of the solar cycle; taking also into account the sharp decrease of the trapped particles flux near the edge of the radiation belts, they show a reasonable agreement.
The energy spectra of 3He and 4He presented in Figure 2 are in good agreement with calculations for atmospheric helium source (dotted and solid line, for two different equatorial pitch-angles). The thick line is the sum of the p + He and p + O contributions.

Figure 3 In Figure 3 the ratio 3He/4He as a function of energy is shown; the dotted line is the theoretical calculation for atmospheric oxygen source at 0= 80 degrees, while solid and dashed lines correspond to the atmospheric helium source at two different equatorial pitch angles, 0= 60 degrees 0=80 degrees.


For more details about NINA analysis of geomagnetically trapped particles, see the NINA Publications.