transients). Due to a large geometric factor ($\Gamma \sim 80 cm^{2}sr$) it could detect even relatively small electron fluxes outside the zones of captured radiation. The FON-2 charged-particle detector ($\Delta E_{e} = 0.04-1.5$ MeV, $\Delta E_{p} = 2-200$ MeV), which was free from overloading in the radiation belts because of its small geometric factor ($\Gamma \sim 0.5 cm^2sr$), was used for background measurements when the “Mir” station crossed the South-Atlantic anomaly and spurs of the outer radiation belt.

Since the relatively large orbital inclination and periodic crossings of the zones of captured radiation the PX-2 instrument background count rates underwent variations. However, the combination of active and passive shields greatly reduced the background variations, in particular, the latitudinal variations in the main X-ray channels 25-50 and 50-100 keV. To extend the sensitivity range of the instrument the latitudinal count rate variations in high energy photon channels (100-200, 200-300 keV) were removed using regression analysis of the PX-2 X-ray channel outputs ($N_x$) and the NEGA-1 gamma-quanta channel outputs ($N_{\gamma}$). Since the NEGA-1 detectors were inside the OS “Mir” orbital module, they detected mainly the local gamma-emission. The additional count rate in a given X-ray channel attributable to the local emission may 