Solar gamma-ray spectrometer GRIS onboard the International Space Station

GRIS (Gamma and Roentgen Irradiation of the Sun) is a scientific instrument for detection of hard X-rays and gamma-rays of solar flares with the energies from 50keV to 200MeV and for registration of solar neutrons with energies above 30MeV. The experiment will be performed since 2019 onboard the International Space Station. The instrument includes two spectrometers: the low energy spectrometer based on a fast scintillator with high energy resolution 3.5–4.5% at 662keV (LaBr3(Ce) or CeBr3) and dimensions ø7.62×7.62cm, and the high energy spectrometer based on CsI(Tl) scintillator ø12×15cm (which is also intended for neutron registration). The apparatus will be mounted on the oriented platform outside the Zvezda service module in 2019. Simulated response of the detectors to background radiation and to solar flares of different magnitudes and compositions obtained with GEANT4 toolkit confirms the instrument’s possibility to measure different components of the solar flares spectra: narrow gamma lines, pion decay component, etc. with a sufficient confidence due to the usage of two types of detectors.