Pergamon Adv. Space Res. Vol. 21, No. 12, pp. 1801-1804, 1998 01998 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-1177/98 $19.00 + 0.00 PII: S0273-1177(98)00071-4 ENERGETIC NEUTRON AND GAMMA-RAY SPECTRA UNDER THE EARTH RADIATION BELTS ACCORDING TO "SALUTE-7"-"KOSMOS- 1686" ORBITAL COMPLEX AND "CORONAS-I" SATELLITE DATA A. V. Bogomolov*, A. V. Dmitriev*, I. N. Myagkova*, S. P. Ryumin*, O. N. Smirnova** and I. M. Sobolevsky** *Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119899 Moscow, Russia **Institutefor Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia ABSTRACT The spectra of neutrons >10 MeV and gamma-rays 1.5-100 MeV under the Earth Radiation Belts, restored from the data, obtained onboard orbital complex "SALUTE-7"-"KOSMOS-1686", are presented. The spectra shapes are similar to those for albedo neutrons and gamma-rays, but absolute values of their fluxes (0.2 cm "2 s"1 for neutrons, 0.8 cm -2 s"1 for gamma-rays at the equator and 1.2 cm "2 s"l, 1.9 cm -2 s-I , accordingly, at L=I.9) are several times as large. It is possibly explained by the fact that most of the detected particles were produced by the cosmic ray interactions with the orbital complex matter. Neutron and gamma-ray fluxes obtained from "CORONAS-I" data are near those for albedo particles. ©1998 COSPAR. Published by Elsevier Science Ltd. INTRODUCTION There are several reasons for interest in measurements of high-energy neutron and gamma-ray fluxes in near- Earth space. These particles form a significant part of the background during solar neutron, solar and cosmic gamma-ray observations. Information on atmospheric albedo neutrons is necessary for better understanding of their role in the formation of Earth's radiation belts. And, finally, neutrons in near-Earth space, including local neutrons, i. e. those produced in the spacecraft matter by Galactic Cosmic Ray (GCR) interactions, are important contributors to radiation hazard during space missions. At present, the majority of published results on albedo neutron fluxes were obtained for the geomagnetic cut-off rigidity R = 4.5 GV and are mainly concerned with energies below 20 MeV. The data of experimental observations for higher energies (in particular, for >100 MeV) and data obtained at other latitudes are scanty and widely scattered. This is the same for data about albedo gamma-rays too. EXPERIMENT The SONG and NEGA instruments were used to detect energetic neutron and gamma-ray fluxes. The "SOlar Neutrons and Gamma-rays" (SONG) instrument was designed to provide gamma-ray detection capability in the 0.12-116 MeV energy range and neutron detection capability above 10 MeV on the "Complex Orbital near-Earth Observations of the Activity of tbe Sun" (CORONAS-I) satellite. The experiment "NEutrons and GAmma-rays" (NEGA) on the "SALUTE-7"-"KOSMOS-1686" orbital complex was flown to test the SONG Pulse Shape Discrimination of neutrons in Csl(TI) and to determine neutron and gamma-ray background on high inclination orbits. The NEGA-instrument consisted of scintillation crystal CsI(TI) measuring 7.5 cm in both diameter and height, surrounded by a 4n active anticoincidance shield of 2-era thick plastic scintillator. One photomultiplier tube, FEU-110, viewed the whole system. NEGA measured neutrons in three intervals of energy release (4.6-13, 1801