Radiation Environment Measurements from CREAM and CREDO During the Approach to Solar Maximum

Results from the Cosmic Radiation Environment Monitors (CREAM and CREDO) have been reported from a range of platforms during the declining phase of solar cycle 22 and a number of implications drawn for radiation environment and shielding models. Since these reports, the CREAM monitor has flown on a number of Shuttle visits to MIR during 1997-1998 with an extended deployment on MIR during January to May 1998. In all cases an active monitor measured charge-deposition spectra at various locations, while passive packages comprising neutron activation foils, neutron bubble detectors and thermoluminescent dosimeters obtained integrated data at these and other sites. Movement of the South Atlantic Anomaly is observed and cannot be fitted by simply updating the geomagnetic field model. The data from MIR are compared with those from previous Shuttle missions and show comparable secondary neutron fluencies and dose rates. Meanwhile a CREDO-3 particle telescope has been included in the Microelectronics and Photonics Test Bed in highly eccentric, high inclination orbit and has been returning data since November 1997. This experiment measures proton fluxes greater than 38 MeV and linear energy transfer spectra of cosmic rays and solar particle events in the range 100-20 000 MeV/(g cm-2). The data have been extended to July 2000 and are used both to correlate with device behavior and to compare with models of trapped radiation, cosmic rays and solar particles. A number of solar particle events have been observed as cycle 23 builds up. Following a relatively quiet year in 1999, the recent event of July 14, 2000 is observed to compete with the October 1989 events in terms of proton fluency but has a somewhat lower heavy ion fraction.