THE DORELI PROJECT: CROSS CHECKING AND INTER-CALIBRATING OF RADIATION DETECTORS ON BOARD THE COLUMBUS LABORATORY OF THE INTERNATIONAL SPACE STATION

Abstract

The space radiation environment in the International Space Station (ISS) is among the most complex radiation environments humans encounter. Measuring the radiation load inside the ISS, its changes with the ISS orbits and relevant internal shielding distributions is essential to evaluate the radiation risk. Conducting simultaneous measurements of the space radiation environment using a diverse set of detectors allows for cross-calibration and cross-verification of the individual instruments, resulting in refined measurements that contribute to a more comprehensive understanding of the radiation environment as a whole. Moreover, refined measurements using these approach enhance the independence of the data obtained from the specific characteristics of each of the detectors. In 2021 we started a collaboration aimed at comparing measurements from four radiation detector systems exploiting the colocation of these instruments in the COLUMBUS laboratory, ISS. The instruments under study are: LIDAL (University of Rome Tor Vergata, URTV), REM (NASA-JSC/SRAG) and the DOSTEL-1 -2 units (DLR, CAU), All four detectors utilize silicon technology, but differing hardware design approaches and sensor characteristics. LIDAL is a telescope (18 striped silicon planes + 2 segmented scintillators planes, 8 x 16 cm2) 49 cm long. REM is a hybrid silicon pixel detector (Timepix) containing a matrix of 256 x 256 pixels at a 55 micron pitch for a total sensing area of 1.982 cm2. The DOSTELs are silicon telescopes using two Canberra PIPS (Passivated Implanted Planar Silicon) round detectors (6.93 cm2) mounted at a distance of 15mm. The two DOSTEL instruments are positioned beneath the EPM rack in Columbus with telescope viewing directions fixed in the X and Y ISS directions. LIDAL is periodically rotated along the three ISS directions X, Y, Z. The REM detector, positioned in the LIDAL field of view and flat on one of the lids of the LIDAL detector, follows all LIDAL rotations. The total joint period of measurements now covers more than four years (less for REM which joined later) allowing a detailed study of a relevant portion of solar cycle (from solar minimum to the approach of solar maximum). Due to the relevant differences among the detectors the measurements provide different data, with the differences related primarily to field of view and energy acceptance. Understanding these differences is the first step to enhance the data analyses for each detector and to extract synergic results which would not have been possible using the detectors individually. Besides showing the remarkable similarity among the results, the remaining differences will be mostly accounted for by the shielding distributions at each sensor location and by the different hardware strategies employed (triggers, energy acceptances). The combined data will be used to maximize the exploitation of the analysis results. Fluxes and dose rates versus time and versus the McIllwain’s magnetic coordinate L along with spectral results will be presented and discussed. Finally, it will be emphasized that the DORELI project represents a use case for the RadLab effort, an initiative within the Open Science Data Repository (OSDR) at NASA Ames Research Center which will be discussed elsewhere in this conference.