Although designed primarily as a hard X-ray imager and spectrometer, the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is also capable of measuring the polarization of hard X-rays (20-100 keV) from solar flares. This capability arises from the inclusion of a small unobstructed Be scattering element that is strategically located within the cryostat that houses the array of nine germanium detectors. The Ge detectors are segmented, with both a front and rear active volume. Low energy photons (below about 100 keV) can reach a rear segment of a Ge detector only indirectly, by scattering. Low energy photons from the Sun have a direct path to the Be and have a high probability of Compton scattering into a rear segment of a Ge detector. The azimuthal distribution of these scattered photons carries with it a signature of the linear polarization of the incident flux. Sensitivity estimates, based on simulations and in-flight background measurements, indicate that a 20-100 keV polarization sensitivity of less than a few percent can be achieved for X-class flares.
Space Science Center, Physics
Digital Object Identifier (DOI)
Mark L. McConnell ; David M. Smith ; A. Gordon Emslie ; Robert P. Lin and James M. Ryan "Hard x-ray polarimetry with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)", Proc. SPIE 4843, Polarimetry in Astronomy, 8 (February 1, 2003); doi:10.1117/12.458879; http://dx.doi.org/10.1117/12.458879
© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering.