RHESSI observes solar photons over three orders of magnitude in energy (3 keV to 17 MeV) with a single instrument: a set of nine cryogenically cooled coaxial germanium detectors (GeD).  With their extremely high energy resolution, RHESSI can resolve the line shape of every known solar gamma-ray line except the neutron capture line at 2.223 MeV. High resolution also allows clean separation of thermal and non-thermal hard x-rays and the accurate measurement of even extremely steep power-law spectra. Detector segmentation, fast signal processing, and two sets of movable attenuators allow RHESSI to make high-quality spectra and images of flares across seven orders of magnitude in intensity.

The front segment thickness is chosen to stop photons up to ~150 keV, where photoelectric absorption dominates, while minimizing the active volume for background. Front-incident photons that Compton-scatter, and background photons or particles entering from the rear, are rejected by anticoincidence with the rear segment.

Photons with energies from ~150 keV to ~20 MeV, including all nuclear gamma-ray lines, stop primarily in the thick rear segment alone, with smaller fractions stopping in the front segment, depositing energy in both the front and rear segments, or in two or more GeDs. All these modes contribute to the total photopeak efficiency.

• Germanium Detectors
  
• Cryostat
  
• Cryocooler
  
• Data Monitor
  
• The RHESSI Spectrometer  - D. Smith  (September 2002)
• Behind, Beneath, and Before RHESSI Spectroscopy - D. Smith (April, 2002)
• Problems, Peculiarities, and Phenomena in RHESSI Spectroscopy - D. Smith (April 2002)
• RHESSI Spectroscopy Status and Issues - D. Smith (October 2002)
• RHESSI Detector Voltage Record - D. Smith (September 2002)
• RHESSI GEANT Model - D. Smith (June 2001)  Files included in RHESSI GEANT mass model
• Post-mission Calibration Report - A. Inglis and A. Shih (2024)
• RHESSI Calibration Software User Manual - A. Inglis and A. Shih (2024)