How are Gamma Rays Produced During Solar Flares? : Just as electrons are accelerated during solar flares, free protons and the nuclei of heavier elements in the solar atmosphere are also accelerated. Some accelerated protons encounter the nuclei of carbon, oxygen, neon and other elements found in the solar atmosphere. When a proton collides with one of these nuclei, the nucleus is excited to a higher energy level. The excited nucleus gives off a gamma-ray photon with a specific energy characteristic of the element involved and returns to its original energy level or ground state. Alternatively, an accelerated heavy nucleus can interact with an ambient low-energy proton and become excited to a higher energy level. It continues on at a similar velocity and emits the characteristic gamma ray as it decays back to the ground state. Because of the velocity of the heavy nucleus, the gamma-ray energy is Doppler shifted up or down, depending on whether the nucleus is moving towards or away from the observer, respectively. The process is illustrated above.
How are X-rays Produced in Solar Flares? : The X-rays are believed to be produced by the electrons accelerated in the solar corona during the flare. As the electrons travel at velocities about one third the speed of light in the corona, a small fraction of them (1 in 100,000) suffer close encounters with the ambient protons, as indicated below. In such an interaction, the electron is attracted towards the proton as a result of the opposite charges, and its path is bent. An X-ray photon is produced at the point of the electron's closest approach to the proton. This is known as bremsstrahlung, from the German word meaning braking radiation. By detecting these X-ray photons with HESSI, scientists will be able to determine where and how many electrons are accelerated and to what energies.
Last Updated by Gilbert Prevost on Monday, 23 March, 1998