The Gamma Ray

Normally you can't detect gamma rays from the Sun, even from outer space, for their intensity is so low. But when protons and heavier ions are accelerated to high speed during solar flares, and beamed down into the chromosphere, they produce nuclear reactions and generate gamma rays, the most energetic kind of radiation detected from solar flares, tte gamma rays have energies of about one MeV, equivalent to a thousand keV, so the gamma rays are ten to one hundred times more energetic than the hard X-rays and soft X-rays detected during solar flares. Like X-rays, the gamma rays are totally absorbed in our atmosphere and must be observed from space.

tte high-speed flare protons slam into the dense, lower atmosphere, like a bullet hitting a concrete wall, shattering nuclei in a process called spallation, tte nuclear fragments are initially excited, but then relax to their former state by emitting gamma rays. Other abundant nuclei are energized by collision with the flare-accelerated protons, and emit gamma rays to get rid of the excess energy. Nuclear de-excitation gamma-ray lines observed during solar flares include those from excited nuclei of carbon, oxygen, nitrogen, neon, magnesium, silicon and iron; most recently detected from the Reuven Ramaty High Energy Spectroscopic Imager, abbreviated RHESSI.

During bombardment by flare-accelerated ions, energetic neutrons can be torn out of the nuclei of atoms. Many of these neutrons are eventually captured by ambient, or non-flaring, hydrogen nuclei, the protons, in the photosphere, making deuterons, the nuclei of deuterium atoms, and emitting one of the Sun's strongest gamma-ray lines at 2.223 MeV (Fig. 7.9). tte neutrons must slow down and lose some energy by collisions before the protons can capture them, so the gamma-ray line is delayed by a minute or two from the onset of impulsive flare emission.

Neutrons produced by accelerated particle interactions during solar flares can also escape from the Sun, avoiding capture there. Neutrons with energies above 1,000 MeV have even been directly measured in space near Earth, in the 1980s from the Solar Maximum Mission, abbreviated SMM, and in the 1990s from the Compton Gamma Ray

FIG. 7.9 Flare spectral lines at high energy The energy spectrum of radiation from a flare on 28 October 2003 exhibits two prominent spectral lines and numerous less intense, narrow ones. The line with an energy of511 keV, or 0.511 MeV, is emitted when electrons collide

FIG. 7.9 Flare spectral lines at high energy The energy spectrum of radiation from a flare on 28 October 2003 exhibits two prominent spectral lines and numerous less intense, narrow ones. The line with an energy of511 keV, or 0.511 MeV, is emitted when electrons collide

10"1

ated electrons. This data was obtained from the Ramaty

High Energy Solar Spectroscopic

Imager, abbreviated RHESSI, a NASA spacecraft. (Courtesy of Brian R. Dennis, NASA.)

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment