 Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of an ordinary detector.  The high energy of gamma rays enables them to pass through many kinds of materials, including human tissue. Very dense materials, such as lead, are commonly used as shielding to slow or stop gamma rays. Gamma-ray detectors typically contain densely packed crystal blocks. As gamma rays pass through, they collide with electrons in the crystal. This process, called Compton scattering, creates charged particles that can be detected by a sensor. Similar to all exposure to ionising radiation, high exposures to gamma rays can cause immediate damage to cells. Low levels of exposure carry a risk of cancer that rises with increased exposure. Nevertheless, gamma rays can be used to selectively kill already developed cancer cells. Your cells normally grow and divide to form new cells. But cancer cells grow and divide faster than most normal cells. Radiation works by making small breaks in the DNA inside cells. These breaks keep cancer cells from growing and dividing and cause them to die. Gamma rays from radioactive Cobalt-60 are aimed at the tumour from many different angles at once, and deliver a large dose of radiation exactly to the tumour. Astronomy 
Gamma-ray bursts are the most energetic electromagnetic events since the Big Bang and can release more energy in 10 seconds than our Sun will emit in its entire 10-billion-year expected lifetime! Scientists theorize that they occur when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole. Gamma-ray astronomy explores these exotic objects. NASA's Swift satellite recorded the gamma-ray blast caused by a black hole being born 12.8 billion light years away. This object is among the most distant objects ever detected. 
Scientists can use gamma rays to determine the elements on other planets. The first spacecraft to visit Mercury in 30 years, and the first ever to orbit that planet, MESSENGER mapped the entire planet, discovered abundant water ice in shadows at the poles, and unlocked knowledge about Mercury's geology and magnetic field. The 'MErcury Surface, Space Environment, Geochemistry, and Ranging' gamma ray spectrometer satellite
measured gamma rays emitted by the nuclei of atoms on Mercury's surface that were struck by cosmic rays (high-energy particles from space). When struck by cosmic rays, chemical elements in soils and rocks emit gamma rays. These data can help scientists look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium. The gamma-ray spectrometer on NASA's Mars Odyssey Orbiter also detected and mapped these on the planet Mars, in particular showing hydrogen concentrations in Martian surface soils. |