As gamma rays pass through, they collide with electrons in the crystal. Gamma-ray detectors typically contain densely packed crystal blocks. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of a detector. Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. Credit: NASA/DOE/International LAT Team SOURCES OF GAMMA RAYS Prompted extensive efforts to assess the potential damage to life onĮarth due to increased levels of UV-B radiation.Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Scientific concern over ozone depletion in the upper atmosphere has ![]() Without the layer of ozone in the stratosphere to protect us fromĮxcessive amounts of UV-B radiation, life as we know it would not exist. Regions during certain times of the year. This means that more ultraviolet radiation can pass through theĪtmosphere to the Earths surface, particularly at the poles and nearby (the layer of atmosphere ranging from about 11 to 50 km in altitude). The mid-1970s, human activities have been changing the chemistry of theĪtmosphere in a way that reduces the amount of ozone in the stratosphere UV radiation and prevents most of it from reaching the Earth. A layer of ozone in the upper atmosphere absorbs In addition to their own resiliency, living things and the cells theyĪre made of are protected from excessive amounts of UV radiation by aĬhemical called ozone. Makes DNA somewhat resilient to damage by UV-B. Removes the damaged section of DNA, and replaces it with the properĬomponents (based on information elsewhere on the DNA molecule). A special enzyme arrives at the damage site, (Illustration by David Herring)īut living cells are smart. Over millions of years ofĮvolving in the presence of UV-B radiation, cells have developed theĪbility to repair DNA. Instead of across the ladder. This makes a bulge, and the distortedĭNA molecule does not function properly. In one common damage event, adjacent bases bond with each other, (UV) photons harm the DNA molecules of living organisms in different As a result,ĭistorted proteins can be made, or cells can die. Illustrates one such change in shape due to exposure to UV-B radiation.Ĭhanges in the DNA molecule often mean that protein-building enzymesĬannot read the DNA code at that point on the molecule. (Illustration by Robert Simmon)ĭNA readily absorbs UV-B radiation, which commonly changes the shape Represents a small portion of the spectrum, from 290 to 320 nanometer Ultraviolet B radiation, harmful to living organisms, In a range of wavelengths, which are delineated into major divisions for ![]() UV-B causes damage at the molecular level to the fundamental buildingīlock of life deoxyribonucleic acid (DNA). (UV-B includes light with wavelengths down to 280 nm, but little to no radiation below 290 nm reaches the Earth’s surface). The incoming radiation at shorter wavelengths, 290-320 nm, falls within the UV-B part of the electromagnetic spectrum. Harmful role in that it causes sunburn on human skin and cataracts in Longer UV wavelengths of 320-400 nm, called UV-A, plays a helpfulĪnd essential role in formation of Vitamin D by the skin, and plays a The harmful effects as well as the helpful ones. ![]() Yet UV radiation atĭifferent wavelengths differs in its effects, and we have to live with BiologicalĪctions of many kinds have evolved to deal with it. ![]() UV radiation from the sun has always played important roles in ourĮnvironment, and affects nearly all living organisms. This is shorter than wavelengths of visible light, which areĪnd harmful effects of ultraviolet (UV) radiation from the Wavelengths between 290 and 400 nm (nanometers, or billionths of a Ultraviolet (UV) radiation that reaches the Earths surface is in The shorter the wavelength, the moreĮnergetic the radiation, and the greater the potential for harm. The sun radiates energy in a wide range of wavelengths, most of whichĪre invisible to human eyes. At the time of publication, it represented the best available science. This page contains archived content and is no longer being updated.
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