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Because of its lower photon energy, visible light can sometimes pass through many kilometers of a substance, while higher frequencies like UV, x ray, and \(\gamma\) rays are absorbed, because they have sufficient photon energy to ionize the material.
- 29.4: Photon Momentum
A more massive particle with the same momentum would have an...
- The Photoelectric Effect
The electron would be stopped by a retarding potential of...
- 29.4: Photon Momentum
It consists of the shortest wavelength electromagnetic waves, typically shorter than those of X-rays. With frequencies above 30 exahertz (3 × 1019 Hz) and wavelengths less than 10 picometers (1 × 10−11 m), gamma ray photons have the highest photon energy of any form of electromagnetic radiation.
- Overview
- Gamma rays
- Development of the classical radiation theory
Six years after the discovery of radioactivity (1896) by Henri Becquerel of France, the New Zealand-born British physicist Ernest Rutherford found that three different kinds of radiation are emitted in the decay of radioactive substances; these he called alpha, beta, and gamma rays in sequence of their ability to penetrate matter. The alpha particles were found to be identical with the nuclei of helium atoms, and the beta rays were identified as electrons. In 1912 it was shown that the much more penetrating gamma rays have all the properties of very energetic electromagnetic radiation, or photons. Gamma-ray photons are between 10,000 and 10,000,000 times more energetic than the photons of visible light when they originate from radioactive atomic nuclei. Gamma rays with a million million times higher energy make up a very small part of the cosmic rays that reach Earth from supernovae or from other galaxies. The origin of the most-energetic gamma rays is not yet known.
During radioactive decay, an unstable nucleus usually emits alpha particles, electrons, gamma rays, and neutrinos spontaneously. In nuclear fission, the unstable nucleus breaks into fragments, which are themselves complex nuclei, along with such particles as neutrons and protons. The resultant stable nuclei or nuclear fragments are usually in a highly excited state and then reach their low-energy ground state by emitting one or more gamma rays. Such a decay scheme is shown schematically in Figure 7 for the unstable nucleus sodium-24 (24Na). Much of what is known about the internal structure and energies of nuclei has been obtained from the emission or resonant absorption of gamma rays by nuclei. Absorption of gamma rays by nuclei can cause them to eject neutrons or alpha particles or it can even split a nucleus like a bursting bubble in what is called photodisintegration. A gamma particle hitting a hydrogen nucleus (that is, a proton), for example, produces a positive pi-meson and a neutron or a neutral pi-meson and a proton. Neutral pi-mesons, in turn, have a very brief mean life of 1.8 × 10−16 second and decay into two gamma rays of energy hν ≈ 70 MeV. When an energetic gamma ray hν > 1.02 MeV passes a nucleus, it may disappear while creating an electron–positron pair. Gamma photons interact with matter by discrete elementary processes that include resonant absorption, photodisintegration, ionization, scattering (Compton scattering), or pair production.
Gamma rays are detected by their ability to ionize gas atoms or to create electron–hole pairs in semiconductors or insulators. By counting the rate of charge pulses or voltage pulses or by measuring the scintillation of the light emitted by the subsequently recombining electron–hole pairs, one can determine the number and energy of gamma rays striking an ionization detector or scintillation counter.
Both the specific energy of the gamma-ray photon emitted as well as the half-life of the specific radioactive decay process that yields the photon identify the type of nuclei at hand and their concentrations. By bombarding stable nuclei with neutrons, one can artificially convert more than 70 different stable nuclei into radioactive nuclei and use their characteristic gamma emission for purposes of identification, for impurity analysis of metallurgical specimens (neutron-activation analysis), or as radioactive tracers with which to determine the functions or malfunctions of human organs, to follow the life cycles of organisms, or to determine the effects of chemicals on biological systems and plants.
Six years after the discovery of radioactivity (1896) by Henri Becquerel of France, the New Zealand-born British physicist Ernest Rutherford found that three different kinds of radiation are emitted in the decay of radioactive substances; these he called alpha, beta, and gamma rays in sequence of their ability to penetrate matter. The alpha particles were found to be identical with the nuclei of helium atoms, and the beta rays were identified as electrons. In 1912 it was shown that the much more penetrating gamma rays have all the properties of very energetic electromagnetic radiation, or photons. Gamma-ray photons are between 10,000 and 10,000,000 times more energetic than the photons of visible light when they originate from radioactive atomic nuclei. Gamma rays with a million million times higher energy make up a very small part of the cosmic rays that reach Earth from supernovae or from other galaxies. The origin of the most-energetic gamma rays is not yet known.
During radioactive decay, an unstable nucleus usually emits alpha particles, electrons, gamma rays, and neutrinos spontaneously. In nuclear fission, the unstable nucleus breaks into fragments, which are themselves complex nuclei, along with such particles as neutrons and protons. The resultant stable nuclei or nuclear fragments are usually in a highly excited state and then reach their low-energy ground state by emitting one or more gamma rays. Such a decay scheme is shown schematically in Figure 7 for the unstable nucleus sodium-24 (24Na). Much of what is known about the internal structure and energies of nuclei has been obtained from the emission or resonant absorption of gamma rays by nuclei. Absorption of gamma rays by nuclei can cause them to eject neutrons or alpha particles or it can even split a nucleus like a bursting bubble in what is called photodisintegration. A gamma particle hitting a hydrogen nucleus (that is, a proton), for example, produces a positive pi-meson and a neutron or a neutral pi-meson and a proton. Neutral pi-mesons, in turn, have a very brief mean life of 1.8 × 10−16 second and decay into two gamma rays of energy hν ≈ 70 MeV. When an energetic gamma ray hν > 1.02 MeV passes a nucleus, it may disappear while creating an electron–positron pair. Gamma photons interact with matter by discrete elementary processes that include resonant absorption, photodisintegration, ionization, scattering (Compton scattering), or pair production.
Gamma rays are detected by their ability to ionize gas atoms or to create electron–hole pairs in semiconductors or insulators. By counting the rate of charge pulses or voltage pulses or by measuring the scintillation of the light emitted by the subsequently recombining electron–hole pairs, one can determine the number and energy of gamma rays striking an ionization detector or scintillation counter.
Both the specific energy of the gamma-ray photon emitted as well as the half-life of the specific radioactive decay process that yields the photon identify the type of nuclei at hand and their concentrations. By bombarding stable nuclei with neutrons, one can artificially convert more than 70 different stable nuclei into radioactive nuclei and use their characteristic gamma emission for purposes of identification, for impurity analysis of metallurgical specimens (neutron-activation analysis), or as radioactive tracers with which to determine the functions or malfunctions of human organs, to follow the life cycles of organisms, or to determine the effects of chemicals on biological systems and plants.
The classical electromagnetic radiation theory “remains for all time one of the greatest triumphs of human intellectual endeavor.” So said Max Planck in 1931, commemorating the 100th anniversary of the birth of the Scottish physicist James Clerk Maxwell, the prime originator of this theory. The theory was indeed of great significance, for it not on...
Gamma rays, X-rays, and extreme ultraviolet rays are called ionizing radiation because their high photon energy is able to ionize atoms, causing chemical reactions. Longer-wavelength radiation such as visible light is nonionizing; the photons do not have sufficient energy to ionize atoms.
Nov 14, 2014 · Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays.
When we compare photon energies from the EM spectrum in Figure 1 with energies in the table, we can see how effects vary with the type of EM radiation. Gamma rays, a form of nuclear and cosmic EM radiation, can have the highest frequencies and, hence, the highest photon energies in the EM spectrum.
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Aug 10, 2016 · Gamma-ray bursts are the most energetic and luminous 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!
