Emission of gamma rays

Am is produced when 239Pu is exposed to neutrons, such as may occur in nuclear reactors. (239Pu, it should be noted, is produced when uranium 238 [238U], is exposed to neutrons.) The reaction sequence involves the successive absorption of neutrons and emission of gamma rays, written as (n,y) and the emission of a beta particle, (3. ... 

The numerical combination of protons and neutrons in most nuclides is such that the nucleus is quantum mechanically stable and the atom is said to be stable, i.e., not radioactive however, if there are too few or too many neutrons, the nucleus is unstable and the atom is said to be radioactive. Unstable nuclides undergo radioactive transformation, a process in which a neutron or proton converts into the other and a beta particle is emitted, or else an alpha particle is emitted. Each type of decay is typically accompanied by the emission of gamma rays. These unstable atoms are called radionuclides their emissions are called ionizing radiation and the whole property is called radioactivity. Transformation or decay results in the formation of new nuclides some of which may themselves be radionuclides, while others are stable nuclides. This series of transformations is called the decay chain of the radionuclide. The first radionuclide in the chain is called the parent the subsequent products of the transformation are called progeny, daughters, or decay products. 

Radioactive isotopes that decay by the emission of alpha or beta radiation undergo a change in the nature of their nuclei and are converted into isotopes of other elements. The emission of gamma rays, on the other hand, does not change the nature of the nuclei of the radioisotopes from which the rays are emitted. Gamma rays are a form of dissipation of nuclear energy. 

The fact that neutrinos are emitted during the transformation provides an opportunity for direct observation of the reactions taking place at the heart of the Sun. Note that antimatter is produced in this strange reaction, in the form of the positton or antielectron e+. The positrons generated immediately annihilate with electrons in the surrounding medium with subsequent emission of gamma rays. 

The chemical effect of a nuclear transformation was observed by Szilard and Chalmers (78) in 1934. They irradiated liquid ethyl iodide with neutrons and found that radioactive iodine could be extracted into water. The effect was attributed to the rupture of the carbon-iodine bond by the mechanical recoil imparted to the iodine nucleus by the incident neutron. Subsequently Fermi et al. (/) showed that the recoil energy given to the nucleus by the emission of gamma rays following thermal neutron capture was sufficient to break the bonds holding the capturing atom to the remainder of the molecule. 

Because gamma rays are massless, the emission of gamma rays by themselves cannot result in the formation of a new atom. Table 4-3 summarizes the basic characteristics of alpha, beta, and gamma radiation. 

Single photon emitters decay under the emission of gamma rays with energies between 100 and 360 keV. 

Prepd from radioactive chromium ( ICr) which has a half-life of 26.5 days. The emission of gamma rays is applicable to biological tagging and tracing. Other properties identical with those of Ordinary sodium chromate. Available as soln for intravenous injection or for mixing with blood. Unbound chromate in the plasma can be reduced with ascorbic add or may be removed by separation aud washing of cells. 

Positron emission occurs only when the energy difference between the parent radionuclide and the products exceeds 1.02 MeV (the energy equivalent of the sum of the masses of an electron and a positron). The atom s recoil, as for beta-particle emission, is a few electron volts. At lesser energy differences, a proton in the nucleus can be converted to a neutron by electron capture, i.e., the capture by the nucleus of an atomic electron from, most probably, an inner electron shell (see discussion below of CEs). The process of electron capture parallels positron emission and may occur in the same isotope. It is accompanied by emission of a neutrino and characteristic X rays due to the rearrangement of atomic electrons. Electron capture may also be signaled by the subsequent emission of gamma rays. Examples of these decays are given in Sections 9.3.4 and 9.3.6. 

This new instrumentation would allow detailed investigations of several fundamental astrophysical issues including the formation of the Solar System, the life and death of stars, the composition and velocity distribution of interstellar material, and the power sources of quasars and active galaxies. For example, a particularly interesting radioisotope is Ti which decays with the emission of gamma-ray lines at 68 and 78 keV, just the energies... 

The de-excitation of nickel-60 is accompanied by the emission of gamma-ray photons having energies 1.17 MeV and 1.33 MeV. 

Summing of events, either a result of coincident emission of gamma rays in the decay chain of the nuclide of interest or of random coincident emissions, can lead to significant losses or potential additions to an otherwise clean peak (De Bruin and Blaauw 1992 Becker et al. 1994). While coincidence losses are not an issue for comparator NAA, calibration, and/or computational correction must be applied (Debertin and Helmer 1988 Blaauw and Celsema 1999) to arrive at true peak areas for other methods of calibration. 

Many radionuclides decay with the emission of gamma rays (photons). These photons can be detected and identified by their characteristic energies by using a germanium detector, a lithimn-drifted germanium detector, or a scintillation detection system. 

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