Activation by neutrons

Neutron Activation Ana.lysis, A measured sample activated by neutron bombardment emits gamma rays that are used to determine the mercury content by proton-spectmm scanning. Mercury concentrations as low as 0.05 ppb have been determined by this method. 

When corrosion products are deposited on the fuel surfaces, they are activated by neutron capture. Some of the most prominent of these activities are 55Fe, 63Ni, 60Co, 54Mn, 58Co, and 59Fe. These radionuclides will then be found in the reactor coolant. 

Examples of Szilard-Chalmers reactions are given in Table 9.4. Radionuclides of the halides may be obtained in high specific activities by neutron irradiation of alkyl or aryl halides or of the salts of the oxoacids. Radionuclides of other elements may also be produced in high specific activities by neutron irradiation of covalent compounds. 

Neutron activation This is the term used for neutron reactions that result in the formation of radioactive nuclides. This type of reaction is used in solid-state use-once devices containing one or more materials that are activated by neutron radiation. The induced activity of each material can be measured and the neutron exposure can then be calculated from these activities. 

The second source of contamination in normal reactor operation is induced activity by neutron irradiation of the coolant. The amount of... 

McMillan, Edwin. 1939. Radioactive recoils from uranium activated by neutrons. Phys. Rev. 55 510... 

For more generalized forms of the above Bateman equations including activation by neutron capture see Eqs. (1.29)-(1.30) in Chap. 38, Vol. 4, cited from Rubinson (1949). 

Some of the accessible reactions are directly important in the nucleosynthetic processes while other experiments can only serve as tests of the theoretical approaches (Kiss et al. 2008). The reactions can either be studied in online beam experiments detecting directly emitted y-rays or particles. Another important type of experiment is that of activation (see, e.g., Gyiirky et al. 2006, and references therein). A material sample is activated by neutron, proton, or a beams at the energy of interest and the long-term radiation is counted over an extended period of time. Alternatively, the amount of the nuclei produced by the activation can be measured by the very sensitive accelerator mass spectrometry (AMS), which has become an important tool also for astrophysical measurements. It is especially well suited to study neutron-induced reactions producing different isotopes of the same element. 

Helium is used as a cover gas for the moderator system because it is chemically inert and is not activated by neutron irradiation. Radiolysis of the heavy water moderator in the calandria results in the production of deuterium and oxygen gases. Circulation of the cover gas to catalytic recombiners reforms heavy water and prevents accumulation of these gases. The deuterium and oxygen concentrations are maintained well below levels at which an explosion hazard would exist. 

The major source of radiation in an operational plant is the reactor core and the surrounding materials that are activated by neutrons that escape from the core. 

Activation of impurities contained in the coolant or moderator (e.g. Na present as an impurity in water is activated by neutron capture to produce Na) ... 

Air is usually present in the water coolant-moderator system in dissolved or gaseous form and is activated by neutrons producing N, Ar and other isotopes. 

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