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Analytical Test Methods for Polymer Characterization
Published in Nicholas P. Cheremisinoff, Elastomer Technology Handbook, 2020
Nicholas P. Cheremisinoff, Boyko Randi, Leidy Laura
Neutron activation analysis is a method of elemental analysis in which nonradioactive elements are converted to radioactive ones by neutron bombardment, and the elements of interest are determined from resulting radioactivity (Figure 43). High-energy (14-MeV) neutrons are generated by the reaction of medium-energy deuterium ions with titrium. For oxygen analysis, the carefully weighed sample is irradiated for 15 s to convert a small amount of the oxygen-16 to nitrogen-16, which emits α rays with a half-life of 7.4 s. The irradiated sample is transferred to a scintillation detector where the α rays are counted for 30 s to insure that all usable radioactivity has been counted and that no significant radioactivity remains in the sample. The system is calibrated with standards of known oxygen content.
The radiation background
Published in R.J. Pentreath, Nuclear Power, Man and the Environment, 2019
The neutron flux results not only in fissions of other uranium nuclei; neutrons may also be captured by the materials of the bomb casing and by debris sucked into the fireball which results from the explosion. The isotopes of many elements may thereby be made radioactive by neutron capture: these are the neutron activation products. Typical of such radionuclides are those of elements such as iron, zinc, manganese and cobalt – all of which are essential trace elements. The type, and amounts, of neutron activation products formed will depend upon where, and at what height, the bomb was exploded. Elements in the atmosphere are also subject to neutron interactions, notably nitrogen, which produces some 1.26 PBq (34 kCi) of 14C per megaton. A much smaller amount of 3H is also produced.
Biological and Health Effects of Radiation
Published in Philip T. Underhill, Naturally Occurring Radioactive Material, 2018
Although not a method for radioactive materials to enter the body, radionuclides can be formed inside the body by exposure to neutron radiation. This process is known as neutron activation. Neutron radiation is encountered in the oil industry in the form of radioactive sources used for well logging. However, activation of biological tissues is not a significant aspect of the hazard from these sources.
Reactor Physics Analysis Assessment of Feasibility of Using Advanced, Nonconventional Fuels in a Pressure Tube Heavy Water Reactor to Destroy Long-Lived Fission Products
Published in Nuclear Technology, 2021
While the focus of this study is on the transmutation/consumption/destruction of seven key LLFP isotopes, it is also recognized that minor actinides and various neutron activation products are of concern for long-term storage in DGRs since they will also contribute to long-term radiation dose and radiotoxicity. Activation products are those radioactive isotopes produced by neutron activation of different elements and isotopes found in reactor structural components and coolant during reactor operations. Some of the long-lived activation products are produced by the irradiation of trace impurities of certain elements. Examples of such long-lived activation products include 36Cl (Thalf-life = 301 000 years), 14C (Thalf-life = 5730 years), and 41Ca (Thalf-life = 103 000 years) (Refs. 5 and 6).
Thermal neutron scattering properties of Bismuth crystal filter
Published in Journal of Nuclear Science and Technology, 2021
Lipeng Wang, Liangzhi Cao, Hongchun Wu, Lingti Kong, Yongqiang Tang
High-intensity thermal neutron beam is in strong demand in nuclear technology applications. Examples of such applications include thermal-neutron BNCT (Boron Neutron Therapy), thermal neutron radiography and prompt gamma neutron activation analysis, etc. Thermal neutron filter is mainly used for thermal neutron beam spectral shaping in the research reactor to obtain such beam. Its object is to increase the neutron-to-gamma ratio for thermal neutrons and make them more effective in thermal neutron experiment by reducing the fraction of epithermal and fast neutrons as well as absorbing gamma rays. In recent years, many materials have been studied as the thermal neutron filters with their scattering. However, most of them are not competent for large size and quantities required for single-crystal neutron filter. Bi metal is considered to be a promising candidate material with a high desirable Debye temperature for large-size thermal neutron filters [1]. Bi metal has been used as epithermal neutron and fast neutron scatters in major research reactors both at home and abroad. Meanwhile, it can also effectively shield gamma rays because of its large atomic mass. However, at present, the thermal neutron scattering cross-sections of Bi nuclide are lacking in standard ENDF libraries [2]. By using traditional neutronic code such as MCNP [3], the thermal neutron beam in reactor channel can only be simulated with the free gas model of Bi, which is quite different from the real situation. Previously the semi-empirical formulas have been adopted by several researchers for the thermal scattering of Bi metal, which permit the thermal diffuse scattering (TDS) to be calculated as an approximate function of material constants, temperature and neutron energy. Furthermore, the contribution of Bragg scattering for poly- and mono-crystal Bi can be considered or neglected on demand [4–7]. Nevertheless, the urgent demand for high fidelity calculation of thermal neutron scattering cannot be fulfilled, and the discrepancy with experimental result cannot be eliminated. An accurate description of the physical mechanism of thermal neutron scattering process with Bi is therefore essential. The dependence of the total thermal scattering cross-sections on Bi parameters, including the TDS, Bragg scattering, neutron capture , and the secondary neutron spectrum, should be identified.