Interactions of Ionizing Radiation with Matter and Direct Energy Conversion
Ionizing radiation is a broad term which refers to the fact that different types of radiation will create ion pairs in matter. Ionizing radiation includes ions (e.g., fission fragments and alpha particles), beta particles, gamma rays, x-rays, and neutrons
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Interactions of Ionizing Radiation with Matter and Direct Energy Conversion
Abstract Ionizing radiation is a broad term which refers to the fact that different types of radiation will create ion pairs in matter. Ionizing radiation includes ions (e.g., fission fragments and alpha particles), beta particles, gamma rays, x-rays, and neutrons. Radioisotopes emit ionizing radiation and are viewed as the primary power source for nuclear batteries. This chapter will explore various radioisotope sources and their properties. The transducers which can be used in concert with radioisotope sources will be discussed. Keywords Radiation interactions
3.1
Range Transducers
Ionizing Radiation Types and Ranges
Each type of ionizing radiation source has a characteristic range. Consider a material in the solid phase, for example. Swift heavy ions such as fission fragments and alpha particles will deposit their energy within a solid over a distance of micrometers. Electrons deposit their energy over a range of millimeters. Particles which possess high energy and either no rest mass or no net charge, such as gamma rays and neutrons, deposit their energy over a range of meters.
3.1.1
Fission Fragments
The shortest transport scale lengths are for ions, and the most massive ions are the fragments produced by fission. Fission commonly occurs through spontaneous decay of a heavy atom like californium-252, which releases fast neutron energy and fission fragments. The neutron energy and fission yield spectra are shown in Figs. 3.1 and 3.2 respectively. Products of a spontaneous fission event are shown in Eq. (3.1) where ffl is the light fission fragment, ffh is the heavy fission fragment, m is the statistical average number of prompt fission neutrons, nfast, released during © Springer International Publishing Switzerland 2016 M. Prelas et al., Nuclear Batteries and Radioisotopes, Lecture Notes in Energy 56, DOI 10.1007/978-3-319-41724-0_3
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3 Interactions of Ionizing Radiation with Matter …
Fig. 3.1 Energy spectrum of neutrons produced by the spontaneous fission of Cf-252 [1]
Fig. 3.2 Spontaneous fission yields of Cf-252 [3]
fission and are emitted with a typical fast neutron distribution [1, 2]. Fission can also be stimulated by neutron capture, whereby a nucleus absorbs an incident neutron, becomes unstable, and breaks apart. An example of fission initiated through the interaction of thermal neutrons with a fissile material, such as uranium-235, is shown
3.1 Ionizing Radiation Types and Ranges
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in Eq. (3.2); where nth is a thermal neutron with energy on the order of 25 MeV. Thermal fission also releases fast neutrons and fission fragments; the neutron energy distribution and bimodal fission yield distribution of U-235 are shown in Figs. 3.3 and 3.4, respectively. The average energy produced by particles released in the
Fig. 3.3 Neutrons energy spectrum produced by the thermal fission of U-235 [4]
Fig. 3.4 U-235 fission yields for high- and low-energy (thermal) incident neutrons [4]
3 Interactions of Ionizing Radiation with Mat
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