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Radioactivity and Matter
Published in Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff, Radiation and Radioactivity on Earth and Beyond, 2020
Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff
Heavy nuclei like uranium can also decay by splitting into two lighter nuclei: this phenomenon is known as spontaneous fission. It is only infrequently observed for uranium, but competes increasingly with α-emission when the atomic number increases. For the heaviest nuclei produced artificially, it represents the predominant mode of decay (Figure 11).
Radiation protection in the nuclear industry
Published in Alan Martin, Sam Harbison, Karen Beach, Peter Cole, An Introduction to Radiation Protection, 2018
Alan Martin, Sam Harbison, Karen Beach, Peter Cole
Fission is the splitting of a nucleus into two approximately equal parts known as fission fragments. Certain types of heavy nuclei, notably uranium and thorium, are found to undergo spontaneous fission at a rather low rate. Others can be made to fission by the addition of energy, for example by bombardment with neutrons. Materials which can be made to fission in this way are said to be fissile. The process of fission results in the release of energy, mainly in the form of kinetic energy of the fission fragments. This is rapidly converted into thermal energy and raises the temperature of the fuel material. Of naturally occurring materials, only the isotope uranium-235 (U-235) is fissile to a significant extent. This constitutes only 0.7% by weight of natural uranium, the remaining 99.3% being mainly U-238.
Nuclei and Radiations
Published in José Guillermo Sánchez León, ® Beyond Mathematics, 2017
Some very heavy nuclei may experience spontaneous fission. The next function displays the first five such elements: Take [Transpose [Cases [Table[IsotopeData [#, prop], {prop, {"Symbol", "SpontaneousFission"}}] & /@ IsotopeData[], Except[{_, False}]]][[1]], 5] {230Th, 232Th, 231Pa, 234Pa, 230U}
A membrane, pseudo-vertical p-i-n diamond detector
Published in Journal of Nuclear Science and Technology, 2023
Tetsuichi Kishishita, Kimiyoshi Ichikawa, Kazuya Tauchi, Masayoshi Shoji, Masayuki Hagiwara, Satoshi Koizumi, Manobu M. Tanaka
Figure 1 (left) shows a 3D image of the expected flooded primary containment vessel at the Fukushima NPP. The urgent task is the localization and characterization of the fuel debris in the flooded primary containment vessel (PCV) on-site. This is achievable by detecting spontaneous fission neutrons emitted from submerged fuel debris. According to the current estimate, a neutron flux is in the range of – n/cm/s with a -ray dose rate of up to 100 Gy/h, emitted by the widely dispersed CS [6]. In order to separate the rare signals of neutrons associated with the debris from large amounts of background -rays, the neutron converters, e.g.BC or LiF, will be directly coated on the diamond surface. The detector system is installed on the ROV (remotely operated vehicle), as shown in Figure 1 (right). Using the multi-phased array sonar and the acoustic sub-bottom profiling system, the detector system reconstructs the position of the fuel debris in real time.
Post-Neutron Mass Yield Distribution in the Spontaneous Fission of 252Cf
Published in Nuclear Science and Engineering, 2021
H. Naik, S. P. Dange, W. Jang, R. J. Singh
Spontaneous fission is primarily observed in actinides with mass numbers of 230 or more.4,5 The neutrons emitted from the spontaneous fission of 238U itself is sufficient to start a U-based fuel reactor. However, a better way to start a nuclear reactor is to use the neutrons from the spontaneous fission of 252Cf. This is because 252Cf has an effective half-life of 2.645 years, with a spontaneous fission half-life of 85.5 years (Refs. 6 , 7, and 8). So, the neutron emission rate is significantly higher in the spontaneous fission of 252Cf than in other relatively long-lived actinides such as 244Cm, 238Pu, 240Pu, 242Pu, and 238U.
Post-Neutron Fission Product Yield Distribution in the Spontaneous Fission of 244Cm
Published in Nuclear Science and Engineering, 2023
Mass yield, charge yield, and kinetic energy distributions in the low energy fission of actinides provide information about the effect of the nuclear structure and the dynamics of descent from saddle to scission.1,2 In the neutron-induced fission of actinides, the compound nucleus acquires excitation energy from the kinetic energy of the incident neutron and its binding energy. This excitation energy in neutron-induced fission is higher than the fission barrier and thus causes fission. On the other hand, the spontaneous fission of actinides takes place in the ground (g) state due to quantum tunneling arising from the Coulomb repulsion of the protons inside the nucleus. Thus the role of the nuclear structure effect can be better examined in the spontaneous fission of actinides. Spontaneous fission is primarily observed in even-even actinides with mass numbers of 230 and above.1,2 Mass yield and kinetic energy distribution studies of the spontaneous fission of heavier and lighter actinides have been carried out by using online physical techniques.3–8 The mass yield distribution studies in the spontaneous fission of heavier actinides5,9–15 within the mass region of 259 to 242 and for lighter actinides, such as 240Pu (Ref. 16) and 238U (Refs. 17 through 22), have been carried out using radiochemical methods. On the other hand, data on the charge yield distribution in the spontaneous fission of actinides based on the radiochemical method and off-line γ-ray spectrometric technique are available in an exhaustive way for the 252Cf(SF) reaction and have been compiled by Wahl.23 This is because 252Cf has an effective half-life of 2.645 years and a spontaneous fission half-life of 85.5 years.24–28 The spontaneous fission of heavier actinides above 252Cf are less studied due to their short half-lives. Similarly, the spontaneous fission of lighter actinides below 252Cf are also less studied due to very low specific activity based on their long half-lives. Some data on charge yield distributions using radiochemical and off-line γ-ray spectrometric techniques are available only for heavy mass fission products in the spontaneous fission of 244Cm (Ref. 29). This is due to the effective half-life of 244Cm, which is 18.1 ± 0.1 years with a long spontaneous fission half-life of 1.32 ± 0.02 × 107 years.24–28