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Energy and the First Law of Thermodynamics
Published in Kavati Venkateswarlu, Engineering Thermodynamics, 2020
Except for radioactivity, most of the transformations of states of matter that occur at terrestrial temperatures are chemical. At very high temperatures (exceeding 106 K) that are usually attained in the stars, nuclei collide and undergo nuclear reactions just like molecules collide and react at terrestrial temperatures. The electrons and nuclei of atoms are totally uncertain at these temperatures. Matter turns into an unknown state and the transformations that take place are between nuclei, and hence it is called nuclear chemistry. The nuclear reactions that occur in stars called nucleosynthesis result in the elements heavier than hydrogen on earth and other planets. Just like unstable molecules that dissociate into other more stable molecules, the radioactive elements are formed due to disintegration of some of the unstable nuclei that were synthesized in the stars.
The structure of matter
Published in Alan Martin, Sam Harbison, Karen Beach, Peter Cole, An Introduction to Radiation Protection, 2018
Alan Martin, Sam Harbison, Karen Beach, Peter Cole
In the early stages of the evolution of the universe, the two elements hydrogen and helium constituted essentially 100% of matter (apart from a very small quantity of lithium). However, processes occurring during the life cycles of early generations of stars resulted in the production of heavier elements by successive fusion reactions. This process, known as nucleosynthesis, eventually led to the creation of all the elements that are found on Earth today.
New Energy Sources
Published in Fang Lin Luo, Hong Ye, Renewable Energy Systems, 2013
The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron absorbs energy. The opposite is true for the reverse process, nuclear fission. This means that fusion generally occurs for lighter elements only, and likewise, that fission normally occurs only for heavier elements. There are extreme astrophysical events that can lead to short periods of fusion with heavier nuclei. This process gives rise to nucleosynthesis, the creation of the heavy elements during events like supernovas.
Neutron energy dependence of delayed neutron yields and its assessments
Published in Journal of Nuclear Science and Technology, 2018
Some fission fragments located on neutron-rich side of the nuclear chart emit neutrons after the -decay, which are the so-called delayed neutrons. Delayed neutron yields resulting from neutron-induced fission of actinide nuclides are crucial to making a light water reactor controllable because they lengthen the reactor period to a timescale long enough to keep the critical state of the reactor. Delayed neutrons play a meaningful role in other research fields as well. One of the examples is -process nucleosynthesis, which is the leading candidate for producing heavy elements by successive neutron capture at an astronomical site. At the ‘freeze-out’ phase where environmental neutrons are exhausted in the astronomical sites, nuclides produced by the -process start going towards the -stability line by -decay. Then, the delayed neutron emission from some nuclei accompanied by -decay shifts the abundance pattern of the elements by re-accumulation of the neutron density [1]. Delayed neutrons also have potential to be applied to the interrogation of actinides for homeland security [2,3].