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Seed Nucleus
A seed nucleus is an isotope that is the starting point for any of a variety of fusion chain reactions. The mix of nuclei produced at the conclusion of the chain reaction generally depends strongly on the relative availability of the seed nucleus or nuclei and the component being fused--whether neutrons as in the r-process and s-process or protons as in the rp-process. A smaller proportion of seed nuclei will generally result in products of larger mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ..., whereas a larger seed-to-neutron or seed-to-proton ratio will tend to produce comparatively lighter masses. Nuclear physics {{nuclear-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have almost the same chemical properties, they have different atomic masses and physical properties. The term isotope is formed from the Greek roots isos ( ἴσος "equal") and topos ( τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. It was coined by Scottish doctor and writer Margaret Todd in 1913 in a suggestion to the British chemist Frederick Soddy. The number of protons within the atom's nucleus is called its atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic numbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chain Reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. Chain reactions are one way that systems which are not in thermodynamic equilibrium can release energy or increase entropy in order to reach a state of higher entropy. For example, a system may not be able to reach a lower energy state by releasing energy into the environment, because it is hindered or prevented in some way from taking the path that will result in the energy release. If a reaction results in a small energy release making way for more energy releases in an expanding chain, then the system will typically collapse explosively until much or all of the stored energy has been released. A macroscopic metaphor for chain reactions is thus a snowball causing a larger snowball until finally an avalanche results ("snowball effect"). This is a result of stored gravitation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons. Their properties and interactions are described by nuclear physics. Protons and neutrons are not elementary particles; each is composed of three quarks. The chemical properties of an atom are mostly determined by the configuration of electrons that orbit the atom's heavy nucleus. The electron configuration is determined by the charge of the nucleus, which is determined by the number of protons, or atomic number. The number of neutrons is the neutron number. Neutrons do not affect the electron configuration, but the sum of atomic and neutron numbers is the mass of the nucleus. Atoms of a chemical element t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
R-process
In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and ''s''-process. The ''r''-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The ''r''-process can typically synthesize the heaviest four isotopes of every heavy element, and the two heaviest isotopes, which are referred to as ''r-only nuclei'', can be created via the ''r''-process only. Abundance peaks for the ''r''-process occur near mass numbers (elements Se, Br, and Kr), (elements Te, I, and Xe) and (elements Os, Ir, and Pt). The ''r''-process entails a succession of ''rapid'' neutron captures (hence the name) by one or more heavy seed nuclei, typically beginning with nuclei in the abundance peak centered on 56Fe. The captures must be rapid in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S-process
The slow neutron-capture process, or ''s''-process, is a series of reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The ''s''-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron. In the ''s''-process, a seed nucleus undergoes neutron capture to form an isotope with one higher atomic mass. If the new isotope is stable, a series of increases in mass can occur, but if it is unstable, then beta decay will occur, producing an element of the next higher atomic number. The process is ''slow'' (hence the name) in the sense that there is sufficient time for this radioactive decay to occur before another neutron is captured. A series of these reactions produces stable isotopes by moving along the valley of beta-decay stable isobars in the table of nuclides. A range of elements and isotopes can be produced by the ''s''-process, because of the intervention of alpha decay steps ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rp-process
The rp-process (rapid proton capture process) consists of consecutive proton captures onto seed nuclei to produce heavier elements. It is a nucleosynthesis process and, along with the ''s''-process and the ''r''-process, may be responsible for the generation of many of the heavy elements present in the universe. However, it is notably different from the other processes mentioned in that it occurs on the proton-rich side of stability as opposed to on the neutron-rich side of stability. The end point of the rp-process (the highest-mass element it can create) is not yet well established, but recent research has indicated that in neutron stars it cannot progress beyond tellurium. The rp-process is inhibited by alpha decay, which puts an upper limit on the end point at 104Te, the lightest observed alpha-decaying nuclide, and the proton drip line in light antimony isotopes. At this point, further proton captures result in prompt proton emission or alpha emission, and thus the pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Mass
The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1 Da is defined as of the mass of a free carbon-12 atom at rest in its ground state. The protons and neutrons of the nucleus account for nearly all of the total mass of atoms, with the electrons and nuclear binding energy making minor contributions. Thus, the numeric value of the atomic mass when expressed in daltons has nearly the same value as the mass number. Conversion between mass in kilograms and mass in daltons can be done using the atomic mass constant m_= = 1\ \rm . The formula used for conversion is: :1\ = m_ = 1.660\ 539\ 066\ 60(50)\times 10^\ \mathrm , where M_ is the molar mass constant, N_ is the Avogadro constant, and M(^\mathrm) is the experimentally determined molar mass of carbon-12. The relative isotopic mass (see ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
