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The net binding energy of a nucleus is that of the nuclear attraction, minus the disruptive energy of the electric force. As nuclei get heavier than helium, their net binding energy per nucleon (deduced from the difference in mass between the nucleus and the sum of masses of component nucleons) grows more and more slowly, reaching its peak at iron.
The helium atom. Depicted are the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. Helium-4 (4 He) is a stable isotope of the element helium.
The atomic binding energy of the atom is the energy required to disassemble an atom into free electrons and a nucleus. [4] It is the sum of the ionization energies of all the electrons belonging to a specific atom. The atomic binding energy derives from the electromagnetic interaction of the electrons with the nucleus, mediated by photons.
When nuclei fuse, a very large amount of energy is released and the combined nucleus assumes a lower energy level. The binding energy per nucleon increases with mass number up to nickel-62. Stars like the Sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen ...
The binding energy is subtracted from the sum of the proton and neutron masses because the mass of the nucleus is less than that sum. This property, called the mass defect , is necessary for a stable nucleus; within a nucleus, the nuclides are trapped by a potential well .
In the shell model for the nucleus, magic numbers are the numbers of nucleons at which a shell is filled. For instance, the magic number 8 occurs when the 1s 1/2, 1p 3/2, 1p 1/2 energy levels are filled, as there is a large energy gap between the 1p 1/2 and the next highest 1d 5/2 energy levels.
Some stable helium-3 (two protons and one neutron) is produced in fusion reactions from hydrogen, though its estimated abundance in the universe is about 10 −5 relative to helium-4. [92] Binding energy per nucleon of common isotopes. The binding energy per particle of helium-4 is significantly larger than all nearby nuclides.
The nucleus of helium-4 is particularly stable, having a doubly magic configuration and larger binding energy per nucleon than 8 Be. As the total energy of 8 Be is greater than that of two alpha particles, the decay into two alpha particles is energetically favorable, [5] and the synthesis of 8 Be from two 4 He nuclei is endothermic