Isobar (nuclide)

Nuclear physics
Nucleus Nucleons p n Nuclear matter Nuclear force Nuclear structure Nuclear reaction
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Nuclides' classification Isotopes – equal Z Isobars – equal A Isotones – equal N N − Z Isomers – equal all the above Mirror nuclei – Z ↔ N Stable Magic Even/odd Halo Borromean
Nuclear stability Binding energy p–n ratio Drip line Island of stability Valley of stability Stable nuclide
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Capturing processes electron 2× neutron s r proton p rp
High-energy processes Spallation by cosmic ray Photodisintegration
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The term "isobars" (originally "isobares") for nuclides was suggested by British chemist Alfred Walter Stewart in 1918.^[2] It is derived from Greek ἴσος (isos) 'equal', and βάρος (baros) 'weight'.^[3]

Mass

The same mass number implies neither the same mass of nuclei, nor equal atomic masses of corresponding nuclides. From the Weizsäcker formula for the mass of a nucleus:

${\displaystyle m(A,Z)=Zm_{p}+Nm_{n}-a_{V}A+a_{S}A^{2/3}+a_{C}{\frac {Z^{2}}{A^{1/3}}}+a_{A}{\frac {(N-Z)^{2}}{A}}-\delta (A,Z)}$

where mass number A equals to the sum of atomic number Z and number of neutrons N, and m_p, m_n, a_V, a_S, a_C, a_A are constants, one can see that the mass depends on Z and N non-linearly, even for a constant mass number. For

In theory, no two stable nuclides have the same mass number (since no two nuclides that have the same mass number are both stable to beta decay and double beta decay), and no stable nuclides exist for mass numbers 5, 8, 143–155, 160–162, and ≥ 165, since in theory, the beta-decay stable nuclides for these mass numbers can undergo alpha decay.

See also

• Isotopes (nuclides having the same number of protons)
• Isotones (nuclides having the same number of neutrons)
• Nuclear isomers (different excited states of the same nuclide)
• Magic number (physics)
• Electron capture

Bibliography

Sprawls, Perry (1993). "5 – Characteristics and Structure of Matter". Physical Principles of Medical Imaging (2 ed.).