Nucleons are the heavy building blocks (baryons) that make up atomic nuclei: protons and neutrons. Together with the electrons, the nucleons form an atom.
The type and number of nucleons in an atomic nucleus are important for the assignment of the nucleus to the chemical elements:
- The number of protons characterizes a specific chemical element E and is called the atomic number Z (= proton number): ZE.
- The additional number of neutrons determines which isotope of an element it is.
- The sum of nucleons is expressed as mass number A: AE
- Symbolism of a defined isotope or nuclide: AZE. The neutron number N results from the difference between the mass number and the neutron number: N = A - Z.
- A single atomic nucleus with a defined number of protons and neutrons is called nuclide.
Relatively exact values are known for the masses of the individual nucleons (see below). However, the isotope mass or nuclide mass only roughly corresponds to the sum of the masses of the individual nuclear building blocks; it is slightly lower due to the nuclear binding energy released during nuclear formation (mass defect).
The table below lists the properties of proton and neutron; The values correspond to the specified values according to CODATA 2018 [1] or are derived from them:
| Neutron | Proton | |
|---|---|---|
| Symbol | n | p, p+ |
| Mass | 1.00866491595(49) u 1.67492749804(95) × 10-27 kg 1838.68366173(89) me | 1.007276466621(53) u 1.6726219 2369(51) × 10-27 kg 1836.15267343(11) me |
| Molar mass | 1.00866491560(57) × 10-3 kg mol-1 | 1.00727646627(31) × 10-3 kg mol-1 |
| Mass energy equivalent | 1.50534976287(86) × 10-10 J | 1.50327761598(46) × 10-10 J |
| Rest energy | 939.56542052(54) MeV | 938.27208816(29) MeV |
| Charge | 0 | +1e |
| Charge radius | -0.1155(17) fm2 | 0.8409(4) fm |
| Compton wavelength | 1.31959090581(75) × 10-15 m | 1.32140985539(40) × 10-15 m |
| Magnetic moment | -9.6623651(23) × 10-27 J/T -1.91304273(45) μN | 1.41060679736(60) × 10-26 J/T 2.7928473441(42) μN |
| Gyromagnetic ratio γ | 1.83247171(43) × 108 s-1 T -1 29.1646931(69) MHz T -1 | 2.6752218744(11) × 108 s-1 T -1 42.577478518(18) MHz T -1 shielded Proton γยด: 2.675153151(29) × 108 s-1 T -1 42.57638474(46) MHz T -1 |
| g factor | -3.82608545(90) | 5.5856946882(84) |
| Spin | +1/2 | +1/2 |
| Isospin | 1/2 | 1/2 |
| Half-life | 610 s (free n) | stable |
| Quarks | udd | uud |
[1] - Eite Tiesinga, Peter J. Mohr, David B. Newell, and Barry N. Taylor:
CODATA recommended values of the fundamental physical constants: 2018.
In: Rev. Mod. Phys. 93, 025010, (2021), DOI 10.1103/RevModPhys.93.025010.
Last update: 2023-12-01
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