Proton

The valence quark content of a proton. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons.

Classification| Baryon
Composition| 2 up quarks (u), 1 down quark (d)
Statistics| Fermionic
Interactions| Gravity, electromagnetic, weak, strong
Symbol| p, p+, N+, 11H+
antiparticle| Antiproton
Theorized| William Prout (1815)
Discovered| Observed as H+ by Eugen Goldstein (1886). Identified in other nuclei (and named) by Ernest Rutherford (1917–1920).
Mass| 1.67262192369(51)×10−27 kg[1]

mean lifetime| > 0.96×1030 years[2] (stable)
electric charge| +1 e
Charge radius| 0.84075(64) fm
electric dipole moment| < 2.1×10−25 e⋅cm[3]
|s|z}}ability| 0.00112(4) fm3
Magnetic moment|

|s|z}}ability| 1.9(5)×10−4 fm3
Spin| ⁠1/2⁠ ħ
Isospin| ⁠1/2⁠
Parity| +1
Condensed| I(JP) = ⁠1/2⁠(⁠1/2⁠+)

A proton is a stable subatomic particle, symbol p, H+, or 1H+ with a positive electric charge of +1 e (elementary charge). Its mass is slightly less than the mass of a neutron and approximately 1836 times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with a mass of approximately one dalton, are jointly referred to as nucleons (particles present in atomic nuclei).

One or more protons are present in the nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z). Since each element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines the number of atomic electrons and consequently the identity and chemical characteristics of the element.

The word proton is Greek for "first", and the name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions.[4] Protons were therefore a candidate to be a fundamental or elementary particle, and hence a building block of nitrogen and all other heavier atomic nuclei.

Although protons were originally considered to be elementary particles, in the modern Standard Model of particle physics, protons are known to be composite particles, containing three valence quarks, and together with neutrons are now classified as hadrons. Protons are composed of two up quarks of charge +⁠2/3⁠e each, and one down quark of charge −⁠1/3⁠e. The rest masses of quarks contribute only about 1% of a proton's mass.[5] The remainder of a proton's mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. The proton charge radius is around 0.841 fm but two different kinds of measurements give slightly different values.[6]

At sufficiently low temperatures and kinetic energies, free protons will bind electrons in any matter they traverse.

Free protons are routinely used for accelerators for proton therapy or various particle physics experiments, with the most powerful example being the Large Hadron Collider.

## Contents

* 1 Description
* 2 History
* 3 Occurrence
* 4 Stability
* 5 Quarks and the mass of a proton
* 6 Charge radius
* 6.1 Pressure inside the proton
* 6.2 Charge radius in solvated proton, hydronium
* 7 Interaction of free protons with ordinary matter
* 8 Proton in chemistry
* 8.1 Atomic number
* 8.2 Hydrogen ion
* 8.3 Proton nuclear magnetic resonance (NMR)
* 9 Human exposure
* 10 Antiproton
* 11 See also
* 12 References
* 13 Further reading
* 14 External links

## Description

Nuclear physics

Nucleus * Nucleons (p, n) * Nuclear matter * Nuclear force * Nuclear structure * Nuclear reaction

Models of the nucleus

Liquid drop * Nuclear shell model * Interacting boson model * Ab initio

Nuclides' classification

Stable * Magic * Even/odd * Halo&nbsp;(Borromean)

Nuclear stability

Binding energy * p–n ratio * Drip line * Island of stability * Valley of stability * Stable nuclide

Radioactive decay

Alpha α * Beta β (2β, β+) * K/L capture * Isomeric (Gamma γ * Internal conversion) * Spontaneous fission * Cluster decay * Neutron emission * Proton emission

Nuclear fission

Spontaneous * Products (pair breaking) * Photofission

Capturing processes

electron (2×) * neutron (s * r) * proton (p * rp)

High-energy processes

Spallation (by cosmic ray) * Photodisintegration

Nucleosynthesis and
nuclear astrophysics

Nuclear fusion
Processes: Stellar * Big Bang * Supernova
Nuclides: Primordial * Cosmogenic * Artificial

High-energy nuclear physics

Quark–gluon plasma * RHIC * LHC

* v
* t
* e

| Unsolved problem in physics:

How do the quarks and gluons carry the spin of protons?

(more unsolved problems in physics)

|

Protons are spin-⁠1/2⁠ fermions and are composed of three valence quarks,[7] making them baryons (a sub-type of hadrons). The two up quarks and one down quark of a proton are held together by the strong force, mediated by gluons.[8]: 21–22 A modern perspective has a proton composed of the valence quarks (up, up, down), the gluons, and transitory pairs of sea quarks. Protons have a positive charge distribution, which decays approximately exponentially, with a root mean square charge radius of about 0.8 fm.[9]

Protons and neutrons are both nucleons, which may be bound together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the hydrogen atom (with the chemical symbol "H") is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons.

## History

The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout used early values of atomic weight to devise what later researchers called Prout's hypothesis: all atoms are composed of integer combinations of hydrogen atoms (which he called "protyles"). When more accurate values of the atomic weights were measured, the integer relationship failed. Nevertheless the concept continued to intrigue scientists and would eventually emerge again a century later.[10]: 39–42

Ernest Rutherford at the first Solvay Conference, 1911 Proton detected in an isopropanol cloud chamber

In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) exiting from perforations in the discharge tube. Wilhelm Wien in 1898 showed that these rays had a charge opposite to the negative electrons discovered by J. J. Thomson, but with a much higher mass to charge ratio.[11] Later that year Thomson was able to determine a value for the magnitude of the electric charge, e,[12]: 86 and show that the canal rays included material with charge-to-mass ratio (q/m) consistent with the hydrogen ion.[13]: 406

Following the discovery of the atomic nucleus by Ernest Rutherford in 1913, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge. Van den Broek speculated that the nucleus contained alpha particles with four positive charges and two electrons, the first version of the nuclear-electron hypothesis. (The modern model of two positive protons and two neutrons would take many years to discover).[14]: 20 Also in 1913 Niels Bohr presented a theory of atomic structure which predicted electronic transitions related to nuclear charge. This was confirmed experimentally by Henry Moseley in 1913 when he showed that the energy of X-ray spectra lines of many elements followed a pattern based on atomic number.

In 1919, after a long series of sporadic experiments interrupted by WWI, Rutherford discovered what he called artificial disintegration of nitrogen atoms. Using alpha particles from radium to strike air, Rutherford detected scintillation on a zinc sulfide screen at a distance, up to 28 cm, well beyond the distance of alpha-particle range of travel but instead corresponding to the range of travel of hydrogen atoms.[15] By 1920 he concluded that these hydrogen nuclei were a constituent part of the nitrogen nucleus. This result has been described as the discovery of protons.[16]

When Rutherford described his results at the British Association for the Advancement of Science August 1920 he was asked by Oliver Lodge for a new name for the positive hydrogen nucleus to avoid confusion with the neutral hydrogen atom.[17] Rutherford initially suggested both proton (the neuter singular of the Greek word for "first", πρῶτον) and prouton (after Prout).[18] Rutherford later reported that the meeting had accepted his suggestion that the hydrogen nucleus be named the "proton", following Prout's word "protyle".[19] The first use of the word "proton" in the scientific literature appeared in 1920.[20][12][14]: 23

Rutherford initially assumed that the alpha particle merely knocked a proton out of nitrogen, turning it into carbon. Patrick Blackett's cloud chamber images in 1925 demonstrated that the alpha particle was absorbed. If the alpha particle were not absorbed, then 3 charged particles, a negatively charged carbon, a proton, and an alpha particle, would be expected. The 3 charged particles would create three tracks in the cloud chamber, but only 2 tracks in the cloud chamber were observed. Blackett proposed that the alpha particle is absorbed by the nitrogen atom. Heavy oxygen (17O), not carbon, was the product.[21][14] This was the first reported nuclear reaction, 14
N + α → 17
O + p.

## Occurrence

One or more bound protons are present in the nucleus of every atom. Free protons are found naturally in a number of situations in which energies or temperatures are high enough to separate them from electrons, for which they have some affinity. Free protons occur occasionally on Earth: thunderstorms can produce protons with energies of up to several tens of megaelectronvolt.[22][23] Free protons exist in plasmas in which temperatures are too high to allow them to combine with electrons.[24] Free protons of high energy and velocity make up 90% of cosmic rays, which propagate through the interstellar medium.[25] Free protons are emitted directly from atomic nuclei in some rare types of radioactive decay.[26] Protons also result (along with electrons and antineutrinos) from the radioactive decay of free neutrons, which are unstable.[27]

## Stability

Main article: Physics:Proton decay

| Unsolved problem in physics:

Are protons fundamentally stable? Or do they decay with a finite lifetime as predicted by some extensions to the standard model?

(more unsolved problems in physics)

|

The spontaneous decay of free protons has never been observed, and protons are therefore considered stable particles according to the Standard Model. However, some grand unified theories (GUTs) of particle physics predict that proton decay should take place with lifetimes between 1031 and 1036 years. The experimental lower bound for the mean lifetime is 0.96×1030 years.[2]

The mean lifetime measures decay to any product. Lifetimes for decay to specific products is also measured. For example, experiments at the Super-Kamiokande detector in Japan gave lower limits for proton mean lifetime of 1.6×1034 years for decay to an antimuon and a neutral pion, and 2.4×1034 years for decay to a positron and a neutral pion.[28][2]

Protons are known to transform into neutrons through the process of electron capture (also called inverse beta decay). For free protons, this process does not occur spontaneously but only when energy is supplied. The equation is:

p+ \+ e− → Neutron + Electron neutrino

The process is reversible; neutrons can convert back to protons through beta decay, a common form of radioactive decay. In fact, a free neutron decays this way, with a mean lifetime of about 15 minutes. A proton can also transform into a neutron through beta plus decay (β+ decay).[citation needed]

According to quantum field theory, the mean proper lifetime of protons τp becomes finite when they are accelerating with proper acceleration a, and τp decreases with increasing a. Acceleration gives rise to a non-vanishing probability for the transition p+ → n \+ e+ \+ νe. This was a matter of concern in the later 1990s because τp is a scalar that can be measured by the inertial and coaccelerated observers. In the inertial frame, the accelerating proton should decay according to the formula above. However, according to the coaccelerated observer the proton is at rest and hence should not decay. This puzzle is solved by realizing that in the coaccelerated frame there is a thermal bath due to Fulling–Davies–Unruh effect, an intrinsic effect of quantum field theory. In this thermal bath, experienced by the proton, there are electrons and antineutrinos with which the proton may interact according to the processes:

1. p+ \+ e− → n \+ ν,
2. p+ \+ ν → n \+ e+ and
3. p+ \+ e− \+ ν → n.

Adding the contributions of each of these processes, one should obtain τp.[29][30][31][32]

## Quarks and the mass of a proton

In quantum chromodynamics, the modern theory of the nuclear force, most of the mass of protons and neutrons is explained by special relativity. The mass of a proton is about 80–100 times greater than the sum of the rest masses of its three valence quarks, while the gluons have zero rest mass. The extra energy of the quarks and gluons in a proton, as compared to the rest energy of the quarks alone in the QCD vacuum, accounts for almost 99% of the proton's mass. The rest mass of a proton is, thus, the invariant mass of the system of moving quarks and gluons that make up the particle, and, in such systems, even the energy of massless particles confined to a system is still measured as part of the rest mass of the system.

Two terms are used in referring to the mass of the quarks that make up protons: current quark mass refers to the mass of a quark by itself, while constituent quark mass refers to the current quark mass plus the mass of the gluon particle field surrounding the quark.[33]: 285–286 [34]: 150–151 These masses typically have very different values. The kinetic energy of the quarks that is a consequence of confinement is a contribution (see Mass in special relativity). Using lattice QCD calculations, the contributions to the mass of the proton are the quark condensate (~9%, comprising the up and down quarks and a sea of virtual strange quarks), the quark kinetic energy (~32%), the gluon kinetic energy (~37%), and the anomalous gluonic contribution (~23%, comprising contributions from condensates of all quark flavors).[35]

The constituent quark model wavefunction for the proton is |p↑⟩=118(2|u↑d↓u↑⟩+2|u↑u↑d↓⟩+2|d↓u↑u↑⟩−|u↑u↓d↑⟩−|u↑d↑u↓⟩−|u↓d↑u↑⟩−|d↑u↓u↑⟩−|d↑u↑u↓⟩−|u↓u↑d↑⟩).

The internal dynamics of protons are complicated, because they are determined by the quarks' exchanging gluons, and interacting with various vacuum condensates. Lattice QCD provides a way of calculating the mass of a proton directly from the theory to any accuracy, in principle. The most recent calculations[36][37] claim that the mass is determined to better than 4% accuracy, even to 1% accuracy (see Figure S5 in Dürr et al.[37]). These claims are still controversial, because the calculations cannot yet be done with quarks as light as they are in the real world. This means that the predictions are found by a process of extrapolation, which can introduce systematic errors.[38] It is hard to tell whether these errors are controlled properly, because the quantities that are compared to experiment are the masses of the hadrons, which are known in advance.

These recent calculations are performed by massive supercomputers, and, as noted by Boffi and Pasquini: "a detailed description of the nucleon structure is still missing because ... long-distance behavior requires a nonperturbative and/or numerical treatment ..."[39] More conceptual approaches to the structure of protons are: the topological soliton approach originally due to Tony Skyrme and the more accurate AdS/QCD approach that extends it to include a string theory of gluons,[40] various QCD-inspired models like the bag model and the constituent quark model, which were popular in the 1980s, and the SVZ sum rules, which allow for rough approximate mass calculations.[41] These methods do not have the same accuracy as the more brute-force lattice QCD methods, at least not yet.

## Charge radius

Main article: Physics:Proton radius puzzle

The CODATA recommended value of a proton's charge radius is . The radius of the proton measured by electron–proton scattering differs from the value measured via the Lamb shift in muonic hydrogen (an exotic atom made of a proton and a negatively charged muon).[6] As a muon is 200 times heavier than an electron, resulting in a smaller atomic orbital, it is much more sensitive to the proton's charge radius and thus allows a more precise measurement.[42] Subsequent improved scattering and electron-spectroscopy measurements agree with the new small radius. Work continues to refine and check this new value.[43]

A third kind of high precision measurement agrees most closely with the value given by the muonic hydrogen spectroscopy but unexplained differences remain. The exact nature of what these measurement mean has also been questioned.[44]

### Pressure inside the proton

Since the proton is composed of quarks confined by gluons, an equivalent pressure that acts on the quarks can be defined. The size of that pressure and other details about it are controversial.

In 2018 this pressure was reported to be on the order 1035 Pa, which is greater than the pressure inside a neutron star. It was said to be maximum at the centre, positive (repulsive) to a radial distance of about 0.6 fm, negative (attractive) at greater distances, and very weak beyond about 2 fm. These numbers were derived by a combination of a theoretical model and experimental Compton scattering of high-energy electrons.[45][46][47] However, these results have been challenged as also being consistent with zero pressure[48] and as effectively providing the pressure profile shape by selection of the model.[49]

### Charge radius in solvated proton, hydronium

The radius of the hydrated proton appears in the Born equation for calculating the hydration enthalpy of hydronium.

## Interaction of free protons with ordinary matter

Although protons have affinity for oppositely charged electrons, this is a relatively low-energy interaction and so free protons must lose sufficient velocity (and kinetic energy) in order to become closely associated and bound to electrons. High energy protons, in traversing ordinary matter, lose energy by collisions with atomic nuclei, and by ionization of atoms (removing electrons) until they are slowed sufficiently to be captured by the electron cloud in a normal atom.

However, in such an association with an electron, the character of the bound proton is not changed, and it remains a proton. The attraction of low-energy free protons to any electrons present in normal matter (such as the electrons in normal atoms) causes free protons to stop and to form a new chemical bond with an atom. Such a bond happens at any sufficiently "cold" temperature (that is, comparable to temperatures at the surface of the Sun) and with any type of atom. Thus, in interaction with any type of normal (non-plasma) matter, low-velocity free protons do not remain free but are attracted to electrons in any atom or molecule with which they come into contact, causing the proton and molecule to combine. Such molecules are then said to be "protonated", and chemically they are simply compounds of hydrogen, often positively charged. Often, as a result, they become so-called Brønsted acids. For example, a proton captured by a water molecule in water becomes hydronium, the aqueous cation H
3O+

## Proton in chemistry

### Atomic number

In chemistry, the number of protons in the nucleus of an atom is known as the atomic number, which determines the chemical element to which the atom belongs. For example, the atomic number of chlorine is 17; this means that each chlorine atom has 17 protons and that all atoms with 17 protons are chlorine atoms. The chemical properties of each atom are determined by the number of (negatively charged) electrons, which for neutral atoms is equal to the number of (positive) protons so that the total charge is zero. For example, a neutral chlorine atom has 17 protons and 17 electrons, whereas a Cl− anion has 17 protons and 18 electrons for a total charge of −1 e.

All atoms of a given element are not necessarily identical, however. The number of neutrons may vary to form different isotopes, and energy levels may differ, resulting in different nuclear isomers. For example, there are two stable isotopes of chlorine: 3517Cl with 35 − 17 = 18 neutrons and 3717Cl with 37 − 17 = 20 neutrons.

### Hydrogen ion

Protium, the most common isotope of hydrogen, consists of one proton and one electron (it has no neutrons). The term hydrogen ion (H+) implies that that H-atom has lost its one electron, causing only a proton to remain. Thus, in chemistry, the terms proton and hydrogen ion (for the protium isotope) are used synonymously.

The proton is a unique chemical species, being a bare nucleus. As a consequence it has no independent existence in the condensed state and is invariably found bound by a pair of electrons to another atom.

Ross Stewart, The Proton: Application to Organic Chemistry (1985, p. 1)

In chemistry, the term proton refers to the hydrogen ion, H+. Since the atomic number of hydrogen is 1, a hydrogen ion has no electrons and corresponds to a bare nucleus, consisting of a proton (and 0 neutrons for the most abundant isotope protium 11H). The proton is a "bare charge" with only about 1/64,000 of the radius of a hydrogen atom, and so is extremely reactive chemically. The free proton, thus, has an extremely short lifetime in chemical systems such as liquids and it reacts immediately with the electron cloud of any available molecule. In aqueous solution, it forms the hydronium ion, H3O+, which in turn is further solvated by water molecules in clusters such as [H5O2]+ and [H9O4]+.[50]

The transfer of H+ in an acid–base reaction is usually referred to as "proton transfer". The acid is referred to as a proton donor and the base as a proton acceptor. Likewise, biochemical terms such as proton pump and proton channel refer to the movement of hydrated H+ ions.

The ion produced by removing the electron from a deuterium atom is known as a deuteron, not a proton. Likewise, removing an electron from a tritium atom produces a triton.

### Proton nuclear magnetic resonance (NMR)

Also in chemistry, the term proton NMR refers to the observation of hydrogen-1 nuclei in (mostly organic) molecules by nuclear magnetic resonance. This method uses the quantized spin magnetic moment of the proton, which is due to its angular momentum (or spin), which in turn has a magnitude of one-half the reduced Planck constant. (ℏ/2). The name refers to examination of protons as they occur in protium (hydrogen-1 atoms) in compounds, and does not imply that free protons exist in the compound being studied.

## Human exposure

Main article: Astronomy:Effect of spaceflight on the human body

See also: Physics:Proton therapy

The Apollo Lunar Surface Experiments Packages (ALSEP) determined that more than 95% of the particles in the solar wind are electrons and protons, in approximately equal numbers.[51][52]

> Because the Solar Wind Spectrometer made continuous measurements, it was possible to measure how the Earth's magnetic field affects arriving solar wind particles. For about two-thirds of each orbit, the Moon is outside of the Earth's magnetic field. At these times, a typical proton density was 10 to 20 per cubic centimeter, with most protons having velocities between 400 and 650 kilometers per second. For about five days of each month, the Moon is inside the Earth's geomagnetic tail, and typically no solar wind particles were detectable. For the remainder of each lunar orbit, the Moon is in a transitional region known as the magnetosheath, where the Earth's magnetic field affects the solar wind, but does not completely exclude it. In this region, the particle flux is reduced, with typical proton velocities of 250 to 450 kilometers per second. During the lunar night, the spectrometer was shielded from the solar wind by the Moon and no solar wind particles were measured.[51]

Protons also have extrasolar origin from galactic cosmic rays, where they make up about 90% of the total particle flux. These protons often have higher energy than solar wind protons, and their intensity is far more uniform and less variable than protons coming from the Sun, the production of which is heavily affected by solar proton events such as coronal mass ejections.

Research has been performed on the dose-rate effects of protons, as typically found in space travel, on human health.[52][53] To be more specific, there are hopes to identify what specific chromosomes are damaged, and to define the damage, during cancer development from proton exposure.[52] Another study looks into determining "the effects of exposure to proton irradiation on neurochemical and behavioral endpoints, including dopaminergic functioning, amphetamine-induced conditioned taste aversion learning, and spatial learning and memory as measured by the Morris water maze.[53] Electrical charging of a spacecraft due to interplanetary proton bombardment has also been proposed for study.[54] There are many more studies that pertain to space travel, including galactic cosmic rays and their possible health effects, and solar proton event exposure.

The American Biostack and Soviet Biorack space travel experiments have demonstrated the severity of molecular damage induced by heavy ions on microorganisms including Artemia cysts.[55]

## Antiproton

Main article: Physics:Antiproton

CPT-symmetry puts strong constraints on the relative properties of particles and antiparticles and, therefore, is open to stringent tests. For example, the charges of a proton and antiproton must sum to exactly zero. This equality has been tested to one part in 108. The equality of their masses has also been tested to better than one part in 108. By holding antiprotons in a Penning trap, the equality of the charge-to-mass ratio of protons and antiprotons has been tested to one part in 6×109.[56] The measured magnetic moments of protons and antiprotons have been found to be equal and opposite within 0.8 ppm.[57]

## See also

* Fermionic field
* Hydrogen
* Hydron
* List of particles
* Proton–proton chain
* Quark model
* Proton spin crisis
* Proton therapy

## References

1. ↑ "2018 CODATA Value: proton mass". The NIST Reference on Constants, Units, and Uncertainty. NIST. 20 May 2019. http://physics.nist.gov/cgi-bin/cuu/Value?mp. Retrieved 2019-05-20.
2. ↑ 2.0 2.1 2.2 S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024) and 2025 update. p
3. ↑ Sahoo, B. K. (2017-01-17). "Improved limits on the hadronic and semihadronic $CP$ violating parameters and role of a dark force carrier in the electric dipole moment of $^{199}\mathrm{Hg}$". Physical Review D 95 (1). doi:10.1103/PhysRevD.95.013002. https://link.aps.org/doi/10.1103/PhysRevD.95.013002.
4. ↑ "proton | Definition, Mass, Charge, & Facts". Encyclopedia Britannica. https://www.britannica.com/science/proton-subatomic-particle. Retrieved 2018-10-20.
5. ↑ Cho, Adrian (2 April 2010). "Mass of the Common Quark Finally Nailed Down". American Association for the Advancement of Science. https://www.science.org/content/article/mass-common-quark-finally-nailed-down.
6. ↑ 6.0 6.1 N Baryons S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024) and 2025 update
7. ↑ Adair, R. K. (1989). The Great Design: Particles, Fields, and Creation. Oxford University Press. p. 214. Bibcode: 1988gdpf.book.....A.
8. ↑ Cottingham, W. N.; Greenwood, D. A. (1986). An Introduction to Nuclear Physics. Cambridge University Press. ISBN 978-0-521-65733-4.
9. ↑ Basdevant, J.-L.; Rich, J.; Spiro, M. (2005). Fundamentals in Nuclear Physics. Springer. p. 155. ISBN 978-0-387-01672-6. https://books.google.com/books?id=OFx7P9mgC9oC&q=helium+"nuclear+structure"&pg=PA375. Retrieved 2020-11-19.
10. ↑ Department of Chemistry and Biochemistry UCLA Eric R. Scerri Lecturer (2006-10-12). The Periodic Table: Its Story and Its Significance: Its Story and Its Significance. Oxford University Press. ISBN 978-0-19-534567-4.
11. ↑ Wien, Wilhelm (1904). "Über positive Elektronen und die Existenz hoher Atomgewichte". Annalen der Physik 318 (4): 669–677. doi:10.1002/andp.18943180404. Bibcode: 1904AnP...318..669W. https://zenodo.org/record/2190505. Retrieved 2020-07-13.
12. ↑ 12.0 12.1 Pais, A. (1986). Inward Bound. Oxford University Press. p. 296. ISBN 0-19-851997-4. https://archive.org/details/inwardboundofmat00pais_0. Pais believed the first science literature use of the word proton occurs in "Physics at the British Association". Nature 106 (2663): 357–358. 1920. doi:10.1038/106357a0. Bibcode: 1920Natur.106..357..
13. ↑ Whittaker, E. T. (Edmund Taylor) (1910). A history of the theories of aether and electricity: from the age of Descartes to the close of the nineteenth century. University of California Libraries. London; New York: Longmans, Green. https://archive.org/details/historyoftheorie00whitrich.
14. ↑ 14.0 14.1 14.2 Stuewer, Roger H. (1983). "The Nuclear Electron Hypothesis". in Shea, William R.. Otto Hahn and the Rise of Nuclear Physics. Dordrecht: Springer Netherlands. pp. 19–67. doi:10.1007/978-94-009-7133-2_2. ISBN 978-94-009-7135-6. http://link.springer.com/10.1007/978-94-009-7133-2_2.
15. ↑ Rutherford, E. (1919-06-01). "LIV. Collision of α particles with light atoms. IV. An anomalous effect in nitrogen". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 37 (222): 581–587. doi:10.1080/14786440608635919. ISSN 1941-5982.
16. ↑ Petrucci, R. H.; Harwood, W. S.; Herring, F. G. (2002). General Chemistry (8th ed.). Upper Saddle River, N.J. : Prentice Hall. p. 41. ISBN 978-0-13-033445-9. https://archive.org/details/generalchemistry00hill.
17. ↑ See meeting report and announcement
18. ↑ Romer A (1997). "Proton or prouton? Rutherford and the depths of the atom". American Journal of Physics 65 (8): 707. doi:10.1119/1.18640. Bibcode: 1997AmJPh..65..707R.
19. ↑ Rutherford reported acceptance by the British Association in a footnote to Masson, O. (1921). "XXIV. The constitution of atoms". Philosophical Magazine. Series 6 41 (242): 281–285. doi:10.1080/14786442108636219. https://zenodo.org/record/1430963. Retrieved 2019-06-21.
20. ↑ OED proton (3rd ed.), Oxford University Press, September 2005, http://oed.com/search?searchType=dictionary&q=proton, retrieved 24 March 2021 (Subscription or UK public library membership required.)
21. ↑ Blackett, P. M. S. (1925-02-02). "The ejection of protons from nitrogen nuclei, photographed by the Wilson method" (in en). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character 107 (742): 349–360. doi:10.1098/rspa.1925.0029. ISSN 0950-1207. Bibcode: 1925RSPSA.107..349B.
22. ↑ Köhn, C.; Ebert, U. (2015). "Calculation of beams of positrons, neutrons and protons associated with terrestrial gamma-ray flashes". Journal of Geophysical Research: Atmospheres 23 (4): 1620–1635. doi:10.1002/2014JD022229. Bibcode: 2015JGRD..120.1620K. https://ir.cwi.nl/pub/23845/23845D.pdf. Retrieved 2019-08-25.
23. ↑ Köhn, C.; Diniz, G.; Harakeh, Muhsin (2017). "Production mechanisms of leptons, photons, and hadrons and their possible feedback close to lightning leaders". Journal of Geophysical Research: Atmospheres 122 (2): 1365–1383. doi:10.1002/2016JD025445. PMID 28357174. Bibcode: 2017JGRD..122.1365K.
24. ↑ Ebeling, W.; Reinholz, H.; Röpke, G. (2021). "Equation of state of hydrogen, helium, and solar plasmas". Contributions to Plasma Physics 61 (10). doi:10.1002/ctpp.202100085. Bibcode: 2021CoPP...61E0085E.
25. ↑ "What are cosmic rays?". NASA. http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html. "mirror copy, also archived". http://certificate.ulo.ucl.ac.uk/modules/year_one/NASA_GSFC/goddard/imagine.gsfc.nasa.gov/docs/science/know_l2/cosmic_rays.html.
26. ↑ Poenaru, Dorin N., ed (2001) (in English). Nuclei Far from Stability and Astrophysics. Dordrecht: Springer Netherlands. pp. 79–81. doi:10.1007/978-94-010-0708-5. ISBN 978-0-7923-6937-0. http://link.springer.com/10.1007/978-94-010-0708-5.
27. ↑ UCNτ Collaboration; Gonzalez, F. M.; Fries, E. M.; Cude-Woods, C.; Bailey, T.; Blatnik, M.; Broussard, L. J.; Callahan, N. B. et al. (2021-10-13). "Improved Neutron Lifetime Measurement with UCNτ". Physical Review Letters 127 (16). doi:10.1103/PhysRevLett.127.162501. PMID 34723594. Bibcode: 2021PhRvL.127p2501G. https://par.nsf.gov/servlets/purl/10304438. Retrieved 2024-04-01.
28. ↑ Super-Kamiokande Collaboration; Takenaka, A.; Abe, K.; Bronner, C.; Hayato, Y.; Ikeda, M.; Imaizumi, S.; Ito, H. et al. (2020-12-22). "Search for proton decay via p->e+π0 and p->μ+π0 with an enlarged fiducial volume in Super-Kamiokande I-IV". Physical Review D 102 (11). doi:10.1103/PhysRevD.102.112011. https://link.aps.org/doi/10.1103/PhysRevD.102.112011.
29. ↑ Vanzella, Daniel A. T.; Matsas, George E. A. (2001-09-25). "Decay of Accelerated Protons and the Existence of the Fulling–Davies–Unruh Effect". Physical Review Letters 87 (15). doi:10.1103/PhysRevLett.87.151301. PMID 11580689. Bibcode: 2001PhRvL..87o1301V. https://link.aps.org/doi/10.1103/PhysRevLett.87.151301.
30. ↑ Matsas, George E. A.; Vanzella, Daniel A. T. (1999-03-16). "Decay of protons and neutrons induced by acceleration". Physical Review D 59 (9). doi:10.1103/PhysRevD.59.094004. Bibcode: 1999PhRvD..59i4004M. https://link.aps.org/doi/10.1103/PhysRevD.59.094004. Retrieved 2022-07-24.
31. ↑ Vanzella, Daniel A. T.; Matsas, George E. A. (2000-12-06). "Weak decay of uniformly accelerated protons and related processes". Physical Review D 63 (1). doi:10.1103/PhysRevD.63.014010. Bibcode: 2000PhRvD..63a4010V. https://link.aps.org/doi/10.1103/PhysRevD.63.014010. Retrieved 2022-07-24.
32. ↑ Matsas, George E. A.; Vanzella, Daniel a. T. (2002-12-01). "The fulling–davies–unruh effect is mandatory: the proton's testimony". International Journal of Modern Physics D 11 (10): 1573–1577. doi:10.1142/S0218271802002918. ISSN 0218-2718. https://www.worldscientific.com/doi/abs/10.1142/S0218271802002918. Retrieved 2022-07-24.
33. ↑ Watson, A. (2004). The Quantum Quark. Cambridge University Press. pp. 285–286. ISBN 978-0-521-82907-6.
34. ↑ Smith, Timothy Paul (2003). Hidden Worlds: Hunting for Quarks in Ordinary Matter. Princeton University Press. ISBN 978-0-691-05773-6. Bibcode: 2003hwhq.book.....S.
35. ↑ André Walker-Loud (19 November 2018). "Dissecting the Mass of the Proton". Physics 11. doi:10.1103/Physics.11.118. Bibcode: 2018PhyOJ..11..118W. https://physics.aps.org/articles/v11/118. Retrieved 2021-06-04.
36. ↑ Cowen, Ron (20 December 2008). "Standard Model Gets Right Answer for Proton, Neutron Masses" (in en). Science News 174 (13): p. 13. https://www.sciencenews.org/article/standard-model-gets-right-answer-proton-neutron-masses.
37. ↑ 37.0 37.1 Durr, S.; Fodor, Z.; Frison, J.; Hoelbling, C.; Hoffmann, R.; Katz, S.D.; Krieg, S.; Kurth, T. et al. (2008). "Ab Initio Determination of Light Hadron Masses". Science 322 (5905): 1224–1227. doi:10.1126/science.1163233. PMID 19023076. Bibcode: 2008Sci...322.1224D.
38. ↑ Perdrisat, C. F.; Punjabi, V.; Vanderhaeghen, M. (2007). "Nucleon electromagnetic form factors". Progress in Particle and Nuclear Physics 59 (2): 694–764. doi:10.1016/j.ppnp.2007.05.001. Bibcode: 2007PrPNP..59..694P.
39. ↑ Boffi, Sigfrido; Pasquini, Barbara (2007). "Generalized parton distributions and the structure of the nucleon". Rivista del Nuovo Cimento 30 (9): 387. doi:10.1393/ncr/i2007-10025-7. Bibcode: 2007NCimR..30..387B.
40. ↑ Joshua, Erlich (December 2008). "Recent Results in AdS/QCD". Bibcode: 2008arXiv0812.4976E.
41. ↑ Pietro, Colangelo; Alex, Khodjamirian (October 2000). "QCD Sum Rules, a Modern Perspective". in M., Shifman. At the Frontier of Particle Physics: Handbook of QCD. World Scientific Publishing. pp. 1495–1576. doi:10.1142/9789812810458_0033. ISBN 978-981-02-4445-3. Bibcode: 2001afpp.book.1495C.
42. ↑ Pohl, Randolf et al. (8 July 2010). "The size of the proton". Nature 466 (7303): 213–216. doi:10.1038/nature09250. PMID 20613837. Bibcode: 2010Natur.466..213P.
43. ↑ Karr, Jean-Philippe; Marchand, Dominique; Voutier, Eric (November 2020). "The proton size" (in en). Nature Reviews Physics 2 (11): 601–614. doi:10.1038/s42254-020-0229-x. ISSN 2522-5820. Bibcode: 2020NatRP...2..601K. https://www.nature.com/articles/s42254-020-0229-x. Retrieved 2024-03-28.
44. ↑ Gao, H.; Vanderhaeghen, M. (2022-01-21). "The proton charge radius" (in en). Reviews of Modern Physics 94 (1). doi:10.1103/RevModPhys.94.015002. ISSN 0034-6861. Bibcode: 2022RvMP...94a5002G. https://link.aps.org/doi/10.1103/RevModPhys.94.015002.
45. ↑ Burkert, V. D.; Elouadrhiri, L.; Girod, F. X. (16 May 2018). "The pressure distribution inside the proton". Nature 557 (7705): 396–399. doi:10.1038/s41586-018-0060-z. PMID 29769668. Bibcode: 2018Natur.557..396B.
46. ↑ "Wood C. Swirling Forces, Crushing Pressures Measured in the Proton. Quanta Magazine March 14, 2024". 14 March 2024. https://www.quantamagazine.org/swirling-forces-crushing-pressures-measured-in-the-proton-20240314/.
47. ↑ Burkert, V. D. et al. (2023-12-22). "Colloquium: Gravitational form factors of the proton". Reviews of Modern Physics 95 (4). doi:10.1103/RevModPhys.95.041002. ISSN 0034-6861. Bibcode: 2023RvMP...95d1002B.
48. ↑ Kumerički, Krešimir (June 2019). "Measurability of pressure inside the proton" (in en). Nature 570 (7759): E1–E2. doi:10.1038/s41586-019-1211-6. ISSN 0028-0836. PMID 31168113. Bibcode: 2019Natur.570E...1K. https://www.nature.com/articles/s41586-019-1211-6. Retrieved 2024-03-27.
49. ↑ Dutrieux, H.; Lorcé, C.; Moutarde, H.; Sznajder, P.; Trawiński, A.; Wagner, J. (April 2021). "Phenomenological assessment of proton mechanical properties from deeply virtual Compton scattering" (in en). The European Physical Journal C 81 (4): 300. doi:10.1140/epjc/s10052-021-09069-w. ISSN 1434-6044. Bibcode: 2021EPJC...81..300D. https://link.springer.com/10.1140/epjc/s10052-021-09069-w.
50. ↑ Headrick, J. M.; Diken, E. G.; Walters, R. S.; Hammer, N. I.; Christie, R. A.; Cui, J.; Myshakin, E. M.; Duncan, M. A. et al. (2005). "Spectral Signatures of Hydrated Proton Vibrations in Water Clusters". Science 308 (5729): 1765–1769. doi:10.1126/science.1113094. PMID 15961665. Bibcode: 2005Sci...308.1765H.
51. ↑ 51.0 51.1 "Apollo 11 Mission". Lunar and Planetary Institute. 2009. http://www.lpi.usra.edu/lunar/missions/apollo/apollo_11/experiments/swc/.
52. ↑ 52.0 52.1 52.2 "Space Travel and Cancer Linked? Stony Brook Researcher Secures NASA Grant to Study Effects of Space Radiation". Brookhaven National Laboratory. 12 December 2007. http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=07-X17.
53. ↑ 53.0 53.1 Carrihill-Knoll, K L; Rabin, B M; Shukitt-Hale, B; Joseph, J A; Carey, A (May 2007). "Amphetamine-induced taste aversion learning in young and old F-344 rats following exposure to 56Fe particles". GeroScience 29 (2–3): 69–76. doi:10.1007/s11357-007-9032-1. ISSN 2509-2723. PMID 19424832.
54. ↑ Green, N. W.; Frederickson, A. R. (2006). "A Study of Spacecraft Charging due to Exposure to Interplanetary Protons". AIP Conference Proceedings 813: 694–700. doi:10.1063/1.2169250. Bibcode: 2006AIPC..813..694G. http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/39501/1/05-0657.pdf. Retrieved 2009-06-12.
55. ↑ Planel, H. (2004). Space and life: an introduction to space biology and medicine. CRC Press. pp. 135–138. ISBN 978-0-415-31759-7. https://books.google.com/books?id=rnUFZ24RUdYC&pg=PA135. Retrieved 2020-07-13.
56. ↑ Gabrielse, G. (2006). "Antiproton mass measurements". International Journal of Mass Spectrometry 251 (2–3): 273–280. doi:10.1016/j.ijms.2006.02.013. Bibcode: 2006IJMSp.251..273G.
57. ↑ "BASE precisely measures antiproton's magnetic moment" (in en). https://home.cern/news/news/physics/base-precisely-measures-antiprotons-magnetic-moment.

## Further reading

* Ball, Richard D.; Candido, Alessandro; Cruz-Martinez, Juan; Forte, Stefano; Giani, Tommaso; Hekhorn, Felix; Kudashkin, Kirill; Magni, Giacomo et al. (August 2022). "Evidence for intrinsic charm quarks in the proton" (in en). Nature 608 (7923): 483–487. doi:10.1038/s41586-022-04998-2. ISSN 1476-4687. PMID 35978125. Bibcode: 2022Natur.608..483N.
* Gao, H.; Vanderhaeghen, M. (2022-01-21). "The proton charge radius" (in en). Reviews of Modern Physics 94 (1). doi:10.1103/RevModPhys.94.015002. ISSN 0034-6861. Bibcode: 2022RvMP...94a5002G. https://link.aps.org/doi/10.1103/RevModPhys.94.015002.

## External links

* Particle Data Group at LBL
* Large Hadron Collider
* Eaves, Laurence; Copeland, Ed; Padilla, Antonio (Tony) (2010). "The shrinking proton". Brady Haran for the University of Nottingham. http://www.sixtysymbols.com/videos/protonradius.htm.
* MIT proton visualization project:
* Inside the Proton, the 'Most Complicated Thing You Could Possibly Imagine', Quanta Magazine, Oct 19 2022
* Visualizing the Proton, Arts at MIT, 2022

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