What is Proton: Definition and 830 Discussions

A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are jointly referred to as "nucleons" (particles present in atomic nuclei).
One or more protons are present in the nucleus of every atom; they are a necessary part of the nucleus. 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 has a unique number of protons, each element has its own unique atomic number.
The word proton is Greek for "first", and this 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. Protons were therefore a candidate to be a fundamental particle, and hence a building block of nitrogen and all other heavier atomic nuclei.
Although protons were originally considered fundamental or elementary particles, in the modern Standard Model of particle physics, protons are classified as hadrons, like neutrons, the other nucleon. Protons are composite particles composed of three valence quarks: two up quarks of charge +2/3e and one down quark of charge −1/3e. The rest masses of quarks contribute only about 1% of a proton's mass. 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. Because protons are not fundamental particles, they possess a measurable size; the root mean square charge radius of a proton is about 0.84–0.87 fm (or 0.84×10−15 to 0.87×10−15 m). In 2019, two different studies, using different techniques, have found the radius of the proton to be 0.833 fm, with an uncertainty of ±0.010 fm.Free protons occur occasionally on Earth: thunderstorms can produce protons with energies of up to several tens of MeV. At sufficiently low temperatures and kinetic energies, free protons will bind to electrons. However, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, until it is captured by the electron cloud of an atom. The result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom, which is chemically a free radical. Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules (H2), which are the most common molecular component of molecular clouds in interstellar space.
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.

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  1. heroslayer99

    What is the definition of the dalton (Da) unit?

    I am very confused with this question, firstly, I am unsure what is meant by the "unified atomic mass unit" I know that it is defined as "1/12 of the mass of an atom of carbon 12", but this sounds like it takes into account the electrons, i.e that is this means to me that unified atomic mass...
  2. J

    Electron bound to proton by gravity

    Hello everyone, I have the problem above. I chose to put ##F_G = F_Z## to solve it and end up with a radius ##r = 1.04\cdot 10^{-7}##m. Solutions on the internet choose to put the gravitational force equal to the centrifugal force and obviously end up with a completely different solution. I...
  3. M

    Tangential acceleration of proton due to a changing magnetic field

    ##\displaystyle R=\frac{mv}{qB}\implies v=\frac{RqB}{m}## where ##v## is the speed of the proton ##\displaystyle\frac{dv}{dt}=\frac{Rq}{m}\frac{dB}{dt}## On substituting the values, I get ##\displaystyle\frac{dv}{dt}=9.58\times 10^4\ m/s^2## This answer, however, is incorrect. Where have I...
  4. Astronuc

    I Experiment finds gluon mass in the proton (?)

    Article published at Phys.org - Experiment finds gluon mass in the proton https://phys.org/news/2023-03-gluon-mass-proton.html An interesting diagram accompanies the article. Article in Nature (requires subscription or purchase, but one can read the abstract)...
  5. S

    I Observing Proton Decay & Antineutrinos

    antineutrino? I was looking at this article, which says that a proton that interacts with an antineutrion transforms (or whatever the proper verb is here) into a neutron & positron. But this begs the question that if we're trying to observe a proton decaying, how would we know that it had not...
  6. C

    Max speed of proton in cyclotron

    For this problem, The solution is, However, I don't understand why they say just before the proton escapes? Are they assuming that the B-field is only at a portion of region which means that only half or so of the circular path is within the B-field so only half of the path have a magnetic...
  7. S

    I Are the proton and electron quantum entangled in the hydrogen atom?

    The proton and electron are described by separate wavefunctions. When they come together in the hydrogen atom are they quantum entangled and have a joint wavefunction.
  8. J

    I Removing a proton with a particle accelerator

    What would it look like if I used a particle accelerator to remove a proton from a particular element? What would the physical change in the element look like if observed? Would the element appear to "magically" change into something else right before your very eyes, as if by some kind of spooky...
  9. C

    Angle between proton velocity and B-field

    For this problem, The solution is, However, this may seem like a silly question, but do we need both angles? Many thanks!
  10. .Scott

    Brains Entangle Proton Spins

    From phys.org:
  11. Astronuc

    I Proton electric polarizability and structure (recent measurement)

    Measured proton electromagnetic structure deviates from theoretical predictions https://www.nature.com/articles/s41586-022-05248-1Meanwhile - https://www.jlab.org/human_resources/recruiting/ELECTRON-ION COLLIDER JOB OPPORTUNITIES
  12. M

    The density of a proton (hydrogen nucleus)

    First of all i want is to check if my answer is right or not because i am really not sure about my answer. Because the length is given in the form of a diameter we will divide that by 2 so we get it in the form of radius, 2.4fm / 2 = 1.2fm = r Then we will convert the radius from "fm" to "m" so...
  13. J

    Earth's magnetic force on a proton

    Plug in the elementary charge for q, 1000 m/s for v, 50 microtesla for B and 90 degrees for theta and I get about 8e-21 Netwons. But apparently this is wrong, anyone know why? Thank you.
  14. dirb

    The time for a proton to reach a certain velocity

    A nuclear reactor is built to fuse two hydrogen atoms that are already ionized to protons. However, the electric field of the protons are becoming a significant obstacle. If the reaction was to be defined as H2--> 2H++2e-, if the mass of a proton is mp, the radius of a proton r the charge of an...
  15. edfink234

    How to understand Proton Structure-function (pdf)

    I don't understand the attached image, which shows the structure-function of the proton, for the cases of 1. point-like particle 2. 3 non-interacting quarks 3. 3 quarks interacting via gluons 4. valence and sea quarks interacting via gluons Can someone please explain this to me? I would greatly...
  16. S

    Speed and direction of proton after collision

    I don't really understand the question. A proton collides obliquely with another proton means that the first proton moves at certain angle with respect to horizontal? This is my sketch: Is that correct? If yes, is it solvable since there are so many unknowns? Thanks
  17. W

    B Is it the nucleus or a proton at the center?

    Which one is closer to reality, is it this picture https://en.wikipedia.org/wiki/Hydrogen#/media/File:Hydrogen_atom.svg or this https://www.naturphilosophie.co.uk/heart-hydrogen-atom/? The reason why I asked the question is according to the picture of hydrogen atom at Wikipedia, which is the...
  18. thegroundhog

    I LIGO: Detecting Differences Less Than a Proton Length - How is It Possible?

    I read that the LIGO detector in the US was able to detect a difference of less that the length of a proton, or maybe even less than this. How is this possible? The perpendicular arms won't be the same length down to the nearest proton length. Also, at such small lengths the microclimate on each...
  19. Johann0101

    Gravity's Pull: How Far is the Proton Above the Electron?

    An electron is held up against the force of gravity by attraction of a fixed proton some distance above it. How far above the electron is the proton?
  20. T

    Acetic acid as a proton donor

    The solubility product for water is 10 to the minus fourteenth power.(water forming hydronium ion and its complement). What is the solubility product of pure acetic acid forming HHOAC(+) and OAC(-) ?
  21. S

    I Nuclear knockout reactions - why does a proton knockout a neutron?

    I am studying the synthesis of FDG for a job interview. The process of creating the F-18 used in FDG involves the collision of O-18 with an accelerated proton -- the proton kicks out a neutron and everything adds up. I am just wondering why a neutron is specifically knocked out, why wouldn't...
  22. A

    I Orbital magnetic dipole moment of a proton

    hi every one what is the amount of orbital magnetic dipole moment of proton? this different with the intrinsic magnetic.
  23. G

    I Proton decay at the end of the Universe

    I wish this forum allowed indentation using tabs. Some of these questions are dependent on the answers to others. I have used outline numbers to indicate nested questions. I have BA in physics and mathematics, 40+ years ago. I was thinking (always a dangerous thing). I had some questions. I...
  24. Tareq Naushad

    I Free electron path without a nearby proton

    In absence of a positive electric field created by proton what type of behavior an electron shows? I am talking about a free electron like from a electron gun in deep space . Pauli's exclusion, orbitals, energy level etc. which are normal in an atom for electron will be absent for an electron...
  25. P

    Work Done on A Proton in an Electric Field

    W=-qEd =-(1.6*10^-19)(23)(0.75) = -2.76*10^-18 J However, the answer is 2.76*10^-18 J. Why is the word done positive and not negative? Since it's traveling in the same direction as the electric field, shouldn't it be negative work?
  26. T

    B Is there a formula to obtain the mass of a proton from c?

    Just as E= hc/λ is anyone aware of a mathematical formula to obtain the mass of a proton from C ?
  27. H

    Bending proton beams under magnetic field

    I haven't taken a physics courses in some time and I'm having trouble getting started with this textbook question. I know that there will be relativistic effects present, but I can deal with that. The problem is how I can approach the problem. I initially thought of a geometric way to set up...
  28. Adams2020

    I Loss of electron & proton energy due to radiation

    Can you compare the energy loss of electrons and protons due to the radiation they emit? In fact, I want to know which of the two loses more energy when it emits radiation.
  29. Sj4600

    Electric Potential Energy Question: Electron and Proton accelerating between charged plates

    Ve=0m/s Vp= 0m/s Qe/Qp= 1.60E-19 Me=9.11E-31 Mp-1.67E-27 Ive pretty much gathered all of the equations I think I need to solve the problem. I just am stuck. The last step I realize that the forces would be equal to each other so I have mp x ap = me x ae but then when I try to solve for the...
  30. L

    B Does an electron have kinetic energy when attached to a proton?

    does an electron have kinetic energy when attached to a proton? if not, what is it transformed into?
  31. A

    A Energy needed to convert a bound proton to a neutron?

    Hey everyone, I've got a question on converting bound protons into neutrons. a. What are some methods used to achieve the proton-to-neutron conversion in atomic nuclei? I'm familiar with particle scattering off a proton in the nucleus. I'm also aware of (n,p) reactions. Are there any other...
  32. K

    I Exploring the Quark Stars: Hexaquarks and Proton Decay

    Question: Is it believed a "quark star" exists within all neutron stars, or just heavier neutron stars. Do protons actually decay under this pressure (quark soup)? Are Hexaquark bosons able to remain stable beyond the limit of a proton, or would they decay at the same time of a regular...
  33. L

    QED, Electron-Proton Scattering: Rosenbluth cross-section

    Hello, this problem is causing headaches, it would be very helpful if you could tell me if you know of a book where you can solve it. Maybe my English is lousy because I use a translator. Thank you very much.
  34. M

    Work done by pushing a proton into the sphere with non-uniform charge

    I have already calculated full charge inside the sphere: e = ∫ρ dV = 2πBr^2 And I know that electric potential on the edge of the sphere is: U = e/ 4πεr The idea is that I calculate work by the change of electric potential energy, but to do that, I have to calculate electric potential energy in...
  35. M

    Can Two Protons Have the Same Speed After an Elastic Collision?

    m1v1i + m2v2i = (m1+m2)vf (1.67 × 10^-27)v1i = (1.67 × 10^-27 + 1.67 × 10^-27) vf (1.67 × 10^-27/3.34 × 10^-27)v1i = (3.34 × 10^-27/3.34 × 10^-27) vf (1.67 × 10^-27/3.34 × 10^-27)v1i = vf (0.5)(v1i) = vf not sure what to do from here nor if I'm in the correct path ?
  36. r-swald

    Find how far a proton travels between capacitor plates

    I first attempted to use kinematics, but to find acceleration I would need to find the force either by finding the e-field first and multiplying it with q, or just kQq / r^2. However, I was not given second charge or surface charge density. Is there another way I could go about making the...
  37. V

    Motion of a Proton in Electric and Magnetic Fields

    a) 248*10^3 eV for 248kV Calculate the energy in J K=248*10^3*1.6*10^-19 =396.8*10^-19 J b) K=(1/2)mv^2 v=sqrt(2k/m) =sqrt((2*396.8*10^-19)/1.67*10^-27) =218^10^3 m/s c) r=mv/qB =1.67*10^-27*218*10^3/1.6*10^-19*1.5*10^-4 =15.17 mr=mv/qB...
  38. A

    A Proton Precession in Hydrogen-Rich Liquids

    When a hydogen rich is subjected to a strong magnetic field , the protons ( which has a magnetic moment) lines up along the applied field in a parallel or anti parallel state. My doubt is that- protons ( Hydrogen ion) in a hydrogen rich liquid cannot exist as an ion in a liquid because it...
  39. weningth

    A Deriving the Callan-Gross Relation via the Parton Model

    I want to derive the Callan-Gross relation from the parton model but I am having some problems obtaining the textbook result. I am following M.D. Schwartz: Quantum Field Theory and the Standard Model (pp.672, 675, 678). Starting from the hard scattering coefficient obtained from the partonic...
  40. P

    Charged proton enters an electric field

    I tried to do Net force with electric field = E x q minus the gravitational force= mg. However, this gives me a negative net force suggesting the proton is moving downwards. I'm not sure this is correct as the initial velocity was horizontal. Was there no gravitational force before? Am I missing...
  41. NoctusPartem

    How can I calculate the smallest speed of a proton in a nucleus?

    My approach: Assuming non-relativistic velocity: $$p = mv$$ $$mvL = \frac{\bar{h}}{2}$$ $$v = \frac{\bar{h}}{2mL} = \frac{h}{4\pi mL}$$ $$v = (6.626*10^-34) / (4pi * 1.67*10^-27 * 4.3*10^-15)$$ $$v = 7.34*10^6 = .0245c$$ This answer is incorrect. What have I done wrong? --- Edit: My...
  42. cookiemnstr510510

    Most acidic proton: first semester organic chemistry

    Hello All, I have attached my questions with pictures in attached photos. Look at screen shot 46 first then screen shot 47. I am having trouble ranking acidic protons. In my Organic book it has the order of: 1)Charge 2)Atom Type 3)Hybridization 4)Resonance 5)Induction Things I know: S is able...
  43. I

    Minimum separation between incoming proton and alpha particle

    Proton is going towards the ##\alpha## particle. So, I am thinking of using the conservation of energy as the initial kinetic energy of the proton is known and initial interaction potential energy is zero. But, we don't know the kinetic energies of proton and ##\alpha## particle when they are at...
  44. mfb

    I New proton radius measurement with electrons favors "muon value"

    Publication News article It looks increasingly like something is wrong with the older electron-based results. The story of "with electrons you measure one thing, with muons another" doesn't work any more. Is that a good thing (there might be some conclusion what the radius is in the next years)...
  45. G

    Proton Decay: Exploring Entropy's Effects

    Dear admins and moderators, I am sure this subject has come up many times before, and could well be a stupid question. If so, could you direct me to the relevant thread(s)? Setting aside its itinerant electron, (Hydrogen Atom,) the Proton is THE building block of the Universe. "...Despite...
  46. epotratz

    I Voltage between electron and proton in ground state hydrogen atom?

    I’m not sure if this belongs in classic or quantum physics... but here it is...Is it possible to calculate the “voltage” between an electron and a proton in a ground state hydrogen atom?I know the ionization energy is 13.6 eV, so I assume it's safe to say the voltage is 13.6 volts at a certain...
  47. F

    Proton Structure: De Broglie Wavelength & Resolution

    Hi all. I'd personally consider the De Broglie wavelength λ=h/p, with p being the momentum of the electron beam. I get $$\lambda \simeq 0.6 \times 10^{-18} m $$ and since the radius of a quark is ## \leq 10^{-19} m ##, the proton structure can't be resolved. I'm quite sure there's something...
  48. B

    I Focused proton beam waist diameter

    According to this link (https://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/collisions.htm) the LHC achieves a beam waist diameter of approximately 64 microns. What limits them from getting a tighter focal point? Are lower energy beams easier or harder to focus tightly?
  49. B

    Current Transformer Proton Accelerator

    Suppose you place a current transformer into a vacuum and flow ionized hydrogen through the center of it. The ionized hydrogen would act as the secondary winding of the current transformer. How specifically would the acceleration that the hydrogen ions experience be calculated?
  50. B

    Parallel Plate Pulsed Proton Beam Generator (Thought Experiment)

    I am trying to come up with a design for a device with which to generate a rapidly pulsed proton beam (on the order of 1 pulse per ms). My thought was to apply a 10 kV potential between two parallel plates (each with a hole in their center) and inject a steady stream of hydrogen gas through the...
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