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Hot answers tagged protons

198

Ah, I know this one! What's in a proton? A proton is really made of excitations in quantum fields (kind of like localized waves). Remember that. Any time you hear any other description of the composition of a proton, it's just some approximation of the behavior of quantum fields in terms of something people are likely to be more familiar with. We need to ...

110

Free neutrons in flight are not deflected by electric fields. Objects which are not deflected by electric fields are electrically neutral. The energy of the strong proton-neutron interaction varies with distance in a different way than the energy in an electrical interaction. In an interaction between two electrical charges, the potential energy varies ...

79

There are multiple reasons why protons are heavier than electrons. As you suggested, there are empirical and theoretical evidence behind this. I'll begin with the empirical, since they have important historical context associated with them. As a preface, this will be a fairly long post as I'll be explaining the context behind the experiments and the theories....

72

What you are looking for is isotopes with neutron–proton ratio N/Z less than 1. You can find these isotopes, for example, in this list from Wikipedia. As you can see, you are looking for members of the table with N less than Z. In these table you are looking for isotopes that are roughly above the gray zone (also known as band or belt of stability). The ...

68

You are not correct in your latter part of the analysis; the chemical properties (which is mostly what matters in ordinary matter) almost only depend on the electron shell, and in particular the outermost electrons (called the valence electrons). So more protons mean more electrons and a different electron shell, meaning different chemical properties. Why ...

67

As noted "why" is a tricky question but we may ask what is the most fundamental view known concerning this question. Electrons and protons are very different beasts. Electrons as far as we can tell are elementary, participating in the electromagnetic and so-called weak interactions. On the other hand protons are known to consist of quarks. Quarks are very ...

57

Your friend is correct: there's only one type of proton. The proton is the lightest baryon. It has charge $+1$, spin $1/2$, and baryon number $+1$. These three quantum numbers are so fundamental that if you try to change any of them, the result won't be a proton. For example, if you change the charge to $0$, you get the neutron, and if you change the spin ...

47

It is an experimental fact that all electrons and also all protons (but this often applies also to nuclei, atoms and even molecules) are indistinguishable from one another, i.e. they both are identical particles. Imagine to perform the following experiment: you take two objects A and B, perform as many measurements as you want on them, put them into a "...

44

What is the experimental evidence that the nucleons are made up of three quarks? Some strong pieces of evidence for the quark model of the proton and the neutron, not stated in another answer, are the magnetic moment of the proton and the magnetic moment of the neutron, which are consistent with the quark model and are inconsistent with the magnetic ...

43

You can't consider a proton just as three quarks (called valence quarks, because they determine the quantum numbers) because virtual quarks and antiquarks are constantly being created and anhilated via strong force. So a proton is more like a quark sea. In fact, this process gives most part of the proton's mass (the valence quarks are just the 2% of the mass)...

42

According to Wikipedia: Other than protium (ordinary hydrogen), helium-3 is the only stable isotope of any element with more protons than neutrons.

37

A neutron is not "a proton and an electron". A neutron is not composed of a proton and an electron inside of the neutron. In quantum mechanics, particles can appear and disappear or change into other particles. With the neutron, one of the down quarks can decay change into an up quark by emitting a W boson, turning into a proton. The W boson quickly decays ...

37

You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be. When the neutron star forms, most of the protons and electrons combine together to form neutrons This is mostly correct. The process ...

33

It's just an empirical value. According to our current knowledge, the masses actually come from some more fundamental quantities - the electron yukawa coupling and the Higgs field vev, in the case of the electron mass; and the QCD confinement scale (which in turn comes from the strong coupling constant), in the case of the proton mass. But where those ...

32

Note that the original SU(3) quark model was entirely mathematical (The Eightfold Way) and was a brilliant way to explain the observed spectra of baryons and meson. The whimsically named quarks were not intended to represent real objects. Per @Geoffrey's answer, it was Deep Inelastic Scattering: $$e^-+p \rightarrow e^-+X$$ often written: $$e(p, X)e'$$...

32

If you shoot an electron or a proton at a nucleus at moderate energies (a few hundred $\mathrm{MeV}$ to a few $\mathrm{GeV}$) it will usually either bounce off the whole nucleus or break up the nucleus. But every once in a while (and this gets rarer and rarer the harder you throw it in) it will actually bounce off of a single nucleon. At the right energies ...

28

This is actually a really good question. (And I'm not one of these people who insists that there's no such thing as a dumb question; I just think we shouldn't be embarrassed to ask dumb questions. Anyway, this isn't a dumb question.) As you may know, collisions between two protons (like those the LHC usually does) can produce many different types of ...

28

This does not violate the exclusion principle because the exclusion principle merely states that there cannot be more than one fermion in the same quantum mechanical state. In the case of two protons and two neutrons, the different particle species don't exclude each other to begin with (because a neutron state is different from a proton state). Furthermore,...

27

There are two very relevant facts that inform this answer: (1) The rest mass energy of a neutron is 1.29 MeV higher than that of a proton. $(m_n - m_p)c^2 = 1.29$ MeV. (2) The total number of neutrons plus protons (essentially the only baryons present) is a constant. Neutrons and protons can transform into one another via reactions moderated by the weak ...

24

The question you are asking has been answered in terms of popularized description. The real physics picture is not simple and depends a lot on a number of experimental measurements by many experiments. If you look at figure 9.18 of the link you will see that the composition of the proton changes according to the momentum transfer from the probing particle. ...

24

I would say that charge is a theoretical prescription describing a way of how a particle interacts with electromagnetic field. Since we are talking about a theory that should describe and predict various phenomena, we need to start with definition of fundamental object. If we are talking about Newtonian mechanics we face phenomena related to interactions of ...

23

There is a rigorous formal analysis which lets you do this. The true problem, of course allows both the proton and the electron to move. The corresponding Schrödinger equation thus has the coordinates of both as variables. To simplify things, one usually transforms those variables to the relative separation and the centre-of-mass position. It turns out that ...

22

Suppose that the strong nuclear force were instead caused by Coulomb interactions. Since we know how strong the binding energies are (of the order of $\sim 1\ \text{MeV}$, as can be gleaned by say, looking at a table of alpha particle energies) and how far apart the nucleons are (about a proton radius, or $a_p\sim1\ \text{fm}$) we know how charged the ...

21

There is another fundamental force of nature apart from the electromagnetic and the gravitational force. This is the strong nuclear force. Its presence is in between the interactions of protons and neutrons themselves or between protons and neutrons. Unfortunately, the strong force has no macroscopic effect as to feel the interaction themselves because the ...

21

This is an interesting and non-trivial problem. Basically the Coulomb potential assumes a point particle but, if the proton is modelled as a solid sphere of finite radius, part of the electron wave function would be "inside" the proton, where the assumption of point charge no longer holds. To account for this one must modify the Coulomb potential from $1/... 20 Also, it is obvious that adding (or subtracting) electrons does not make a difference [...] The two differences you describe between copper and zinc are in fact due to the electrons in the atoms. So the crucial difference between the two atoms is that they have different electron configurations in the electrically neutral state (when the number of electrons ... 20 The key to the answer is observation. We have already observed a lot of small and huge things interacting with each other. Unscientific answer would be: there could be a multitude of subtypes of a proton, but we simply haven't invented yet the experiments which show those subtle differences. Scientific answer is NO. Per Occam's razor, if we found a ... 20 A neutron isn't a proton and an electron. The reaction involved in beta decay is $$n \to p + e^- + \bar{\nu}_e$$ where$\bar{\nu}_e\$ is an electron anti-neutrino. But even that doesn't mean a neutron is a proton plus an electron plus a anti-neutrino. It means that a neutron's quantum numbers are the same as a state consisting of a proton an electron and ...

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