Wikipedia:Reference desk/Archives/Science/2021 December 6
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December 6
[edit]Protons and neutrons in Atomic nucleus
[edit]Atomic nucleus has diagrams of nuclei with the protons and neutrons as spheres. For a given isotope with a large number of nucleons (e.g. lead-208), do the protons and neutrons in the nucleus always have the same arrangement?
(Or are those images an oversimplification?) Bubba73 You talkin' to me? 03:33, 6 December 2021 (UTC)
- Technetium 99m is a different arrangement and half-life and is ellipsoidal I think. There are many such nuclear isomers, some are numbered things like m2 cause an isotope has more than one "imperfect form". Nuclei also have nuclear shells. Sagittarian Milky Way (talk) 03:53, 6 December 2021 (UTC)
- There is a section for Atomic nucleus#Composition and shape that has some details and refs (and the surprising detail that some of the nuclear particles might exist at the exact same location as each other). Searching for "shape isomer" in the the nuclear isomer article finds some additional relevant info. The Nilsson model is some complex math, but it makes the point that some observed nuclear properties contradict a perfect spherical shape. DMacks (talk) 04:16, 6 December 2021 (UTC)
- These images are an oversimplification. As the caption of the image with red and blue balls states: "In this diagram, protons and neutrons look like little balls stuck together, but an actual nucleus (as understood by modern nuclear physics) cannot be explained like this, but only by using quantum mechanics." The "balls" do not occupy definable locations; they may apparate as suddenly and silently as Dumbledore where the observer happens to be looking, but also somewhere else. Also, as long as we use models from the macroscopic world, the protons and neutrons are more like bean bags with jumping beans. --Lambiam 04:24, 6 December 2021 (UTC)
- Thanks, I read most of the article, but I didn't read that important caption. Bubba73 You talkin' to me? 04:47, 6 December 2021 (UTC)
- At the scale of subatomic particles, location is not defined well enough for things to have a "shape" in a traditional sense. For the purpose of visual representation, we often draw protons, neutrons, and electrons as little circles on paper (or represent them with physical spheres), the real particles are not well modeled in that way. They are likely point particles, and we have what might be thought of as "regions of probability" for those point particles to most likely be (in the case of electrons, those would be in various electron orbitals, while for protons and neutrons, that region would be the atomic nucleus. It's important not to think of these places as well-defined objects on their own, but rather regions where something is most likely to be found; however we can't get more finely tuned than that: we can't (for example) say where within an atomic orbital an electron is located, or where within a nucleus a particular proton is located, just that it is most likely located in that region. The modern quantum theory explaining the nucleus is known as quantum chromodynamics. --Jayron32 13:14, 6 December 2021 (UTC)
- Our various articles are consistent that protons and neutrons have a spacial extent in some sense, measured variously to be a little less than a femptometer. Charge radius in particular even notes distinct radial probability regions of a neutron for its different constituent quarks. DMacks (talk) 13:27, 6 December 2021 (UTC)
- How do you convert the mass of an object to the radius of the smallest sphere that contains it 1-standard deviation of the time (~68%)? It's probably in the article's alienese somewhere but not in a form of math that I can do. I would like to see a line graph with the size of this sphere on one axis and the particle's mass on the other. Sagittarian Milky Way (talk) 15:16, 6 December 2021 (UTC)
- The charge radius, or any of various other size measures, does not define a hard bound but is based on the average value of something that has a considerable variation, each time an observer measures it, possibly even depending on the specific measuring setup. Just look at the range of values given in the lead section of our article Proton, and compare these with the 2014 CODATA recommended value given in Charge radius § Modern measurements. The individual measurements have values with a probability density that decreases exponentially with increasing radii. --Lambiam 18:15, 6 December 2021 (UTC)
- Yeah that's what I mean, where is this 1-sigma radius? ~68% of the time you measure the position to a few attometers (do you need future technology?) it will be inside but you'll have circa no fucking clue of its velocity and every so often it will be on Mars but less once per 10many measurements. Sagittarian Milky Way (talk) 19:12, 6 December 2021 (UTC)
- The charge radius, or any of various other size measures, does not define a hard bound but is based on the average value of something that has a considerable variation, each time an observer measures it, possibly even depending on the specific measuring setup. Just look at the range of values given in the lead section of our article Proton, and compare these with the 2014 CODATA recommended value given in Charge radius § Modern measurements. The individual measurements have values with a probability density that decreases exponentially with increasing radii. --Lambiam 18:15, 6 December 2021 (UTC)
- At the scale of subatomic particles, location is not defined well enough for things to have a "shape" in a traditional sense. For the purpose of visual representation, we often draw protons, neutrons, and electrons as little circles on paper (or represent them with physical spheres), the real particles are not well modeled in that way. They are likely point particles, and we have what might be thought of as "regions of probability" for those point particles to most likely be (in the case of electrons, those would be in various electron orbitals, while for protons and neutrons, that region would be the atomic nucleus. It's important not to think of these places as well-defined objects on their own, but rather regions where something is most likely to be found; however we can't get more finely tuned than that: we can't (for example) say where within an atomic orbital an electron is located, or where within a nucleus a particular proton is located, just that it is most likely located in that region. The modern quantum theory explaining the nucleus is known as quantum chromodynamics. --Jayron32 13:14, 6 December 2021 (UTC)