4 ms·

I remember when I toured a research nuclear reactor and I was talking with the nuclear phd student and I said something about an alpha particle and the protons

I remember when I toured a research nuclear reactor and I was talking with the nuclear phd student and I said something about an alpha particle and the protons and neutrons. And they were trying to say alpha particles aren't made up of protons and neutrons. Made me realize than that even an expert in the field might not know something that I would have thought was common knowledge.

thaumasiotes 5y ago
There are some pretty obvious followup questions: - What are alpha particles made of? - When an element undergoes alpha decay, its atomic number is reduced by two. Where do the protons go?
- deleted 5y ago
  [deleted]
- cjtrowbridge 5y ago
  An alpha particle is a particle produced during alpha decay. It's always just a helium-4 which is made of two protons and two neutrons but with no electrons. This is why we have to mine for helium because it is produced in the ground by alpha decay. It's different from normal helium because it doesn't have any electrons and it has an empty orbital which means it really really would like to have some electrons and also it's going crazy fast when it is created so that's why it's dangerous. But then once it takes those electrons from somewhere it becomes normal helium. You just don't want that happening in your body. It seems like the other commenters in this thread are alluding to the electron thing maybe? Not exactly sure what point they're making.
  - shkkmo 5y ago
    I believe that is clear, those questions were intended to be read as ones to put to the nuclear engineer who claimed an alpha particle was not made of two nuetrons and two protons.
  - tsimionescu 5y ago
    As far as I understand, the claim is actually that an Alpha particle is made up of quarks and gluons, the same number you would find in 2 protons and 2 neutrons, but that the proton and neutron are different things. It sounds like there's a very technical distinction about exactly how you define a particle. Essentially, I believe that the claim is something like saying that modeling an alpha particle as 2 neutrons and 2 protons loses some information that you would have if you model it as 12 quarks, because the 12 quarks interact in (slightly) different ways than a proton and a neutron would.
    - jhgb 5y ago
      But that sounds like a difference between two models, not a difference between two physical objects. To me it seems that if you were to follow this line of thinking religiously, you could then never say things like "an atom of carbon has six protons", since, well, they're not quite protons according to this logic.
dekhn 5y ago
Right. I was pretty surprised and amused when I was learning nuclear chemistry and realized: an alpha particle is also a helium-4 nuclei, a beta particle is an electron/positron, and a gamma ray is just high energy electromagnetic radiation. This is sort of because the discoveries were made before people were really aware of helium nuclei, electrons/positrons, or high energy EM, they just ran physical experiments in a lab and saw there were different kinds of radiation that had different physical properties, and under close inspection of those properties, the nature of the radiation was deduced.
dylan604 5y ago
It's not uncommon for someone to be so focused on their specific area of a field that they loose sight of the rest of the areas.
lamontcg 5y ago
They may have been so into their own bellybutton lint that they were very concerned about the difference between bound quarks on a QCD lattice compared to just elmer's gluing 2 free neutrons and 2 free protons together or something like that.
- marcosdumay 5y ago
  Yes, I have heard a lot of times how atom nuclei and alpha particles aren't made of protons and neutrons. It's always on this sense. Some times the difference is relevant (and people dealing with radioactivity see those times more often than others), but some people insist on the pedantic distinction even when it isn't.
  - adrian_b 5y ago
    The binding energy of protons & neutrons into nuclei is less than 1% of their mass, so the energy required to separate a nucleus, like an alpha particle, into all its constituent protons and neutrons, is negligible in comparison with the energies required for interactions so intense that they would generate any other hadrons except protons and neutrons, for example pi mesons, which would expose the inner structure of protons and neutrons. This is an important feature of nature, whose consequence is that the most convenient way of understanding the world is that the first approximation, which is useful for almost all practical purposes, is to consider everything as composed of protons, neutrons and electrons, which are bound by strong, electromagnetic and gravitational forces and that there are also positrons (antielectrons), which can be generated in sufficiently intense interactions and which will annihilate with electrons. Only for few purposes it is necessary to go beyond this and take into account that there are many other hadrons composed of quarks, besides protons and neutrons, and that there are also other leptons. The distinction between these 2 level of approximation is important and whoever likes to think that alpha particles as not being made of protons of neutrons fails to get it. Of course, for many purposes you can ignore the strong nuclear forces and you can consider the surrounding world as being made of electrons and of a little less than 300 kinds of long lived nuclei, which are bound by electromagnetic and gravitational forces. At this other level of approximation, you should ignore the proton-neutron composition of any nucleus, but when you talk about alpha particles, you normally mean helium nuclei having a kinetic energy high enough to not be negligible in comparison with the binding energies of nuclei, so you are not in a situation when you can ignore the nuclear compositions. In any physical model, it is important to specify clearly which is the level of approximation at which it works. Mixing randomly various levels of approximation of the structure of things is usually a bad strategy.
Ekaros 5y ago
I would think that not thinking alpha particle as "made up" from protons and neutrons helpful abstraction in thinking about fission. Yes, they are, but we can't really form them or deform them at will. Specially when you already deal with free neutrons.

thaumasiotes 5y ago

There are some pretty obvious followup questions: - What are alpha particles made of? - When an element undergoes alpha decay, its atomic number is reduced by two. Where do the protons go?

deleted 5y ago
[deleted]
cjtrowbridge 5y ago
An alpha particle is a particle produced during alpha decay. It's always just a helium-4 which is made of two protons and two neutrons but with no electrons. This is why we have to mine for helium because it is produced in the ground by alpha decay. It's different from normal helium because it doesn't have any electrons and it has an empty orbital which means it really really would like to have some electrons and also it's going crazy fast when it is created so that's why it's dangerous. But then once it takes those electrons from somewhere it becomes normal helium. You just don't want that happening in your body. It seems like the other commenters in this thread are alluding to the electron thing maybe? Not exactly sure what point they're making.
- shkkmo 5y ago
  I believe that is clear, those questions were intended to be read as ones to put to the nuclear engineer who claimed an alpha particle was not made of two nuetrons and two protons.
- tsimionescu 5y ago
  As far as I understand, the claim is actually that an Alpha particle is made up of quarks and gluons, the same number you would find in 2 protons and 2 neutrons, but that the proton and neutron are different things. It sounds like there's a very technical distinction about exactly how you define a particle. Essentially, I believe that the claim is something like saying that modeling an alpha particle as 2 neutrons and 2 protons loses some information that you would have if you model it as 12 quarks, because the 12 quarks interact in (slightly) different ways than a proton and a neutron would.
  - jhgb 5y ago
    But that sounds like a difference between two models, not a difference between two physical objects. To me it seems that if you were to follow this line of thinking religiously, you could then never say things like "an atom of carbon has six protons", since, well, they're not quite protons according to this logic.

dekhn 5y ago

Right. I was pretty surprised and amused when I was learning nuclear chemistry and realized: an alpha particle is also a helium-4 nuclei, a beta particle is an electron/positron, and a gamma ray is just high energy electromagnetic radiation. This is sort of because the discoveries were made before people were really aware of helium nuclei, electrons/positrons, or high energy EM, they just ran physical experiments in a lab and saw there were different kinds of radiation that had different physical properties, and under close inspection of those properties, the nature of the radiation was deduced.

dylan604 5y ago

It's not uncommon for someone to be so focused on their specific area of a field that they loose sight of the rest of the areas.

lamontcg 5y ago

They may have been so into their own bellybutton lint that they were very concerned about the difference between bound quarks on a QCD lattice compared to just elmer's gluing 2 free neutrons and 2 free protons together or something like that.

marcosdumay 5y ago
Yes, I have heard a lot of times how atom nuclei and alpha particles aren't made of protons and neutrons. It's always on this sense. Some times the difference is relevant (and people dealing with radioactivity see those times more often than others), but some people insist on the pedantic distinction even when it isn't.
- adrian_b 5y ago
  The binding energy of protons & neutrons into nuclei is less than 1% of their mass, so the energy required to separate a nucleus, like an alpha particle, into all its constituent protons and neutrons, is negligible in comparison with the energies required for interactions so intense that they would generate any other hadrons except protons and neutrons, for example pi mesons, which would expose the inner structure of protons and neutrons. This is an important feature of nature, whose consequence is that the most convenient way of understanding the world is that the first approximation, which is useful for almost all practical purposes, is to consider everything as composed of protons, neutrons and electrons, which are bound by strong, electromagnetic and gravitational forces and that there are also positrons (antielectrons), which can be generated in sufficiently intense interactions and which will annihilate with electrons. Only for few purposes it is necessary to go beyond this and take into account that there are many other hadrons composed of quarks, besides protons and neutrons, and that there are also other leptons. The distinction between these 2 level of approximation is important and whoever likes to think that alpha particles as not being made of protons of neutrons fails to get it. Of course, for many purposes you can ignore the strong nuclear forces and you can consider the surrounding world as being made of electrons and of a little less than 300 kinds of long lived nuclei, which are bound by electromagnetic and gravitational forces. At this other level of approximation, you should ignore the proton-neutron composition of any nucleus, but when you talk about alpha particles, you normally mean helium nuclei having a kinetic energy high enough to not be negligible in comparison with the binding energies of nuclei, so you are not in a situation when you can ignore the nuclear compositions. In any physical model, it is important to specify clearly which is the level of approximation at which it works. Mixing randomly various levels of approximation of the structure of things is usually a bad strategy.

Ekaros 5y ago

I would think that not thinking alpha particle as "made up" from protons and neutrons helpful abstraction in thinking about fission. Yes, they are, but we can't really form them or deform them at will. Specially when you already deal with free neutrons.