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.
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.
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.
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.
Yes, but very smart people are often hyperfocused on their own particular bellybutton lint like I said.
For someone whose whole job revolves around the quark structure of nuclei they may see it important enough to "correct" someone who only thinks of nuclei as protons and neutrons flying around each other in relative isolation like planets.
Add a dash or ten of Asperger's (we're talking about nuclear physicists here) and that's how you wind up with an expert "correcting" a non-expert about a casual fact which is 99.9% correct.
Thinking that the expert was too dumb to know that fact is probably the wrong interpretation.
Thinking that the expert was making a social/communication mistake is probably the right one.
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.
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.
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.
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.
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.
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.
