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B Beta plus decay

  1. Aug 10, 2017 #1

    I have a question about beta plus decay.
    I have read through the previous post regarding this decay, but I did not find anyone mentioning what I wonder about. Also, some post dates back to 2009, and maybe some recent findings in physics can explain things in a "better" way.

    So according to wikipedia "
    However, β+ decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton.
    β+ decay can only happen inside nuclei when the daughter nucleus has a greater binding energy (and
    therefore a lower total energy) than the mother nucleus.

    To me, this implies that the atom knows beforehand that the daughter should have lower total energy.
    Which is strange...

    If not, then one would say that everything happens, but only the "allowed" things exists.
    But this is even more strange.

    So, how does the physics explain such a dilemma?

    Thank you for your time
  2. jcsd
  3. Aug 10, 2017 #2


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    You know how when you place a ball on a slope, it may spontaneously roll down, but it'll never roll up by itself?
    Do you find it strange that the ball 'knows' which configuration has lower energy state? Or do you find it strange that it's only 'allowed' for the ball to start rolling down and not up or sideways?

    It's exactly like that with decay processes. A ball doesn't have to know where it'll end up beforehand, but if there's anywhere to roll down to, it'll likely roll down. Same with a nucleus - it doesn't have to know what it'll decay into beforehand. As long as there is a configuration with lower energy state available, a decay can happen.
  4. Aug 10, 2017 #3


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    You can calculate the probability that something decays within a given time span, e. g. a second. If you do this calculation for radioactive particles like a free neutron, you get a non-zero value in the calculation. If you do the calculation for stable particles like a free proton, you get exactly zero (at least according to known physics).
    The proton does not have to "know" the neutron mass. The proton would behave the same if there wouldn't be a concept of neutrons at all*. If there would be a possible decay, then it could happen at any time, and the probability can be calculated based on the particle properties.

    *within the scope of this thread. Please don't start with quantum field theory in a [b]-level thread.
  5. Aug 11, 2017 #4
    No, this is news to me.

    But if I understood you both correctly, it is something along the lines
    Almost like, nucleus gives away its energy in a certain frequency, throws it out and take it in again, and proton is susceptible to decay with a certain frequency, and when the probability matches, it happens.

    Sorry Sir, I have no idea what this means.
    But last time I made a post I do not remember having to choose something before posting.
    Who can tell what a question in physics might generate a kind of answer.
  6. Aug 11, 2017 #5


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    Ignore that part.
    There are some technical details where you could argue that my post is not exactly correct, but to understand them you need much more advanced physics. I made that comment to keep these details out, they wouldn't help you.
    No, that description does not work.
  7. Aug 12, 2017 #6


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    Wait, go back a few steps, even uphill if necessary. The idea that a ball will, on its own, roll downhill, is "news" to you?

    I definitely want to find out first why this is not something you already know.

  8. Aug 12, 2017 #7
    Well, would you be so kind to explain?
    I really thought that, that summarized both your posts.
    That there is a probability for something to happen. And probability happen when things match up or when physics allows it. And it would not make sense that the first time particle A in a complex system "tries" something, things goes its way. It feels like things should happen constantly, and only when allowed, it does happen. Allowed - being governed by physic law.

    Yes sir, but I maybe I did not comment that properly. It is for sure the gravitational force causing the roll.
    I gave a conservative answer due to chosen word "spontaneous".

    Thank you
  9. Aug 12, 2017 #8


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    It doesn't make any sense, I can't break that down to smaller parts.
    An unstable particle does nothing before it decays. It just stays a particle.
    There is nothing that "matches up".
    That feeling is wrong.
  10. Aug 15, 2017 #9


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    I don't understand well the questions... but there are certain properties in physics that are conserved. The conservation of energy and momentum are so strong principles into the physics community (since they've never been seen violated), that physicists at some point "discovered" a new particle thanks to wanting to keep that principle. That particle was the neutrino. So indeed, everything that is allowed can happen with some probability. Now "what is allowed or not?" is answered by everything is tested everyday.

    Yet, conservation of energy and momentum is pretty much anywhere, so you can't say "it knew beforehand", it is made to obey that since nature wants it that way. A particle doesn't know anything beforehand since there is no "conciousness of a single particle" (and you should avoid thinking or even continuing writing on those lines).. It's like trying to feed full 200 people when you only have 1 chip. It's not some kind of previous knowledge but an impossibility for you to do it. In a similar manner it's impossible for nature to "give birth" to extra energy that would be necessary for an isolated proton to decay into a neutron+positron.
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