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What is particle spin , and does it have anything to do with radio activity?

  1. Aug 18, 2003 #1
    What is particle "spin", and does it have anything to do with radio activity?

    I keep hearing about the "spin" of sub-atomic particles like such-and-such particle has a spin of 1/2 or 1. I heard even some have a spin of 2. And it also seems that I have heard that some radioactive particles have a higher spin (or lower - don't remember) than normal. Is this scorce on crack, or can you back-up/explain any of this? I'm just curious.
  2. jcsd
  3. Aug 18, 2003 #2
    Spin is a intrinsic property of the particle, like its mass. And it has nothing to do with radioactivity. Isospin, might have somehting to do with radioactivity, but I can't rrecal off the top of my head

  4. Aug 18, 2003 #3


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    Spin is the intrinisic angular momentum of a particle or group of particles, which is in additon to it's angular momntum due to it's orbital motion.

    Isopin's a little bit different as it only possesd by hadrons and is always conserved in strong interactions but not electromgnetic interactions.
  5. Aug 18, 2003 #4


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    I don't think quantum spin is really the same as spin as we traditionally thing. I think we know it possesses a strong relativistic element, and that the "spin" analogy is sometimes useful, but it is important to remember it isn't the same.

    By spin 1 or 0.5, we really mean 1 * hbar or 0.5 * hbar. Whether the particle has integer spin or half-integer spin is very influential on it's behaviour. Integer spin particles (eg. photons) are called bosons, follow the laws know as Bose-Einstein statistics, while half integer spins are called Fermions (eg. electrons) and follow Fermi-Dirac statistics.

    If I remember correctly, of course.

    EDIT: which I don't, because I am an idiot.

    The units of spin are of course in 1/2 * hbar, where hbar = h/(2*pi). Ie a particle with +1 units of spin has really +1 * 0.5 * h/2pi, which preserves the uncertainty principle.

    I hope that's right.
    Last edited: Aug 19, 2003
  6. Aug 18, 2003 #5
    Spin is the change of quantum mechanical phase with change of plane angle, and as F.Z. says it has to do with relativity too. Special relativity allows boosts (accelerations) and turns in the three space dimensions, for spin 1/2 states, boosts change the modulus of the amplitude, turns change the phase of the amplitude. The Dirac γ matrices describe these changes.
  7. Aug 18, 2003 #6


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    No it is sort of the same as angular momentum, as I said before tit contributes to the total angular momentum of a particle along with it's orbital angular momentum, though sometimes it is of treated as the particle spinning on it's axis, this is not actually the case it's just an intrinsic property of that particle.

    Also spin is actually given by √s(s+1)h/2π, where s is the spin quantum number which is usually a half or an integer.
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