Talk:Rutherford scattering
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[edit] Errors in article
The section "Details of calculating nuclear size" doesn't seem to match what Rutherford actually did (see the link to his paper at the bottom of the article). The calculation doesn't make much sense anyway, since:
- (1) It assumes without justification that the alpha particles don't penetrate the nucleus
- (2) It only deals with particles that are colliding head-on with the nucleus (Rutherford's actual calculation considers deflection by an angle)
- (3) It makes the "size of the nucleus" dependent on the velocity of the alpha particles. Rutherford was interested in how spread out the nuclear charge was in the atom, which has nothing to do with the velocity of the alpha particles (which aren't even part of the atom)
- (4) It makes no mention of the small number of large angle deflections, contradicting the claim earlier in the article that this piece of data was how Rutherford knew the nucleus was small.
- (5) At best, it could only be an upper bound estimate -- but there's no reason to think it's a good one unless the alpha particles have nearly the energy they'd need to penetrate the nucleus. No justification is given for this assumption.
Either the section needs to be removed, or reworked to address these issues. Either way, unless someone can show it's what Rutherford actually did, it's not relevant to this article. The cited paper of Rutherford's gives an estimate of b (not the estimate given in the article, since Rutherford used a different value of the nuclear charge) but it doesn't claim that b is the size of the nucleus. It just argues that the nucleus is small and localized to the center of the atom, based on various calculations showing that this assumption matches the data on what fraction of particles were deflected by various angles.
Reply: Yes, the mentioned section is indeed wrong, in particular the calculation. The particle is definitely *not* at rest at the point closest to the nucleus, it only has tangential velocity.
- Actually, I'm quite sure that at closest approach, the alpha particle momentarily has a velocity of 0. Also, if I'm not mistaken, what the article is calculating is the distance of closest approach. ie, the closest distance between an alpha particle and a gold nucleus colliding head on, which then gives the upper bound for the size of the nucleus. So it seems to make sense if you read it carefully. No? Cjsk 13:02, 19 November 2006 (UTC)
