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Re: [Phys-l] Electron vs. Alpha particle...



You are right that a single collision would have a negligible effect of an alpha particle. But why are alpha particles slowed down, as they travel through air, wood, aluminum, etc.? Becaus of zilions of such "collisions."

In the context of the "point particles" model the distance of minimum approach can always be calculated. It depends on the initial energy of the relative motion, and on the impact parameter. For a head-on collision the impact parameter is zero, but the distance of the minimum approach is not zero. So match for the classical model approximation of reality. That model has been used very successfully to calculate ranges of alpha particles, using an adjustable parameter (which takes under consideration non-classical effects).

Ludwik
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On Jan 12, 2011, at 5:38 PM, Jeff Loats wrote:

Hi all,

In discussing Rutherford scattering I ask students to use the simple case of
an alpha particle colliding head on with an electron at rest. The idea is to
use conservation of energy and momentum to show that in a classical
"billiard ball" model, the alpha particle can ignore electrons in its path
to a good approximation.

This term a curious student asked some great questions about what would
happen when such a collision took place.

This exceeded my knowledge a bit, so I thought I would ask here.

What would happen if an alpha particle was fired head-on at an
electron.

(I know the question is posed in an incorrect "billiard ball" fashion.)

Any insights?

Jeff
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Ludwik

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