Determine the size of nuclei

2011-04-03 10:15 pm

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Q : I don't understand why by using the eq. loss KE= gain in PE can determine the upper limit size of nucleus (=r) as the speed of a-particle can be varied and the pt. where the KE of a-particle is zero can be any other pt. where the distance is larger than the upper limit size of nucleus

(i.e. 1.KE of a-particle is unknown (OR equal to 0.1c ??) and 2.the pt. where a-particle KE=0 may not necersary at the upper limit size of nucleus (=r) if the charges of nucleus is great, a greater electrostatic replusive force exert on a-particle and a-particle loss all KE before reaching to r) OR my deductions are wrong?

THX FOR HELP!

回答 (1)

天同

2011-04-03 11:42 pm

✔ 最佳答案

The use of the equation: KE loss = PE gain is just a result of the Law of Conservation of Energy when applied to electrostatics.

1.No, this is not true. The energy of alpha particles from a given radionuclides is well known. Alpha particles display a "line sprectrum" instead of a "broad spectrum" as in the case of beta particles. All alpha particles coming from a specific radioanuclide have the same energy.

Examples, Americium-241, alpha particle energy = 5.485 MeV; Polonium-201, alpha particle energy = 5.304 MeV

2. The charge on the nuclide has already been taken care of in the equation by the "atomic number Z". The equation applies to alpha paticles approaching the nucleus along a "head-on" collision path. The value of r thus gives the nearest distance from the centre of the nucleus that an alpha particle could reach. Hence, it is the "upper limit" of the size of the nucleus.

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