I was studying Rutherford's gold foil experiment from my high school textbook. It states that ' by performing experiments in which fast electrons instead of alpha particles are projectiles that bombard target made up of various elements the sizes of nuclei of various elements have been accurately measured.' I am totally confused with this statement. I know that original experiment used the fact that distance of closest approach for the alpha particles was used to infer the size of nucleus. But how electrons can lead to more accurate results? What I would think and what I have found from other sources is something like this.... If electrons were used then they due to their size and charge they would have got easily affected by the electrons of the atom that come in their way. In fact due to the fact that alpha particles are positively charged and have significant mass they could overcome the interactions with the electrons. Then what the author intends to say. Or what is wrong with my thought process? Someone please explain.
2 Answers
This link and links therein should help:
The scattering of electrons from nuclei has given us the most precise information about nuclear size and charge distribution. The electron is a better nuclear probe than the alpha particles of Rutherford scattering because it is a point particle and can penetrate the nucleus.
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For low energies and under conditions where the electron does not penetrate the nucleus, the electron scattering can be described by the Rutherford formula.
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As the energy of the electrons is raised enough to make them an effective nuclear probe, a number of other effects become significant, and the scattering behavior diverges from the Rutherford formula. The probing electrons are relativistic, they produce significant nuclear recoil, and they interact via their magnetic moment as well as by their charge. When the magnetic moment and recoil are taken into account, the expression is called the Mott cross section
It is that energetic electrons are used as the probe for the nucleus. The probability for the electron to scatter off the electrons of the atoms is small, and gets smaller as the energy gets higher. The orbitals are mostly empty space for a high energy electron.
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$\begingroup$ But how the penetration power of high energy electrons useful for inference of some information about the nucleus? ... Thank you. $\endgroup$– gksFeb 1, 2019 at 8:03
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$\begingroup$ The electrons scatter on the electric fields of the nucleus , as the formula in the link says.The electron has a negative charge, when it hits a nucleus it scatters off its positive charge and the scattering can be predicted . the nuclei have dimensions of order fermi, $10^-15$, the electron is a point particle so the scatterings can define the size of the nuecleus using a fit to the scattering data. the nuclear mass enters the Mott crossection. $\endgroup$– anna vFeb 1, 2019 at 12:55
Electrons are preferable because, unlike alpha particles, they are point-like particles and only interact with nuclei electromagnetically, so interpretation of experimental results is easier. Small electron mass can be compensated by higher energy (for example, energy of alpha particles in Rutherford's experiments was about 8 MeV, energy of electrons in Hofstadter's experiments was about 200 MeV).
