# What would happen if the alpha particles directly hit the electrons in the gold foil in Rutherford's experiment? [closed]

What would happen if the alpha particles directly hit the electrons in the gold foil in Rutherford's experiment? Would it get ionized or is there no probability of such a thing happening ?

• An energetic charged ion in a solid will come to an equilibrium charge state, based on the Z of the ion and the velocity of the ion. There are plenty of ion-electron interactions (they are Rutherford scattering as well) that result in energy loss. Jun 10 '21 at 18:49

The alpha particles used in this experiment have an energy of about $$5.59\ \mathrm{MeV}$$. This energy is too high; the alpha particle cannot simply capture two electrons and form a stable helium atom. By way of comparison, the first and second ionization energy of helium is $$24.6\ \mathrm{eV}$$ and $$54.4\ \mathrm{eV}$$, respectively.

Nevertheless, alpha particles cause frequent direct ionizations within a narrow diameter around a relatively straight track. This transfer of energy from the alpha particles to electrons causes an approximately continuous deceleration of the alpha particle. For $$5.59\ \mathrm{MeV}$$ alpha particles in gold, the initial electronic stopping power is about $$220\ \mathrm{MeV\ cm^2\ g^{-1}}$$. With a high density of $$19.3\ \mathrm{g\ cm^{-3}}$$, this means the initial linear energy transfer is about $$4200\ \mathrm{MeV\ cm^{-1}}$$. Therefore, the alpha particle loses its energy very quickly so that the range of the alpha particle in gold is very short. The continuous slowing down approximation (CSDA) range of $$5.59\ \mathrm{MeV}$$ alpha particles in gold is about $$0.020\ \mathrm{g\ cm^{-2}}$$. Considering the density of $$19.3\ \mathrm{g\ cm^{-3}}$$ again, the resulting range in gold is about $$0.0010\ \mathrm{cm}$$. (Clearly, the gold foil in the experiment had to be very thin.)

Only after the alpha particle has slowed down like this, it can finally capture two electrons and form a stable helium atom.

• IS IT POSSIBLE FOR ALPHA PARTICLE TO HIT THE GOLD ELECTRONS AND GET IONIZED AS THEY MOVE IN A VERY HIGH SPEED AND THEY DON'T GET THE SUFFICIENT TIME FOR ATTRACTING EACH OTHER ? Jun 12 '21 at 4:41
• @RitabantaGhosh No. It is obviously not possible for alpha particles to get ionized any further since they are already fully ionized $\ce{He^{2+}}$ and don't have any electrons left. And please don't use all caps. Jun 12 '21 at 8:39
• Can the alpha particles get neutral by accepting electrons ? Jun 15 '21 at 3:03

An alpha particle is basically a helium nucleus, with two positively charged protons and no electrons, the particle would react with any electrons it comes into contact with. However it likely depends on which electron it interacts with, and how close the particle comes that determine the outcome.

As ScienceDirect describes here -

In some cases, this force is not sufficient to separate the electron from the atom, but the electron is raised to a higher energy state and the atom is said to be “excited.” In other cases, the attractive force is sufficient to remove the electron from the atom (ionization). The closer an alpha particle passes near an electron the stronger the force and the higher the probability an ionizing event will occur.

In Layman's words, as the alpha particle gets closer to the electron, the more likely it is to take the electron from its orbital for itself. Electrons further form the nucleus of the gold atoms in the sheet would have been easier to ionize, as they'd have les ionisation energy.

• The alpha particle causes many ionizations, but that doesn't mean that it can take the electrons for itself. Otherwise, the interactions would already stop after two ionizations. Jun 10 '21 at 17:17
• The sciencedirect aggregation things are a bit dubious, I must say. I really don't like it. Sure, you are getting text from papers, but you don't see any of the context that surrounds it, and that's often critical to understanding a paper. I firmly believe that you can't learn stuff by reading random paragraphs from random papers. Jun 11 '21 at 15:20
• I see... apologies for any inconveniences, I'll use multiple more reliable sources in any future answers. Jun 12 '21 at 16:05