What does an alpha decay look like?

Answer 1

It can be difficult to visualize something so small that it cannot be seen directly with any light-based instrument. But we can make a stab at it, so let's do that.

An atomic nucleus is tiny beyond anything we've ever seen. It's really, really small. But picture a fuzzy sphere hanging in space. (The electrons will not be part of the picture because they are far, far away on the scale in which an atomic nucleus would be visible.) There's a little vibrating fuzzy sphere, and something is happening to it. Is it changing shape in subtle ways?

A very short distance from the nucleus, we'll see a tiny fuzzy sphere appear almost out of nowhere. That's the alpha particle, and its much smaller than the nucleus. It is composed of a pair of protons and a pair of neutrons bound together. It's a helium-4 nucleus, but you may have figured that out. The reason it seems to "magically appear" near the nucleus is because the alpha particle is believed to escape the nucleus via the mechanism of quantum mechanical tunneling. In one moment, the nucleus is whole, though it is unstable, and the next instant it has lost some of its mass and the alpha particle appears. That little alpha particle has tunneled out of the nucleus and was not seen actually exiting the mass of that nucleus. We might add that the nucleus has just undergone a nuclear transformation, and we call it nuclear transmutation. Where one chemical element existed before, another one that is two atomic numbers down on the Periodic Table will be left.

That alpha particle, the one that slipped unseen from the nucleus, will appear, but it won't be still. It will materialize and be off in a flash. It comes away with a tremendous amount of kinetic energy. It's really moving! It will rocket out away from the nucleus and blow through the electron cloud like it wasn't even there. It's a helium-4 nucleus as we mentioned, and its a nucleus without electrons, but it is moving far too quickly to have a high probability of "capturing" any electrons from the atom from which it arose. It isn't taking any "baggage" with it. There will be some "shape changes" in the nucleus of the atom that the alpha particle left, but it ends up a bit smaller and as indistinct in our view as it was in the beginning.

Following the alpha particle farther out, we'll see that little guy slamming into air or whatever else is in its way. These "collisions" will be scattering events, and atoms will be ionized in the process. If any solid material is present, the alpha particle will pretty much be hammered into a stop. Alpha particles don't have a lot of penetrating power. A piece of paper will block them. The alpha particle will then snatch a couple of electrons from just about anywhere around it, and the "transformation" of that alpha particle into a helium-4 atom will be complete.

Answer 2

Alpha decay is the emission of a helium atomic nucleus.