Why do large atoms eject alphas?

Question

Why not 1 neutron attached to 2 protons?
Or 1 proton attached to 2 neutrons?

Why does it always have to be 2 neutrons and 2 protons attached to each other???

Two of them were tied for best answer in my opinion so I had no choice but to put it to a vote. Sorry.

Answer 1

Well, "always" is a pretty large set of circumstances. Large atoms also emit betas and gammas and the occasional neutron but that's not your question.

The answer has to do with stability of the resulting nuclei. In general, an atom that emits an alpha is trying to reach a configuration where the proton to neutron ratio gives it more stability. The particle that is ejected also need to be stable

1 proton plus 2 neutrons is deuterium - and this is, simply, quite rare in the universe. 2 protons plus one neutron is helium3 - again quite rare. The most "reasonable" particle is helium4 - and that's the 2 plus 2 configuration that you have observed.

This is highly simplistic - for more, refer to any good text on nuclear decay

Answer 2

Atoms occur in Nature as Isotopes.That means the Nucleus of the atom is a little too heavy to remain in that structure relative to the pressure of space.
Therefore the nucleus loses some of that excess mass to form a more stable nucleus and atom.
Two neutrons and two protons form a Nucleus which is the core of the Helium atom.It is basically an ioniozed Helium atom. The radiation of nucleii dont eject an hydrogen atom. The masses that nucleii can eject occurs out of balanced pairs which is a proton and neutron .
The Number of neutron radiated depends on the type of isotope. We use free neutrons to create Nuclear fisson.
The Nucleus atoms are in stable formation if its number of protons and neutrons fall into the Magic Numbers in the shells of the Nucleus.

Answer 3

The nuclei of atoms consist of protons and neutrons. An alpha particle is made of two of each. So the stuff to form an alpha pre-exists in the core of all atoms except hydrogen, which has only one proton at its core.

Two of the four fundamental forces of nature are the strong and weak atomic forces. Combined, these two very short-ranged forces hold the nuclei together. They are the glue so to speak.

But as the number of positively charged protons increases (i.e., higher atomic numbers on the atomic chart) the weak and strong atomic forces are less able to counteract the repulsive forces of the protons. Thus, at the higher atomic numbers, the elements are increasingly unstable. (For the most part...however, there are "islands" of stability at the high end according to E.O. Lawrence, but that's another story.)

Thus, the very stable helium atom splits off the large unstable parent atom as an alpha particle. Helium (He) consists of two protons and two neutrons. Because it is at the low end of the atomic numbers (2), it is very stable and no further disintegration is likely. In fact, a reason He splits off, and not some other particle, is because it is so stable.

Answer 4

For the best illustration of the tendency for decay, see any discussion on your experience level on the Weizsacker semi-empirical formula. From it, you will see the energetic favorability of alpha decay for atoms with mass number over 191. The answers to your specific question can also be settled on energetic grounds using that formula. It calculates the nuclear binding energy, not precise but th trends are correct by the nature of its construction. If you have a physics background, perhaps you might try to locate a book by Blatt and Weisskopf on theoretical nuclear physics. Not sure if it is still in print. I used it decades ago and it seemed excellent then.