Uranium-238 decays into thorium-234. how do scientists explain why this happens

When an atom has more neutrons in the nucleus than protons, it is said to be unstable. The benchmark element for this is Iron. Iron is the most stable in nature. Logically, elements lighter than Iron undergo nuclear fusion (combining), while elements heavier than ion undergo nuclear fission (breaking). These elements spontaneously decay by giving off sub-atomic particles.

U-238 means that the Uranium isotope contains 238 neutrons and protons. We know that the atomic number of Uranium is equal to 92. Therefore, the number of neutrons is: 238 - 92 = 146 neutrons. So, U-238 contains 92 protons and 146 neutrons. Similarly, Thorium-234 having an atomic number of 90 will have an amount of neutrons equal to: 234 - 90 = 144 neutrons. Let's compare the difference between U-238 and Th-234:

Protons: 92 → 90

Neutrons: 146 → 144

Therefore, for U-238 to transform to Th-234, it must give off 2 protons and 2 neutrons. This is a characteristic of alpha decay or alpha radiation. It gives off an alpha particle during nuclear fission. An alpha particle is simply a Helium atom, which contains 2 protons and 2 neutrons.