When radioactive uranium decays to produce thorium, it also emits a particle. As seen in the balanced nuclear equation, this particle can BEST be described as

The decay of uranium to thorium has been best described as the alpha decay.

The nuclear decay has been given as the decomposition of the atom by emitting radiations. The emission has been responsible for the change in the nucleus of the atom to the daughter nuclei with smaller mass.

The decay of Uranium to thorium has been the spontaneous alpha decay. There has been the loss in the mass of uranium in the form of energy, resulting on the thorium nucleus.

Thus, the decay of uranium to thorium has been best described as the alpha decay.

For more information about the nuclear decay, refer to the link:

link

an alpha particle or helium nucleus

Explanation:

Uranium spontaneously undergoes alpha decay. During an alpha decay, the uranium nucleus spontaneously decays to produce a thorium nucleus, alpha particles and energy.

The balanced nuclear equation is shown in the image attached to this answer for clarity.