Which change occurs when an atom undergoes alpha decay? The nucleus loses mass and a new element is produced.
The nucleus gains a proton and a new element is produced.
The nucleus loses energy and remains the same element.
The nucleus loses a neutron and remains the same element.

In alpha decay, an alpha particle (a helium nucleus) is emitted from the radioactive atom, and the atom therefore loses
2 protons, and becomes a new element.

Loss of Small Particles from the Nucleus

The nucleus of an unstable isotope can lose one of several particles:
Neutron (n)
Loss of a neutron gives a different isotope of the same element. The atomic number (number of protons, determining the element) remains the same but the atomic mass reduces by about 1 amu.

Alpha particle ()
An alpha particle is a helium nucleus, 2 protons and 2 neutrons, loss of an alpha particle give a new element with an atomic number 2 less than the original isotope and an atomic mass that is lower by about 4 amu.

Beta minus particle ()
This is an electron. An electron can be lost from the nucleus when one of the neutrons in that nucleus splits into a proton and an electron. Beta decay forms a new isotope with an atomic mass greater by 1 than the original isotope but the atomic mass is nearly unchanged.

Beta plus particle ()
This is a positron and it results from a proton in the nucleus splitting into a positron and a neutron. When the positron leaves the nucleus it always collides with an electron, annialating both in a burst of gamma radiation. Loss of a beta plus particle gives a new element with an atomic number 1 less than the original isotope and an atomic mass that is nearly unchanged.

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