Alpha particles were deflected by the positively charged

See explanation

Explanation:

In Rutherford's experiment, a gold foil was bombarded with positively charged alpha particles. A zinc sulphide screen was used to observe the movement of the alpha particles during the experiment.

A few particles passed through without deflection while some particles were deflected through large angles.  This observation led Rutherford to the conclusion that the atom was made up of a dense positively charged nucleus where most of its mass was concentrated.

beta decay is the answer

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.