42. Two types of isotopes occur in nature, stable and radioactive. All the atoms
of an isotope have the same number of protons in their nuclei; thus, they
have the same atomic weight. Radioactive isotopes, however, are capable
of emitting, or radiating, alpha particles or beta particles from their nuclei,
which reduces the atomic weight. Depending on the type of particle emitted,
the atomic number may also be reduced. When such radiation occurs, the
original element is changed into another element of lower atomic weight.
The reduction in mass of the atom releases energy in the form of gamma
radiation. Since the radioactive isotopes emit particles, they are in a
The two types of isotopes occurring in nature are ___________________
and ________________________ .