In every instance where an unstable isotope undergoes radioactive decay, one or more atoms with a different number of protons than the decaying atom are created. According to the Purdue University College of Science Chemical Education Division Group, this takes a variety of forms, from alpha decay where a helium nucleus is released, to beta decay where an electron or positron is emitted, or an electron is absorbed.
Spontaneous fission, where one large atom splits into two of similar size, also occurs. Radioactive decay is actually the source of many materials humans use every day. Helium, for instance, is both lighter than air and quite inert, so once released it escapes the atmosphere readily. New sources of helium are actually mined, trapped underground after being produced by alpha decay of unstable isotopes as explained by the Purdue University College of Science Chemical Education Division Group. Uranium-238 is one isotope that produces helium, with thorium as the other byproduct.
One type of beta decay emits electrons from the nucleus, as with the conversion of potassium-40 to calcium. The electron is emitted from an unstable neutron, which then changes into a proton, changing the element. The reverse can also happen with potassium-40 in another type of beta decay, where the atom absorbs an electron into a proton, changing the proton to a neutron and becoming argon. The final type of beta decay, which again is illustrated with potassium-40 atom becoming an argon atom, involves the release of a positron, transforming a proton into a neutron.