When helium capture occurs with a carbon 12 nucleus, the carbon 12 nucleus becomes a carbon 14 nucleus, which is a stable isotope of carbon. This process is known as carbon-14 dating and is used to determine the age of organic materials. The carbon 14 nucleus is formed through the interaction of cosmic rays with the atmosphere, which causes the helium nucleus to collide with a carbon nucleus. The resulting carbon 14 nucleus has an extra neutron, making it heavier than a carbon 12 nucleus, but it is still stable and does not decay.