Energy Release in Nuclear Fusion

When you have two atoms of the same element, and these two atoms have different numbers of neutrons, the two atoms have just about the same chemical properties. However, their nuclear properties are quite different. These two atoms are called nuclear isotopes.

All nuclear isotopes of a single element form a set of nuclides. The terms 'isotope' and 'nuclide' only differ in their conventional usage; isotope refers to any of the different nuclei of an element, and nuclide refers to one specific nucleus of an element. The terms 'isotope' and 'nuclide' are often used interchangeably.

When you have two atoms from two different elements, and they have the same mass number, the two atoms are called isobars. Boron-12 (¹²B) and carbon-12 (¹²C) are isobars because they are two different elements, but they have the same number of neutrons.