The members of the family of uranium 238, therefore, have 4n+2 nucleons, whereas uranium 235 has 4n+3 and thorium 232 has 4n. In principle, the fourth family (4n+1) should exist, but the ancestor, neptunium 237, has a relatively ‘very short’ half-life of 2.14 million years. As a result, this family has had ample time to disappear since the nucleosynthesis of neptunium 237 at the heart of the stars which preceded our Sun.