Why are there atomic clocks but no nuclear clocks? After all, an atom's nucleus is typically surrounded by many electrons, so in principle it should be less susceptible to outside noise (in the form of light). A nucleus, for high-atomic number atoms, contains more particles than does the element's electrons. It holds nearly the entire mass of the atom while taking up only about 1/100,000th of the atom's space. While the first atomic clock was invented in 1949, no nuclear clock has yet been feasible.