Atomic Nuclei

Atomic nuclei come in a dizzying number of varieties. Scientists have discovered 118 chemical elements, distinguished [blank] the number of protons in their nuclei. Each of those elements has a variety of isotopes, different versions of the element formed by switching up the number of neutrons inside the nucleus. Scientists have predicted the existence of [blank] 8,000 isotopes of known elements, but only about 3,300 have made an appearance in detectors. Researchers expect FRIB will make a [blank] dent in the missing isotopes. It may identify 80 percent of possible isotopes for all the elements up through uranium, including many never seen before. The most familiar nuclei are [blank] of the roughly 250 isotopes that are stable: they don't decay to other types of atoms. The ranks of stable isotopes include the nitrogen-14 and oxygen-16 in the air we breathe and the carbon-12 found in all known living things. The number following the element's name [blank] the total number of protons and neutrons in the nucleus.