How Many Neutrons and Protons Can Get Along? Maybe 7,000

Image: This illustration of the nuclear landscape shows atomic isotopes arranged by an increasing number of protons (up) and neutrons (right). The dark blue blocks represent stable isotopes, while the lighter blue blocks are unstable isotopes that have been observed. The gray blocks are possible isotopes that have not yet been observed. The yellow clouds represent the drip lines that bound the possible nuclides. A June 2012 study estimated total of roughly 7,000 nuclides are possible. Credit: Andy Sproles, Oak Ridge National Laboratory

Scientists have long wondered whether there is a limit to the number of protons and neutrons that can be clustered together to form the nucleus of an atom. A new study comes closer than ever to finding the answer by estimating the total number of nucleus variations that can exist.

The periodic table of elements includes 118 known species of atoms, and each of these exists (either naturally or synthetically) in several versions with differing numbers of neutrons, giving rise to a total of about 3,000 different atomic nuclei. As technology has improved over the years, physicists have been building heavier and heavier atoms — element 117 was created only last year, and researchers are hot on the trail of 119. New projects are in the works to add and subtract neutrons to known elements to create ever more exotic variations, known as isotopes.

But where does it end?

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