Magic numbers” of protons and neutrons can make an atomic nucleus exceptionally stable—and a new one has just been added to the existing menagerie that helps sketch a fuller picture of the complicated inner workings of atoms. By smashing beams of nuclei together at high speeds, researchers have discovered that when a calcium atom has 34 neutrons in its nucleus, things stay pretty quiet—at least for a few milliseconds. The discovery overturns some of scientists’ previous notions about magic numbers and opens up a new line of inquiry for nuclear physics.
Inside nuclei, protons and neutrons fill up separate buckets—called shells—with each shell characterized by a different energy level that can accommodate only a certain number of particles. A nucleus holds a magic number of protons or neutrons when the particles completely fill its shells without any room left for adding more, rendering it stable and longer-lived than other nuclei. But magic numbers don’t behave quite as expected when too many neutrons are packed in relative to the number of protons. (Most stable versions of elements, called isotopes, have roughly equal numbers of protons and neutrons.)
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