magic number

When a heavy atomic nucleus splits into two fragments, an invisible quantum thread remains between them. This thread is entanglement: the state of one fragment is instantly linked to the state of the other, as if they were still a single whole. For the first time, physicists have precisely calculated how long and strong such a thread can be, tracing the fission process step by step.

The atomic nucleus is not a bag of marbles but an ordered structure where protons and neutrons fill shells, much like electrons in an atom. When a shell is filled, the nucleus becomes especially stable, and the number of particles is called magic. For calcium with 20 protons, the classic magic neutron numbers are 20 and 28.

In nuclear physics, a puzzle has long been nagging: why among elements lighter than bismuth, only technetium (No. 43) and promethium (No. 61) have no stable isotope at all? All their neighbors in the periodic table can boast at least one long-lived variant, but these two seem to fall out of the general pattern.

At the center of every atom lies a nucleus — a dense ball of protons and neutrons. These particles don't just crowd together randomly; they fill strict energy levels, much like floors in a skyscraper. When a floor is completely filled, the nucleus becomes especially stable — physicists call this a magic number.

An atomic nucleus is not just a ball of protons and neutrons. It has a shape, and that shape can change. The tin-116 nucleus was long considered almost perfectly spherical: it has 50 protons — a 'magic' number that usually gives a nucleus spherical symmetry. But a new ultra-precise measurement showed otherwise.

The atomic nucleus is not just a jumble of protons and neutrons. The particles inside arrange themselves in layers, like spectators in a stadium: the lower rows are filled, and each new proton or neutron looks for a spot on a higher tier. When a row is completely filled, the nucleus becomes especially stable — physicists call this a magic number.

The atomic nucleus is not a solid ball but a dense swarm of tiny particles called quarks, glued together by a special glue (the strong force). In light nuclei, such as calcium, this swarm is simply arranged: the numbers of the two quark types, up and down, are almost equal, like the white and black keys in an octave.

An ordinary atomic nucleus is like a tight ball: protons and neutrons are packed closely together. But some light nuclei, such as helium-6, are different. Two neutrons seem to step aside and form a dilute cloud around the nucleus — called a halo.

Inside an atom's nucleus, protons and neutrons stack in layers, like spectators in a packed hall. When a layer is full, the nucleus becomes especially stable — physicists call these 'full rows' magic numbers. One of them, 32, has long been elusive: in nuclei with 32 neutrons, its effect is weak, and in some neighbors it seems absent altogether.

When matter accumulates on the surface of a neutron star, the ultra-dense remnant of a dead star, an explosion occurs, akin to a giant thermonuclear bomb. In this inferno, nuclei of elements not found on Earth are born within seconds. To understand which ones, their masses must be known with great precision.

A bell doesn't ring with a single note — after being struck, it sounds with several harmonics at once. An atomic nucleus vibrates in much the same way: after a collision, it can oscillate, and these oscillations show up in the emitted gamma rays.

Like long-distance runners, atomic nuclei, from light helium to heavy iron, race toward us across the Galaxy. At the finish line, in a detector on a high-altitude balloon, we see that heavy nuclei arrive a bit more exhausted than light ones. The difference is small, but it repeats from flight to flight.

High above Earth, a satellite flies, and inside it is an instrument the size of a small wardrobe. It catches particles that have been racing through the galaxy for billions of years and finally slam into the detector. Such particles are called cosmic rays, and they bring news of distant stellar explosions.

High above the Antarctic ice sheet, a balloon with a detector floated for twenty days. It caught tiny particles that had been traveling toward us for millions of years from distant stellar explosions. Now scientists have sorted through the catch and reported how much energy the protons and nuclei of different elements carried.