isotope

Inside an atomic nucleus, protons and neutrons don't sit still like peas in a pod. Each particle occupies its own orbit — a region of space where it can be found. The larger the orbit, the more 'smeared out' the particle is.

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.

The atomic nucleus isn't always round like a billiard ball. Some nuclei stretch out like a rugby ball, while others become pear-shaped — with one end thicker than the other.

The atomic nucleus is usually pictured as a dense ball where protons and neutrons are mixed together. But in some isotopes, neutrons can stick out far beyond this ball, forming a diffuse shell — a neutron halo. This is especially common in nuclei with many more neutrons than protons.

A copper oxide crystal looks like a dark red pebble. But when a short laser pulse hits it, pairs are born inside: an electron and a 'hole'—a place where an electron is missing. Such a pair is called an exciton and behaves almost like a hydrogen atom: the particles circle each other, bound by electric attraction.

A uranium-235 nucleus that captures a slow neutron doesn't immediately fly apart into fragments. Instead, it seems to get stuck in two 'pits'—states with different shapes. The first, the ground state, is a slightly elongated drop. The second, the isomeric state, is a drop stretched further but not yet torn.

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.

In a quiet room, you can hear the faintest whisper. Likewise, in the hydrogen atom, the lightest of all, an uninvited guest is easier to spot. That guest could be the Z' boson, a mediator particle of a new force predicted by many unification theories. The Standard Model already has its own mediator — the Z boson.

In nuclear physics, the belief long reigned that two neutrons cannot form a bound state — they attract too weakly and immediately fly apart. However, on the surface of neutron-rich nuclei, where the matter density drops to a thousandth of normal nuclear density, the situation changes dramatically.

An atomic nucleus is like a crowded bus. To free up space, a group of two protons and two neutrons — a helium nucleus, an alpha particle — exits through the front door: this is alpha decay, described by George Gamow as tunneling under an energy barrier.

The atomic nucleus is not a billiard ball but rather a hazy cloud that constantly changes its contours. Protons and neutrons inside are in continuous motion, and the nucleus can take on many different shapes: elongated, flattened, or pear-like. To describe this quivering diversity, physicists usually picked a few most probable shapes and mixed them, like an artist mixing paints on a palette.

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.

Usually, isotopes are separated by exploiting the difference in nuclear weight. That difference is tiny, like sorting grains of sand that differ by one hundredth of a millimeter. The new method ignores weight and instead looks at the nucleus's rotation: its spin. The laser hits the molecules twice with a short pause in between.

Two tin nuclei collide at about two-thirds the speed of light. For an instant, a hot, dense cloud forms, and protons fly out in all directions. If you catch pairs of protons and measure how often they fly off in the same direction, you can work out the size of that cloud. This method is called femtoscopy: it works like a microscope for nuclear scales.

An ordinary crystal is like an apartment building: electrons move through shared hallways and staircases, influencing each other through the walls. Now, imagine removing all the walls, leaving just a single line of apartments. How would the residents behave? Hydrogen has nothing to do with it, but the collective behavior of electrons takes center stage.

Every molecule is like a set of building blocks: the same pieces can be assembled in different ways. Two assemblies with the same atoms but different geometry are called isomers. If one can be turned into the other by a simple rotation around a bond, they are conformers, like a bent arm versus a straight one.

When a baker kneads dough, the grains of flour can tell you which mill they came from. It's the same with Earth: the composition of iron in its depths preserves a memory of where the pieces that assembled the planet were born.

An electron in an atom is like a note on a string: it has a set of allowed energies, and the physicist's task is to find these notes. Usually, the space around the nucleus is divided into small pieces and the behavior of the electron in each piece is calculated. The finer the pieces, the more accurate the answer.

An atomic nucleus isn't always round. It can stretch out like a melon or flatten like a pumpkin. And its size depends on this shape — just as the size of a pie depends on the shape of the dough. Scientists calculated the shapes and sizes of nuclei of berkelium isotopes — a heavy element produced in reactors.

The atomic nucleus isn't a frozen ball but a seething collective of protons and neutrons. They whirl, collide, and arrange themselves into patterns that physicists see as "bands"—ladders of energy levels. In niobium and technetium nuclei, four such ladders have been found, but the last one stubbornly refused to fit the calculations.

Deep inside a dying star, just before it goes supernova, nuclear reactions determine which chemical elements will be scattered across the cosmos. One such reaction is the collision of an oxygen nucleus with a proton, producing a nitrogen nucleus and an alpha particle (a helium nucleus).

In collisions of heavy nuclei, a fireball of thousands of particles is born. Among them are pions and kaons, two kinds of light particles that look very much alike. To understand what happens in this fireball, physicists need to know exactly how many of each particle flew out.

An atomic nucleus usually lives in a single energy state, like a ball resting on the floor. But thorium-229 has a rare exception: the nucleus can get stuck on a tiny step above the floor — the so-called isomeric state. This step is so low that it can be nudged by ordinary light, not just hard radiation.

Every year, in the United States alone, doctors perform more than 16 million scans using the radioactive isotope technetium-99m. It lights up the heart, bones, and lungs in images, helping to find tumors or check blood flow. But the isotope itself has a half-life of only six hours, so you can't stockpile it: you need a steady supply.

The neutron is a particle with no charge but with internal structure. Like a ball that looks smooth on the outside but has a complex filling inside. Scientists have long wanted to understand how electric and magnetic forces are distributed inside the neutron. To do this, you need to "feel" it — collide it with its antiparticle and see what happens.

Neutrons in an atomic nucleus aren't all held equally tight. If you peel them off one by one, like leaves from a cabbage, the energy required changes each time. For isotopes with 149 particles in the nucleus (lanthanum, cerium, praseodymium), this energy has just been remeasured, and one number didn't match the previous value.

When an extra neutron is added to an atomic nucleus, it starts behaving like an overfilled cup: one more drop and it spills over. Physicists at the French facility GANIL orchestrated such a 'pass' of a neutron from a deuteron (the nucleus of heavy hydrogen) to an oxygen-19 nucleus.

Deep inside stars, light nuclei fuse, giving birth to helium and streams of neutrons. On Earth, we recreate this process by combining deuterium and tritium — special isotopes of hydrogen.

Light consists of portions — photons. Max Planck was the first to understand that light is emitted in quanta. Today, we can guide single photons. When such a photon encounters a fast shutter, it cannot be sliced — half a photon doesn't exist. Instead, a quantum mixture of states with different photon numbers emerges: zero, one, two, three..

Atoms, like a swarm of fireflies, shine in unison. When they flash together, the light multiplies — a hundred atoms shine ten thousand times brighter than one. Physicists have turned this trick into a heat engine. A typical motor needs both a hot and a cold source, but here the atoms operate with just a cold one.