The Heavy Ion Accelerator — Making Nuclei That Do Not Exist

Not looking — colliding

A nucleus is far too small to see. It is smaller than the ripples of light itself, so light simply passes it by. That leaves one approach: throw something at it and watch how it bounces.

About a century ago this method revealed that an atom is mostly empty with something very hard at the centre. Particles fired at thin gold foil nearly all went straight through — and just occasionally one came back.

An accelerator is that same method built much larger and much harder. The harder you throw, the deeper you see.

How you push it

Strip a few electrons from an atom and what remains carries positive charge — and anything charged can be pushed electrically. Push once, wait, push again, push again. It is the rhythm of pushing a swing: each push in time adds to the last.

Pushing is not enough. The beam has to be bent onto the path you want and gathered so it does not spread. Magnets do that. An accelerator is therefore a long row of pushers and bending magnets.

A hundred million degrees, and 269 below

The magnets must be very strong, and ordinary wire cannot do it: current heats wire, and more current heats it more, until it fails.

But some materials, made cold enough, lose their resistance entirely. Nothing heats up, so the current can be as large as you like. This is superconductivity — at the price of chilling the thing to around 269 degrees below zero.

The fusion machine in the previous article struggles to reach a hundred million degrees. This machine struggles in the opposite direction. The hottest and the coldest things in the universe are both in Daejeon.

What comes out of a collision

When nuclei strike hard enough they shatter, and among the fragments is what we came for: rare isotopes.

Isotopes are the same element at different weights. A nucleus holds protons and neutrons; the proton count fixes which element it is. Change only the neutrons and you have the same name on a different body.

Rare isotopes are the ones that do not occur in nature at all, or vanish almost the instant they form. RAON exists to make them briefly and measure them before they go.

A little further in

Why make what does not exist

Where did gold come from? Not from Earth. Stars made it — inside them, and in the moments they are torn apart.

That process runs through intermediate steps: light nuclei swallowing neutron after neutron on the way to becoming heavy. Almost all of those way-stations are rare isotopes that nature does not keep, because they turn into something else at once.

So to know how gold was made you need the properties of those way-stations — and the universe will not show you the moment. You make it here instead, briefly. An accelerator is in the end a way of re-staging one instant inside a star.

What makes RAON different

There are two ways to make rare isotopes: accelerate light ions into a heavy target, or accelerate heavy ions into a light one. The first makes it easier to sort out what you produced; the second can catch things that live a very short time.

Most accelerators in the world use one or the other. RAON was built to chain them: make rare isotopes by the first route, then accelerate those and strike again. That reaches rarer things than either route alone, and RAON is the first to attempt the combination.

If an element nobody has seen turns up here, there is talk of calling it koreanium — by custom the discoverers name it.

Honestly, it is half-built

The project took more than a decade and slipped repeatedly. The low-energy section is finished and producing beam, and universities and institutes have begun using it for nuclear and astrophysics experiments. The high-energy section is not yet built.

RAON is therefore not a finished facility but a half-finished one already at work. Large scientific facilities usually are: you use what stands while you build the rest.

What you would study to do this

One accelerator needs far more than nuclear physics.

1. Someone who decides what to strike and what to look for — nuclear and astrophysics.
2. Someone who designs how the particles are pushed and gathered — accelerator physics.
3. Someone who reaches 269 below and holds it — cryogenics and superconductivity.
4. Someone who empties 550 metres and keeps the structure standing — mechanical and vacuum engineering.
5. Someone who catches the fragments and sifts the flood of data — detectors and computing.

That is the quiet virtue of a large facility. It is not only for people who were good at physics. Making things cold, making them empty, handling the data — all needed, and all just as hard.

RAON is run by the Institute for Rare Isotope Science under the Institute for Basic Science. It sits not in Daedeok Science Town but in the Sindong district to its north — the lone dot above the others when you open Daejeon on the map.

The question that remainsIf nature can only be understood after we briefly manufacture what nature does not keep — how much of what we call nature is found, and how much is made?