Physicists who uncovered the first particle accelerator were honored with a Nobel Prize 75 years ago – their work shaped physics, medicine and even art research

While scientists are known for their dedication to their research, crawling on the floor to avoid electrocution for the sake of a measurement seems a little excessive. But this is what British physicist John Cockcroft and Irish physicist Ernest T.S. Walton had to do in the early 1930s while studying the structure of atomic nuclei. Luckily, their efforts led to their receiving the Nobel Prize in 1951.

In the early 1930s, scientists were just beginning to discover the extraordinary world hidden inside the atom, which is made up of a dense center, called the nucleus, with electrons orbiting around it.

Nobel laureate Ernest Rutherford had already shown that radioactive materials sometimes emitted particles, naturally changing the makeup of their atomic nuclei. When energetic particles collided with atomic nuclei, they could trigger a reaction that rearranges the protons and neutrons in the nucleus – sometimes transforming one element into another. But scientists could only study this phenomenon using particles from radioactive decays, which had limited energy and intensity available.

Cockcroft and Walton wondered whether they could instead create these collisions using particles accelerated by a machine.

The first particle accelerator

Working under Rutherford at the famous Cavendish Laboratory at the University of Cambridge, Cockcroft and Walton developed the first machine capable of deliberately accelerating hydrogen atoms, made up of a single proton, to high energies. The high-voltage system they developed could produce up to 800,000 volts, which is the same as over 500,000 AA batteries.

This first particle accelerator design was a far cry from the massive machines you can find today. While the apparatus of Cockroft and Walton could fit in a room, modern accelerators at facilities like CERN in Switzerland can reach up to 17 miles (27 kilometers) in length. Still, the 1932 design laid down essential scientific bedrock. Over the past 75 years, accelerator technology has led to many cutting-edge physics breakthroughs.

A particle accelerator uses electric fields to increase the energy of charged particles, such as positively charged protons or negatively charged electrons. It then directs the stream of particles onto a target. By studying what happens when these energetic particles collide with target materials, scientists can investigate the shapes and sizes of atomic nuclei.

This idea is somewhat similar to a microscopic racetrack. Instead of accelerating cars, it accelerates particles that are far too small to see with the naked eye.

In 1932, Cockcroft and Walton directed their accelerated protons at a lithium target and observed something remarkable. In the collision, the lithium nuclei produced two alpha particles, which are made up of two protons and two neutrons.

With this experiment, Cockcroft and Walton showed that scientists could build machines to probe and transform nuclei. They helped establish particle accelerators as an essential tool for nuclear physicists and beyond.

Modern use of accelerators in physics

The developments Cockcroft and Walton made marked the first step toward widespread use of particle accelerators, which continues today.

The world’s largest and most powerful accelerator is the Large Hadron Collider at CERN, which makes protons travel so fast that they could circle the Earth more than seven times in one second.

As experimental nuclear physicists, we perform most of our research at accelerator facilities around the world. These include the accelerators at our home institutions: the Edwards Accelerator Laboratory at Ohio University and the Facility for Rare Isotope Beams at Michigan State University.

In our research, we use particle accelerators to study the nuclear reactions that take place when stars explode out in space. The accelerator facility is essential for recreating in the laboratory the exact conditions that exist inside stars. This research teaches us about the life and death of stars and how nuclear reactions inside them build the elements you see all around you.

Accelerators beyond physics

While basic research laboratories are a natural place to find particle accelerators, the technology spreads into many other areas.

One key area is medicine. Over 1,500 accelerators are used for cancer diagnosis and treatment. One use involves directing a beam of protons or other heavier particles into the patient, targeting unwanted cancerous cells (proton/heavy ion therapy).

Drug developers also use accelerators to produce radiopharmaceuticals, which are drugs that contain a radioactive isotope. A radioactive isotope is a variant of an element that exists only for a short time and emits radiation when it decays. Medical practitioners use these radiopharmaceuticals to diagnose and treat disease, including cancer. Because the radioactive isotopes exist only for minutes or hours before decaying, many hospitals have their own accelerators so that they can produce them locally.

A lesser known use of accelerators is in art and archaeology. Accelerator-based techniques can determine the types of elements and molecules present in an artifact. They can identify the material an object is made of or hint at the manufacturing techniques used to create them. This information can help authenticate art pieces or tell researchers about the cultural heritage of objects.

The Louvre museum in Paris has its own dedicated accelerator, installed in 1988. It is the only accelerator in the world exclusively used for cultural heritage purposes.

Finally, the findings from accelerator experiments help scientists design satellites. Along with the rockets and spacecraft that transport them into orbit, satellites are constantly bombarded with fast moving particles that travel through space called cosmic rays. These rays can damage the delicate electronics on satellites. High-energy accelerators help scientists test these space technologies and prepare them to stand up to radiation from cosmic rays.

The legacy of Cockcroft and Walton echoes throughout accelerator laboratories around the world. Their pioneering work accelerated the field of nuclear science. It also propelled the development of modern accelerators that are vastly more powerful and sophisticated.

Artemis Spyrou receives funding from the US National Science Foundation.

Andrea Richard receives funding from the Department of Energy, National Nuclear Security Administration.