| Lawrence invents the cyclotron
Photo: Four-inch copper-encased cyclotron, one of Ernest Lawrence's ealiest models
When Ernest Orlando Lawrence (1901-1958) got his PhD in physics, the hottest topic was bombarding the atom's nucleus to see what new particles it might produce. Ernest Rutherford had only recently shown that striking the atom of one element could make it emit electrons and turn into a different element.
Lawrence joined the physics faculty of the University of California (Berkeley) in 1928 and got intrigued with this new physics. So far, people had used alpha particles (the product of natural radioactivity) and protons (hydrogen atoms, containing a positive charge of 1) to bombard other atoms. But they had about exhausted that field of research. To learn more, they needed an artificial way to accelerate these particles to greater energy. Several accelerators were invented to give the bombarding particle a huge "kick" of electric potential. But it seemed that you'd need a kick of about 1 million volts to get the required acceleration, and making a machine to withstand that power was nearly impossible.
Around this time, Lawrence happened to read a German paper describing a linear accelerator that boosted a particle's energy in steps using alternating electric fields. This did increase the particle's speed but to really get it up to the desired energy, the accelerator would have had to be impractically long. Lawrence knew that a magnetic field would deflect the charged particles into a curved path. By making the particles go in a spiral, he could boost their energy bit by bit each time they circled an electrode. The circular machine could fit in one room. The particles would spiral outward as they gained more energy, and when they were moving fast enough, they'd shoot out of the device with amazing force into a collector.
The university gave Lawrence the go-ahead to build what he called the cyclotron in 1930. With some graduate students, he tried a number of different set-ups. They had success using electrodes, a radio frequency oscillator producing 10 watts, a vacuum, hydrogen ions, and a 10 cm electromagnet. The whole contraption was quite small. With a larger magnet, Lawrence's team was able to produce 80,000 electron volts in 1931, and later the same year, with a 25 cm cyclotron, 1 million electron volts. Cyclotrons got successively larger, with new and different capacities. A 69 cm cyclotron could accelerate ions containing both protons and neutrons. With this, researchers produced artificial radioisotopes like technicium and carbon-14 used in medicine and tracer research. In 1939, a 152 cm device was being used for medical purposes, and Lawrence won the Nobel Prize in physics. Work was begun on a 467 cm machine in 1940, but World War II interrupted its development. Lawrence's team turned its attention to producing the uranium-235 needed for the atomic bomb.
The development of the cyclotron and the growth of Lawrence's Radiation Laboratory had tremendous implications for science and the way it's done. This new tool could probe the atom's nucleus and offered applications in medicine and chemical research. It launched the modern era of high-energy physics. But it also launched the era of "big science"-- a new way of organizing scientific work. To feed and care for these increasingly large, complex, and expensive tools required more staff and above all, more money. Governments and corporations saw they had a stake in such research and stepped in as funders.
Ernest Lawrence died in 1958. In 1961, element 103 was discovered and named "lawrencium" in his honor.
Home | People and Discoveries Menu | Help
WGBH | PBS Online | Search | Feedback | Shop
© 1998 WGBH