A family of scholars
Ilya Mikhailovich Frank was born on October 23, 1908, in St Petersburg, the younger son of Mikhail Lyudvigovich Frank and Yelizaveta Mikhailovna Gratsianova. His father was a mathematician from a Jewish family who had been expelled from Moscow University for taking part in student revolutionary activity, then reinstated, and who became a professor after the October Revolution. His mother was a physician of the Russian Orthodox faith.
It was a family that prized learning. His uncle was Semyon Frank, a religious philosopher whom the Soviet government expelled from the country in 1922. His elder brother, Gleb Frank, became a leading biophysicist and a member of the USSR Academy of Sciences. Ilya grew up in the turbulent years of revolution and civil war, and like many children of the intelligentsia he was drawn early to mathematics and science.
Learning to see light
Frank studied mathematics and theoretical physics at Moscow State University. From his second year he worked in the laboratory of Sergei Vavilov, a specialist in luminescence, the faint light that some materials give off when they are excited. Vavilov became his mentor for life, and later described Frank as a highly versatile experimental physicist with a strong command of theory.
After graduating in 1930, Frank moved to the State Optical Institute in Leningrad, where he worked in the laboratory of A. N. Terenin and wrote his first paper, on luminescence, with Vavilov. His research on light and on photochemistry earned him the degree of Doctor of Physical and Mathematical Sciences in 1935. By then he had already followed Vavilov to the Physics Institute of the USSR Academy of Sciences, later named the P. N. Lebedev Physical Institute, which moved from Leningrad to Moscow in 1934. There, in the laboratory of D. V. Skobeltsyn, he began to work in nuclear physics, studying how gamma rays create pairs of electrons and positrons.
A glow that should not have been there
In 1934 Pavel Cherenkov, a graduate student of Vavilov’s, noticed something odd. When he exposed liquids to the gamma rays from radium, they gave off a weak bluish light that did not behave like ordinary luminescence. It appeared even in pure water, it was not quenched by the chemicals that normally dim luminescence, and it was strongly directional. Marie Curie and others had seen a pale blue light around radium solutions decades earlier, but no one had explained it.
In 1937, Vavilov asked Frank to help with the puzzle, and Frank and the theorist Igor Tamm worked out the answer. A charged particle, such as a fast electron knocked loose by a gamma ray, can travel through water or glass faster than light itself travels in that material. Nothing outruns light in a vacuum, but light slows down in water to about three quarters of its vacuum speed, and a fast enough particle can overtake it. When it does, it leaves behind a shock wave of light, much as a supersonic jet leaves a sonic boom or a speedboat leaves a V-shaped wake.
Frank and Tamm showed that this light is emitted in a cone at an angle that depends on how fast the particle is moving, and they calculated how much energy it radiates, a result still known as the Frank–Tamm formula. Their theory matched Cherenkov’s measurements in detail and turned a curiosity into a precise tool. The effect is known in Russia as Vavilov–Cherenkov radiation and elsewhere as Cherenkov radiation.
A tool used across science
Because the angle and brightness of Cherenkov light reveal a particle’s speed, physicists quickly saw that it could be used to identify particles. Cherenkov counters became standard equipment at particle accelerators, and ring-imaging detectors, which photograph the cone of light, now help sort particles in experiments such as ALICE at CERN.
The same light made it possible to study the most elusive particles in nature. Giant tanks of ultra-pure water or ice, such as Super-Kamiokande in Japan, the Sudbury Neutrino Observatory in Canada and IceCube at the South Pole, detect neutrinos by catching the faint Cherenkov flashes from the particles they produce. Telescopes such as VERITAS, H.E.S.S. and MAGIC watch for the brief blue flashes made in the atmosphere when very high energy gamma rays from space strike it, allowing astronomers to study exploding stars and distant galaxies.
Closer to everyday life, Cherenkov light is the blue glow seen in the water around nuclear reactor cores, and inspectors use it to check spent fuel for nuclear safeguards. Biologists use it to detect tiny amounts of radioactively labelled molecules, and doctors and medical physicists have begun to use it to image radioactive tracers in the body and to watch, in real time, the shape of a radiotherapy beam on a patient’s skin.
Neutrons, reactors and Dubna
Frank’s own career moved steadily into nuclear physics. In 1941 he became head of the Atomic Nucleus Laboratory at the Lebedev Institute, and from 1940 he also lectured at Moscow State University, where he became a professor in 1944. In 1945, with Vitaly Ginzburg, he predicted another form of light, transition radiation, which a fast charged particle gives off when it crosses the boundary between two different materials. It was confirmed experimentally only years later and opened a new field of research.
After the Second World War he worked closely with Igor Kurchatov on reactor physics, and his laboratory took part in the then secret work that led to the first Soviet uranium-graphite reactor, studying how neutrons spread and slow down. That experience shaped the rest of his life. In 1957 he was invited to the new international Joint Institute for Nuclear Research at Dubna, north of Moscow, to found and direct its Laboratory of Neutron Physics.
The laboratory was built around an unusual machine: a fast reactor that produces neutrons in short, intense pulses. The first IBR pulsed reactor came into operation in 1960, followed by IBR-30 and, in 1984, IBR-2. Pulsed neutrons made it possible to measure neutron energies by timing them over a flight path, and Frank’s laboratory developed these techniques into powerful tools for studying nuclei, materials and the structure of matter. Scientists from many countries came to Dubna to use them.
Recognition
Frank, Tamm and Cherenkov, together with Vavilov, received a Stalin Prize in 1946 for the discovery and explanation of the new radiation. In 1958 Frank shared the Nobel Prize in Physics with Cherenkov and Tamm for the discovery and interpretation of the Cherenkov effect. He was elected a corresponding member of the USSR Academy of Sciences in 1946 and a full member in 1968, and he received further state prizes in 1953 and 1971.
He led the Dubna laboratory until 1988 and then became its honorary director. The laboratory now bears his name, the Frank Laboratory of Neutron Physics, and in 2008 Russia issued a postage stamp with his portrait to mark the centenary of his birth.
Jewish roots in a Soviet life
Frank’s Jewish heritage came through his father, Mikhail Frank, who came from a Jewish family; his mother was Russian Orthodox. The family belonged to the assimilated Russian intelligentsia, and his uncle Semyon Frank, also born into the Jewish family, became a Christian philosopher. Nothing in the record suggests that Ilya Frank practised Judaism, and in the officially atheist Soviet Union of his day religious life of any kind was discouraged.
He is nonetheless counted among the Jewish Nobel laureates by the Jewish Virtual Library. His life spanned a period when many Soviet scientists of Jewish descent faced quotas and suspicion, yet his career was built on decades of steady work inside the country’s leading physics institutions.
The man
In 1937, the same year he and Tamm explained the Cherenkov glow, Frank married Ella Abramovna Beilikhis, a historian. Their son, Alexander, born that year, also became a physicist. Colleagues remembered Frank as a scientist who kept a lifelong interest in the optics of moving charges, returning again and again to the problems of light emitted by fast particles that had made his name, while running a large laboratory devoted to neutrons.
He spent the last decades of his life in Dubna and Moscow, teaching, writing and guiding younger physicists. Ilya Frank died in Moscow on June 22, 1990, at the age of 81.
Legacy
Frank’s legacy is a way of seeing the invisible. The theory he worked out with Tamm in 1937 explains why a particle moving faster than light in a material leaves a cone of blue light behind it, and that explanation turned the effect into one of the most useful signals in physics. Every time a neutrino observatory records a flash in a tank of water, a gamma-ray telescope catches a burst of light in the night sky, or a reactor inspector checks the glow of spent fuel, they are relying on the physics he helped to explain.
His second legacy is institutional. The neutron laboratory he founded at Dubna, with its pulsed reactors, has trained generations of scientists and still serves researchers from many countries who use neutrons to study materials, from metals to biological molecules.
Sources & further reading
Il´ja M. Frank, Biographical, NobelPrize.org · Ilya Frank, Wikipedia · I. M. Frank, Frank Laboratory of Neutron Physics, JINR · Il’ja Mikhailovich Frank, Jewish Virtual Library · Cherenkov radiation, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.