Cecil Frank Powell Biography

Cecil Frank Powell's research into cloud chambers and the detection of subatomic particles led to his development of photographic emulsion systems to detect and identify fast-moving particles, especially those found in cosmic rays. This enabled him to discover the pi-meson, a particle formed from nuclear reactions within cosmic rays. Powell was awarded the 1950 Nobel Prize in physics for his work in this area. He also was a member of the British Atomic Energy Project during World War II, though in his later years he became an advocate for nuclear disarmament.

Powell was born on November 5, 1903, at Tonbridge, Kent, England. His father, Frank Powell, was a gunsmith, and his mother, Elizabeth Caroline Bisacre, came from a family of skilled technicians. Powell developed an interest in science at an early age after becoming captivated by a chemistry book he saw in a store. Inspired by the book to conduct his own chemistry experiments, he eventually convinced his family to let him purchase the makings of a home chemistry set.

Studies at Cambridge under Rutherford and Wilson

In 1914 Powell won a scholarship to the Judd School in Tonbridge. Upon graduation from Judd, he earned two more scholarships that allowed him to attend Sidney Sussex College at Cambridge University. He graduated in 1925 with a degree in physics but turned down a teaching job to continue his graduate work at Cambridge.

At the time Ernest Rutherford , the Nobel-Prize winning physicist who had determined the structure of the atom, was the director of the Cavendish Laboratories at Cambridge. It was under C. T. R. Wilson , the inventor of the cloud chamber, that Powell conducted his doctoral research, a study of condensation phenomena in cloud chambers, for which he was awarded his Ph.D. in 1927. Cloud chambers are devices that reveal ionized particles by producing a trail of water droplets from air saturated with water. Powell accepted an appointment as research assistant to A. M. Tyndall at Bristol College. In succession he became lecturer in physics, a reader in physics, the Melville Wills Professor of Physics (1948), the Henry Overton Wills Professor of Physics and director of the H. H. Wills Physics Laboratory (1964), and vice-chancellor of the University at Bristol (1964).

Develops Photographic Detection Devices

Powell's initial work at Bristol involved the study of ion mobility in gases--the way electrically charged atoms behave in gases. By 1938, however, Powell became interested in particle detection devices. That interest, which first developed while he was studying cloud chambers, was rekindled when he learned that photographic emulsions could be used to detect particles in the atmosphere. For a number of years, Wilson's cloud chamber had been the instrument of choice for detecting subatomic particles, such as those produced in radioactive reactions and cosmic rays. However, the cloud chamber possessed one serious disadvantage--it required a brief resting phase each time it was used. In contrast, photographic emulsions were ready at all times to record events.

Like other scientists, Powell had been aware of the potential of photographic emulsions for this purpose, but no one had yet used them successfully. The main problem was that emulsions were not sensitive enough to be used for detection purposes, so Powell decided to find a way to overcome this limitation. His first year of research proved disappointing; he found that neither the emulsions nor the microscopes available were of sufficient quality to obtain the results he wanted. His research was interrupted by World War II, and he became involved with the British Atomic Energy Project for its duration. After the war, he again tackled the technical challenges of using photographic emulsions for detection purposes, this time with much greater success.

In 1946 at Powell's request, Ilford Ltd., a photographic company, developed a new emulsion that could more clearly record particle tracks. Powell and his colleagues used this new detection system to study cosmic radiation at altitudes of up to 9,000 ft (27,432 m). These studies resulted in the discovery of a new particle, the pion (or pi-meson), that had been predicted by the Japanese physicist Hideki Yukawa in 1935. The pion proved to be a cohesive force within the atomic nucleus, as was the K-meson, another particle discovered by Powell shortly thereafter. It was partly for these discoveries that Powell was awarded the 1950 Nobel Prize in physics. Over the next decade Powell continued his studies of cosmic radiation. As balloon technology improved, he launched his detectors higher into the atmosphere, in some cases reaching and maintaining altitudes of 90,000 ft (27,432 m) for many hours. A key element in the success of this research program was the collaborative effort among scientists, technicians, and laypersons throughout Europe who collected and monitored his equipment. That experience proved to be especially helpful in the early 1960s, when Powell became involved in organizing the European Center for Nuclear Research (CERN) in Geneva, Switzerland. Powell served as chairman of CERN's Science Policy Committee from 1961 to 1963.

During the 1950s Powell became increasingly concerned about social problems related to scientific and technological development. He served as president of the Association of Scientific Workers from 1952 to 1954, and as president of the World Federation of Scientific Workers from 1956 until his death. A founding member of the Pugwash Movement for Science and World Affairs, he lent his signature to Bertrand Russell's 1955 petition calling for nuclear disarmament.

Powell was married in 1932 to Isobel Therese Artner, with whom he had two daughters. He died on August 9, 1969, at Bellano, Lake Como, Italy, while on vacation to celebrate his retirement from Bristol a few months earlier. Powell's awards in addition to the Nobel Prize included the Hughes Medal in 1949 and the Royal Medal of the Royal Society in 1961, the Rutherford Medal and Prize in 1961, the Lomonosov Gold Medal of the Soviet Academy of Sciences in 1967, and the Guthrie Prize and Medal of the Institute of Physics and Physical Society in 1969.