Cecil Frank Powell (5 December 1903 – 9 August 1969) was a Britishexperimental physicist who received theNobel Prize in Physics in 1950 for heading the team that developed the photographic method of studying nuclear processes, and for the resulting discovery of thepion (pi-meson).[2]
During his time at Bristol University, Powell applied himself to the development of techniques for measuring the mobility of positive ions, to establishing the nature of the ions in common gases, and to the construction and use of aCockcroft–Walton generator to study the scattering ofatomic nuclei.[4] He also began to develop methods employing specialisedphotographic emulsions to facilitate the recording of the tracks ofelementary particles, and in 1938 began applying this technique to the study ofcosmic radiation,[4] exposing photographic plates at high-altitude, at the tops of mountains and using specially designed balloons,[9] collaborating in the study withGiuseppe Occhialini,Hugh Muirhead, andCésar Lattes. This work led in 1947 to the discovery of thepion (pi-meson),[10] which proved to be the hypothetical particle proposed in 1935 byHideki Yukawa in his theory ofnuclear forces.[11]
In 1950, Powell was awarded theNobel Prize in Physics "for his development of the photographic method of studying nuclear processes and his discoveries regarding mesons made with this method."[2] Lattes was working with him at the time of the discovery and had improved the sensitivity of the photographic emulsion. Lattes was the first to write an article describing the discovery that would lead to the Nobel Prize.[12]Debendra Mohan Bose andBibha Chowdhuri published three consecutive papers inNature, but could not continue further investigation on account of "non-availability of more sensitive emulsion plates" during the war years.
Seven years after this discovery of mesons by Bose and Chowdhuri, Powell made the same discovery ofpions andmuons and further decay of muons toelectrons… using the same technique". He acknowledged in his book, "In 1941, Bose and Chaudhuri (sic) had pointed it out that it is possible, in principle, to distinguish between the tracks ofprotons and mesons in an emulsion… They concluded that many of thecharged particles arrested in their plates were lighter than protons, their mean mass being … the physical basis of their method was correct and their work represents the first approach to the scattering method of determining momenta of charged particles by observation of their tracks in emulsion". In fact, the measured mass of the particle by Bose and Chowdhuri was very close to the accepted value measured by Powell who used improved "full-tone" plates.[13] From 1952, Powell was appointed director of several expeditions to Sardinia and the Po Valley, Italy, utilizing high-altitude balloon flights.[4]
Giuseppe Occhialini had a wooden bench built with Powell's name carved into acommemorative plaque, and then transported it toPremana, a village in the mountains aboveLake Como.[21] It was installed on the path where he died, outside the Rifugio Capanna Vittoria (now the Capanna Vittoria restaurant), on the Alpe Giumello, inCasargo.[19] Occhialini's reason was, "...if that bench had already been there, Powell would probably have stopped to rest there."[21]
"In recognition of his pioneering work on the development of the photographic emulsion technique in the investigation of cosmic rays and the outstanding results derived therefrom on the elementary particles in cosmic radiation."
In October 2011, a replacementcommemorative plaque was installed in Downside Road, Bristol.[5]
In 2013, theInternational Inner Wheel Club ofLecco, inLombardy, Northern Italy, erected a sign in memory of Powell, close to where he died, at the Capanna Vittoria restaurant, on the Alpe Giumello, in Casargo.[19]
^"Cecil Powell".Goethe-Universität Frankfurt. Johann Wolfgang Goethe-Universität Frankfurt am Main. Archived fromthe original on 27 March 2009. Retrieved14 September 2009.
^"Powell, Cecil".Encyclopædia Britannica. London: Encyclopædia Britannica Limited. 1962.
