The Nuffield Cyclotron at Birmingham
Fifty-one years of the Nuffield Cyclotron (article by Dr N M Clarke, 2001)The cyclotron has been a significant research tool of nuclear physics for more than fifty years, and new cyclotrons continue to be built both for research and for the production of radioisotopes, whose use for industrial and medical purposes is now a world-wide industry.
In 1937, the Professor of Physics, Marcus Oliphant, enlisted the help of the then Prime Minister, Neville Chamberlain, to persuade Lord Nuffield to make a gift of 60,000 pounds to build a cyclotron at Birmingham. Oliphant made the long journey to Berkeley, California, U.S.A. in 1938 to visit E.O. Lawrence, the inventor of the cyclotron. Lawrence was designing his fourth machine, the 60 inch "Crocker" cyclotron, and Oliphant returned with a complete set of drawings. Before the outbreak of the second World War, Oliphant had managed to acquire a DC generator, and steel for the magnets, and a vacuum vessel, but the Physics workshops had to finish winding the magnet coils in 1944. During the second World War the University was hit by incendiary bombs and the cyclotron was saved in the nick of time by the fire wardens. The cyclotron was completed between 1945 and 1948 under the supervision of John Fremlin and involved a number of postgraduate students and huge efforts by the mechanical workshop.
The cyclotron first produced internal beam during the period from July 1948. The archive of the School of Physics has most of the operators' log-books from January 1949 onwards which reveal many attempts to extract external beam from the machine, eventually achieved in 1950. The Birmingham Post for July 12th 1950 showed a faked picture of Professor John Fremlin apparently gazing into the emerging external beam! During the next few years, the cyclotron was used to make many new radioisotopes, and a combined team from Physics and Chemistry pioneered a highspeed 'bucket brigade' technique for processsing the target material to chemically separate and measure the short lived isotopes - Ken and Alma Chackett were a husband and wife part of this team. The first forays into the production of industrial radioisotopes such as 22Na were made before 1953. The Nuffield machine was perhaps the first to accelerate heavy-ion beams (14N), but much of the pure physics research concentrated on the use of beams of protons, deuterons, helium-3 and helium-4 which produced much data on the interactions of nuclei and led to the important development of the Optical Model of nuclear scattering. It was on the outstanding work pioneered by names such as Oliphant, Fremlin, Philip Moon, Rudolf Peierls and John Walker, that the reputation of nuclear physics at Birmingham was founded In the 1960s, the pure physics research moved to another pre-war cyclotron, the newly restored Radial Ridge machine in East Physics. This machine had been constructed at Cambridge before World War II as a flat field machine, and so was actually older than the Nuffield machine, but was re-designed at Birmingham as one of the world's first machines with alternating gradient focusing. This left the Nuffield machine to concentrate on the developing field of medical physics. In the next decade, the Mermaid project constructed a moving bed within a shielded facility housing whole body scanners, and using neutron beams, carried out non-invasive investigations into skeletal calcium content and into heavy metal poisons such as lead and cadmium. During the period from 1980 onwards, the techniques were developed to supply medical and industrial radioisotopes. During the 1990s, in a collaboration with the City Hospital, the Nuffield machine was producing enough krypton generators for some 50 hospitals each week. These generators contain the radioisotope 81Rb whose decay product (81mKr) is used for lung function scanning and for identifying pulmonary embolisms; it is ideal for this role as the krypton gas mixes easily with air drawn into the lungs. In addition, the Nuffield machine was a major supplier to Amersham International of 22Na for positron emission tomography, and 109Cd, used for monitoring environmental pollution via X-ray fluorescence - especially useful for detecting heavy metals like lead.
A symposium was held in the School of Physics and Astronomy on 23/24thJune 1998 to celebrate "50 years of the Nuffield Cyclotron". It attracted many speakers who had connections with Birmingham or the Nuffield machine over the years, and four overseas speakers. Our guest of honour and most amusing after-dinner speaker was Ken Chackett, whose role in the early days of the Nuffield cyclotron has been mentioned above. He is also remembered for his ideas about alpha particle clusters in nuclei through the "Buckshot" model, as well as the use of tracer methods in medical and dental work. Following an extensive review of the Nuffield cyclotron operations in March 1999, it was announced that the cyclotron would close on 1st October 1999 because of the uncertainties in the market for radio-pharmaceuticals, and the enormous cost of additional shielding material which would be required to meet new standards when the West and Nuffield buildings were refurbished as part of the School's building plans. The Nuffield machine was to be de-commissioned over the following three years. Historically, the Nuffield may be an important machine in cyclotron technology; until its closure, it remained the oldest, continuously working cyclotron in the world, and as a copy of the Crocker machine it is one of the last direct links to the father of the cyclotron, E.O. Lawrence. Its fifty-one years of use in pure physics, medical physics and radioisotope production would certainly have pleased Lord Nuffield who wanted it used for the benefit of humanity. Its history encapsulates the progress of many such machines from research tool, through special applications, to the modern hospital isotope producer, now available as "Cyclotron-in-a-big-box, driven by a PC"!
However, cyclotrons at Birmingham are not quite finished; the Radial Ridge machine finished its career in pure research physics in 1986 after two decades of outstanding contributions to precision measurements of nuclear scattering and reactions with deuterons, helium-3 and alpha particles. With 'single-turn extraction', a high resolution beam-line and two versatile scattering chambers built by Brian England, the productivity of this machine was unmatched by any other University cyclotron in the world. At one time, it was the only cyclotron in the world that had ion sources which could produce both polarised deuterons and polarised 3He. After it ceased pure research, the machine was used for the production of medical isotopes for hospitals, but now its main function is to produce short-lived positron emitting isotopes for positron emission tomography (PET) and positron emission particle tracking (PEPT) studies within the Nuclear Physics Group. This machine also provides beams for undergraduate student projects, for detector testing, and for radiation damage studies. Beam energies of 6, 12, 33 and 24 MeV are available for 1H, 2H, 3He and 4He ions, with intensities ranging from a few nanoAmps up to tens of microamps with raster scanning and water cooled targets. Very low intensity beams (106s-1) of protons can be produced for damage studies, using residual hydrogen in the machine.
N M Clarke, 4th September 2001
(edited for this web-page by C. Wheldon June 2010).
This article is an amended version of an article which first appeared in the 1999 Newsletter of the School of Physics and Astronomy.