Louis Harold Gray

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Louis Harold Gray (10 November 1905 - 9 July 1965) was a British physicist who worked mainly on the effects of radiation on biological systems, inventing the field of radiobiology as he went. A summary of his work is given below. Amongst many other achievements, he defined a unit of radiation dosage which was later named after him as an SI unit, the Gray.

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Summary of Career

1933 Hospital physicist at Mount Vernon Hospital, London
1936 Developed the Bragg-Gray equation, the basis for the cavity ionization method of measuring gamma-ray energy absorption by materials
1937 Built an early neutron generator at Mount Vernon used
1938 Studied biological effects of neutrons using the generator
1940 Developed concept of RBE (Relative Biological Effectiveness) of doses of neutrons
1952 Initiated research into cells in hypoxic tumors and hyperbaric oxygen
1953 Set up Gray Laboratory at Mount Vernon Hospital
1953 - 1960 Under Gray’s direction, Jack W. Boag developed pulse radiolysis
1962 Ed Hart (ANL) and Boag discovered the hydrated electron using pulse radiolysis at Gray Lab

This discovery initiated a new direction for chemistry research that is still very active today and is vital for understanding of the effects of radiation on biological tissue, for instance in cancer treatment.

Louis Harold Gray, only child of a London family, grew up in poor surroundings. His father was a man of few words who took his boy on long Sunday walks. The two of them practised mental calculations by posing mathematical problems to one another. Harold's mother was good with her hands and from her he learned to wallpaper, bake and sew; an aunt showed him how to make a bookshelf out of old wooden crates. This was the beginning of a hobby that accompanied Gray until the end of his life: furniture-making. At school, the boy showed an avid interest in the natural sciences and mathematics. He found languages less interesting, learning Latin to improve his grasp of technical terms and French as the key to specialist literature in that language. At the age of 13, Hal, as he was dubbed by his contemporaries, received for his good marks a stipend for studies at Christ's Hospital, a renowned boarding school. He saw his parents during the holidays only. Hal loved school and studied until late at night. One of his instructors gave him private lessons in chemistry and showed him interesting experiments. Another invited him and his class-mates to discuss philosophy and Greek history over tea and cake. Hal later retained vivid memories of his physics teacher in particular, who dipped bananas in liquefied air, then knocked them to pieces with a hammer.

At the age of 18, Gray was fascinated by nuclear physics, a field initiated a few years before at the University of Cambridge when the physics professor and Nobel prize-winner Ernest Rutherford (1871-1937) was the first to achieve nuclear transformation. Rutherford was a kind of national hero to the English, so Gray was convinced he had it made when he found out, on Christmas day of 1923, that he had received a scholarship to study at Trinity College, Cambridge, the city where Rutherford taught. At Trinity College, Gray took physics, mathematics and chemistry, passing the examination after two years at the top of his class. Having concluded the second level at the top of his class as well, Gray was accorded the special privilege of membership in that holy-of-holies of British natural science, Cavendish Laboratory in Cambridge. Besides his idol Rutherford, the cream of Britain's physicists taught there: the Nobel prize-winner Sir Joseph Thomson (1856-1940), discoverer of the electron and Sir James Chadwick (1891-1974), discoverer of the neutron. It was a great privilege, and a difficult challenge as well, to belong to such a distinguished circle. Gray went to work with a will. First he investigated the effects of every type of radiation known at the time on material substances. Then he set to work trying to measure cosmic radiation, about which almost nothing was known at the time. The cavity-chamber principle, still known today as the Bragg-Gray principle, was formulated by Gray in co-operation with Nobel prize-winner William Lawrence Bragg (1890-1971), Rutherford's successor. Another of Gray's areas of activity was the absorption of hard gamma rays. He selected this subject for his dissertation and was awarded a further scholarship by Trinity College.

Gray's years in Cambridge were happy years for him, not only with regard to his scientific work in nuclear physics. It was also in Cambridge that he became acquainted with his future partner, a student of theology who awakened his interest for literature. He read to her for hours on end, for she had been blind since her youth. With the help of Braille script she managed to complete her studies and became a Methodist preacher. Gray also worked as a lay preacher and was active in social programmes. Gray found research in the little-known field of nuclear physics exciting, but he was dissatisfied with its impractical side. What he really wanted was to apply his knowledge for the good of mankind. He followed with considerable interest the efforts of medical research to develop methods of treating cancerous growths with ionising radiation. Mount Vernon Hospital in Northwood, a London suburb, was a leading institution in the field. When he found out that this hospital was looking for a physicist to measure radium radiation and X-rays and investigate their effects on living tissue, he took the position without hesitation even though the pay was much less than in Cambridge. He was excited to be doing something new. Radiobiology, a borderline discipline drawing on biology, medicine and physics, was in its infancy at the time. Gray's contributions gave this new science the basis it needed. Here he found his life's work. His most important tool was a 400 kV neutron generator with which he was able to measure directly the effects of ionising radiation on biological materials. He collected an immense mass of data over a period of seven years. This collection of data proved of incalculable value in the development of radiotherapy of cancer. Gray refused an invitation to return to Cambridge during the Second World War to work on neutron research - it was against his nature to participate in military research.

After the war, Gray took on a position at the Radio-therapeutic Research Institute of London's Hammersmith Hospital, where he had the opportunity to build a powerful cyclotron. This machine enabled him to make further progress in investigation of the biological effects of irradiation. His objective was to intensify the effect of the ionising rays on tumorous cells while sparing the surrounding healthy tissue.

Gray had to discontinue his research at Hammersmith Hospital in 1954 due to personal differences with the clinic directorship.2 He then returned to Mount Vernon Hospital in Northwood, where the world's first radiobiological institute was built according to his plans. This institute today bears his name: Gray Laboratory of the Cancer Research Campaign.3 When the new building was to be dedicated, a comical error was revealed. The tea kitchen had been forgotten - and that by the passionate tea-drinker Hal Gray! Clinic personnel laughed about that one for years. Gray himself, a humorous fellow, laughed with them.

The research institute was equipped with the most modern equipment available and offered ideal working conditions. Many renowned radiobiologists were honoured to work here under Professor Gray. The main objective of his investigations was the "oxygen effect", i.e. the influence of oxygen on the radiosensitivity of cells and the use of inert gases as a radiation protection measure. The new method of electron spin resonance spectroscopy was also investigated at length. Gray's work was widely respected among experts. Numerous organisations and expert committees requested his membership and advice. The British Institute of Radiology elected him their president; he became a fellow of the Royal Society. He was awarded the R–ntgen Prize and the Faraday Medal for his-contributions in the field of radiation research. Who else but Harold Gray, the father of radiobiology, could be selected to chair the international congress of the International Association for Radiation Research at Harrogate in 1962? The preparations for this congress took three years. The work demanded too much of the ambitious scientist. Shortly before the end of the congress, Gray suffered a stroke from which he never fully recovered. He died on July 9th, 1965 in Northwood. His ashes were taken to the small Channel Island of Alderney, the "green paradise" where he had spent his holidays for so many years.

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