Rays instead of scalpels¹

The Gray (Gy) is the derived SI unit for absorbed dose, specific energy and kerma (kinetic energy in matter). This unit was named after the English physicist and radiobiologist Louis Harold Gray.1 One Gray is the dose of energy absorbed by a homogeneously distributed material with a mass of 1 kilogram when exposed to ionising radiation bearing 1 joule of energy. So 1 Gy = 1 J/kg

Louis Harold Gray (1905 - 65), the only child of a London family, grew up in modest surroundings. His father, employed as a telegraphist by the General Post Office, was a man of few words who took his boy on long Sunday walks. They 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 Hal (as he was dubbed by his contemporaries), 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. Much later his wife recounted, "Hal sang in the bath on the day when they told him, 'No more Latin'". At the age of 13, Hal was a successful candidate in a scholarship examination to obtain a stipend for studies at Christ's Hospital, a renowned boarding school. While a pupil there he saw his parents almost only during the school holidays. Hal loved school and studied until late at night. One of his instructors gave him private lessons in chemistry and Hal witnessed interesting experiments. He and his class-mates were also invited to evening discussions on philosophy and Greek history by his principal science teacher. Hal later retained vivid memories of his physics teacher in particular, who on one occasion arranged for the dipping of bananas in liquefied air, then knocked them to pieces with a hammer.

At the age of 18, Gray was fascinated by experimental nuclear physics, a field in which the University of Cambridge was then pre-eminent. Its physics professor and Nobel prize-winner, Ernest Rutherford (1871-1937) was the first to achieve nuclear transformation and performed experiments which established the previously unknown existence of the atomic nucleus. 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, of which Rutherford was a member. At Trinity College, Gray took physics, mathematics and chemistry, passing an examination after two years at the top of his class. Having concluded the second part of his Tripos examination 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, the Cavendish Laboratory in Cambridge. Besides his idol Rutherford, the cream of Britain's physicists taught there, including the Nobel prize-winners Sir Joseph Thomson (1856-1940), discoverer of the electron (and Master of Trinity College) and Sir James Chadwick (1891-1974), discoverer of the neutron (and Gray's PhD supervisor). It was a great privilege, and a difficult challenge, to belong to such a distinguished circle. Gray went to work with a will. First he set to work trying to measure cosmic radiation, about which almost nothing was then known. Then he investigated the effects of every type of radiation known at the time on different substances. The cavity-chamber principle, still known today as the Bragg-Gray principle, was formulated independently by Gray and the Nobel prize-winner William Henry Bragg. Another of Gray's areas of activity was the absorption of hard gamma rays. He selected this subject for his PhD dissertation and was awarded a further scholarship and a fellowship 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 wife a student of English and 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, obtained her degree and also became a Methodist lay 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 had followed with considerable interest the efforts of medical research to develop methods of treating cancerous growths with ionising radiation. Mount Vernon Hospital in Northwood, Middlesex, close to London was a leading institution in the field. When he found out that this hospital was looking for a physicist to study radium radiation and X-rays and investigate their effects on living tissue, he took the position without hesitation even though the pay was less than in Cambridge. He was excited to be doing something new and especially to work towards aiding mankind. Radiobiology, the study of interactions between ionising radiation and living matter, is a young, multidisciplinary science drawing on biology, medicine, biochemistry and physics and 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. Gray designed and constructed this accelerator with some technical assistance. He collected an immense mass of data over a period of seven years. His analysis of this data proved of incalculable value in the development of radiotherapy for 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, for he was a firm pacifist during all his adult life.

After the war, Gray took on a position at the Medical Research Council's Radio-therapeutic Research Unit at London's Hammersmith Hospital, where he built a strong and loyal team with which he greatly advanced radiobiological knowledge. His objective was to use this knowledge to increase 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 1953 due to personal differences with the Unit's Director, who was a clinician and not a scientific researcher. 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: the Gray Laboratory of the Cancer Research Campaign. 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! The Laboratory's personnel laughed about that one for years. Gray himself, a fellow with a sense of humour, 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 Roentgen Prize and the Faraday Medal for his contributions to 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. A few months after 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.

¹Adapted from a paper in the book "My Name is BECQUEREL. The stories of the scientists whose names were given to the international units of measure" by Ernst Schwenk, 1994 Hoechst Aktiengesellschaft, Frankfurt am Main, translated from German by Michael Beall.

²Find the full story in the paper "1953: The events leading to the birth of the Gray Laboratory at Mount Vernon Hospital" by Oliver Scott.