Version of June 16th 2003

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A Brief History of the Harvard University Cyclotrons.

Richard Wilson,
Mallinckrodt Research Professor of Physics
Harvard University


       This is a brief history of the two cyclotrons built at Harvard University and used between  1935 and 2002.  It is a distinguished history and I, Richard Wilson, am proud to have been a part of it for 47 of these 67 years.   In addition to this web based history, which can be added to at any time, a small hard copy book is published.  In addition there is a  a collection of 800 photographs of the cyclotron, its work, its staff and its place in the community which have been scanned and are avaliable for those who wish.   Some of them are available on an adjunct to this site.  http://physics/ or http://physics.harvard.physics/~wilson/cycloron/web/website .  Of course the Harvard University Archives have papers of many of the participants for the eager historian,  and several hardware items are in the museum of scientific instruments.    The work falls naturally into four  periods.   The first period was that of the construction and use of the first cyclotron from 1935 to 1943 when it was dismantled and taken away for war work.   The second is the construction and initial use of the first cyclotron from 1945 to 1955.  The third period starts with a major upgrade in 1955 and continues until the end of major physics research in 1968, and the fourth period is of intensive use for radiotherapy until final closure in summer 2002.   Production of radioactive isotopes was an important part of the operation of the first cyclotron, but was only very incidental in the second cyclotron.    Further deatil, often unedited, can be found on

Historical Background

       In the first third of the twentieth century  the study of Physics at Harvard for both graduate and undergraduate students continued administratively under the Faculty of Arts and  Sciences.  The space occupied for study and experimentation grew with the construction of  Lyman laboratory in the 1930s, one which  included a research library.  The First World War had  initiated the Department of Physics' role in defense.  Its members had taught military personnel, served in the military, and performed defense research.  The 1930s saw increased interest and investigation into the fields of nuclear science and the beginnings of computer science.  In order  to meet the research needs of its faculty, the Physics Department oversaw construction of a particle  accelerator - a cyclotron.   

       The cyclotron had been invented in Berkeley California in 1929 by Ernest Lawrence and  constructed by Lawrence and his graduate student M. Stanley Livingston.   Although the first nuclear disintegration experiments had been performed by Cockroft and Walton in the  Cavendish laboratory in Cambridge UK, using a rectifier multiplication device which carries their  name,  the cyclotrons proved to be very useful in the 1930s in nuclear disintegration experiments, and following the discovery of artificial radioactivity in 1934 by Joliot-Curie, were used widely in producing a  variety of radioactive nuclei.    Some of these radioactive nuclei were of interest in astrophysics,  some of interest in the study of nuclei themselves and some were useful in nuclear medicine -both in diagnosis and in treatment.     It seemed that every major university should have a  cyclotron and indeed they were built at a number of places - Princeton, MIT (built by M. Stanley Livingston), Cornell (built by Stanley Livingston), Rochester built by S.N. Van Voorhis and Lee  Dubridge and at Yale by E. C. Pollard and H. L. Schultz.   

        Although there was agreement that Harvard University must have a cyclotron, there was less agreement on what such a device was.    This is well illustrated in
the following page of cartoons about the Cyclotron.

The First Harvard University Cyclotron

       Harvard faculty began thinking about a cyclotron as early as 1935. It was to be built as a joint project between the Graduate School of Engineering, (now replaced by the Division of  Engineering and Applied Physics) Professor Harry Mimno represented Electrical Engineering,and Associate Professors Kenneth Bainbridge and  Jabez C. Street represented the physics department. Edward M. Purcell (later Nobel Laureate for Nuclear Magnetic resonance) was awared the PhD in 1938 for a theis on "The Focussing of Charged Particles by a Spherical Condenser."  He became a Faculty Instructor in Physics, what was then the new title for what is now Assistant Professor, a five year term rank.    In  1936 the construction of the cyclotron begun in the Gordon McKay laboratory, a wooden world war I building on the east side of Oxford Street. The magnet weighed 85 tons and had a 41minch diameter pole tip.  It accelerated protons up to energy of 12 Mev.  In 1960s a new Engineering Science building was  built on the southern part of the Gordon McKay laboratory and the northern part was dismantled as a fire hazard in 1965 and in 2002 a new building is being finished in its location to house various administrative offices.

       By 1938 the cyclotron construction was complete and a photograph shows Professor Street,  left, posing with Professor Bainbridge, right, and a graduate student  Dr R. W. Hickman (kneeling).  Dr Hickman wrote his PhD thesis on the Franck-Hertz experiment.  By 1943  he was Lecturer on Physics and Communication Engineering, Assistant Director of the Physics Laboratories (under T. L. Lyman) and Assistant Director of the wartime Radio Research  Laboratory (under F. L. Terman from Stanford).  Later he became Director of the Physics Laboratories until his retirement about 1968.  Another photograph shows a scientist, probably  Professor Street, showing on a blackboard the operation of the accelerating system of the two dees.  

       The cyclotron had an external beam which slowed and stopped as it passed through the air.   This gives a dramatic picture of the ionization of the air.    The external beam was used for  producing radioactive isotopes for medical purposes.  A photograph shows a technician handling  one of the sources.  The report of the physics department to the university in  1939 states that  radioactive materials supplied to Harvard Medical School, New York  Memorial Hospital and  Massachusetts General Hospital in addition to uses for physics at Woods Hole Meteorological Station, MIT physics department and members of Williams College and Purdue University.   It  supported the work of  14 researchers in Harvard departments.    Interestingly, there seemed to  be no interest from the graduate school of engineering after the initial construction.    In 1940 to 1941 the physics department reported that the cyclotron had been in operation for over 1,000 hours.   But the end of this fruitful period, and of the first Harvard Cyclotron was near.

       On September 3rd 1939 Great Britain and France declared war on Nazi Germany and after the Japanese attack on Pearl Harbor in December 1941 the United States joined the war -now called World war II.   Again many members of the Harvard physics faculty served the war effort in various ways.  Some faculty members, including Professor K.T Bainbridge, had already  been  called to help develop radar at  the radiation laboratory at MIT by E. O. Lawrence on behalf of the NDRC.   But in 1943 after the establishment of Los Alamos that Professor Bainbridge was recruited away to work on the Manhattan Project of the U.S. Army, at Los Alamos, New Mexico to join a highly secret team assembled by Robert Oppenheimer to work on the development of the first atomic bomb.    While there it became clear that a cyclotron was needed to measure various nuclear reaction cross sections of interest, and supplement the work already being ably carried out at the Princeton cyclotron.   Discussions began at a high administrative level, and top secret level,  between Harvard President James B. Conant (then away from Cambridge) and General Groves and it was agreed that Harvard would sell the   cyclotron to the US government for $1 with an informal promise of a cyclotron to replace it when the war was over.   It appears that Paul Buck, then Provost of Harvard University, was not informed of these discussions and he later reported informally how much he agonized over making the decision to send the cyclotron.

       The young scientist Robert R Wilson was sent to Harvard to negotiate the purchase and arrange the transfer.  Since the atomic bomb project was top secret, the purpose of the purchase had to be disguised from those not cleared for secret information.   A medical physicist, Dr Hymer Friedell, accompanied Robert Wilson.    The "cover story" is that the cyclotron was needed for medical treatment of military personnel and it was sent  to St Louis to be forwarded to  an "unknown destination" (Los Alamos).  Robert Wilson oversaw the shipment and Dr Hymer  Friedell discusses this story in an oral history on record with US DOE .  The late Professor John W. DeWire of Cornell told of being dispatched from Los Alamos to Cambridge where he took up residence whilst overseeing the dismantelment and shipping of the cyclotron to Los Alamos via St Louis.

       From the files we show  a photograph of Robert Wilson (center) discussing the issue with  physics department chairman Percy Bridgman (right) with another man, believed but not  confirmed to be, the late Hymer Friedell on the left.   We can find no contemporary account of  exactly what was said at the meeting but Bob Wilson who was well known for dramatic (but  essentially accurate) summaries said 30 years later that Bridgeman's response was "if you want  it for what you say you want it for you can't have it.  If you want it for what I think you want it for, of course you can have it."

       At the time of writing the source and amount of funds for this first cyclotron is still being  researched.   My memory from discussion with the late Roger Hickman is that the construction cost was about $40,000 of which about $20,000 came from the Rockefeller Foundation which  then funded medical research.    

The Second Harvard Cyclotron 1945-1955

         Immediately following World  War II, a new cyclotron and nuclear laboratory were   planned.    Professor Bainbridge, still at Los Alamos in the fall of 1945, wrote several letters   (copies are available here1. 2. 3. 4) to colleagues at Harvard to plan a new building instead of Gordon  McKay laboratory.  The letters show that he was, at first,  unsure whether the old cyclotron would   be a new cyclotron would be built.  Wasting no time, in 1945 Harvard University appropriated a sum of $425,000 to expand research facilities in Nuclear Physics.  However, this amount was not enough to fund the construction of both a new cyclotron and a new laboratory.  The U.S. Navy   began a program of funding a program in basic science and through its Office of Naval Research (later a joint program of ONR and AEC administered by ONR) this department of the US   government fulfilled the unwritten obligation of 1943 and offered the funding for the construction of a 160-ton cyclotron.  Harvard provided the funds for the construction of a building to house   both the cyclotron and a connecting laboratory.  The building was originally called the Nuclear   Laboratory and other nuclear facilities such as a betatron were contemplated.    

       We divide the history here into three phases.  The first initial phase encompassed the design and initial construction, operation at 90 Mev and the research up until 1955.    This work is encompassed in this chapter.    The second phase began in 1955 when the energy was raised   to 165 Mev, and the work done on nuclear physics for the next 12 years.   Then we define a third  phase of the 35 years from 1967 to 2002 years during which time the primary work was on   medical treatment.

       Initially the driving force for the new cyclotron was Professor Kenneth Bainbridge.   He   persuaded Robert R Wilson to join the Harvard faculty as Associate Professor of Physics, on his departure from Los Alamos in Summer 1946, and head up the team for the design and  construction.   By agreement, Bob Wilson was to spend the year on leave at Berkeley working  with staff there on cyclotron design while Ken Bainbridge was to keep things going at Cambridge.   In 1947, Bob came to Cambridge but only spent 6 months before taking up a new post as  Professor of Physics and head of the Laboratory for Nuclear Science at Cornell University.   Bob  later commented that one of the facts that influenced him in his departure was being asked to do double teaching duty to make up for his "goofing off" for a year in Berkeley!    So Ken Bainbridge took over from  him officially in 1946-7 as the Director of the Cyclotron.   But Bob's year had been very  productive.  In addition to establishing the major design parameters, Bob wrote a famous small letter to the American Journal of Radiology which presaged the later medical work.    He was motivated to give some time to medical application as “atonement for involvement in the development of ther bomb at Los Alamos".

         At a conference in Cambridge, UK in September 1946,  which was attended by Richard Wilson, then a  graduate student at Oxford, Professor Bainbridge described  the plans for the new cyclotron.   It was to occupy an empty area (see photograph ) between the old Gordon McKay laboratory on the east side of Oxford Street and the Divinity school on  Divinity Avenue.   As Professor Bainbridge mischievously said, the planned neutron beam would  head straight for the divinity school supposedly sending the occupants to the heavens  prematurely.   At a  group meeting  Mr (later Dr) David Bodansky remembers  an emphastic statement of  Professor Bainbridge.  referring to the proposed medical work which was envisaged to be merely the production of radioactive isotopes,   Bainbridge declared "There will  no rats running around THIS cyclotron."   Such blanket predictions are dangerous and often soon contradicted.   Dr. R.B. "Tex"   Holt, an Assistant Professor  at Harvard had a  wife who  was doing medical research at one of the major Boston hospitals.  She irradiated some of her animals in the area adjacent to the cyclotron soon after the first beam was obtained in 1949.   But this was an isolated study, and the laboratory was  free of the smell of animals until Dr. Raymond (Ray) Kjellberg preformed his experiments on dogs and monkeys in 1963 preparatory to his pioneering neurosurgery treatments.

            In 1948 Professor Norman Ramsey was recruited from Columbia University and became director of the Cyclotron Laboratory.   Lee Davenport, who had the nebulous title of "Coordinator" stayed on and provided an effective transition.  He was given the title of Assciate Director (according to a written record) or Deputy Director (according to Professor Ramsey's memory).   The 1947 - 1948 year was very productive.  The  main components of the cyclotron were  installed.  The 650 ton magnet iron had been fabricated in Pittsburgh, PA, and machined at the "local"  Watertown Arsenal.   It was 23 ft long, 15.5 ft high and 10 ft wide.  The magnet was moved in 14 separate sections, on 3rd or 4th December 1947.  The magnet  was  rigged into place by a special crew of riggers from California who had done much of the rigging  for the cyclotron and other accelerators there.   The set of  photographs here shows the magnet assembly by Albert (Pop) Poperell with his special crew from Bigge Drayage Co. of California, as written up in the Boston Globe of January 11th  1948.     The magnet coils, each weighing 37 tons,  of which 30 tons was copper, were wound in the General Electric coil winding shop in Pittsfield,  MA and were the largest coils (14 ft diameter) that could be shipped on the Boston and Maine Railroad to North  Cambridge.  Even then they could not come on the direct Boston and Albany mainline because of inadequate clearances.   It was the clearance on this railroad that was the final arbiter of the  cyclotron energy!    When it became time for the coils to be shipped from Springfield, GE wanted  a responsible Harvard person to "collect" them.   It was arranged that the chairman of the  Department would undertake this task.  The chairman, Professor John H. Van Vleck, was a railroad buff  from his boyhood and gladly agreed provided that he could ride on the footplate of the engine.  Mr W.A. Williams, head of GE Power Transformer division accompanied the train with the first coil, and Van, with Harvard engineer Frank B. Robie accompanied the second coil. From the vantage point of the footplate Van took several photographs of the ride three of which are shown here. 

           From then on construction proceeded rapidly.  The logbook shows that on June 3rd 1949 at 2:03 in the morning, the first beam was obtained.  Present were Norman F. Ramsey, Al. J. Pote, Robert (Bob) Mack, G.P.W. (unknown), Peter Van Heerden, and Lee L. Davenport.   At the celebratory party the champagne cork made a dent in the ceiling plaster board.  This dent was carefully preserved until an unfortunate redecoration sometime about 1980 destroyed the historical dent.   The  first of this set of photographs shows  Professor Ramsey and Associate Director  Lee Davenport posing for the newspapers in the control room on June 10th just before the formal dedication of the cyclotron on June15th 1949. Later photographs in the set show how little it changed over the years.  Provost Paul Buck was chairman of the dedication.  There was a distinguished set of speakers at either the dedication or the subsequent dinner at the Harvard Club.   In addition to Norman F. Ramsey, and Lee L. Davenport, Captain A.L. Pleasant, ONR, (Boston), Alan T. Waterman (ONR Washington), Dr Urner Lidell, H.M.Macneille, Division of Research of the US Atomic Energy Commission (AEC.   The enthusiasm of Davenport and Ramsey was great. O:ne day, after a formal dinner with the President they returned to the cyclotron, in their dinner jackets, to find a leak using a new helium  leak detector that had been delivered that afternoon.   Alas no one else was present to take a  photograph to record the event.  A chart shows the staff during this construction period,  and a  photograph shows many of the staff.    Many stories of this period were told at the 50th anniversary celebration by Norman Ramsey and Lee Davenport.

               The beam for the next 6 years was not at the full design energy but at a reduced energy of 110 Mev, and sometimes as low as 95 Mev,  because of a (temporary) failure to make the oscillator work over the full frequency range and the lack of obvious need for immediate work at a higher energy.   Professor Ramsey,  desirous of pursuing active research work at the cyclotron and even more productive work on  molecular beams (which work later won him the 1989 Nobel prize in physics),  arranged for Dr.R.B. Holt (Harvard PhD 1947) to become the  director of the cyclotron from 1950 to 1952.

            Several first rate students obtained their PhD from work at the cyclotron at this time.  David Bodansky, Norton Hintz and Robert Birge were the first.   The photograph shows two of them, Robert Birge and Ann Chamberlain (later Birge),  looking at the counters on which their data was recorded.  At the top of the equipment rack are two binary scalers (counters) based upon the 25 year old Eccles-Jordan circuit, modified by E.B. Lewis at Cambridge in 1935 for nuclear applications, and further developed at Los Alamos by Elmore and Sands.  The student had to note the lamp which showed the state of each binary in this 64A fold scaler, and  perform by slide rule the appropriate arithmetic. Dr Robert Birge, son of the University of California Physics Professor Raymond Birge, was destined later to become a senior research fellow himself at the University of California at Berkeley, and Ann Chamberlain,  later to become Ann Birge,  became a Professor at Hayward College in California.   Other students include a South African, Dr David Hillman,  who later became a biology Professor in Hebrew  University in Jerusalem.   

           Nikolaas (Nico) Bloembergen, then a junior fellow in the Society of Fellows,  also tried his hand at using the cyclotron.  He, together with Peter van Heerden,  measured range - energy relationships using the internal cyclotron  beam and compared them to theory.  But Nicholaas was to move on to win the 1981  Nobel Prize in physics  with his paramagnetic maser and his research on non linear optics.   In 1950   Professor Karl Strauch joined Harvard, firstly as a Junior Fellow until 1953 when he became an  Assistant Professor. He worked tirelessly with the cyclotron for the next 10 years.  Shortly there after Walter Selove  was appointed Assistant Professor before moving on in 1956 to the University of Pennsylvania.   

           The  ONR nuclear research contract, of which the cyclotron was the largest part, was the  largest - and at first the only - government contract in the physics department.   As a   consequence the cyclotron laboratory became an employer of graduate students, even of those  whose thesis work would be elsewhere.  Two obtained their PhD before the cyclotron operated.  William Cross worked on "The Conservation of Energy and Momentum in Compton Scattering (PhD 1950) and Leo Lavatelli on "Photoelectric Absorption" in 1951.   Harold I. Ewen was also awarded the  PhD in 1951.  Ewen  with  Professor Purcell,   used  an antenna outside the south face of Lyman Laboratory to measure "Radiation from Galactic Hydrogen at 1420 Megacycles per Second" a direct proof of the existence of interstellar hydrogen.   Another  was Paul Martin, who was awarded the PhD in 1954 for a thesis on "Bound State Problems in Electrodynamics"  and who later became Dean of  Applied Sciences.   He remembers working in the electronic shop.   Other non-cyclotron guests  were also welcomed.  In 1955-1956 Harold Furth was building pulsed high field magnets before  high field superconductors were known - but he was awarded the PhD in 1960 for a thesis on "Magnetic Analysis of K- interactions in nuclei".

           Space for research was scarce so in 1951/2 the nuclear laboratory  building was  extended to the north side to make room for an expanded machine shop and a few offices.   Other appointments of note at this time included  Andreas M. (Andy) Koehler who was appointed at the cyclotron in some capacity that no one remembers, and which capacity Andy very quickly outgrew,  and William (Bill) Preston (Ph.D. Harvard 1936) who remained as director for 20 years.    At the memorial service for Bill, Richard Wilson gave a eulogy outlining his work as a scientific administrator.

The Second Harvard Cyclotron 1955-1967

       By 1953 it was already becoming apparent that the energy of 95 Mev was too low  for a long term program of nuclear and particle physics.   The pi meson mass had been  determined to be 137 Mev, and to produce pi mesons in appreciable numbers needed an energy of 300 Mev or more.  In addition, measurements at other cyclotrons (Rochester,  Harwell, Chicago) had shown that protons become polarized by scattering from nuclei and nucleons at energies of 130 Mev and above, but at 90 Mev the polarization is low.   At the  time this was merely an empirical observation, but it can be explained by noting that a nucleon of energy about 70 - 90 Mev suffers a phase change of 180 degrees as it passes  through a heavy nucleus making the nucleus appear to be opaque (in atomic physics this is the Townsend-Ramsauer effect).  In 1955 for example,   Professor Mme Joliot-Curie increased the planned energy of the cyclotron being built at Orsay near Paris, for this reason.   Before 1953 the way of obtaining an external proton beam was by scattering from an internal target, with a consequent large loss of intensity.   But in 1953 a scheme was  proposed by James Tuck and Lee Teng to extract the proton beam from the Chicago cyclotron by a regenerative oscillation scheme.    The theory of this process was expanded   by Le Couteur in Liverpool and used to extract the beam from the Liverpool cyclotron in 1954.   In September 1955 it was decided, therefore, to rebuild the Harvard cyclotron.   This rebuild coincided with the arrival at Harvard of Richard Wilson , the present  historian, as Assistant Professor of Physics.  Several steps were taken simultaneously:

- (1)  The magnet was shimmed to allow cyclotron operation to a higher energy of 165   Mev.

- (2)  The RF oscillator was adjusted so that it would oscillate over the full range of frequencies necessary-

- (3)  A beam extraction system of the LeCouteur design was constructed. 

    As the beam accelerated and occupied a larger diameter orbit in the cyclotron, the protons entered a regenerator (shown in the top left hand picture of this group of five pictures),  consisting of two pieces of high saturation iron, one above and below the orbiting protons at one azimuth.  The regenerator was adjusted to provide an increase of magnetic field with radius that was close to Le Couteur's recipe as shown in the top right drawing of the same group of five pictures.   Shims we placed at a smaller radius (as shown in the bottom left picture) to compensate for an otherwise incorrect field profile at smaller radius.  An  oscillation was set up between the fall off the main magnetic field and the localized increased field of the regenerator.  The bottom right picture of this group of five shows an extraction channel located at the maximum of the oscillation (at an  azimuth just before the regenerator).   These photographs were  taken after dismantlement of the cyclotron.     The rebuild had a feature unique to Harvard.  It was realized that particles in the regenerator- field fall off oscillation would  all have the same energy in contrast to the distribution of energies of protons striking a target under ordinary conditions.  Two regenerators were constructed.  One, together with the extraction channel,  was used  to extract the beam   completely, and the other to make the monochromatic beam strike a carbon target at the other side of the cyclotron, from which target scattered, polarized, protons were brought out for experiments.   This is illustrated in the fifth drawing in the bottom center.   Which experimental program was in progress depended upon which  regenerator was inserted into the magnet.   

       The cyclotron was shut down for the rebuild in the first week of October 1955,   and the beam was successfully extracted at the higher energy at the end of April 1956.   The faculty and staff were, as usual for the time, enthusiastic and dedicated.  For example,   Professors Strauch and Wilson were shimming the main magnet until 10 p.m. on   Christmas Eve.  Their wives forgave them.  Experiments started again within a few   months.   Details of the upgrade were published : "Some features of regenerativedeflection and their application to the Harvard synchrocyclotron," G. Calame, P.F.Cooper, Jr., S. Engelsberg, G.L. Gerstein, A.M. Koehler, A. Kuckes, J.W. Meadows, K.Strauch and R. Wilson, Nucl. Instr. 1, 169 (1957).    Subsequent improvements included a modification of the rotating condenser  to adjust the frequency-time characteristics and improve the duty cycle (Koehler and LeFransois) and a stochastic extraction scheme (Gottschalk) to improve the duty cycle still further.  
        Over the next 10 years a number of physics experiments were performed.   In addition to the persons mentioned, other faculty and research fellows who worked at the cyclotron in this period include:  visiting scientist Allan Cormack (later to receive the Nobel prize in medicine) Assistant Professor Douglas Miller,  Research Fellow David Measday.    Dr Palmieri became Assistant Professor for a few years and Dr Gottschalk became Professor at Northeastern University and still used the cyclotron.  

        The first set of experiments was a systematic study of nucleon - nucleon scattering at the energy of 160 Mev (p-p) and 135 Mev (n-p).   The set included measurements of the cross section, the polarization on scattering, the depolarization on scattering, and the rotation of the plane of polarization both in and out of the plane. These experiments were described in PhD theses of Palmieri,  Wang, Thorndike, Hee, LeFrancois, Hoffmann, Hobbie, and published in several published papers.  These experiments enabled a full phase shift analysis of the nucleon-nucleon interaction to be performed at this energy, and fits to be made to potential models.  Taken together with analyses at higher energies, these showed that the spin orbit interaction was of shorter range that the rest of the interaction – deciding between the rival models of two groups of theorists, Signell and Marshak on the one hand and Gammel and Thaler on the other.    The fact was later described by detailed models.   This work on nucleon-nucleon scattering was discussed in a small book Nucleon-Nucleon Scattering (Wiley-Interscience) by Richard Wilson.

        Typically the cyclotron was operated by the scientists performing the experiment and at first only he or she would be present on a night shift.  Later it became clear that a second person was important for safety:  the experimenter could fall down, drop a lead brick onto his toe, or otherwise get hurt.  The shift change was a typical time to discuss data.  On one Sunday morning Dr Allan Cormack had been on night shift, Professor Norman Ramsey was coming on day shift, and Professor Richard Wilson came by to discuss the data.  But priorities changed when it was noted that the beam had disappeared, and the magnet current had gone up too high.   The magnet current was regulated by comparing the voltage across a shunt with a reference, and amplifying the difference to run a bidirectional (Selsyn) motor.  The motor operated a variable transformer (Variac) which controlled the DC field of the DC generator.   The drive for the variac was a chain and sprocket system, with limit switches.  The system had failed, the limit switches failed to work, the chain had broken and the motor was struggling against the stops.   Dr Cormack and  Professor Ramsey sprang into action.    An instant redesign took place.  An O ring was used instead of the sprocket and chain drive, and two pulleys were made, one each machined by Dr Cormack and Professor Ramsey.  No limit switches were needed because the O ring could slip if the drive went too far.    This system was installed within the hour, and survived for about 20 years before the motor-generator set was replaced by a rectifier system acquired surplus when the Cambridge Electron Accelerator shut down.    Of the three persons present that morning both  Dr Cormack and Dr Ramsey were later awarded the Nobel prize but neither of them for their skill as a machinist.

      Assistant Professor Douglas Miller set out to use the polarized neutron beam (obtained by producing neutrons at an angle of 30 degrees from the incident protons) to study neutron proton scattering.   This led to the PhD theses of Russell Hobbie, and Norman Strax.  Later, this neutron beam was improved and was more monochromatic, by allowing the external proton beam to impinge on a liquid deuterium target, by Dr David Measday, a research fellow recruited from Oxford University, who later went to Canada and became director of the Triumpf laboratory.  Other studies included proton-proton inelastic scattering showing collisions from deep shells (Gottschalk) small angle scattering (Steinberg), neutron crossections ( Carpenter); deuteron pickup reactions (Cooper).p-d elastic scattering (Postma) and inelastic scattering (Kuckes).   Particularly notable was the first measurement of bremsstrahlung in proton-proton collisions by Shlaer and Gottshalk.

        The Cyclotron staff, led by Bill Preston and Andy Koehler, continued to be outstanding.   No prhotograph seems to exist of all the staff together, but some photographs have been located of individual machinists, assembly staff and electronic shop staff.  Most of these were transferred to work on high energy experiments at the Cambridge Electron Accelerator and elsewhere as the program shifted its focus.

Proton radiotherapy - first steps (1962 – 1967)

        As noted earlier, the first suggestion that protons could usefully be used for radiotherapy was made by Associate Professor Robert R. Wilson of Harvard University in 1947.   But this idea lay dormant for many years.   It was resuscitated by Dr William (Bill) Sweet, head of the neurosurgery department in Massachussets General Hospital,  in the 1960s, who recruited an able colleague Dr. Raymond (Ray) Kjellberg to try using protons to treat various neurological lesions.   Curiously Bill Sweet, being a trustee of Associated Universities Inc which operated Brookhaven National Laboratory, first asked Brookhaven laboratory to enquire where he could find a suitable proton beam only to be told that there was one in his own back yard at Harvard!     The director of the cyclotron (Bill Preston) and Andy Koehler enthusiastically made them welcome.   Not so welcome was the animal smell accompanying the first experiments on dogs and monkeys!.  The treatment of the first patient was described at the 2nd International Congress of Neuroligical Sugeons in Washington on October 17th 1991.  A two year old girl was treated for a palm sized tumor, just above the pituitary.  It shrank 80%.  But the improvement did not last;   the girl died within a couple of years.   From then on, Dr Kelleberg decided to concentrate on diseases where removal of the pituitary gland or pituitary ablation could help.   These included agromely and  diabetic retinopathy.  (in the 1970s he concentrated on arterovenous malformations).   By 1969 Dr Kjellberg and his associate Dr Bernard Kliman had treated 46 cases of agromely and in 21 cases the hormone levels had dropped to normal levels.   

        It was opportune that the space program was just beginning and the National Aeronautics and Space Administration (NASA) were interested in the medical effects of 150 Mev protons.  150 Mev is close to the peak of the spectrum of protons that would be encountered by astronauts.   The physical reason for this is the same as mentioned earlier:  At 100 Mev and below, nuclei are opaque to neutrons and protons and are absorbed more readily.  Any incident spectrum which has more low energy than high energy particles, will have the low energy ones absorbed, leaving a peak just above the energy where the nucleai become opaque.  Sensing an opportunity, a “medical annex” to the cyclotron was built  using $182,000 of NASA funds.  (Photograph of medical annex)  It was dedicated on November 7th 1963.
Who wanted the Cyclotron?  Who would pay for it? (1967 – 1973)
    By 1967 the Office of Naval Research was closing down their basic research program.   Although they continued to fund basic nuclear physics at Harvard till 1970, they would no longer provide funds for the cyclotron.   The  decision was faced on what to do with the cyclotron.   The cyclotron was no longer central to the physics research program of Harvard University and the physics faculty were no longer willing to write proposals to justify a contract.  It is important for the reader of this history to understand the role physicists like to play in discoveries and development.   A physicist likes to make a discovery and is delighted when it has an application that can work for the general good.  But, as a physicist, he does not need to be persoanlly involved in the development of that idea, although some physicists are.   Professors pipkin, Ramsey, Strauch and Wilson were delighted with the continued interest, and in particular the applications to medicine,  and were happy to encourage scientists from other disciplines, but wanted themselves to engage in other basic science activities.  Interestingly, as the list of publications shows, there was, as shown in the attached list, a considerable interest from outside Harvard University, and even Ph.D. degrees were awarded at other institutions for work done here.   Harvard was, of course, proud of the fact that it was able to help these other local institutions.   But these outside scientists did not pay for the basic costs.   The basic costs had to be  covered by the Harvard University contract.  

        The most obvious choice was to close the cyclotron completely, to dismantle it and use or sell the bits and pieces for other experiments or programs.  The building was of great interest to the high energy physics program including Professors Ramsey, Strauch and Wilson who had ceased their experiments with the cyclotron.  The exciting high energy program involved not only preparing experiments for the adjacent Cambridge Electron Accelerator, including a planned electron-positron storage ring,  but also had begun to prepare experiments for Fermilab and CERN.   They were using at least half of the Cyclotron Laboratory office building and its machine shop, and in 1972 converted the basement to productive use.  They had already taken over the adjacent historic Palfrey House as office building, and the Dunbar laboratory, released by the geology department for a computer and related work.   An assembly area under a 30 ton crane was very attractive.     But the medical program of Dr Ray Kjellberg was showing great promise and it seemed improper to abandon it.    Already in 1965 Dr Kjellberg discussed with Massachusetts General Hospital whether they could take over operation of the laboratory.  There followed a 5 year period of discussion, irrevocable decisions,  revoking the decisions, and further discussions.   These are recorded in a series of letters to various administrators about closing the cyclotron.   All options were considered.   Moving it to another University (such as Northeastern) who wanted it, (in the same way the Berekeley 60 inch cyclotron moved to UC Davis), allowing another organization, hospital, University or merely different faculty, to run it;  or closing completely.   The first decision, noted in a 1967 letter from the director, Dr Preston, to the Dean Franklin Ford was to close the cyclotron at the end of December 1967 when ONR support terminated.  What was thought at the time to be the last "run",  and actually the  first of many "last runs",  on February 6th 1968,  was by Allan Cormack (then at Tufts University) and Mildred Widgoff (of Brown University) probably on proton radiography.  There was no fanfare but Allan in his typical courteous fashion, wrote to Bill Preston to thank all connected with the cyclotron for their hospitality.
    But events proceeded slowly.  The always astute Harvard administrator Dick Pratt (who had started the Office of Research Contracts at Harvard University) had persuaded the Office of Naval Research to commit the US Navy to remove the cyclotron if so requested.   But they had no funds allocated for this.  At their request estimates were prepared for the cost of this by HCL staff.  These estimates of the cost for removal ranged from $191,000 to $240,000.  Anxious to recoup what they could, the Navy put the cyclotron on the Excess Property List.   Dr Kjelleberg had some (limited success) in obtaining support from MGH for the costs of running the cyclotron.   It was proposed to run the cyclotron one or two days a week till this was resolved.  The conditions were described in a letter from Bill Preston to administrator Henry Murphy at MGH on July 28th 1968 and described in a letter to Dean Franklin Ford on October 8th 1968.   But then another irrevocable decision was made to close the cyclotron in 1969 as noted in a letter by Professor Frank Pipkin.  In March 1970 the US Congress, under pressure from anti Vietnam war protestors,  passed the Mansfield amendment which prevented further funding by the US Navy of any work at universities.  The Harvard generic "nuclear physics" contract was at an end.  If the cyclotron funding had not already ceased it would have been terminated by July 1st 1970.
        A preferred alternative to dismantling the cyclotron, and for the high energy group to take the building,  was “give” the cyclotron to Massachussets General Hospital or Harvard Medical School with an informal undertaking by appropriate physics department members to help in any problems that arose during operation.   MGH would pay for operation and pay some sort of rent for the space represented by the building.   Negotiations continued about this throughout the four years.   This ran into a two fold snag.  Firstly Dr Kjellberg was not in the center of Harvard’s medical activities and the medical community were not as aware of the possibilities as were the physicists (although Dr Milford Schulz, head of the Radiation Medicine Department at MGH supported it).  Richard Wilson, the present scribbler, who was at the time Chairman of the High Energy Physics Committee of the department wrote to, and then went to see, the Dean of Harvard Medical School,  Dr  Ebert,  Harvard Medical School to encourage HMS would support the cyclotron.   But Dr Ebert had found no support in his faculty.   Physicians thought that the resources of the school were better committed to finding the causes of cancer than of treating it.  Moreover, cancer experts were arguing that chemotherapy was a more promising choice for patient treatment than radiotherapy.   While both these arguments seemed plausible at the time, it is now clear that they were wildly over optimistic.  35 years later the causes of cancer are still elusive, and chemotherapy, by itself, is far less effective that when combined with radiotherapy.   Rightly or wrongly,  medical funding to keep the cyclotron did not seem to be forthcoming and it was decided to close the cyclotron and make the building available by 1970.    But other events intervened.

        Already in 1970 there was a very marked cut back in funding for the Cambridge Electron Accelerator, leaving only a program on electron positron colliding beams, the "By Pass"  program in place.   Then in 1972 the federal axe fell.   The US Atomic Energy Commission (AEC) withdrew funding starting in summer 1973.   Without any known source of funds, Harvard and MIT decided to close the CEA.   That would left plenty of space for the remaining high energy physics program.    Moreover there was a reduction in the Harvard contract for high energy experiments, even though these experiments would now have to be elsewhere and travel funds would be neded.  The whole program was thereby reduced.  There was no pressure to shut the cyclotron down if even a small amount of funding could be found.    

        The cyclotron was finally rescued by two important steps.  Andreas (Andy) Koehler proposed a budget to the physics department showing that the cyclotron be kept alive for one or two days a week, funded by  patient fees from Dr Kjellberg’s patients.   It was necessary for the someone to “guarantee” the budget and to hold the bag if the fees failed to arrive.   Since both MGH and the Medical School had showed reluctance to do this,   Dr Preston and Professor Wilson  persuaded the physics department to do so.   A noteworthy part of the budget was that Andy Koehler went on half pay - but of course he has NEVER been on half time.     The second step was the arrival in Boston of Dr Herman Suit, to become the new Chief of the newly established Department of Radiation Medicine at MGH.    At a special Saturday morning meeting with Dr Samuel Hellman of the Joint Center for radiothapy at the Medical School, Dr Suit declared to Professor Wilson that one of the attractions of moving from Texas to Boston was that he could use proton therapy. Professor Wilson, slightly overplaying his hand, agreed that the physics department would keep the cyclotron open - which it did.   About this time Dr Suit arranged a set of small meetings in the Boston/Cambridge area to discuss whether indeed protons were the best option when compared to helium or carbon ions, or negative pions. For a number of reasons the community agreed that protons were the best option.  This increased the local support considerably. One of Dr Suit's first appointments was of the physicist Dr Michael Goitein,  (Pictured on the left) who had gained his PhD some 3 years before from Harvard Physics Deparment for a thesis on elcctron proton scattering under the guidance of Professor Richard Wilson.  Dr Goitein was an expert in the use of computers.  He had, as a student, put the electron scattering experimental program "on-line" and had been awarded the IBM graduate student fellowship. This interest and experience was to be put to good use later.   The stage was now set for a most productive 30 year period of the operation of the Harvard Cyclotron. Locally  we were aided by a fortuitous circumstance.  The Atomic Energy Commission had established an information exchenge program with the Soviet Union. Dr John Lawrence of UC Berkeley was asked to head a 3 man team to study proton therapy in Russia. He chose to take with him to the USSR, Dr Kligerman, radiotherapist  from the University of Pennsylvania, and Andy Koehler. On a return visit, the Russian 3 person team visited Harvard and Richard Wilson hosted a small party for all physicists and physicians involved with the HCL program - about 30 in all -  and other physics department members interested.    The Department Chairman, then Professor Paul Martin, was convinced of the importance of the program.    

        Funding was the most difficult task.    Dr Ganz of MGH, pediatrician for Dr Kjellberg's children, suggested to Dr Charles Regan of Massachussets Eye and Ear hopsital that the proton beam was ideal for treating eye tumrs and in particular the heridatary tumor retinablastoma.   Interestingly, we treated only a handful of retinablastomas, but in 2003 they are high on the list of new treatment modalities for NPTC.  Dr Regan put in a proposal to NIH but it was turned down, largely because of inadequate communication between Mass. Eye and Ear and HCL.  Dr Regan mistakenly described the alpha particle beam (not the proton beam) and Dr Preston felt only able to give suport that cost FAS nothing.    Both these defects in the proposal were remedied in a new proposal that was finally successful, that involved Dr Ian Constable and Dr Evangelos Gragoudas.  Nonetheless  medical funding was slow in coming,   so that the physicists  Koehler, Preston and Wilson (called the Biomedical Group in the Harvard archives), started searching.    On the principle of starting with the largest pocket, we approached the medical program of the Atomic Energy Commission which at the time were spending some $4 million a year on proton and alpha radiotherapy at Lawrence Berkeley Laboratory, hoping for a small fraction - perhaps 10% of this sum.    No luck.   But providentially the National Science Foundation started a new program, “Research Appropriate for National Needs”  (RANN).  The cyclotron received two grants for this work.   The first was to adapt the Harvard Cyclotron and for clinical trials.    The second was a pilot study of detecting calcium in the extremities of the body by proton bombardment producing the radioactive potassium K38 and detecting the characteristic 2.16 Mev gamma ray.   In addition fees from the neurosurgery patients brought by Dr Kjellberg continued to arrive.   

    Proton Radiography

    There were also other attempts to use the cyclotron for interesting medical purposes.    In the late 1960s, Andy Koehler conceived the idea of using the beam for "proton radiography" - measuring the density of material rather than the high Z material shown on an X ray of a CAT scan.  The aim was an early diagnoses of cancer which would manifest itself in a small density change - and therefor a change in the range of the protons.   The beam has a well defined range, which range in centimeters is determined primarily by the energy and the density of the material.  This if the density increases a few percent because of a tumor, the range will decrease a few percent - and that should be measureable.    This would be better than an ordinary radiograph where small density changes were hard to observe.  Ordinary X rays at the time depended upon the fact that photon absorptin tends to vary as the atomic number (Z) to the 4th power.   Blood, containing iron shows up, and if barium or other high Z material is in the food, they show up better. The first test of the idea was dramatic, and showed itself in a famous "lambrk chop" radiograph (photograph) taken by Andy and shown in many colloquia and conferences.  The procedure, but stargely enough not this dramatic picture, was published in Science (see reference list).   This stimulated much interest, in the scientific world.  In addition to Andy,  Allan Cormack (by then at Tufts University) and Mildred Widgoff (from Brown University) and Dr Seward (from University of Chicago) worked on this idea at Harvard Cyclotron.   Allan Cormack had an even bolder approach.   Could not the proton beam be used firstly to determine the position of the tumor and then to treat it?  In this way, he hoped, an effciient, and therefore cheap, procedure could be devised for treating tumors.    

    This general idea was also picked up by Dr Ken Hansen, a former Harvard Student who sudied it at Los Alamos National Laboratory.    However, for medicine there was no resolution of the practical matter of making it work well.   Moreover, ordinary radiography, and CAT scans improved very conmsiderably, and (Nuclear) Magnetic Resonance Imaging (MRI) was able to determine the small changes in low Z materials indicating tumors rendering it unnecessary.   Maybe the idea will be resurrected at another time.

Proton radiotherapy - the continued work  (1975 – 2002)

      In 1972 Drs Suit commenced a program of clinically related radiation biological experiments to assess the RBE value to be employed. These were done by Drs. Robertson of the Harvard School of Public Health, Raju of the Los Alamos Laboratory and E. Hall of Columbia University. These were in vitro  studies. In parallel, a long series of RBE assays were performed on intact tissues of the laboratory mouse by Drs. Urano and then Tepper. The result was that 1.10 was chosen to serve as a generic RBE value, viz  all dose levels and tissues.

    Then in February 1974, the first patient was treated using fractionated dose radiation therapy at the equivalent of about 2 Gy/fraction. This patient was a boy with a posterior pelvic sarcoma. The second was a woman with a skull base sarcoma. This category of tumors now includes some 800 with really impressive results. Namely, the 10 year control results are 95% and 45% for chondrosarcoma and chordoma, respectively.  The principal clinicians included Drs  Liebsch, Munzenrider, Austin Seymour, Hug and Suit. The important clinical physicists were Drs Goitein, Verhey and Smith.    In 1975 the first of  2,979 patients was treated for ocular melanoma by a team comprised Drs Evanglos Gragoudas [ophthalmological surgeon of the MEEI], John Munzenrider [radiation oncologist of the MGH] and Michael Goitein [physicist at the MGH].. Dr Goitein developed the first 3D treatment planning software to be implemented in regular clinical work in many parts of the world.  It was first designed for treatment of ocuilar melanoma. He also developed the concept of and brought into clincial practice: DVH, dose volume histogram, DRR [digital reconstructed radiograph], and the display of uncertainty bands around isodose contours. 

    1976 was the year for the start of funding of the first NCI grant for clinical study of proton beam radiation therapy. This funding has been continuous from 1976 to the present. This grant was critical for the conduct of this radiation oncology program. Drs Suit and Goitein served as Co Prini\cipal Investigators to 1976 to 1998 when Dr Jay Loeffler became the PI.

       In 1975 Dr William Preston retired from his positions as director of the cyclotron laboratory and director of the physics laboratories.    The staff now included Dr Robert J. Schneider, Dr Janet Sisterson, Ms Kristen Johnson and Mr Miles Wagner in addition to Andy Koehler as Assitant Director and Bill Preston as Director emeritus.  The management procedure was changed.   The management was vested in the acting director of the laboratory, reviewed by a management  committee chaired by Professor Richard Wilson (other members, Dr S.J Adelstein (Academic Dean HMS), Dr Herman Suit and Dean Richard Leahy) .  This committee reported directly to the Dean of FAS and administratively bypassed the physics department.    By this time the medical program at Harvard Cyclotron laboratory was well under way.   There were three basic prongs.  Each had its peculiarities both in funding and in treatment.    These differences sometimes led to stressful problems.

        One of the reasons for the overall success of the program was the ability of the  Harvard Cyclotron staff to manouver independently of the rivalries and scientific and political differences of the three groups.   Originally the relationship between the Cyclotron Laboratory and MGH was highly informal.  By informal agreement with Dr William (Bill) Sweet, director of the neurosurgery department at MGH, Harvard Cyclotron was treated as an operating room for purposes of liability and responsibility of the surgeons. All Harvard cyclotron personnel were covered by medical malpractice insurance on the general Harvard University policy.   But the increasing number of patients, and the fact there were three programs of which one, the neurosurgery program, was completely separated (on the hospital side) from the others made a more formal agreement necessary - if only to prevent quarrelling between the physicians and surgeons.  This was forced by a stormy interchange in 1977 and made formal and legal. The cyclotron staff also had to be made aware of the demands of patient confidentiality   Harvard University negotiated a one-sided agreement.  MGH was responsible for any liability arising from the treatments, but nonetheless, anyone on the cyclotron staff had the authority to decide NOT to treat a patient if he felt that the planned treatment was inappropriate.    Fortunately such an eventuality never occurred.

      (1)  Neurosurgical (intercranial) lesions treated by the Neurosurgery department of MGH  Dr Raymond N. Kjellberg and Dr Bernard Kliman, later Dr Chapman)
      (2)  Eye tumors treated by Massachusetts Eye and Ear Hospital.  (Dr Ian Constable, Dr Evangelos Gragoudas )
      (3)  Larger tumors treated by the Radiation Medicine Department of MGH. (Dr Herman Suit, Dr Joel Tepper, Dr Michael Goitein, Dr Lynn Verhey)

    We collect here some photographs of the various treatments 

        In the following 27 years each of these groups made major contributions, and each was in its own way essential to the whole program. However from the start  the physicians at  MEEI collaborated very closely with the physicians at the Radiation Medicine Department at MGH and in particular with the physicists (led by Michael Goitein) at MGH.  The software program for 3 dimensional treatment planning which was developed by Michael Goiten was used for both the ocular tumors and the large field tumors as well as being the basis for similar programs at many other medical centers worldwide. In 1981, Professor Richard Wilson went on leave and a change was made.  Dr S. James Adelstein, academic dean in the medical school became Chairman of the management  committee. The reporting was changed to report to the Dean of Applied Sciences instead of the Dean of FAS.  Dr Adelstein remained Chairman for the next 21 years until the shut down in 2002.

        The medical advanttage of all of the treatments followed the point raised by Robert R. Wilson in 1947.     The aim of all radiation treatments is to destroy cancerous and other unwanted tissue, while doing as little damage as possible to the surrounding healthy, and, desired, tissue.   The proton beam succeeds in this for two reasons.  Firstly protons have a well defined range, with a shap increase of ionization at the end of the range first pointed out by Sir William Bragg (the "Bragg peak"). They produce little or no damage beyond the end of the range.  Secondly protons being heavy, scatter less than the electrons commonly used for radiotherapy. If the tumor or other lesion is small,   (less than 1 cm diameter) as in treatments (1) and (2)  it is comparatively easy to install absorbers so that the protons stop on the lesion.  If the lesion is large, as in treatments (3), it is much harder to obtain a uniform dose distribution across the tumor. The photograph shows a typical dose distribution across a pituitary gland.  

        The large field arrangement was a simple one that was designed, as was so much, by Andy Koehler.   Firstly the beam impinged on a scatterer to spread the beam.   This resulted in a beam that was non-uniform in intensity across the beam.  Then an absorber was paced in the center of this beam to absorb the higher intensity portion.  Finally there was a second scatterer.  This double scatterer technique produced a remarkably uniform beam distribution.  Then the range was modulated by a set of absorbers on a wheel that rotated during the treatment, allowing the proton beam to stop at various depths in the tumor in turn.   A plastic bolus was machined for each treatment (photograph) and restricted the sidewise extent of the beam.   

          More promising, perhaps, was the idea that production  of potassium (K38) by proton bombardment of calcium, leading to a bioassay for calcium.   Here the idea is to locate calcium loss in the spine long before calcium loss shows up in the extremities.   In a PhD thesis,  (also funded by NSF in their RANN program) Dr Eilbert was able  to find a reproducability in a phantom, made of hamburger surrounding fossil bones, of 1.5 %.  However medical support was not, at the time, forthcoming and the project was abandoned. At that time also we tried to obtain funding from the National Institutes of Health for a "facility" grant, for keeping the cyclotron alive for a variety of medical purposes including, of course, therapy.  However, this also was unsuccessful.

         From the beginning of this period onwards it was realized that the Harvard cyclotron was not ideal for the medical work it pioneered.  Although the range of protons in tissue was 10-15 cms, this was not enough to reach all tumors from all directions.   In addition it is far preferable for a cyclotron to be located at the hospital.    Already in 1973 Andy Koehler was thinking about small, cheaper, specialized cyclotron designs.   But it was already realized that the cost of the cyclotron itself was a small part of the total treatment cost.  

        Professor Bernard Gottschalk returned to the Harvard Cyclotron Laboratory as a Senior Research Fellow in 1982.   One of the first tasks he undertook was to plan a new accelerator: his choice being a synchrotron because the energy is easily variable.   Although attempts to obtain NIH funds for this new  development failed, his design was useful in the design for the synchrotron at Loma Linda University Medical Center.      That synchrotron was funded in large part by a special grant from the US Departmen of Energy.  This grant was congressionally directed funding from the committee on energy in the House of representatives chaired by Representative Lindy Boggs of Louisiana.  Ms Boggs was very sensitive to the need for proton radiotherapy since her daughter, Mayor of Princeton, died of a choroidal melanoma which metastasized.   They became aware of our (Massachussetts Eye and Ear Infirmary, Massachusetts General Hospital and HCL) successful cures too late.   We were asked by a committee staff member whether we would like to be included in the special appropriation, but Harvard University and MGH do not accept congressionally directed ("pork barrel") funds, so that  a hospital based facility had to wait another 10 years.

        In 1990 after application to NIH design funds were made available for a complete new proton therapy facility - accelerator, beam lines, treatment rooms - the lot.    Professor Michael Goitein, at MGH and Harvard Medical School was the PI of the grant and  undertook the design.   Construction funds were made available in 1994.    The contractor for the fine building was Bechtel, and for the cyclotron and beam lines, IBA of Belgium.    This became the Northeast Proton Therapy Center (NPTC) at MGH built in the exercize yard of the old Charles Street jail.  The building and the first operation of the cyclotron came in on schedule, but reliable operation of the beam, beam transport and gantries was elusive. After much travail,  the first patient was treated in November 2001 and the whole proton therapy program began the switch to NPTC in November 2001, and NPTC picked up the full load by April 2002.

        By 1993 Andy Koehler (shown here in his office) had been with the laboratory 40 years, many of them as acting director or director.  He asked to be relieved of his duties as director, remaining a senior research fellow.  But there was plenty of able talent.  Miles Wagner took  over as director and led the program for the next 9 years.    In 1999 the Harvard cyclotron had been operating for 50 years.   This was a record for cyclotrons, many of which had shut down as nuclear physics and high energy particle physics developed.   We had already had many major parties.  A "final closing" party in 1967;  another "closing party" in 1970, and a 40th anniversary party.   We had to celebrate once again.  We did so with  a one day symposium followed by a dinner at which Andy Koehler's formal retirement was announced. But With Andy, as with so many loyal Harvard people retirement did not mean stopping work.  

        On Wednesday April 10th 2002 the Harvard cyclotron treated its last patient - the 9,115th.  The patient was a  young boy  with bilateral retinoblastoma - a heriditary cancer of the eye.       Starting when he was 2 months old and continuing till he was 4 months old,   he received 22 irradiations to each eye.  We anticipate that he will be cured. A total of 2,979 eye tumors have been treated  along with 3,687 neurosurgical lesions and 2,449 large tumors at various sites. A dedicated group of professors, physicians, physicists,  nurses, operators and technicians  from Harvard and MGH attended a small   celebration of this work in the evening.   The last photographs were taken at this celebration.   But the sucess of the therapy program is not merely the success of the local sucessor (NPTC) at MGH.   It is the success of the 19 other locations where the HCL/MGH treatments have been copied or are planned.

Other experiments - Radiation Damage Studies

        The first use of the cyclotron for radiation damage studies came when ATT needed to test their transistors to see whether they would survive in space.  In space there are a number of cosmic ray protons with a peak in the spectrum around 150 Mev.  In 1961 a former graduate student of Professor Robert Pound, Dr Walter Brown, then at Bell Telephone Laboratories in Murray Hill, NJ, brought some of the equipment to be bombarded with 150 Mev protons in the cyclotron.  The equipment survived the test, and so did the equipment on board the Telestar satellite.   NASA also realized that there was a need to understand not only how equipment behaved in the radiation environment of space, but so also was there a need to understand how people behaved.      That was the primary reason that NASA funded the construction of the Medical Annex to the cyclotron.    NASA also funded a special cyclotron with an energy of about 500 Mev in Newport News, Virginia to perform radiation damage studies for satellite communication equipment and components.   But the NASA cyclotron proved too cumbersome for the task and it was shut down in the late 1960s.    Over the years,  NASA directly, and contractors  for NASA, regularly brought equipment to Harvard Cyclotron laboratory for test.  The scientists would typically have the cyclotron to themselves for the whole weekend (when medical work was not being done) with a cyclotron staff member, most recently Mr Ethan Cascio,  to help them.    

Other experiments - Crossections for radionuclide production

        Experiments on radionuclide production were planned from the earliest days and a radiochemist, Dr James Meadows, was hired as a research fellow.   Over a 5 year period, with a break while the cyclotron was upgraded, he studied various radionuclides.  On his departure for Argonne National Laboratory he was not replaced.     Some irradiations were again performed by Dr Robert Schneider when he was in the laboratory as a post doctoral fellow.   One such was O(p,3p)14C. When he left the cyclotron lab for greener pastures at General Ionics he realized that there was a need for more cross section measurements for proton-induced reactions similar to ones that we had made before, partuclarly to study the long-lived radionuclides that are now extinct but would have been present in the early solar system. Schneider and  Sisterson then measured the cross section and excitation curves for the reaction 27Al(p,pn)26Al at HCL.  The produced 26Al was measured in the Tandem Laboratory at the University of Pennsylvania.     When these results were presented at a meeting,  Bob Reedy of  Los Alamos National Laboratory (now affiliated with the University of New Mexico)  poited out that this and other crosssections are important for his cosmic ray studies.      About that time, also,  titanium foils were irradiated for Dr David Fink of the  University of Pennsylvania,  to determine the cross sections for the reactions producing short-lived radionuclides and the cross sections for Ti(p,x)41Ca.

    Schneider, Koehler and Sisterson bombarded a  piece of the Bruderheim meteorite with a proton beam of uniform intensity. Ed Fireman of the Smithsonian extracted the carbon using his ‘usual’ procedure to produce a CO2 sample, which was sent to the Isotrace Laboratory, University of Toronto for determination of the carbon isotopes using Accelerator Mass Spectroscopy.  The value for the cross section for O(p,3p)14C so determined was much higher than expected. The earlier measurement of HCL was in error due to a mistake in calculating the proton fluence. Once this error was corrected, the corrected cross section was in much better agreement with the historical data and other recent measurements of this cross section made by us at HCL and others.

    Cosmic rays interact directly with extraterrestrial materials to produce small quantities of radionuclides and stable isotopes. In well-documented samples from the lunar surface (rocks and cores) and meteorites a large number of cosmogenic nuclides have been measured. The advances in AMS have allowed these measurements to made routinely in small samples, a great improvement over the heroic efforts previously required to measure the decay products of these long-lived radionuclides. Theoretical models have been developed to interpret these measurements so that we can learn about the history of the object under study or the cosmic rays that fell upon it. Most of these models try and account for explicitly the interactions of all cosmic ray particles with all elements commonly found in these extraterrestrial materials. Therefore, good cross section measurements for relevant reactions are needed over the cosmic ray energy range as input to these models. Most cosmic rays are protons (~98% of solar and ~87% of galactic) cosmic rays, so it was thought that the most important cross sections needed as input to the models are those for proton-induced reactions.  

    Irradiations were made by a collaborative program at three faciltities.  UC  Davis, for energies of 67.5 MeV and below, HCL for energies from ~40 –160 MeV and TRIUMF (Vancouver) for proton energies of 200, 300, 400 and 500 MeV. The irradiations at Davis were made by colleagues at San Jose State University. With the help of the cyclotron operators, I made the irradiations at HCL. Sisterson and Vincent made the irradiations at TRIUMF.    It turns out that neutrons ARE important since  many neutrons are produced in the interactions of galactic cosmic rays, which can penetrate deeply into a body. At depth in an extraterrestrial body such as a meteorite, these secondary neutrons produce most of the cosmogenic nuclides.   Neutron induced crosssections were measured at iThemba LABS (iTL), Somerset West, South Africa using neutron beams at quasi-monoenergetic energies; and using ‘white’ neutron beams at the Los Alamos Neutron Science Center (LANSCE), Los Alamos.   Sisterson and collaborators have been able to show using the cross sections that they measured at high neutron energies for reactions producing 22Na (a radionuclide not produced by low energy neutrons) that including only the cross sections for only some of the pertinent reactions leads to calculated production rates that are closer in value to those measured in lunar rocks.  Dr Sisterson moved to the NPTC at MGH in 1999 where the program continues.

Other experiments - Radionuclide production for medicine and physics

          It is a curious historical development that one of the most important uses of cycotrons in the 1930s was the production of radionuclides, particularly for medicine but also for other physics research.  It was noted above that this was indeed, and important use of the first Harvard  cyclotron.   Although these were discussed in the funding proposal,   these were much less important for the second Harvard cyclotron.   There were several reasons.  The most important perhaps is that neutron rich radionuclides are easily produced in a nuclear reactor, either by neutron bombardment of a stabele element, or as a product of fission.  The cyclotron could produce neutron deficient isotopes, but the intensity was not great and medical needs were served by more intense linear accelerators and special cyclotrons, often lower energy but higher intensity.

        A notable exception was the production of "On Gamma Ray Directional Correlations Disturbed By Extra-nuclear Fields" for the PhD thesis of Dr Gunther Wertheim in 1955.     We also note in the publication list  that Rh 100 was also produced for the thesis of Dr Hohenemser.

Other non cyclotron experiments in the Cycotron laboratory - the CAT scanner

    During 1956-57, while waiting for the counts to be recorded on the scalers, Allan Cormack would discuss his ideas for improving X ray radiography.   He had already thought about the problem while a lecturer at the University of Cape Town and an informal consultant to the local hospital.  It is stupid, he used to say, to limit the information to a simple picture showing the absorption.  This was merely a set of line integrals of the 3 dimensional absorption characateristics.    He found an article from 1919 or thereabouts,  showing that a set of line integrals, taken from all directions could be mathematically converted into a spatial distribution.   Being an excellent experimenter he wanted to show this by experiment.   It so happened that the Cyclotron Laboratory had a strong radioactive source (and a fine colleague in Andy Koehler).   So, in the basement of the Cyclotron Laboratory, Allan with a student, laboriously measured a set of absorption line-integrals for a phantom.  It took a week to convert this into the spatial distribution - a job now done by a computer in a second or less.  So it was that the CAT  scanner (Computer Assisted Tomography) was conceived.     It took Allan's energy and enthusiasm to advertize this among the medical community, but after a few years he had succeeded and in 1979 he shared the Nobel Prize for Medicine with Sir Godfrey Hounsfield from Electrical and Musical Industries (EMI, UK), who had built the first working example, "for development of the concept and first experimental models of CT scanning"

We are all proud to have known Allan and to have helped in a miniscule way, in his success.


    The University wanted the space occupied by the cyclotron for a large underground parking garage and new science buildings on top. Although the last patient was treated on April 10th 2002 the cyclotron kept going 7 more weeks.     The University was not quite ready to begin the process of decommisioning.  In the meantime a backlog of radiation damage studies were performed.  Mr Ethan Cascio, one of the many loyal staff members over the years, was in charge of these radiation damge studies in the last years, and was  responsible for the last operation of the cyclotron performing studies for Minneapolis Honneywell which came an end was at approximately 9 am on Sunday morning June 2nd 2002 when the last radiation damage study was concluded, and the cyclotron was shut down by Harvard administrative staff a day earlier than agreed and switched off for ever.    This was 53 years and 7 hours after the first  beam was an untimely end on June 2nd  2002 when the cycotron .   By October 2002 the office building had been emptied and dismantled and in November 2002 the shield walls and other material in the cyclotron vault itself were being removed.  The magnet shims cut by hand with tin shears by Professors Strauch and Wilson on Christmas Eve 1955 were still in place.   The regenerator and beam extraction equipment were the same as those installed rapidly in summer 1956.   The magnet, the rigging of which took so much trouble and care to install in 1947 was cut up into small pieces and sold as scrap material.   The radiation levels were smaller than had been feared.   In summer 2003 the cyclotron vault is being removed.  

    But the work lives on.  Although Harvard was not the first cyclotron to use protons for radiotherapy it was for many years the most successful,  largely because of the close cooperation between the physics department, the cyclotron staff, and the physicians at MGH.   As we write there are perhaps 19 other institutions now using proton radiotherapy.    In them the Harvard cyclotrons live on.


.    Information below has been collected from a variety of sources.   The initial collection of work of the Harvard  cyclotron, and n particular the medical work, was collected by Professor Janet Sisterson now at Harvard Medical School.   These have been scanned by  Ms. Yanjun Wang and are available for those who desire them. Other sources are the website and a paper by Katherine Sopka in 1978,   " Physics at Harvard during the past half-century, A brief departmental history, Part I: 1928-1950". Kristen Johnson who worked for a year at the archives after the closure of the cyclotron added a number of documents and lists of publications, as did Dr Bernard Gottschalk.   The comments and criticism of many others has been important to avoid the innumerable errors in the first draft.   I especially thatk Professors Norman F. Ramsey and Robert V. Pound.


List of papers published and theses prepared with cyclotron experiments or at the cyclotron laboratory.