Five Nobel Prizes were won based on work at the Bevatron, including the nobel Prize in Physics, for the discovery of the anti-proton. The experiment began with a thin cloud of hydrogen gas. First, scientists extracted protons from the hydrogen atoms, and injected them into the accelerator chamber. As the protons whipped around and around the chamber they went faster and faster, until they approached the speed of light. Which is exactly what happened. Since mass and energy are essentially interchangeable, the Bevatron was able to transform matter into energy, and energy back into even more matter… including, in , for the first time ever, antimatter.
This work won Bevatron scientists the Nobel Prize in physics. It was the first of four Nobels to come from research done here — as well as new insights into things like radiation treatment for cancer, and how to keep astronauts safe from radiation in space. Taking down the Bevatron is a huge endeavor. The cited page is noted as "3 of 5".
The fame of the magnetron did not end with radar. An engineer in the US firm Raytheon a manufacturer of military radar equipment noticed one day, when standing near a magnetron tube, that a chocolate bar in his pocket melted. Then he showed the magnetron a bag of popping corn, which exploded all over the floor. Next, he tried a raw egg in the shell! Today, this very same magnetron, operating on 12 cm wavelength, powers the humble microwave-ovens in our homes. What was your contribution, John, to this work at Malvern?
Then I was allocated to the Counter Measures Group. Its function was to counter enemy-radar by jamming, moving to different frequencies, etc. These gave much stronger reflections to the German radar than aircraft did and, since there were so many of them, they masked the signals from the planes. This technique was also useful for deception. Looking back, this experience with radar and your own hobbies stood you in good stead with your future research.
It did indeed.
I should mention that I worked on high-frequency receivers that scanned a wide range of frequencies to pick up enemy signals. Then, after the war in Europe ended, I was transferred to a group working on missile guidance systems. Radar had top priority in the UK, involving most scientific brains in the country and significant industrial support. In the US, radar was second in priority only to the Manhattan project; it was essential for them to make an Atomic Bomb before Nazi Germany did.
I feel very privileged to have had the opportunity to work on radar during the war. As in any scientific project, it was very exciting and rewarding. I learned a great deal about advanced electronics, pulse - circuitry, etc. This experience and knowledge was of great benefit to me throughout my scientific career. It did, indeed. Our modern enormously complex global air- and marine- transport networks would be impossible to operate without radar. The electronic pulse-circuitry, developed at TRE for radar, was the essential base for the development of computers. Williams and Killburn, from TRE, continued their work at Manchester University and in set up the very first electronic computer with digital storage, which marked the beginning of the computer age.
Radar is even used to detect drivers breaking speed limits! I hope not too. An important spin-off from microwave technology in was the Maser, used today in atomic clocks and measurement of the cosmic background radiation from the Big Bang. Further developments led to the Laser in Since then this has been used in many human activities such as cutting metal, CD and DVD players, barcode scanners, ophthalmology, etc. Today, ultra high power lasers are being trialled to initiate nuclear fusion for power production.
Also the military are working on air-borne lasers to shoot down enemy missiles. After the war some of the people from TRE went back to their universities and started up radar astronomy. They built radio-telescopes and were able to see objects like quasars, which are the most distant things in the universe, and pulsars, which are neutron stars, with the mass of the sun, rotating around in a few milliseconds.
They are cosmic clocks. This had a very big influence on my life in the future. They were a very nice, intelligent group of people, who used to discuss plays, poems, arts, politics, etc. Also, we had lots of social activities, like playing tennis, going for walks, going to concerts, and cycling trips all over the country.
Later on, after the war, we did a lot of hitchhiking trips on the continent, visiting many countries—France, Italy, Switzerland, etc—which was very interesting and educational as well.
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I returned to take my third year, which was called Part 2 of the Natural Science Tripos. Many of us returning from war activities, which were quite different from studying for examinations, were allowed to take two years over Part 2, rather than the normal one. Cambridge had changed a lot because the government gave financial support to people, who had been in the armed forces or in research institutions, to go to university.
People, like me, returned to complete their degrees, while many others came for the first time. They were mostly not from rich homes and they were much more mature than the normal intake of students who were straight from school. They really changed the nature of Cambridge. After the war it became a meritocracy, which I think was a very good thing.
For me, being a shy person, that made things much easier. We enjoyed many social activities like balls, tennis and so on. The physics was great. There were some very brilliant people such as Dirac, Devons, Hartree, Hoyle and many others who gave excellent and stimulating lectures. It was only after the fourth lecture that I realised he was talking about statistical mechanics.
A friend of mine also gained a first-class degree, and we celebrated by blowing soap-bubbles, which floated all over the main court of our College. The first-class degree entitled me to become a research student at Cambridge and also to get a grant from the Department of Scientific and Industrial Research for maintenance. You joined the Cavendish in , and that was a time when nuclear physics in many ways was still in its infancy.
Indeed, it was. First a little history, in , Rutherford demonstrated with his famous experiment on scattering of alpha-particles by a gold foil that the atom had a very small, dense, positively charged core, which he called the nucleus. His atomic model is similar to the solar system, with the sun containing most of the mass, and the planets revolving around it. The radius of the nucleus is about 10, times smaller than the atomic radius of one hundredth millionth of a centimetre!
This showed for the first time that the atom was not a solid-like object as previously envisaged.
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After discovering the nucleus, Rutherford wished to find out its internal structure. He knew from his experiments with radioactivity that very high-energy alpha- and beta-rays must be emitted from the nucleus; also that there must be some very strong short-ranged force to prevent its positively charged components blowing it apart. The lightest nucleus, that of the hydrogen atom, is called the proton. In , Rutherford realised, from a comparison of atomic mass and charge numbers, that all other atomic nuclei must be made up of a mixture of protons and neutrons, particles with similar mass but no electrical charge.
In , the neutron was discovered experimentally by Chadwick at the Cavendish Laboratory. To study nuclei, he had to bang two nuclei together very hard, so that they would stick together or break apart, and observe what happened. For this he required high energy to overcome the repulsive force between the two positive charges. In he carried out the first artificial nuclear transmutation by bombarding nitrogen with alpha-particles and producing oxygen Little could be learnt because alpha-particles from radioactive sources are not emitted at sufficient rates and they fly off in all directions. Rutherford realised that, because nuclei were so small, the probability of a collision between them was minute.
If they were to collide in sufficient numbers, a very intense, well focussed, ion-beam was required. He thought he could achieve this with an apparatus similar to an enormous cathode-ray tube.
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It required a hydrogen-ion-source, mounted in a terminal with high positive voltage; the resulting electric field would accelerate the positively charged ions. In , he put his idea to the Royal Society, saying that, with it, we could do things never possible before.
He obtained a grant from them and asked two junior colleagues, Walton and Cockcroft, to build such a machine, hopefully reaching several million volts. With great difficulty, due to primitive technology, they successfully completed it by They managed to get the accelerating voltage up to kilovolts, giving a proton-beam with an energy of kilo electron-volts keV. With Rutherford, they bombarded a target of lithium-7 with protons. They observed emission of two alpha-particles helium nuclei , each with an energy of 8 million electron-volts MeV. The difference between the initial and final atomic masses showed a deficit of 0.
This reaction showed that the atomic nucleus is a vast storehouse of power. Since then, accelerator technology has advanced with astonishing speed. By the early s, accelerators reached energies high enough to produce new exotic particles. At Berkeley, the gigantic Bevatron, producing protons of 6. It was discovered in followed by the anti-neutron in It collides two proton beams, one circling clockwise and the other anticlockwise, each reaching an energy of several TeV trillion eV. Accelerators have been developed for radiation therapy and for producing radioactive isotopes for medical diagnostics and radiotherapy.
Today, proton and carbon beams from cyclotrons are being used to destroy cancers with great precision. Just going back to for a moment, these ideas were around, but not very much was known about nuclear structure or nuclear reactions in detail. That is exactly right. They knew that the nucleus was composed of neutrons and protons and it was rather like a conglomerate of billiard balls all stuck together. So at that time people often thought that it would behave like a liquid drop, which is rather similar; it has molecules very close to one another that can vibrate collectively together.
Enough was known to actually make nuclear weapons and nuclear reactors because that is about when they started. That is indeed right. After the discovery of the neutron it was realised that even low - energ y neutrons could be used to initiate nuclear reactions, because there was no electrostatic repulsion. In , Hahn and Strassman in Berlin, bombarded uranium with the hope of making heavier elements. Instead, to their surprise, they produced lighter elements such as barium.
They thought that the nucleus behaved like a floppy liquid drop, oscillating and eventually splitting. An enormous release of energy MeV resulted from the Einstein mass-energy equivalence. Of profound importance was the emission of several neutrons in addition to the fission- fragments. If, on average, more than one neutron is captured by other uranium nuclei, inducing further fission, a chain reaction occurs. As soon as this was discovered, it all became highly secret and frantic efforts to make a nuclear weapon began in Britain, the USA and in Germany.
Nuclear fission is now a major source of power. When I began my research in , there was some puzzling evidence. This was rather similar to the noble gases in atoms. It was the beginning of the study of excited states in nuclei. If formed, these states decay down eventually to the lowest state, usually by emitting gamma-rays, which you can study. It was found that, rather than varying smoothly with nucleon number , as you would expect from a liquid - drop model, their energies varied wildly from one nucleus to another.
This suggested that the liquid-drop model was inadequate for this purpose. About two years after I started my research, Maria Mayer developed a rather simple form of independent - particle model, in which the nucleons move more or less independently of one another. Her model explained the magic numbers. It was later developed into the much more powerful Shell Model, which could explain more features; no model can explain all.
At this stage, the effects of quantum mechanics, which are vital for understanding nuclear structure, were really not terribly well understood. The Head of the Cavendish was Lawrence Bragg. He got a Nobel Prize for his work on the famous Bragg scattering law for X-rays.
He very rarely spoke to research students; I think he felt that they were rather beneath him. But one day we heard a lecture by Cecil Powell, who had sent up photographic plates on a balloon to look at cosmic rays and discovered the pi-meson; it was a very simple experiment, of course. That inspired Bragg so much—because he liked such things—that he actually spoke to me when we were collecting our bicycles from the basement. He would suggest a problem on which to work but after that, a brief talk once a month or so would be the most one could expect.
This system was excellent for the best students, fostering initiative and self-reliance, but could be disastrous for weaker students. My PhD supervisor was Bill Burcham. He was in charge of an accelerator that reached up to about one million volts on its terminal, if you were lucky. This was the accelerator that I used. It was a development of the original Cockcroft-Walton machine. The impressive accelerator - hall had to be very big to minimise the chance of sparking to the walls or ceiling. Yes it was. Going into the accelerator-hall, when the high voltage was on, was very exciting; your hair literally stood on end.
Often you would hear an enormous bang and see a brilliant flash. The accelerator was actually very primitive. Its voltage stability was very poor and the energy of the beam was spread over a range of plus or minus 30 keV. It had a very poor vacuum as well. You have to accelerate the ions in a vacuum; otherwise, they just lose all their energy in the air. The vacuum was full of oil vapour from the un-baffled oil-diffusion pumps. When the beam hit the target—which you hoped was very clean—it cracked the oil-vapour and produced a layer of carbon on it. Sometimes, these layers would get so thick that pieces fell off!
So the contrast with equipment today or even 20 years ago must have been something dramatic. Oh, it really was incredible. In those days there were no electronic calculators, no computers, and no transistors. The electronics used valves, which were large and used a lot of power. For instance, when we had to count pulses from detectors using a scaler, we usually put three scalers in parallel; if two of them gave the same result, we would assume that was the correct result.
In fact, we had to make most of our electronics anyway, as there were only a few things that we could buy commercially. Most calculations were done with slide-rules and with pen and paper. Another hazard on winter afternoons was that the nominal supply voltage of 50 Hz , would drop as low as volts, making our electronics unusable. We had to raise it back to volts with a manually operated variac. Failure to quickly wind down the variac would overheat some components, causing damage and malfunction and a strong smell of selenium.
I studied mainly energy - states in light nuclei. Part of my thesis project was to measure gamma-rays in time- coincidence with particles from deuteron-induced reactions and try to learn about the energy levels from which the gamma-rays came. So this gives a vast counting rate in your detectors.
If you want to successfully measure time- coincidences between the particles and gamma-rays of interest, you really need a very short resolving time. At that time, a resolving time of about one microsecond, possible with available electronics of the radar period, was completely inadequate for this task. So I had to develop equipment that would enable me to produce nanosecond resolving times.
Actually, I only managed to get times shorter, but that was good enough; at that time, it was quite an achievement. I had to make instruments and equipment such as amplifiers, double-pulse generators, etc. I also had to make detectors that would produce fast pulses. So I had to make scintillation detectors for both particles and gamma-rays.
All this was a big challenge, which took a lot of time, but I succeeded by my own efforts. Yes, I did. I bombarded lithium-6 with deuterons and was able to establish that the first excited state in lithium-7 had a spin or angular momentum of one half. With another proton-induced reaction, I measured the polarisation of the 6. At that time this was the highest energy gamma-ray whose polarisation had been measured, and this remained true for very many years afterwards.
There was also one other thing I did, which was not experimental, and that concerned a theoretical idea about angular correlations. I rather unwisely thought I should do an experiment to demonstrate this theory. This was a very foolish idea, because I was unable to do it at Cambridge. But in the meantime, in , Litherland and Ferguson published the same idea and got all the credit for it.
Apart from part of my first year, when I collaborated with a second year student, I mainly worked alone.
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There was a very cosmopolitan set of students from many countries at the Cavendish. I completed my experimental work and wrote part of my thesis at the Cavendish. However the grants were given strictly for three years. It was located in Harwell, which is near Oxford. I was attracted there because they offered Harwell Fellowships, which enabled you to do whatever work you were interested in with the facilities that they had.
Their facilities were very good. I was interviewed by a committee headed by Sir John Cock c roft, who was the Director. Yes, he was a remarkable man with a fantastic memory. Although there were 3, employees in Harwell, I would meet him sometimes walking around the establishment and he always knew who I was and addressed me by my name. Sometimes he would come into the lab and talk to people about their research; he always seemed to be well up in what they were doing. He was an unusual man and a great director.
Harwell was never the same after he left. I went to the nuclear physics division, which was headed by Egon Bretscher, who had worked on the atomic bomb project in the US during the war. I got on with him very well, but he was quite an eccentric person. My group leader often used to come out of these meetings with a white face and trembling. A diversionary tactic.
At Harwell, as well as experimentalists, you worked with some theoreticians? Yes there was an excellent theoretical physics group there. It interacted strongly with the experimentalists. I started my research together with Basil Rose, who was a very good experimentalist, and I learned a lot from him. We worked on gamma-rays from radioactive nuclei. At Harwell it was possible to get such sources rather easily, either produced in the local nuclear reactors or sometimes in atomic bomb tests.
Also, at that time we had some outstanding detectors; they were proportional counters filled with xenon or krypton, which had very good energy-resolution. To do these experiments, you really needed good energy resolution. For instance, if you wish to measure two gamma-rays close to one another in energy, you can distinguish them if the width of the peaks from the detector are less than the energy-spacing good resolution , but not otherwise.
So good resolution was essential for these measurements, and enabled us to achieve excellent results. At that time there were some new theoretical developments. The old Shell-Model had been very much refined as a new model from Bohr and Mottelson came along. This indicated that not all nuclei were spherical, as previously thought, but could be deformed into rugby-ball shapes; they could exhibit collective motions, like vibrations or rotations.
This was a very exciting theory at the time. So our experiments were directed at trying to see whether this theory was correct. We found that the nuclei uranium and , and plutonium, behaved almost as perfect rotors, in agreement with the Bohr and Mottelson theory. I did. This greatly broadened my knowledge and understanding of this subject.
In doing so, I noticed two aspects that had not been explained at all before. One was related to the spontaneous fission of odd-mass nuclei. Spontaneous fission occurs when a heavy nucleus, such as uranium, splits up into two by itself. Yes; no neutrons at all. The other one related to the alpha-decay of heavy odd-mass nuclei compared with doubly-even nuclei. I was able to provide two simple but basically correct explanations for both these phenomena and I published them in the review article. Unfortunately I never seemed to learn from my mistakes. I should have published it in a regular journal first.
But there were other discoveries to do with the excitation of heavy nuclei that would have a profound effect on your career. In Copenhagen they discovered a new type of nuclear reaction. Previously, people thought that the two nuclei had to hit one another before any excitation could occur. This is called Coulomb excitation. It turned out to be a very valuable tool because not only does it excite the states but also you can learn various things about them, such as the strength of the gamma- ray transitions and so on.
By this time the original high-resolution proportional counters had been developed into high-pressure proportional counters, which had a much larger efficiency of detection and still gave very good resolution. It occurred to me that I could use these to study the Coulomb excitation of very heavy nuclei. This was very difficult to do, because the targets were radioactive, producing gamma-rays of their own, the gamma-rays of interest were very weak because of high internal conversion, and because a continuous background of gamma-rays was always generated.
Anyway, I was successful in making the first observations of the gamma-rays from these nuclei.
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