I have been asked to talk about the effects of the discovery of fission on the development of physics in Canada. This involves Chalk River and the universities, and three government agencies that have played a key role in shaping university physics: AECB, the Atomic Energy Control Board; NRC, the National Research Council; and NSERC, the Natural Sciences & Engineering Research Council.
Initially the discovery of fission had little impact in Canada. Nuclear physics research was at a low ebb after the Great Depression. There were no particle accelerators; McGill and Queen's were ready to proceed with accelerator projects just as war broke out, but both had to be shelved.
The first notable fission-related experiment (Fig. 1) was done at NRC by George Laurence, who was head of the Radiology Section. He did the experiment in great secrecy, in his spare time, and assisted only by Bern Sargent from Queen's during summer vacations.
Figure 1: Cutaway section of the Laurence "pile", 1941-42
It was the first attempt anywhere to see whether a chain reaction would go with natural uranium using carbon as a moderator. Progress was slow, however, and the result inconclusive - it was clear that purer materials would be required. By the time the experiment was set aside, in the summer of 1942, Fermi was on his ninth uranium-graphite lattice, which gave a k-infinity of 1.007; the Stagg Field pile went critical on December 2, 1942.
Laurence's initiative was not without value. Contacts had been established with classified research in both the US and UK, and when Laurence and Sargent moved to the Montreal Laboratory, they brought valuable experience with them.
The Montreal Lab and the early days at Chalk River have been covered by the previous speakers. I want to draw your attention to the Atomic Energy Control Act which established a five-member Board with wide-ranging powers including authority to make grants in aid of research. The NRC was also a granting agency until 1978 when this function was taken over by NSERC, and it operated many research labs of its own, including the Chalk River project until the foundation of AECL.
In 1948 C.J. Mackenzie became President of the AECB while remaining President of NRC. He was a man deeply convinced of the value of basic science and he wanted Canadian universities to contribute in the field of nuclear research. Accordingly he encouraged universities to apply to the AECB for grants very much larger than those NRC was in the habit of giving, in order to set up major nuclear facilities. Fig. 2 shows the result of this policy over the next decade. In fact it was NRC that contributed to the capital funding for the McMaster reactor, but AECB funded its operation.
|UBC||Van de Graaff||1951|
|McMaster||Swimming Pool Reactor||1959|
Meanwhile, at Chalk River, Mackenzie's original commitment to basic research had been reinforced by Cockcroft and Lewis. Both NRX and NRU had excellent research facilities; indeed NRX was, in its day, the best research reactor in the world. The Van de Graaff was planned in the very early days as part of the commitment to a broad range of nuclear science. It was the ancestor of a series of accelerators that have taken over an increasing fraction of the nuclear physics research at Chalk River. Indeed, today, the principal physics work at NRU is the study of condensed matter by slow neutron scattering.
Figure 3 shows NRX in its heyday with a mass of experiments at the end of the beam tubes. One of the most celebrated (Fig. 4) was John Robson's study of the radioactive decay of the free neutron. It was published in 1950 and is described in one authoritative text as "an experiment of exemplary care and ingenuity". Fig. 5 shows another important Chalk River contribution, a triple-axis neutron spectrometer at NRU in 1958, and its inventor Bert Brockhouse; it is now the standard technique used world wide for the study of condensed matter by neutron inelastic scattering.
Figure 3: Early view of the NRX reactor at Chalk River (1950)
Figure 4: John Robson with equipment used in the first precise measurement of the radioactive decay of the neutron, 1950.
Figure 5: The early triple-axis spectrometer installed at NRU in Chalk River, 1958 and its inventor Bert Brockhouse.
Figure 6 shows the world's first Tandem Accelerator installed at Chalk River in 1959 and (Fig. 7) three distinguished alumni - Harry Gove, Ted Litherland and Al Bromley, the latter having recently been appointed U.S. Presidential Science Adviser.
Figure 6: The world's first tandem accelerator installed at Chalk River in 1959.
Figure 7: Three distinguished alumni of the tandem accelerator at the controls. From the right Ted Litherland, Al Bromley and Harry Gove.
This Tandem and its successors would provide for an evolutionary nuclear physics program. But what would the next step be beyond NRU? Dr. Lewis's answer was the Intense Neutron Generator, ING, designed to out-perform NRU by almost two orders of magnitude.
Figure 8 shows what ING might have looked like. A mile-long linac would have accelerated protons to an energy of 1000 MeV and delivered them to a liquid lead-bismuth target surrounded by a heavy water moderator. To get the required thermal neutron flux of 1016 n cm-2 s-1 a proton current of 65 mA would have been needed and achieving this would be a considerable challenge even today.
Figure 8: The proposed intense neutron generator facility, ING (1967).
ING would also have been a test bed for Dr. Lewis' concept of electronuclear breeding - the injection of accelerator-produced neutrons into a Th-232/U-233 thermal reactor breeding cycle. In this context it is interesting that the decision to go for ING was taken, in 1964, after reviewing a number of alternative programs; two of the unsuccessful proposals were fusion and fast reactors.
No doubt there were many reasons why, in September 1968, the government instructed AECL to terminate the ING project, but one of Chalk River's serious mistakes was its failure to bring the outside community, particularly the universities, into the planning process. The lesson was learnt too late for ING, but ever since then serious attempts have been made to enlist university cooperation, with some successes which I will come to.
Perhaps Chalk River had not appreciated the growth in university-based nuclear physics. Starting in 1961 NRC had followed AECB's lead and funded the construction of seven major nuclear installations in a five year period.
Figure 9 lists the twelve university installations operating at the end of the sixties and the dates they had started to operate. By 1969 they were consuming 4 M$ a year in operating funds, equal to all the rest of the university physics research. Of this 4 M$, 60% came from AECB and 40% from NRC. Obviously this was too large an investment in low energy nuclear physics and already in 1966 NRC had decided to call a moratorium on the construction of such facilities.
|UBC Van de Graaff||1951|
|Alberta Van de Graaff||1962|
|Laval Van de Graaff||1963|
|Queen's Van de Graaff||1966|
This did not apply to TRIUMF, in Vancouver, which was funded through the AECB in 1968. It was enthusiastically supported by George Laurence, by then President of AECB, who convinced Treasury Board. And the decision not to fund ING freed up 1.5 M$ to help get things going.
TRIUMF was a joint initiative by three universities, UBC, Simon Fraser and Victoria, who were soon joined by the University of Alberta. TRIUMF was the third Meson Factory to be built in the world and was much larger than the existing Canadian accelerators, as can be seen from Fig. 10. Figure 11 shows the extensive facilities now in place. As well as pure science experiments in the proton and meson halls, a pion beam is available for cancer therapy, and radio-isotopes are produced on a large scale, mostly in a small dedicated cyclotron.
Figure 10: The lower face of the TRIUMF magnet during construction, 1971.
Figure 11: The layout of the TRIUMF meson facility as it exists today.
Figure 12 compares TRIUMF and ING. A small fraction of the ING beam would have powered a handsome meson factory, and the ING plans included such a facility. By the time it was fully operational in 1977 TRIUMF had cost about 40 million (1967) dollars which is equivalent to 160 million in today's dollars. Its current budget is about 30 M$ a year, which is nearly as much as Canada is spending in all other areas of basic physics research.
|Proton Energy||500 MeV||1000 MeV|
|Current||100 µA||65 mA|
|Estimated Cost (1967)||23 M$||128 M$|
Regarding other current activities, I will come back to NRU at the end of my talk. The nuclear physics program at Chalk River is now based on the Tandem Accelerator Superconducting Cyclotron, TASCC (Fig. 13). The Superconducting Cyclotron - a new idea for a compact and powerful accelerator - was designed and built by the Chalk River Accelerator Physics Branch. The branch was born during the ING days and has undertaken a variety of accelerator projects since then, the cyclotron being its main contribution to physics research.
Figure 13: The layout of the TASCC tandem accelerator, superconducting cyclotron facility at Chalk River.
TASCC can accelerate most elements in the periodic table to an energy of 10 MeV per nucleon or more. It is the largest nuclear physics facility in Canada, after TRIUMF. Much of the research involves people from other institutions, especially from Canadian universities, and one of the principal instruments (Fig. 14) was funded jointly by NSERC and Chalk River at a cost of some 4 M$. It is called the 871 spectrometer and is used for sorting out the complex gamma ray cascades that follow heavy ion reactions.
Figure 14: The 8 pi spectrometer at the TASCC facility at Chalk River.
Of the twelve university installations I showed on an earlier slide, only one has survived as a pure nuclear physics lab, the Saskatchewan electron linac. It has recently been upgraded with a storage ring which converts what was originally a pulsed output into a continuous current of electrons with energies up to 300 MeV. This CW feature is very valuable - it makes coincidence experiments possible - and the Saskatchewan Accelerator is currently unique and much in demand by scientists from inside Canada and abroad.
It was a very economical upgrade. The ring was squeezed into the existing building by the ingenious expedient of hanging it from the ceiling. Figure 15 shows the layout - the original linac, the 180-degree injection line into the racetrack-shaped ring, and the extraction line to the target areas. Figure 16 shows the low-energy end of the linac on the right and the ring above it on the left. Figure 17 shows the 180-degree injection line and the ring in the background.
Figure 15: The layout of the upgraded electron accelerator at the University of Saskatchewan.
Figure 16: Beam lines of the electron linac on the right and the storage ring strung from the ceiling on the left, at the University of Saskatchewan.
Figure 17: The 180-degree injection line and the ring in the background of the electron linac at the University of Saskatchewan.
What of the future? There are at present two major physics projects before the Canadian government and both of them are nuclear (subatomic) - the KAON Factory and the Sudbury Neutrino Observatory.
The KAON Factory (Fig. 18) would use the present TRIUMF cyclotron to inject 100 µA of 500 MeV protons into a complex accelerator system that would increase their energy to 30 GeV. In the context of modern high-energy accelerators this is not a high energy, but the current is very high. As expressed by its proponent, Erich Vogt, it would be at the intensity frontier - a factory making intense beams of secondary particles, notably kaons, antiprotons and neutrinos. Kaons belong to the next generation of mesons after the pions that TRIUMF now produces and they are the first "strange" particles. They are of fundamental interest in their own right - their decay has always been a puzzle - and because of the interesting effects they can produce e.g. when introduced into ordinary nuclei.
Figure 18: Layout of the proposed KAON Factory showing the existing TRIUMF cyclotron near the centre of the 30 GeV Synchrotron ring.
Figure 19 shows the TRIUMF site and indicates roughly where the synchrotron tunnel would be.
Figure 19: A photograph of the TRIUMF site with an indication of where the main 30 GeV synchrotron ring would be placed.
The KAON Factory would cost very roughly half a billion dollars, and last July the Federal and British Columbia Governments each provided five and a half million dollars for a Project Definition Study. The study, expected to take 15 months, will finalize cost estimates and evaluate the scientific and economic benefits. There is much international interest in this project and if Canada decides to go ahead it can expect contributions from abroad amounting to perhaps a quarter of the total cost.
The Sudbury Neutrino Observatory (Fig. 20) is already an international proposal involving the US, the UK and Canada. The uniquely Canadian contributions are the Creighton mine and one thousand tonnes of heavy water. Its prime purpose is to resolve the Solar Neutrino Problem, which is that the measured neutrino flux is a factor two to three smaller than predicted from models of solar energy generation. Neutrino interactions are very improbable (cross sections are about 10-18 barns) so that a large detector is needed to give a reasonable count rate. The rate is still very low so that it is necessary to work at great depth to attenuate cosmic rays, to choose a rock formation of very low radioactivity, and to use ultra pure materials in the detector (Fig. 21). Heavy water is a very advantageous detector - three different neutrino interactions can be studied which will be helpful in resolving the problem. The interactions produce Cerenkov light which is detected in some 2000 50-cm diameter photomultiplier tubes. The capital cost is about 50 M$, and I understand that prospects are good for funding.
Figure 20: A schematic cross section of the Sudbury Neutrino Observatory (SNO) to be placed in the Creighton mine of INCO.
Figure 21: Schematic of the SNO detector.
Both these projects owe their existence to Canada's response to the discovery of fission. It would be stretching things to claim that SNO is a lineal descendant of Pontecorvo's pioneering work at Chalk River in the late forties, but the thousand tonnes of heavy water has a clear enough origin. KAON would be the son of TRIUMF, which was itself delivered by George Laurence following the AECB tradition, established by C.J. Mackenzie, of encouraging the setting up of large nuclear physics facilities at Canadian universities.
This talk has stressed nuclear physics. Let me restore some balance by concluding with a few remarks on neutron scattering in its application to condensed matter physics. Thanks to the NRX and NRU reactors Canada was a pioneer in this business, and there is a strong continuing basic research effort at NRU, and an increasing amount of applied work using this technique which is carried out for industry on a commercial basis. Of the basic research, more than half involves researchers outside the Chalk River Nuclear Laboratories, many from Canadian universities. A new experimental facility is to be installed at NRU next year called DUALSPEC (Fig.22). It is jointly funded by Chalk River and NSERC, on behalf of the university users, at a total cost of about three and a half million dollars.
Figure 22: Model of DUALSPEC, an instrument being installed at the NRU reactor at Chalk River to utilize two of the beam tubes.
DUALSPEC will use two beams from NRU. The lower one (Fig. 23) is for a high-throughput diffractometer for condensed-matter structure studies. It provides a high-intensity monochromatic beam and a large position-sensitive detector for rapid data collection.
Figure 23: The high-throughput diffractometer that forms the lower part of DUALSPEC.
The upper instrument (Fig. 24) is a triple-axis spectrometer with a polarized beam and a polarizing analyzer. These features will permit the study of spin-dependent scattering, which will be particularly useful in the investigation of magnetic materials.
Figure 24: The triple axis spectrometer which forms the upper part of DUALSPEC and which can use a polarized beam and has a polarizing analyser.
With DUALSPEC operational NRU will be saturated. Canada needs a new research reactor. The one at McMaster is obsolescent and a proposal has been advanced to have it upgraded by installing an AECL Maple Core. A first attempt to secure funding for this was not successful, but, in my view, it would be a very economical way of meeting a national requirement, and at a university where the nuclear science program goes back to the early days of fission, indeed to the establishment of Harry Thode's laboratory as a division of the Montreal project in 1943.
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