Praxis Archives – Page 163 of 179

First African school for instrumentation

cernafrica1_6-01 — African setting – the National Accelerator Centre, Faure, near Cape Town, South Africa. The centre’s three cyclotrons are in the large building in the centre of the picture. The photograph was taken facing due east, showing the Helderberg peak against the backdrop of the Hottentots-Holland range.

Every two years since 1987 the ICFA Instrumentation Panel, as an activity of the International Committee for Future Accelerators, has organized an international school of instrumentation. The main aim of the school is to promote interest in nuclear instrumentation among graduate students and young researchers from developing countries. ICFA2001, which was held from 25 March to 8 April, was hosted by the National Accelerator Centre in Faure, near Cape Town, South Africa. It was the first such school to be held on the African continent.

ICFA2001 was devoted to the physics and technologies of instrumentation in elementary particle physics, with a slant towards devices and applications that generate and process image-like information from radiation detectors on a quantum-by-quantum basis. The basic research and spin-offs from the application of such instrumentation to high-energy physics, medicine, microbiology and nuclear sciences, as well as research and development for non-destructive testing in industry, attest to the importance of this vital and continuously growing field.

Instrumentation is usually developed in university laboratories with relatively low investment costs, but access to the latest technology is possible by means of co-operative ventures with other institutes, and in particular with large international research centres and industry. Access to instrumentation technology is a key tenet for the ICFA Instrumentation Panel. At ICFA2001, the organizers, speakers and instructors joined with Kobus Lawrie, Naomi Haasbroek and the rest of the National Accelerator Centre staff in an effort not only to provide access to instrumentation technology and stimulate development in experimental particle physics instrumentation, but also to reinforce the “Science for Africa” motto of South Africa’s National Accelerator Centre.

As far as content and structure were concerned, the main feature of this school – unique to high-energy physics – was its direct, hands-on approach. Students attended morning lectures, after which there were afternoon laboratory sessions lasting four to six hours. Lecture topics this year were wide-ranging, including introductory courses on the physics of particle detection, gaseous detectors, particle identification, calorimetry, silicon detectors, signal processing and data acquisition, as well as several review talks devoted to new technologies, applications in medical physics, molecular biology, astrophysics and data acquisition.

cernafrica2_6-01 — Learning instrumentation in Africa.

The laboratory classes were state-of-the-art instrumentation sessions, led by researchers in the fields in question from universities and research labs all over the world. In some cases they had simply packed up their current research project and shipped it to South Africa, so that students could get a true taste of what is currently of interest.

Students worked in small groups to carry out selected experimental techniques, using multiwire proportional chambers; drift chambers; silicon detectors; microstrip gas chambers; analogue and digital circuits; and data acquisition. They also worked with specific applications in medical imaging, cosmic rays and protein crystallography.

Satisfied students

A measure of its success is that the anonymous student evaluations that were collected at the end of the school overwhelmingly reflected the enthusiasm and satisfaction of the students. As was the case in previous schools, the students placed a strong emphasis on the importance of the laboratory sessions. The labs provided many students with their first hands-on experience of nuclear instrumentation, and offered those students who were well versed in issues of instrumentation a varied and challenging “playground”.

The school also provided a stimulating human experience for its students, some of whom had never attended a scientific meeting abroad, and for whom it was their first excursion outside their home country.

Those involved in running the school also found it rewarding, owing to the energy and enthusiasm that was generated by all who took part. One student even asked if she could skip lunch in order to return to the lab to finish a measurement from the day before. In another instance, Michel Spiro was bombarded with more than 20 questions during his evening public lecture on astrophysics and cosmology. A number of lecturers and instructors are continuing the discussions that they began with students at the school, with a view to potential scientific collaboration.

The decision to hold the school in Africa was made in an attempt to make an impact on young African researchers and postgraduate students who were interested in nuclear instrumentation. Previous workshops had attracted, on average, only one or two African students.

cernafrica3_6-01 — Geoff Hall (back, of Imperial College, London) with students trying hard to make analogue and digital electronic circuits work.

ICFA2001 achieved this goal and was a resounding success. Of the 96 students in the school, 45 were African, and they represented 12 different countries. Not only was the students’ level of preparation high, but all brought with them a remarkable enthusiasm for the subject. Many had a clear understanding of the instrumentation needs faced by their home countries, which were, in general, related to applications such as nuclear medicine and ambient protection (as in the case of a student from Sierra Leone who was working on radioactive waste management). Yet it was clear that such pragmatism is balanced by a common sentiment that involvement in basic research might be a way to slow down the “brain drain” from their home countries.

Follow-up programme

To promote “Science for Africa” further, ICFA has launched a new programme this year that provides a follow-up to the school, by means of a number of summer student placements offered by CERN and DESY (and Fermilab is expected to participate next year). Suitable candidates were easily identified among the students of the school, and all studentships have been accepted.

It was also clear that South Africa might be able to act as a catalyst for science, and, in particular, nuclear physics, at a regional level, providing higher education to students from countries such as Kenya, Zambia and Mozambique. African students who distinguished themselves came not only from South Africa (primarily from the National Accelerator Centre) but also from Kenya, Nigeria and Tanzania.

With “Science for Africa” as its motto, the National Accelerator Centre has made its objectives clear. Indeed, the centre’s leading role in African science was apparent throughout the school, as was the significant support given by local scientific authorities.

Small but active

The facilities at the National Accelerator Centre are good, despite the cashflow crisis in the past couple of years that has triggered a downsizing of its workforce. The centre has overcome that hurdle and has a stable workforce of about 200 staff. Its experimental physics group is small but active and includes several young postgraduates who are working on MScs and PhDs. Significant effort is being made to bridge the age gap and remedy racial disparity.

cernafrica4_6-01 — Members of the silicon microstrip detector laboratory course and some hard-working students. Back, left to right: Paolo Giubellino; Alan Rudge; an ICFA2001 student; Shaun Roe. Front: Alick Macpherson (left) with a group of ICFA2001 students.

With these resources the centre carries out several programmes. Its radiation therapy programme includes impressive facilities for neutron and proton therapy with which hundreds of patients have been treated, while its production of isotopes for medical applications brings in additional income for the centre through their sale on both the national and the international markets. The centre also runs a nuclear physics programme, including the use of a spectrometer to study nuclear reactions, and a new state-of-the-art “gamma ball” (Afrodite), which has attracted foreign experimentalists from such laboratories as INFN-Milano, Italy; and another on material science, using a nuclear microprobe on a 6 MV Van de Graaff accelerator.

Activities are based on a large separated sector cyclotron that accelerates protons to energies of 200 MeV, and heavier particles to much higher energies. Two smaller cyclotrons are also used to provide intense beams of light ions, polarized light ions or heavy ions for injection into the large cyclotron. The beam time from the cyclotron is shared equally among the three main programmes, with some beam allocated specifically to the experimental physics community at weekends, when users come in from several South African universities and from abroad.

ICFA2001 was the eighth edition of the school. Previous editions took place at ICTP Trieste, Italy, in 1987, 1989 and 1991; in Rio de Janeiro, Brazil, in 1990; in Bombay, India, in 1993; in Ljubljana, Slovenia, in 1995; in Léon, Guanajuato, Mexico, in 1997; and in Istanbul, Turkey, in 1999.

The ICFA2001 instrumentation school was jointly supported by the National Research Foundation, DACST, ESCAM and NESCA of South Africa, and by CERN, DESY, INFN, ICTP, IN2P3, RAL, DOE and NSF.

The observatory at the end of the Earth

In September 1997, PhD student Torsten Schmidt began working at DESY Zeuthen, near Berlin. Three months later he was visiting the realm of perpetual ice at the South Pole. The 30-year-old has now been to Antarctica four times to help to build the neutrino telescope AMANDA-II, most recently in December 2000. CERN Courier asked him about his experiences.

Is it difficult to endure three to four weeks at the Pole?

cernpol1_5-01 — An optical module of the AMANDA neutrino detector being lowered into the Antarctic ice.

It varies from person to person. I really like it there. Four weeks is a good time limit. As far as life at the station goes, you could hold out for longer, but since you go down there to work, you keep working more or less continuously for the whole four weeks.

So there’s no time left to have a look around?

There isn’t much to see there, actually. It’s flat, cold and there are at most two “sights” worth seeing: a crashed aeroplane at the end of a runway, which is a trip of two to three hours; and a ski cabin about 10 km away – but trips there will be prohibited next season.

Why is that?

The pole is run by a company, and the company – for whatever reason – has stopped allowing people to go there.

So a company runs the South Pole?

To be more exact, the company was hired by the US National Science Foundation to take care of transportation, logistics and operations. NSF is the real host of the Amundson-Scott station and determines the various science programmes at the Pole.

Another example of a prohibited location is the old station, which was abandoned in the early 1970s. It’s located in the so-called dead sector, which in reality means that anyone who goes there will be on the next plane north and won’t be allowed back to the Pole ever again. It’s simply too dangerous there. The station has been standing there deserted for over 30 years. It’s covered with snow and ice and could collapse at any time.

Isn’t it much too cold, in the winter at least, to do any work outside?

cernpol2_5-01 — Physics under Antarctic conditions — deploying a photomultiplier at AMANDA.

Well, it does get very cold, but in the first few weeks after the last plane left there were days when it was only -40 °C. Deepest winter temperatures are around -80 °C.

Is the new station right at the Pole?

Yes, but so was the old one at one time. The ice actually moves about 10 m each year. So every year on New Year’s Eve, the “new” South Pole is measured, and on New Year’s Day a post is driven into the ice at that point. That’s always a big party for the whole station.

There are, in general, many social events. One might think that it’s boring and lonely at the Pole, but that’s not true. There’s something going on every day. That’s because only 50 of the 250 people who live there are scientists. The rest are “support” people: electricians, roofers or crane operators, both men and women. They work their 8 to 10 hours a day and then they’re done – unlike us researchers. And, of course, they want to enjoy their leisure.

So there are weeks and weekends. What about days and nights?

cernpol3_5-01 — Dedicated research — Torsten Schmidt at the “ceremonial” South Pole.

There is, so to speak, a day and a night for the support people because of their shifts, but there are no routine hours for us researchers. Of course, when work is done in the group, a time has to be agreed upon, but otherwise you’re completely free in that regard. You can’t sleep much anyway because the sun is always shining, but there are hot meals every six hours.

I can live any way that I want, which is something I like very much. If I don’t have to work with other people, then I work for as long as I can, and then go to sleep and lose all sense of time in a flash.

How many hours do you work and sleep in that kind of system?

On average, it’s 12-15 hours of work a day, but if necessary we can work for as long as 30 hours non-stop. After that come five hours of rather fitful sleep. It’s hard to rest any longer. We sleep in huge military tents with about 20 people in each. And since it’s always daytime, there’s no regular lights-out time either.

The result is that people are constantly trudging through the tent in heavy boots and slamming the door. Outside, aeroplanes are landing around the clock. You really have to be dead tired to be able to sleep at all.

The tents must make the place look like a campsite.

Actually, the Amundsen-Scott station is a high-tech place, with a huge metallic dome and several elevated houses. The summer population, however, lives in those 20-30 tents. In the middle is the bathhouse, which includes a very well frequented toilet – the reason being that the dry air means you need to drink as much and as often as possible. But it’s unpleasant when you’ve just lain down to sleep and then have to go outside again – in your whole outfit including trousers, boots and anorak. How often have I cursed that toilet! Some people avoid the trip and put a bottle next to their beds.

What other problems does the Pole novice have to reckon
with?

cernpol4_5-01 — The AMANDA detector slides into the ice.

Along with the small amount of sleep, there’s also the physical strain because of the high altitude. After all, the station is nearly 3000 m above sea level. The air is thin, cold and dry, and you become dehydrated very quickly.

Things are particularly bad in the first few days: every step is a strain; you collapse into bed wearily but still can’t sleep. Even the small climb of 5 m at the exit of the winter camp makes newcomers break into a sweat.

After the weariness has faded, you live very well at the Pole for a few weeks, but then you start to feel the lack of sleep and the exhaustion from the work. At that point it’s time to begin the trip home.

Are there moments that allow you to forget all of the exertions of polar life?

One particularly nice social event is Christmas, of course. Christmas at the Pole is really good fun. On Christmas Eve the Americans organize a party. On Christmas morning there’s the “race around the world” – three laps around the South Pole. After that comes the Christmas meal, which is actually served three times because the team is so large.

New Year’s Eve is naturally a big celebration too. Last time some of the hard-core types even celebrated the New Year in a different time zone every hour – that’s possible at the Pole.

Other highlights last season were bocci-ball and golf. We also go to the sauna at least once a year and then run around the South Pole almost naked.

Alright then, enjoy your next trip to the Pole!

Chaos and Harmony, Perspectives on Scientific Revolutions of the 20th Century

by Trinh Xuan Thuan, Oxford University Press, ISBN 0 19 512917 2.

cernbooks1_5-01 — Beauty in nature — Saturn’s aurora, as seen by the Hubble Space Telescope.

In a refreshing alternative to books that try to promote elegance, as opposed to correctness, as a reason to accept scientific theories, Trinh Xuan Thuan takes his readers on a fascinating romp through the world of modern physics. Starting with a discussion of truth and the elusive concept of beauty as opposed to elegance (a difference that he carefully explains), Thuan zeroes in on inevitability, simplicity and congruence as the key guiding notions in the search for the beautiful theories of nature. Much to his credit, he nevertheless makes it clear that, while truth is ultimately something that is decided by experiment, beauty is a subjective concept.

Although the subject matter of this book is deeply philosophical, it is discussed in wonderfully concrete terms. Rather than making vague statements about staggering cosmic or microcosmic magnitudes, Thuan offers hard facts (e.g. that the Sun turns 400 million tonnes of hydrogen into helium per second). A refreshingly down-to-earth follow-up to the esoteric discussion of truth and beauty is a description of the solar system, and the complex interplay between the strict laws of physics and plain random chance that gives rise to the world we so often take for granted.

In subsequent chapters Thuan describes chaos – with its range of applications from meteorology to medicine – and symmetry, emphasizing the symmetries between electricity and magnetism, and between space and time. A recurring theme in the book is the way in which seemingly opposing principles like these actually work together.

Moving on from classical mechanics and the need for both ordering and disordering principles in order to obtain structure, we meet quantum mechanics. A clear – if perhaps rather standard – introduction, with no mathematics, leads the reader to the inevitable conflict between that greatest of classical theories – Einstein’s General Theory of Relativity – and quantum mechanics. Here the author allows himself a few pages of deviation from the otherwise strict adherence to established fact that forms a great part of the book’s not inconsiderable charm.

A mercifully brief discussion of higher dimensional unification and string theory outlines the basic idea in a balanced way without any Bible-thumping. There’s little hope of steering clear of strings and other speculations these days, but the author makes a good job of maintaining a healthy perspective. The book could, in good faith, be recommended to the lay reader without fear that the line between established fact and interesting speculation be too blurred.

The last two chapters are delightful, and unusual in a book of this kind. The penultimate one invites the reader to think about the nature of life and the origins of its highly sophisticated and diverse structures – and to consider to what degree we can begin to understand these as coming from physics. Thuan discusses how one can find the appropriate level of description for the task, and suggests that we should hope not for detailed explanations of single phenomena but rather for an understanding of the global organizing principles that give rise to life and other complex structures.

The final chapter echoes Wigner’s famous concerns about what he called the “unreasonable effectiveness of mathematics” and asks why thought itself should be so effective – that is, why it is that we are able to make sense of anything, let alone the panoply of physics presented in the foregoing six chapters. Here the text takes an almost metaphysical turn, but, given the nature of the questions being asked, this is to be expected. While the practising scientist is unlikely to find much here that s/he hasn’t already thought about, the discussion is well suited to a layperson and offers quite a range of concepts to consider, from the idea of a Platonic world of mathematical forms, through the limits imposed by Gödel’s theorem, to the question of whether a God is needed, and the issue of why there should be such a thing as consciousness at all.

All in all, at a time when it is becoming increasingly difficult to find popular science books that are suitable for the intelligent non scientist, and that make clear distinctions between known fact and speculation, this book is a winner. The writing is graceful, smooth and rich in historical and cultural background, while at the same time keeping real physics close to the forefront. Perhaps most compelling is the book’s remarkable coherence. Topics flow easily and naturally into each other and one would be hard pressed to guess that it is a translation into English. Most people I know, practising physicists included, could learn something from this book, in addition to enjoying its style. To my high-energy physics colleagues: ask yourself how much you really know about the mechanisms involved in getting matter to clump together and make a planet. After all, there aren’t many of them in this solar system, are there? Get the book and have a look at Chapter 2!

EC to fund project for faster optical detectors

The development of more efficient and faster optical detectors is the subject of a prestigious Ý2 million Research Technology & Development contract awarded by the EC to Sussex University, together with two UK companies, Photek Ltd and Electron Tubes, the Laser Centrum (Hanover), the Autonoma University (Madrid), CIEMAT (Spain) and Novara Technology (Italy).

The project, known as “Impecable” (standing for Improved Photon Efficient Cathodes with Applications in Biological Luminescence), will fund the development of more efficient and faster optical detectors by the newly formed consortium, leading to their subsequent production by Photek and Electron Tubes. Existing industrial and research uses for photon counting, detection and imaging are already immense, but the particular thrust of these new developments should greatly increase their value for medical diagnostics, with medical, biological and new sensor applications.

The new concepts have arisen partly as a result of friendly collaborations over the last ten years between Photek and Peter Townsend at Sussex University: Townsend constructed a new standard for spectral analysis of thermoluminescence based on the Photek photon counting cameras. That equipment has not only advanced basic research into new optical and photonic materials, but is also being applied to problems of mineralogy and geological dating.

Although the Sussex system is still well regarded, there is now a major need to improve the sensitivity for long wavelengths (near infra-red) signals and to have much faster sensors. The work at Sussex led to a patent for a development that can, potentially, give much greater sensitivity and has already established a new technique to speed up the response time of Photek detectors into the sub-nanosecond range. The new grant will take this research further and faster with the aim of giving European dominance to both the subject and any resulting products.

The partners have already begun to interact – the Laser Centrum in Hanover is collaborating with Photek on another EC-funded project (Femto) on laser machining. Electron Tubes and Photek have had discussions in the past, and Sussex-UAM -CIEMAT have also worked on joint projects over many years.

The collaboration between Sussex University and Electron Tubes began more recently when the latter was launched independently of Thorn/EMI. Electron Tubes is a leading European manufacturer of photomultipliers and detector modules that detect light down to single photons. Its role will be the development of new high efficiency photocathode layers and the fundamental measurements on the cathodes to be used in this project.

The detection of low light levels is also critical to a wide variety of industrial and scientific instrumentation. Industrial applications range from the measurement of steel thickness as it is rolled from the furnace through to the identification of oil-bearing rock immediately behind the drill bit as an oil well is formed. Scientific applications range from the detection of solar neutrinos deep underground to astronomical observations of distant stars. The target processes for the new high-efficiency photocathodes will be in the very challenging area of the detection of light emitted during biological processes or from luminescence which distinguishes between healthy and imperfect cells.

Among the applications foreseen for this technology is a new technique for the early diagnosis and subsequent monitoring of Alzheimer’s disease, and luminescence analysis for a variety of types of cancer. Demonstrations of such possibilities are planned within the three-year programme but routine applications will take longer.

Contact Ian Ferguson at sales@photek.co.uk for further information.

Awards highlight top suppliers

cernnews10_4-01 — Award time at the collaboration building the ATLAS experiment at CERN’s LHC collider. ATLAS spokesman Peter Jenni (left) and ATLAS Transition Radiation Tracker (TRT) project leader Daniel Froidevaux present the ATLAS supplier award to Patrick and Simon Hester, directors of UK company Lamina Dielectrics, which supplied 180 000 high-tech straws for the ATLAS TRT.

The CMS and ATLAS collaborations currently building experiments for CERN’s LHC collider have recently been handing out their very own Oscars to their most meritorious suppliers.

At the second such ceremony held at the recent CMS week at CERN, four CMS suppliers received Gold Awards, and the exceptional work by two of them was further rewarded with the CMS Crystal Award for innovation and management.

One Crystal Award went to Japanese firm Kawasaki Heavy Industries which, under a contract with the University of Wisconsin, manufactured six steel discs 15 m in diameter making up the two endcaps of the yoke. Reassembled, the two thinner discs at each end will weigh 300 tonnes, the two intermediate ones 700 tonnes and the two innermost discs 1250 tonnes.

The other Crystal Award recipient was Fermilab contractor Felguera Construcciones Mecanicas, the Spanish firm which produced the wedge-shaped structures for the two 550 tonne half-barrels of the CMS hadron calorimeter. This involved in the region of 1100 tonnes of brass plates, the largest some 4 m in length and weighing in at more than a tonne.

cernnews11_4-01 — This year the collaboration building the CMS experiment at CERN’s LHC collider awarded its highest distinction to two suppliers – the Spanish firm Felguera Construcciones Mecanicas, represented by Ernesto Alavarez (left), and the Japanese firm Kawasaki Heavy Industries, represented by Kazuo Mizuno (right).

The two other companies to receive CMS Gold Awards were Hudong Heavy Machinery, under the CERN-China agreement, for the 30 tonne support carts for each endcap disc, and the American firm Superbolt for more than 1500 high-strength bolts for the endcap discs.

CMS also presented its prize for the most outstanding PhD thesis of 2000. It was the first time such an award has been handed out to underline the important contribution made by students’ work. The winner was Pascal Vanlaer of the Université Libre de Bruxelles for his R&D work on microstrip gas counters and the reconstruction of charged particle tracks.

Just four days earlier, the ATLAS collaboration had organized its first supplier award ceremony. “Firms really appreciate this,” explained ATLAS financial coordinator Markus Nordberg, “because being a CERN supplier is a reference and generates important marketing spin-offs.”

One ATLAS award went to a small UK family business, Lamina Dielectrics, which manufactured the 180 000 straws for the Transition Radiation Tracker. These 1.66 m long polyimide (Kapton) tubes are just 4 mm in diameter and are manufactured to a tolerance of 15 µm. Each straw is produced by winding and bonding together two thin strips of film coated with aluminium and graphite on one side and polyurethane on the other.

The other ATLAS award-winner was Czech firm Valvovna, supplier of 3000 tonnes of steel sheeting for the ATLAS barrel’s tile hadron calorimeter. Even more impressive than the quantity was the precision obtained over the entire manufacturing process. The trapezoidal plates, 4 and 5 mm thick, were manufactured to a tolerance of 0.04 mm.

CERN project brings science and art together

cernart1_4-01 — Italian artist Paola Pivi and her “Moving needles”.

“Throughout history, science and art have had a special relationship,” explained Michael Benson, director of communications at the London Institute. “Artists today are beginning to realize that science provides fertile territory for the imagination.”

cernart2_4-01 — One of Swedish artist Monica Sands’ light boxes.

In spite of the differences between the two disciplines, science and art have had similarly crucial roles to play in human civilization. Throughout history, great minds have embraced both disciplines – the most famous example being Leonardo da Vinci in Renaissance Europe.

However, although modern physics impacts on all aspects of daily life, from information technology and telecommunications to energy and medical imaging, today’s art world has responded little to the cultural upheavals of advancing science. No modern Leonardo has emerged as yet.

cernart3_4-01 — Artist Ken McMullen (left) and his CERN partner Ian Sexton with their “Skin Without Skin – Crumple Work” sculpture. Using CERN technology, Ian translated Ken’s initial idea into a laser-cut steel structure.

The artists involved in the Signatures of the Invisible project – Roger Ackling (UK), Jérôme Basserode (France), Sylvie Blocher (France), Richard Deacon (UK), Bartholomeu dos Santos (Portugal), Patrick Hughes (UK), Ken McMullen (UK), Tim O’Riley (UK), Paola Pivi (Italy) and Monica Sand (Sweden) – have worked with scientists and technicians at CERN to create original works of art that reflect the ideas and techniques of modern physics.

cernart4_4-01 — UK Particle Physics and Astronomy Research Council (PPARC) chief executive Ian Halliday (right) and Sir William Stubbs, rector of the London Institute, against Ken McMullen’s “Roman Lead” work. The lead was mined 2000 years ago in Spain, but the ship that was transporting it to Rome sank. As a result the metal lay for almost two millennia on the seabed and was protected from any radioactive contamination due to cosmic rays. PPARC is one of the major supporters of the Signatures of the Invisible exhibition.

Preliminary visits to CERN, which allowed the artists to meet physicists, visit experiments and discover the potential of CERN’s workshops, led to two years of exchanges and close collaboration, which resulted in Signatures of the Invisible. The exhibition will re-open at Geneva’s Centre d’Art Contemporain in January 2002 before travelling to venues in Stockholm, Lisbon, Paris, Strasbourg, Brussels, Tokyo, Australia (venue to be announced) and New York.

When the bubble chamber first burst onto the scene

Strange particles were first seen in 1947⁽¹⁾ in a cloud chamber of Blackett, triggered by hadron showers produced by cosmic rays. Soon after, other strange particles, then called V particles, were also seen in nuclear emulsions. Progress in our understanding of these new particles was slow, partly because the experimental possibilities were limited to cosmic-ray observations, and partly because the phenomena were so totally outside of what was then known.

cernjack2_4-01 — CERN stalwart Jack Steinberger at 40.

I remember in 1949, on a bulletin board at the Princeton Institute of Advanced Studies, a photomicrograph of a nuclear emulsion event, showing what is now known as a K-meson decaying to three pions. We all saw it. There could be no doubt that something interesting was going on, very different from what was then known, but it was hardly discussed because no-one knew what to do with it.

The copious production of these particles, indicative of the strong interaction, was at odds with their long lifetimes, indicative of the weak interaction. Pais noted in 1952 ⁽²⁾ that this could be understood by inventing a feature of the strong interaction, a selection rule, which would permit their production but forbid their decay via the strong interaction. He implemented this in a mechanism that required the new heavy particles to be produced in pairs. This was extended some months later by Gell-Mann ⁽³⁾, who ingeniously combined the selection rule with the notion of isotopic spin. It required that the pair of Pais be composed of a “strange” and an “antistrange” particle.

Enter the accelerator

cernjack1_4-01 — Fig. 1. Before the bubble chamber – Brookhaven Cosmotron diffusion chamber photograph of a 1.5 GeV negative pion producing two neutral V-particles, seen via their characteristic decays. Tracks 1a and 2a, believed to be a proton and a negative pion respectively, are the decay products of a <font face=”symbol”>L</font>. A kaon is probably seen to decay into a positive and a negative pion (1b, 2b).

The arrival of accelerators of sufficient energy facilitated the study of these new particles enormously. The Brookhaven Cosmotron accelerated protons to 3 GeV, six times the energy of the highest energy cyclotron, and sufficient to produce the new particles in collisions on nuclei, and Ralph Shutt and colleagues had developed a new type of cloud chamber. The V particles produced in cosmic-ray showers had been observed in cloud chambers, but these were very inefficient for accelerator experiments because, once made sensitive by expanding the gas, they would require 1 min of relaxation before they could be expanded again. The accelerator cycle, however, was typically 1 s. The new “diffusion” cloud chamber, in contrast, was continuously sensitive and made it possible to demonstrate the production of strange particles in pairs⁽⁴⁾ and verify the hypothesis of Pais and Gell-Mann (figure 1).

Two years later, in 1955, Gell-Mann and Pais ⁽⁵⁾ noticed that the neutral kaon should exist in two versions, one strange and the other antistrange, one the antiparticle of the other. In addition to the known neutral kaon, there should be another one, with the same mass but with much longer lifetime and with different decays, with opposite symmetry under space inversion.

This idea, which seems obvious now, was not obvious at the time. It was not easy for me to understand or to accept this proposal when I read it, but a few days later T D Lee succeeded in explaining it to me. Once understood, the idea could not be rejected.

The experimental confirmation a year later by Lederman and Landé⁽⁶⁾ marked a big step forward. It was also carried out at the Cosmotron, and used what was, to my knowledge, the largest cloud chamber ever, 1 m in diameter. The large size made it more likely that the long-lived kaon, with a decay path of the order of 10 m, would decay inside. The chamber had been built at the Nevis laboratory some years before, but had never found any use. This, to my knowledge, was also the end of the long and glorious career of the cloud chamber in particle physics.

In 1953 Donald Glaser invented the bubble chamber⁽⁷⁾, which went on to dominate particle physics, especially strange particle research, for the next 20 years. He showed that energetic particle trajectories can be made visible by photographing the bubbles that form within a few milliseconds after particles have traversed a suitably superheated liquid (figure 2).

The bubble chamber

cernjack3_4-01 — Fig.2 Track of a cosmic ray particle in Donald Glaser’s first bubble chamber.

The advantage of the bubble chamber over the cloud chamber at accelerators was two-fold: the higher density of the liquid proportionally increased the number of interactions produced in it, and it was faster to reactivate, matching the frequency of the accelerator cycle.

Within a year, John Woods, in the group of Alvarez at Berkeley, succeeded in producing tracks in liquid hydrogen.⁽⁸⁾ The chamber was a metal cylinder to which glass plates were attached, using indium ribbons as seals. In addition to being a major cryogenic technical achievement, this also demonstrated the crucial fact that for use with accelerators, where the expansion can be timed with respect to the accelerator cycle, the bubble chamber environment need not be as ultra-clean as was the glass vessel of Glaser, which permitted the liquid to survive in its superheated state for relatively long periods.

Three graduate students, John Leitner, Nick Samios, Mel Schwartz, and I began work at Nevis on the design of a practical experimental bubble chamber ⁽⁹⁾ to study strange particle production at the Cosmotron, I think early in 1954. By 1955 we had a 6 inch (15 cm) diameter liquid propane chamber. This was used at the Cosmotron in the first experiment using this new technique. The work profited a great deal from a generous collaboration as well as friendship with the inventor, who was working on a similar project at Brookhaven with his former student, David Rahm. ⁽¹⁰⁾

Rapid action

Our main technical contribution at Nevis was the discovery of a rapid action three-way gas pressure valve, the “Barksdale” valve. This made it possible to recompress the liquid within milliseconds after the expansion, and so to reduce the undesirable thermal effects that result if the pressure remains low for longer times and greater quantities of liquid boil.

As work progressed, we were joined by R Budde from the newly established CERN laboratory, who had been sent to learn about the new technique. The chamber had a serious flaw, which we nevertheless accepted in order to get experimental results – the liquid became clouded and lost its transparency after a few hours of operation. It was then necessary to empty and to refill the chamber, with a consequent loss of time.

The experiment ⁽¹¹⁾used a pion beam of energy 1300 MeV, only slightly more than the minimum required to produce a strange particle pair. There was no magnetic field, so the particle momenta could not be measured. However, the information from the spatial directions of the observed particles, recorded stereoscopically, sufficed to permit the identification of L hyperon and neutral kaon decays, to distinguish collisions on hydrogen from those on carbon, and so identify the processes we wanted to study (figure 3).

cernjack4_4-01 — Fig.3 An early Cosmotron bubble chamber photograph showing the associated production of two strange particles – a positive kaon and a S-.

The lifetimes of most of these particles are of the order of 10^-10s, and consequently their path length is typically some centimetres. The several dozen events obtained gave the first quantitative measure of the production probabilities and angular distributions for negative pion on proton reactions, giving a positive kaon and a S-, and a neutral kaon and a L. In retrospect, the most interesting result was a precocious glimpse of parity violation, soon to be at the centre of the particle physics stage.

The development of bubble chambers went on apace. Within a year the 10 inch (25 cm) hydrogen chamber of Alvarez was in operation at the Bevatron, which was then, with 5 GeV protons, the world’s highest-energy accelerator, and which had permitted the discovery of the antiproton by Chamberlain, Segrè, Wiegand and Ypsilantis in 1955.⁽¹²⁾ In 1959 this was superseded by the 72 inch (1.8 m) chamber, the workhorse of the Bevatron for more than a decade, which led to the discovery of several meson and hyperon resonances.

At Brookhaven the Shutt group made important technical advances. In 1958 its 20 inch (50 cm) chamber came into operation, followed in 1962 by the 80 inch (2 m) chamber. This went on to take 11 million photographs, and the results included the important discovery in 1964 of the triply strange W– hyperon,⁽¹³⁾ confirming the SU(3) symmetry proposed by Gell-Mann to account for the multiplet structure and mass regularities of the observed strange particles, and which mothered the invention of the quark (figure 6).

cernjack7_4-01 — Fig. 6. 1964 – the bubble chamber classic, the production and decay of the W– hyperon in Brookhaven’s 2 m bubble chamber. This remarkable event permitted reconstruction of all particle momenta and the determination of the mass of the W-.

At CERN a 30 cm hydrogen chamber came into operation in 1960, and the 2 m hydrogen chamber in 1964. This became the main CERN tool for the study of resonant and strange particle physics for a decade and kept hundreds of physicists busy and happy. Gargamelle, a very large heavy-liquid (freon) chamber constructed at Ecole Polytechnique in Paris, came to CERN in 1970. It was 2 m in diameter, 4 m long and filled with freon at 20 atm. With a conventional magnet producing a field of almost 2 T, Gargamelle in 1973 was the tool that permitted the discovery of neutral currents.

The Legacy of Léon Van Hove

edited by A Giovannini, World Scientific Series in 20th Century Physics, Vol. 28, ISBN 98102243308, 570pp, £55.

cernbooks1_4-01 — Léon Van Hove – multifaceted contributions to science.

The publication of this volume on Léon Van Hove provides a welcome global view of his multifaceted contributions to science. He was CERN’s research director-general from 1976 to 1980, but some of his most important contributions date from his time outside CERN and are little known to the particle physics community. This book consists of reprints of his major scientific papers together with skilful presentations of their significance, as well as discussions of his impact as teacher and scientific statesman.

Léon Van Hove started his career with three years of underground university studies in wartime Brussels. His training and earliest research was in the field of mathematics. In the late 1940s, however, he turned to theoretical physics.

His first papers on statistical mechanics and quantum field theory were mathematically orientated. His rigorous and important papers in statistical mechanics in 1949 prepared the ground for the advances by Ruelle and by Fisher in the 1960s (R Balescu, T Petrosky and I Prigogine); he initiated the perturbation description of large quantum systems in two fundamental papers in 1955 and 1956 (N M Hugenholz).

In the period 1951-1954 he turned, surprisingly and under the influence of Placzek, to phenomenological work on slow neutron scattering, and demonstrated how the space-time correlation function could be measured directly. His papers were a major stimulus to this field and had enormous influence on experiments and applications as well as on theory (N Gidopolous and S W Lovesey). The experimental work by Brockhouse and Shull that used his approach was awarded the Nobel prize in 1994, four years after Van Hove’s death in 1990.

Van Hove’s remarkable scientific change of direction and contributions to particle physics on being invited to head the CERN Theory Division in 1960 are described by several close collaborators: M Jacob on ultrarelativistic heavy-ion collisions, A Giovannini on multihadron production and J J J Kokkedee, W Kittel and A Bialas on high-energy collisions and internal hadron structure.

Van Hove was also an outstanding teacher, scientific administrator and policy maker. Close associates describe his activities in these diverse areas.

Of his Utrecht PhD students in the 1950s, we learn that several became outstanding physicists, for example the Nobel prizewinner M Veltman. (N M Hugenholtz and Th W Ruijgrok). His activities as leader of the CERN Theory Division and as research director general of CERN are described by F Bonaudi, M Jacob, E Gabathuler and V Soergel, while his period as director at the Max-Planck Institute at Munich is covered by N Schmitz. M Bonnet describes his time as advisor to the European Space Agency and the special role he played in developing the Solar-Terrestrial Programme.

The fact that Léon Van Hove came from a field outside particle physics made him particularly sensitive to the potential of high -energy physics in non-traditional areas. For instance, he realized the scientific significance of ultrarelativistic heavy-ion physics at a time when it was still unpopular at CERN. He threw his scientific weight behind this initiative and even focused his own scientific research on it. His intuition has recently been vindicated by the discovery of quark-gluon plasma effects.

This scientific intuition also showed itself in the bold decisions – described both by colleagues and by Van Hove – leading to the construction of the antiproton-proton collider and the discovery of the W and Z particles. Further, it is an excellent initiative to include an autobiography.

The book closes with a documentation of Van Hove’s opinions and attitudes on various issues, compiled in his own words from his speeches and private papers by his son Michel.

This volume gives a fascinating account of the scientific life of a multifaceted physicist with many talents and is highly recommended.

CERN experience benefits students and specialists

cernfell1_3-01 — CERN’s popular summer student programme has a tradition that goes back to the early years of the organization. Each year some 150 selected students participate in CERN’s research programme under the supervision of CERN scientists and attend a series of specially arranged lectures. The student summer programme is just one of a number of items on CERN’s menu.

CERN’s major contributions to culture range wider than the discovery of the neutral current of the weak interaction, or the carriers of the weak nuclear force. CERN has shown how international collaboration in science works. Different national attitudes complement and reinforce each other, but this needs to be experienced first.

The vitality of the more than 7000 researchers using CERN’s facilities creates a continuous exchange of ideas and people from all over the world. In addition to the advances in frontier science, the technology needed to carry out this research is often years ahead of what industry can provide.

Every year more than 600 new students, scientists and engineers participate in the various schemes over periods ranging from three months to three years. They all benefit from their experience of working in an international collaboration at the forefront of science and/or technology. Returning to their home institutes, they provide a seedbed for new developments.

A significant fraction (about 10%) of CERN’s personnel budget is spent on various fellow, associate and student programmes. As well as promoting the exchange of knowledge between scientists and engineers from all over the world, these programmes are vital elements in the high-level research and technology training of scientists from CERN’s 20 European member states and, to a lesser extent, from other nations too.

The programmes are popular and there are many applications from eager candidates. Their success is largely due to the strict criteria applied in the selection procedures.

The fellowship programme aims to provide advanced training to young CERN member state university-level postgraduates (mostly with doctorates) in a research or technical domain.

Catering for a different need is the associates programme, which offers opportunities for established scientists and engineers from both member states and elsewhere to spend some time – typically a year – at CERN, on leave from their research, teaching, managerial or administrative duties. During their stay at CERN, associates are on detachment from their home institute.

Students and trainees

cernfell2_3-01 — Numbers in CERN’s fellowship programme, showing the increasing contribution from non-member states.

Fulfilling another requirement are the various student programmes (summer students, technical students and doctoral students) for undergraduates and postgraduates in CERN member states. Doctoral and technical student programmes are currently restricted to candidates from applied sciences and engineering, but there is a move to extend this.

In the popular summer student programme, with a tradition going back to CERN’s early years, some 150 students selected each year from many times that number of applications participate in CERN’s research programme under the supervision of CERN scientists, and they also attend a series of specially arranged lectures. Many leading scientists have benefited from this scheme early in their careers.

The trainee programme is new. Numerous member states have shown a very strong interest in using CERN as a training ground in a wide area of hi-tech activities. In the past five years there has been a rapid development of special programmes that are based on bilateral co-operation agreements.

Member states Austria, Denmark, Finland, Norway and Sweden provide additional funds for the student programmes, while Israel, a CERN observer state, contributes to the associate programme. For another observer state, Japan, since 1996 part of the interest in the nation’s financial contribution to the construction of the new LHC accelerator has been used to help to fund a few fellows and short-term associates.

Member states Spain and Portugal provide grants that cover the insurance and living costs of the young people specializing in engineering and technology. An additional CERN contribution offsets the relatively high cost of living in the Geneva area.

At a regional level, about 25 young engineers and technicians spend some time at CERN within the framework of a special French Rhone_Alps Region programme. A few graduates and postgraduates from the Italian Piedmont are funded by the regional Association for the Development of Science and Technology. It is hoped that these special programmes will be integrated into the wider schemes and expanded.

Together, the various student and short-term visitor schemes transfer specialized knowledge and expertise, and make CERN’s mission and work in particle physics and further afield known to a wider public.

A Modern Introduction to Particle Physics

by Fayyazuddin and Riazuddin, 2nd edn, World Scientific ISBN 9810238762 hbk, ISBN 9810238770 pbk.

The first edition of this book by the talented twins from Pakistan, which appeared in 1992, has been updated, with the chapters on neutrino physics, particle mixing and CP violation, and weak decays of heavy flavours having been rewritten. Heavy quark effective field theory and introductory material on supersymmetry and strings are also included.

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