In June 1990, while I was a Fellow at CERN in experimental particle physics, a friend told me that the European Space Agency (ESA) was recruiting new astronauts. Although I loved (and still love!) the physics research work I was doing, and being at CERN in particular, I had always dreamed of going into space one day. It did not take me long to decide that at the very least I should inquire further, though I was concerned that my background was quite unlike the kind of research that is typically performed during manned space flights. I discussed this with the Swedish Space Board before asking them to send me the application papers (a densely written 16 page form), but they confirmed that I was the kind of person that could be of interest to ESA.
The selection process for just six new ESA astronauts took almost two years. Initially, each ESA member state selected up to five candidates, and then ESA chose from the 60 pilots, engineers, medical doctors, physicists and other scientists whose names were put forward. The selection process involved extensive medical screening, as well as several interviews. My CERN background was invaluable – though it is not space science per se, particle physics is closely related to astrophysics and cosmology, and also to radiation, which is a problem for humans and technology in space. My hands-on experience with experimental hardware was useful, but even more important, I believe, was my experience of working in a highly international environment, and the language skills I had gained there.
During one interview, a member of the selection panel remarked that although I had a fairly long publication list, he had noticed that the publications had up to 100 names on them. How could he be sure of my contribution? I had to explain how particle physics experiments are generally performed by large collaborations from many countries. This is increasingly true today, with as many as a thousand collaborators being involved in a single experiment. Fortunately, I was able to point out one or two papers that I had produced myself.
It should be noted that astronauts rarely perform their own experiments in space, and therefore a broad background is important. The exception is when so-called “payload specialists” fly on dedicated science missions, having been selected because of their expertise in a particular scientific field. A mission crew has to deal with technically advanced equipment on a daily basis, and must be able to operate various experiments as well as spacecraft systems. Having worked with particle physics experiments that demand high technology in many fields, I had already been exposed to several areas that one encounters in space activities.
Astronauts are among the prime communicators for the space programme – one could say they are “space ambassadors”. My scientific background has been extremely useful to me during many talks and presentations – in particular during the question-and-answer sessions that often ensue.
The International Space Station (ISS) is certainly “big science”, very much as CERN is. I recognize many similarities, although the ISS is more politicized. There are often complaints that ISS science is too expensive, and that the money could be better spent elsewhere. This is a misunderstanding of the real goals of the ISS, which are to learn how to build and live in space, and to prepare for future space developments. In some ways, it is like the basic science carried out at CERN – we do it out of curiosity, and we do not know what the eventual outcome will be. However, we are convinced that one day we will achieve results that will be of great benefit for all humankind. In the meantime, we take this great opportunity to carry out experiments in a unique environment, and to learn as much as possible about it, in particular how humans react to long periods in space.
I have always tried to combine my interest in particle physics with being an astronaut. I was dreaming of having my own experiment to work on in space, when I heard about the light flashes in the eyes that most astronauts experience in space. It was clear that these are from particles that penetrate the eyes, but until then no-one had put an active detector in space, in front of the eyes, in an effort to correlate particles and light flashes. This eventually led to the Italian-Russian-Swedish SilEye project, based on silicon strip detectors. The collaboration flew two detectors to the Russian space station Mir, and now also has one on the ISS. I hope to get a chance to use it in the summer of 2003, when I am finally scheduled to fly on the space shuttle and spend a week on the ISS.
by Peter T Johnstone, Oxford University Press. Volume 1 ISBN 0198534256 £100.00 (€158); volume 2 ISBN 0198515987 £100.00 (€158); both volumes ISBN 01982496X £175.00 (€277).
This comprehensive two volume set on the theory of topos – the abstract construction of algebraic geometry – owes its title to the Indian tale of four blind men asked to describe an elephant. Each of them inspects a different part of the animal by touch, and each comes up with a very different description. The same, says Johnstone, is true of topos – how you describe them depends on how you approach them.
(Cambridge Lecture Notes in Physics) by Jan Smit, Cambridge University Press, ISBN 0521890519, £21.00 (€33).
This book is based on a series of lectures given by the author at an advanced undergraduate/beginning graduate level.
For readers of Russian, the Joint Institute for Nuclear Research (JINR) in Dubna has just produced the second issue of its Information and Biographical Guide. Including 680 short biographical summaries of the scientists who created JINR and who have worked or are working there, the book profiles specialists in physics, mathematics, chemistry, radiobiology and engineering from more than 20 countries. It is a thorough compilation of JINR history, scientific discoveries, prizes and literature about the Institute and its scientists. Enquiries should be addressed to the editor, M G Shafranova, at shafran@sunse.jinr.ru; fax +7 09621 65767.
by I J R Aitchison and A J G Hey, Institute of Physics Publishing, ISBN 0750308648, £29.99 (€48).
For the third edition of this classic graduate textbook, first published in 1982, the authors have substantially enlarged the text to reflect developments both in university curricula and the field of particle physics. New introductory chapters have been added to give a historical account of the properties of quarks and leptons. Volume 2, covering the non-Abelian gauge theories of QCD and electroweak interactions, is scheduled for publication in 2003.
As a citizen of Antwerp, the place where the Renaissance produced some of its finest atlases, I was of course very pleased to read a book that for once properly explains the work of Gerardus Mercator.
Fortunately (or perhaps unfortunately), I am not familiar with Peter Higgins’ other books that popularize mathematics, so this is an impression of one work only. The author states that he wants to give something interesting to everyone. That is a very large audience, and I’m convinced that reality is somewhat more selective.
The book starts densely; each sentence has its weight, and speed-reading will not work. While I personally like that, it may lose some of the target audience now and then. I found the beginning of the trip rather bumpy; the first figure is a strange map of the world, and the second one has a confusing caption. The explanation of the date line is simply inadequate. A book on mathematics that still uses imperial units in a metric world is also annoying. Some concepts are introduced without any previous explanation. A few errors are merely funny; the inhabitants of the US state of Nevada will be pleased to learn that they share a border with Colorado, so maybe we do need five colours to paint the map!
However, after the rough road of the first 40 pages or so, the going gets good, and I found the reading most pleasing. A book of this type will inevitably talk about how certain parts of mathematics came to be discovered, and that means lots of history and people. Higgins’ book has a number of interesting details that were new to me, including the fact that Abraham Lincoln took Euclid’s elements with him on trips, as a source of mental relaxation.
There is a lot on classical plane geometry, mostly involving triangles. It is very pleasing to be able to refresh your school maths with these excellent chapters. There are some very good summaries of the properties of conical sections, though the accompanying drawings should have been made using proper tools; conical sections are too beautiful to be illustrated with the crude approximations the publishers have allowed. This made me cringe more than once!
The chapter on symmetries seems a bit out of place, especially considering that there is no treatment of groups, fractals, or the theorems of Gödel and Turing. A number of quite recent, but still “classical” developments that are familiar to everyone got no mention: Rubik’s cube for example, and more on Penrose tilings. Today’s computer graphics and printing are almost entirely based on Pierre Bézier’s curve, and some entertaining exposition of its remarkable properties would have been a welcome addition to the geometry parts of the book.
However, the mere fact that I have a thirst for more means I have spent several hours of exciting reading.
Canada’s Perimeter Institute for Theoretical Physics was awarded C$25 million (€16 million) by the Canadian Federal government at a groundbreaking ceremony in June. Soon after, the province of Ontario, which will host the institute, announced that it would be providing a further C$15 million for the institute, bringing total Canadian public funding for the new institute to slightly more than C$54 million.
The Perimeter Institute was founded in 1999 when Mike Lazaridis, founder and chief executive of the company Research in Motion (RIM), set up a board of directors to determine how best to go about establishing a world-class institute devoted to fundamental physics in the Canadian town of Waterloo. After visiting many institutes for advanced research in physics around the world, the board concluded that the new institute should be independent, focusing on foundational, non-directed research, be resident-based with a flat hierarchy, and should have a strong public outreach programme.
The institute was officially launched on 23 October 2000 with a C$100 million donation from Mike Lazaridis and an additional C$20 million from RIM executives Doug Fregin and Jim Balsillie. The City of Waterloo donated a site for the institute’s new building, along with temporary accommodation in a former post office and national revenue building. An international eight-member scientific advisory committee was selected in late 2000, and had its first meeting in Waterloo in spring 2001. Research began in autumn 2001 with a core scientific staff of five and four postdoctoral fellows in quantum gravity, string theory, quantum information theory and quantum computing.
CERN played host to a meeting of First Tuesday Suisse romande, a network for innovation and technology in French-speaking Switzerland, in September. Some 250 people came to the laboratory to learn about the latest developments in Grid computing technology. Topics covered Grid development at CERN and in industry, including an insight into the emerging field of Grid economics and an example of how Grid technologies are having an impact in the medical arena. The event also marked the company Hewlett-Packard joining the CERN openlab for DataGrid applications, other sponsors of this industrial collaboration being Intel and Enterasys Networks.
Now in its fourth year of operation, First Tuesday Suisse romande was founded to provide a forum for entrepreneurs, investors and all those interested in new technology. Its Geneva meetings are held on the first Tuesday of each month, and take the form of a few short presentations followed by an informal networking session. CERN’s director for technology transfer and scientific computing, Hans Hoffmann, plans to host more First Tuesday events at CERN. “The Large Hadron Collider project,” he explains, “is a goldmine of technological innovation, ideally suited for the kind of networking events First Tuesday holds.” This first event was broadcast on the Web to ensure a wider international audience could benefit.
Young accelerator physicists converged on the Portuguese coastal town of Sesimbra in September for the 2002 CERN Accelerator School (CAS) introductory course on particle accelerators. Organized by CAS together with the Laboratório de Instrumentação e Física Experimental de Partículas of Lisbon (LIP), the course covered the basics of accelerator and particle physics, concluding with a series of lectures entitled “Putting it all together”. Thirteen European specialists, chosen for their teaching experience, made up the lecture team, while CERN and LIP shared the organizational responsibilities.
Students came from a range of countries – 13 from Germany, and 12 each from Italy and the UK. France, Canada and Russia each sent three students, and two came from South Korea. There were also students from Belgium, Brazil, Iran, Israel, the Netherlands and Poland, as well as 25 from CERN who were too international to declare a specific nationality, but who no doubt came from Europe. More than 60% of the students were under 35, and about the same percentage had a Masters degree, while fewer than 10% had PhDs. Two-thirds came from accelerator and public sector laboratories, with the remainder made up largely of people from universities.
CAS organizes one such introductory course every two years, interspersed with more advanced courses on specialist technology. It has organized more than 40 courses on accelerator physics and technology since its formation in 1983. Its aim is to train physicists and engineers who design, construct and operate accelerators in laboratories, universities, hospitals and in industry worldwide. Venues are in the European countries that contribute to CERN, and are usually at hotels with conference facilities, where bargain rates are to be had outside the tourist season. Typical attendance is between 50 and 80 students. Each new school produces one or two volumes of proceedings, and these have become the principal body of reference material for the field.
I started working on neutrino detection early in my career. I had rather broad interests in other fields of the physical sciences and worked on a number of other projects. Usually, an experimentalist develops a number of skills and applies them to solving new problems that appear interesting. I was fortunate to live at a time when there were many interesting new developments, and fundamental science was well supported.
In 1942, I received my PhD from Yale in physical chemistry, and went directly into the army as a reserve officer. After the war, I decided to look for a research position with a view to applying chemistry to studies in nuclear physics. After two years with the Monsanto Chemical Company in applied radiochemistry of interest to the Atomic Energy Commission, I was very fortunate in being able to join the newly created Brookhaven National Laboratory, which was dedicated to finding peaceful uses for the atom in all fields of basic science: chemistry, physics, biology, medicine and engineering.
I became a member of the chemistry department in 1948 and remained there until my retirement in 1984. In 1948, a scientist at Brookhaven was able to choose an independent research programme consistent with the laboratory’s effort. After reading a stimulating review paper by H R Crane (Crane 1948), I decided to begin by selecting an experiment in neutrino physics, a field of physics that was wide open to exploration, and a suitable one for applying my background in physical chemistry. So, how lucky I was to land at Brookhaven, where I was encouraged to do exactly what I wanted, and get paid for it!
First experiments
My first experiment was a study of the recoil energy of a lithium-7 nucleus resulting from the electron capture decay of beryllium-7. In a beryllium-7 decay, a single monoenergetic neutrino is emitted with an energy of 0.862 MeV, and the resulting lithium-7 nucleus should recoil with a characteristic energy of 57 eV. A measurement of this process provides evidence for the existence of the neutrino, postulated by Wolfgang Pauli in 1931. An experiment of this nature had been carried out much earlier, but the result was inconclusive. In my experiment, the energy spectrum of a recoiling lithium-7 ion from a surface deposit of beryllium-7 was measured. The energy spectrum of the recoiling lithium-7 was found to agree with that expected from the emission of a single 0.862 MeV neutrino (Davis 1952).
Later, I began working on a radiochemical experiment for detecting neutrinos using a method that was suggested by Bruno Pontecorvo in 1946 (Pontecorvo 1946). Louis Alvarez proposed carrying out the experiment at a reactor, but lost interest in the project (Alvarez 1949). Since no-one else appeared interested in attempting the chlorine-argon neutrino detection method, it seemed a natural and timely experiment for me to work on.
The Pontecorvo method makes use of the neutrino capture reaction, n + 37Cl →37Ar + e–. The reaction produces the isotope argon-37 that decays back to chlorine-37 by the inverse of the capture process, with a half-life of 35 days. In my experiment, carbon tetrachloride served as the target material. After exposing a tank of this liquid to a neutrino source for a month or two, the radioactive argon-37 atoms produced by neutrino capture were removed and counted in a small Geiger counter. The neutrino capture cross-section is extremely small. Therefore, one must use a very large volume of carbon tetrachloride. To observe the argon-37 decays, it was necessary to develop a miniature counter with a very low background counting rate. There are background effects that must be studied as well, particularly those from cosmic rays.
The technology for carrying out the experiment on a relatively large scale, using 1000 gallons of carbon tetrachloride, was developed with the Brookhaven Graphite Research Reactor as the neutrino source. That reactor did not have a high enough neutrino flux to detect with this target size, so neutrinos were not observed. Furthermore, a reactor emits antineutrinos, and the Pontecorvo reaction requires neutrinos. It was not clear in 1952, however, whether neutrinos and antineutrinos were different particles, nor was it clear how they could differ. After all, there are other instances in nature where the particle is its own antiparticle, for example the photon and the neutral kaon.
So, in 1954, I built an experiment using 1000 gallons of carbon tetrachloride in the basement of one of the Savannah River reactors, the most intense antineutrino source in the world. One can calculate the total capture rate from all fission-product antineutrinos by chlorine-37, presuming neutrinos and antineutrinos are equivalent particles. The sensitivity for detecting neutrinos and the flux at this location was sufficiently high to provide a critical test for the neutrino-antineutrino identity. However, the experiment failed to observe a clear signal from reactor neutrinos. The Savannah experiment demonstrated that the argon-37 production rate was a factor of five below the rate expected if neutrinos and the antineutrinos were identical particles (Davis 1957).
While I was at Savannah River doing these experiments, Fred Reines, Clyde Cowan and their associates were performing a beautiful experiment, the first detection of a free antineutrino (Reines and Cowan 1956). Their experiment was a clear demonstration that the neutrino postulated by Pauli was indeed a real particle. They observed antineutrinos being captured by a hydrogen nucleus (proton) producing a positron and a neutron. The measured cross-section was consistent with that expected from Fermi’s theory of b-decay.
In 1957, T D Lee and C N Yang suggested that the neutrino was a two-component particle whose interactions violated the principle of parity conservation. This concept was confirmed in a beta-decay experiment by Chien-Shiung Wu of Columbia and her associates at the National Bureau of Standards. The two-component theory postulates that all neutrinos have spins rotating in a left-handed helicity with respect to their direction of motion. Right-handed antineutrinos will not interact with the chlorine-37 nucleus and produce argon-37 because they have the wrong helicity. The Reines and Cowan experiment should and did observe reactor antineutrinos. All was explained. But this was not the end of the matter.
Pauli and many others did not believe all was as it seemed, and urged that another and more sensitive chlorine-37/argon-37 experiment be performed. To complicate matters, many physicists measured the spins of electrons from many beta-decay sources. They found that the electrons were not necessarily polarized as expected. After a couple of years of improved experiments, these polarization studies ultimately found that the two-component theory was correct.
Don Harmer from Georgia Tech and I set about building a three-times larger chlorine-37/argon-37 experiment. After several years, we obtained a greatly improved result. We found that the argon-37 production rate was a factor of 20 below the expected rate for neutrinos and antineutrinos being identical particles. In this experiment, our sensitivity was limited by the production of argon-37 in our liquid by cosmic rays.
Textbreak=After the Savannah River experiments were terminated, I started thinking about an experiment to measure neutrinos from the Sun. The first step in the plan was to set up one of our detectors as a pilot experiment in a deep mine to measure the background effects and determine the ultimate sensitivity for observing solar neutrinos. The measurements of argon-37 activity could be made more sensitive and specific by using proportional counters. The Sun emits only neutrinos, so the chlorine-argon method was the simplest means of studying solar neutrinos. In 1959, we located a mine near Akron, Ohio, to begin these studies.
Observing the neutrinos from the Sun had the potential of testing the theory that the hydrogen-helium thermal fusion reactions are the source of solar energy. However, the proton-proton chain of reactions in the 1950s was regarded as the principal source of the Sun’s energy, and this chain emitted only low-energy neutrinos from the primary proton-proton reaction. These neutrinos were below the energy threshold of the chlorine-argon reaction. We were saved from this impossible situation, however, by a new development.
In 1958, two nuclear physicists, H D Holmgren and R I Johnston at the Naval Research Laboratory measured the 3He + 4He →7Be + g reaction, and found it had a higher than expected cross-section. It was immediately recognized that this reaction could be important in the terminal stages of the proton-proton cycle. Furthermore, the beryllium-7 could react with a proton and become boron-8. These two radioactive products, beryllium-7 and boron-8, would be the source of energetic neutrinos, ones that could be measured by the chlorine-argon radiochemical method. W A Fowler and A G W Cameron immediately relayed to me these developments. They pointed out that the neutrino flux from these neutrino sources could perhaps be easily observed by the chlorine-argon detector! I might add that Fred Reines was also stimulated by the new findings and immediately embarked on a programme of solar neutrino research (Reines 1967). There was also a very active programme in the Soviet Union in solar neutrino research under M A Markov and G T Zatsepin.
These events ultimately led Brookhaven, with support from the chemistry office of the Atomic Energy Commission, to build a 100 000 gallon chlorine-argon neutrino detector in the Homestake Gold Mine at Lead, South Dakota. The scale of the experiment was determined by a theoretical estimate of the expected neutrino flux and the neutrino capture cross-sections for each solar neutrino source in the Sun. It was necessary to measure the production cross-sections of the neutrino-producing reactions, and derive their rates in the interior of the Sun. The aim was to forecast as accurately as possible the rate of solar neutrino capture in the Homestake detector.
This great effort was largely carried out at the California Institute of Technology under the leadership of Fowler. During this period, John Bahcall calculated the neutrino capture cross-section to produce argon-37 in excited states (Bahcall 1964). Of particular interest was the analog state in argon-37 and a means of calculating other excited states by studying the decay of calcium-37. The effect of these states was to greatly increase the expected neutrino capture rate of the energetic boron-8 neutrinos with energies extending to 15 MeV. Bahcall and I wrote an account of these activities in a volume of papers dedicated to Fowler. As outlined in the article, very many nuclear physicists and astronomers contributed to the basic physics that supported this early effort in solar neutrino astronomy. Our task at Brookhaven was far simpler, and we (Don Harmer, Kenneth Hoffman and myself) had the fun of building a large detector and making it work.
We were very fortunate that the Homestake Mining Company accepted our project. They assisted us in many ways with the building and operation of the experiment. The great depth of the experiment (4850 feet or 1560 m) turned out to be a crucial element.
The observed neutrino capture rate was much lower than was anticipated from the solar model calculations (Davis et al. 1968). In fact, we did not observe a solar neutrino signal at all, and our results were expressed only as upper limits. The low neutrino capture rate was a result that many theorists found difficult to accept. They believed that there must be some chemical inefficiency in the recovery of a few atoms of argon-37 in the massive Homestake detector. We made numerous tests to check the chemical efficiency, and found that the chemical procedures were reliable.
The main difficulty was experimental: the argon-37 counting needed to be improved to search in a more sensitive way for a solar neutrino signal. Brookhaven electronic engineers Veljko Radeka and Lee Rogers solved this problem by devising a pulse rise-time system to discriminate argon-37 decay events from background events. We began using this new system in 1970. After about a year of observations, a clear solar neutrino signal was observed. The signal was smaller than the earlier limit, but we were convinced that the Homestake experiment would in time make a valid measurement of the solar neutrino capture rate in chlorine-37 to compare quantitatively with the solar model calculations.
The pulse rise-time system development gave the Homestake experiment a new life. The solar neutrino production rate was indeed lower than the solar model predictions by a factor of about three. The most likely explanation, in my view at the time, was that the solar model was in error.
Fred Reines organized an in-depth conference on all aspects of solar neutrino research at the University of California’s Irvine campus in 1972. There was an excellent discussion of the theoretical and experimental matters, and new experiments (Trimble and Reines 1973). This conference was of great importance in defining many basic problems and new directions in this new field. Another conference of a similar nature was held at Brookhaven five years later, in 1978. Trevor Pinch made an interesting sociological and historical study of the reaction of the scientific community to the Homestake experiment in his book Confronting Nature (Pinch 1982). We had to wait 18 years for another experiment, the Kamiokande experiment in Japan, to confirm that the solar boron-8 neutrino flux was low.
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