- Email: [email protected]
A modest prehistory of low-temperature detectors
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Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10
A modest prehistory of low-temperature detectors Georges Waysand* Groupe de Physique des Solides, Universit!e Paris 6, Campus Boucicaut 140 rue de Lourmel, 75015 Paris, France Laboratoire Souterrain Bas Bruit de Rustrel, Pays d’Apt Universite! d’Avignon et des Pays du Vaucluse, Rustrel 84400, France Dedicated to the memory of Sandro Vitale
Abstract The early days of low temperature detectors are an entanglement between particle physics, astronomy and lowtemperature physics. They are traced from 1903 to the first of the LTD meetings, ‘‘LTD-zero’’, which took place at the Groupe de Physique des Solides in Paris, in April 1983. r 2003 Published by Elsevier B.V. PACS: 29.40; 64.60; 95.55; 01.65; 01.75 Keywords: Detectors; Metastable states; Space telescope; History of sciences; Sciences and society
1. Introduction This gathering being the 10th session of the LTD meetings, I have been asked by the organizing committee to present their prehistory. Indeed, they are the outcome of a very modest encounter, now nicknamed ‘‘LTD-zero’’. LTD-zero took place at the Groupe de Physique des Solides, at that time associated with Universite! Paris 7, just 20 years ago. It was organized by Fran@ois Vanucci and myself. Sandro Vitale, Director of the School of Medical Physics in Genoa, was one of the speakers. Sandro is best known to our community *Corresponding author. Groupe de Physique des Solides, Universit!e Paris 6, Campus Boucicaut 140 rue de Lourmel, 75015 Paris, France. Tel.: +33-1-43-25-66-40; fax: +33-1-4354-28-78. E-mail address: [email protected] (G. Waysand). URL: http://www.elsevier.nl/inca/publications/store/5/0/5/ 7/0/1. 0168-9002/$ - see front matter r 2003 Published by Elsevier B.V. doi:10.1016/j.nima.2003.11.208
by his elegant experiment on rhenium to demonstrate the X emission fine structure [1]. It was the result of a long race in low-temperature detection. Registering for LTD-zero, he explained in his short letter: ‘‘Presently, I am interested in Josephson tunnel detectors for low energy spectroscopy’’.1 Sandro passed two years ago. This talk is dedicated to his memory. I would like to place our activity in a larger frame, hence the title of this talk: modest prehistory. To explore the entanglement between particle physics, astronomy and low temperatures, my starting point for this sketchy perspective will be 1903, just a century ago: in 28 min from now (and a few pages ahead for the reader), let us hope that we will reach our common LTD birth date: 1983. 1 Sandro Vitale to Fran@ois Vanucci , March 14, 1983 (my archives).
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This centennial choice is more than a calendar coincidence. In 1903, physicists were not many. However, the variety of their interests led to a curious situation which somehow is at the origin of the present division of physics in different fields, each with its own tradition—a division which we feel so strongly in low-temperature detectors.
2. a rays, ‘‘emanations’’yand helium On June 25, 1903 (thus almost day for day a century ago), Marie Sklodowska Curie presented the findings of her work about a rays in her doctoral thesis. For her, a rays were already particles electrically charged and projected at high speeds2 but nobody was certain that their nature was independent of the emitting element. A little celebration in Marie’s honour, was arranged in the evening by Paul Langevin. Ernest Rutherford was among the guests. He was then working in Canada but temporarily in Paris and anxious to meet Marie Curie. He had good reason. His study of the deflection of radiation in magnetic fields had not met with success until he had been sent a strongly radioactive preparation by the Curies. a rays were recognized to be emitted by minerals each time they contained uranium or thorium, but their nature was unclear since gaseous radioactive ‘‘emanations’’ as they were called by Rutherford were also noticed. The most advanced view towards the solution of this problem was indeed put forward by Rutherford and Soddy just a year before:
And again in this year 1903: ‘‘y possibly helium is an ultimate product of the disintegration of one of the radioactive elements, since it is only found in radioactive minerals.’’ Rutherford based his conviction upon an approximate measure of e/m=5000 electromagnetic units against 9650 for hydrogen atom (this one provided by water electrolysis).3 This straightforward method of identification by a crude mass spectrography experiment was at odds with the usual chemical method of analysis of the period: optical spectroscopy. In fact, helium had been discovered by optical spectroscopy. During the solar eclipse of 1868 P.J.C. Janssen, sent to India for observation of the solar spectrum, noticed a new yellow spectral line in the sun. ‘‘It was suspected by Frankland and Lockyer that the line was due to hydrogen; but no means was found of causing that element to show such a line. They therefore came to the conclusion that it must be due to the presence in the solar atmosphere of an element unknown on the earth; and they gave it the name ‘‘helium’’, to suggest its solar origin. Shortly afterwards, Langlet, working in Cleve’s laboratory, discovered helium independently4.’’ Helium at that time was also of interest for the completion of the periodic table which was the main interest of Ramsay. Indeed Soddy, the first of Rutherford’s students, left Canada to work with Ramsay. According to Ramsay (in his Nobel speech for chemistry the next year):
‘‘ythe speculation naturally arises whether the presence of helium in minerals and its invariable association with uranium and thorium, may not be connected with their radioactivity [2].’’
‘‘...we at once began to investigate the properties of the radium emanation; for its life is so much longer than that of the thorium emanation (in the proportion 463,000 to 87) that it is possible to deal with it by ordinary physical methods. The emanation from about 60 milligrams of radium bromide was collected during 8 days; it was introduced into a minute
2
‘‘It was not till 1900 that Madame Curie threw out the suggestion that the a-rays, which were stopped by small thicknesses of metal or glass, proceeding from polonium, might be of the nature of small particles, projected with great velocity, but which lost their energy in passing through matter.’’ William Ramsay (Nobel Lecture for chemistry 1904). Ramsay followed Rutherford and named ‘‘a rays’’ what we call nowadays a rays.
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E. Rutherford, Nobel Lecture. W. Ramsay, Nobel Lecture.
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measuring tube, and its volume determined; it was found to be a self-luminous gas, obeying Boyle’s law; and its volume slowly contracted during four weeks, until at the end of that time only the smallest visible bubble remained, which nevertheless still appeared as a brilliant speck of light; and on heating the tube which had contained the gas, a gas was evolved from the walls, possessing three and a half times the volume of the emanation, which showed the spectrum of helium. It had doubtless been projected with a velocity considerable enough to cause the molecules to imbed themselves in the glass of tube, from which they were expelled at a red heat. Other experiments showed that it is easy, by heating a radium salt which has been prepared for some time, to expel the helium which has accumulated; this result has been repeatedly confirmed, not only by Soddy and myself, but also by other observers.’’ Rutherford and Geiger had calculated, on the assumption that the ‘‘a-particle’’ was a helium atom, that 1 g of radium in equilibrium should produce a volume of 158 mm3 of helium per year. With the exception of the recipe to get helium, these preoccupations were secondary for James Dewar and Kamerlingh Onnes. They were competitors for its liquefaction. Dewar, enjoyed making a show of presenting during his public lectures at the Royal Institution the last experiments he had built. He insisted on using glass, contrary to the advice of his assistants who were aware that presumably at low temperature, radiation heat cannot be neglected. In the end, Dewar’s obstinance resulted in helium being liquified for the first time, not at the Royal Institution in London but at the Natuurkunde Laboratory in Leiden.
3. The golden age of physics The mystery of the emanation was not totally solved. The ‘‘self-luminous gas’’ was evidently not only composed of helium. After many years, in the twenties, it was recognized that the radioactive part of the emanation was a single element
unknown up to then: radon. But that was already the golden (and still innocent) age of physics. Physicists were not many, but each of them could # dream to get his baton de Mar!echal as we say in French. A group photograph of smiling physicists from Leningrad, published in a recent biography of Yacob Frenkel, is a good evidence of this: L. Gurevitch, L. Landau, L. Rosenkevitch, A. Arsenieva, Ya. Frenkel, G. Gamow, M. Manchinskii, D. Ivanenko and G. Mandel are in front of a blackboard upon which someone has written with a piece of chalk: ‘‘ANNO QUANTI XXIX’’ as if it was engraved above the pediment of a temple [3]. Of course, all the achievements of the 1920s and 1930s are our daily tools. But the discovery of the neutron and the positron, the extensive use of the tunnel effect formalism for the description of the a ray emission, and the superfluidity of helium are of extreme importance for what will be low-temperature particle detection. If the late 1920s and 1930s were the golden age of physics, they were also a dark time for societies. Let us just recall the words of the late Nicolas Kurti at the banquet talk of LTD4: ‘‘An important event in the history of the Clarendon was Hitler’s coming to power in Germany in 1933 which resulted in an influx of German academic refugeesy .’’ Let us also remind ourselves of the fate of those in a picture taken on the steps of the lowtemperature laboratory of Kharkov in the Soviet Union in 1934. Seated on a sunny day in the front row are: Shubnikov (shot in 38), Leipunski (jailed, then freed to become a leader of the atomic program), Landau (jailed and according to him saved from a certain death by Kapitza), and finally Kapitza who was denied to return to his Mond Laboratory while he was on vacation in the Soviet Union [4]. The combination of scientific and political factors at the end of the 1930s had created a double movement: *
an internal movement: some physicists faced the emerging division of physics by moving from one field to another: Kapitza was hired by
ARTICLE IN PRESS G. Waysand / Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10
*
Rutherford mostly for doing nuclear physics, but he moved towards low temperatures, contrary to Kurchatov, who started in semiconductors but switched to nuclear physics. an exile movement, mostly from the third Reich, Austria and Italy, because of the nazi antisemitic laws, which created a deep modification of the repartition of the scientific workforce within Europe, and between Europe and the United States.
This scientifico-political context had two important consequences for low-temperature detectors: *
*
the first particle detection at low temperature was performed in Oxford by Nicolas Kurti when he brought (without safety precautions!) a 1.5 g radium source near his adiabatic demagnetization cryostat, and watched the temperature elevation in order to evaluate its cooling power. With Simon and Mendelssohn, he had just arrived from Breslau (nowadays Wroclaw) a few years before. superfluid helium was discovered in Cambridge by Allen and Misener in spite of Stalin y and in Moscow by Kapitza thanks to Stalin.
However low-temperature as a specific field of activity was still in its infancy. There were only around 10 low-temperature laboratories world wide. The first suggestion of a superconducting bolometer was published on the eve of the war [5]. These early developments were almost totally stopped during WWII.
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Schrieffer had provided the microscopic theory, are still not fully appreciated nowadays. The isotope effect (giving an immediate proof of the electron–phonon interaction), the concept of electron pairing, the utilization of many-body problem techniques, and the later direct measurement of the energy gap by tunnel effect are direct importations into condensed matter physics of products, tools and concepts from nuclear and particle physics. However, in the reverse direction, superconductivity is the field from which in 1963 Brian Josephson gave to the notion of the phase of the wave function a physical meaning. Particle theoreticians were happy to describe the vacuum of the Standard Model by analogy with the electromagnetic vacuum inside a superconductor, and more generally enjoyed the concepts of broken symmetries and phase transitions a" la Ginzburg-Landau. In the same way our present description of neutron star is a byproduct of the microscopic understanding of superconductivity. Of course, we should not forget, less mundane but not less important, the numerous utilizations of superconductivity, either already or potentially in use: transition edge sensors, superheated superconducting grains, tunnel and Josephson junctions and more generally all the devices in which a spatial modulation of the order parameter allows the trapping of quasiparticles. This is evident if now we have a look at the main driving force for the development of low-temperature detectors: observational astronomy.
5. Cosmic microwave background and infrared astronomy 4. A new knot between particle physics, cosmology and low-temperature physics: superconductivity After WWII, physics was booming. As a result of specialization, the borders between fields were less permeable. Superconductivity, unexpectedly, was to be an exception for a small number of people. The intertwining between nuclear techniques and theory leading to the breakthrough of the microscopic theory, as well as the feedback on particle physics after Bardeen, Cooper and
The bolometer was invented by Langley in 1881 and presented in its original publication with some verbosity: ‘‘I had flattered myself with the hope of succeeding better than my predecessors. I found however, that though I got results, they were too obscure to be of any great value, and that science possessed no instrument that could deal successfully with quantity of radiant heat so minute.
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I have entered into these preliminary remarks as an explanation of the necessity of such an instrument as that which I have called the Bolometer (bolZ,metron), or Actinic Balance, to the cost of whose construction I have meant to devote the sum the Rumsford Committee did me the honor of proposing that the Academy appropriate. Impelled by the pressure of this actual necessity, I therefore tried to invent something more sensitive than the thermopile, which could be at the same time equally accurate, which should, I mean, be essentially a ‘‘meter’’ and not a mere indicator of the presence of a feeble radiation. This distinction is a radical one [6].’’ In the late 1950s, Scovil and his associates at Bell Labs were building the world’s lowest-noise microwave amplifiers, ruby travelling wave masers. These amplifiers were cooled to 4.2 K or less by liquid helium. They were used by Penzias and Wilson behind a 20-ft horn-reflector and the reference noise source was also cooled at 4.2 K in a separate cryostat. With this combination of instruments the spectrum of the cosmic microwave background, was discovered and measured at that time estimated to be a 3 K black body spectrum [7]. Since then, the study of the cosmic microwave background has been linked to low temperature detection. Infrared spectroscopy was a child of this evolution. Low, one of its pioneers was in 1969 reporting on the state of the art of germanium bolometers. At that time the operating temperature of the typical detector was 2 K, with an area of 1 1 mm2, a focal ratio of f/15 and range of sensitivity from 7 to 14 mm, a background power of Q=2 107 W with a thermal conductance G=10 6 W/K, and a noise equivalent power of 3 10 14 W/Hz1/2. Contrary to most of us in our proposals for new funding, Low was apparently not an optimist, in his conclusion asking himself: ‘‘The questions arise: ‘‘What of the future?’’, as detector sensitivity increases through future developments, can we expect an ever increasing observational sensitivity? It is clear that the answer is negative unless the background power can be reduced...’’
But Low also saw clearly the solution: ‘‘By refrigerating the entire telescope and placing it in space, it should be possible to extend the observational capability by several orders of magnitude [8].’’ That has been done.
6. The background of LTD zero: superheated superconducting grains Simultaneous with Low’s efforts in infrared detection, specialists in superconductivity and theoreticians of phase transitions were puzzled by an irritating issue: Why hysteretic behavior was not observed in type I superconductors in spite of their first order phase transition in a magnetic field? Of course, it was a minor issue, but the understanding of superconductivity has more than once been changed drastically by unexpected experimental facts. Carefully metallurgically prepared pure type I crystals, cylinders, and whiskers were tested in magnetic fields. If their transitions in a magnetic field were hysteretic, it was almost negligible. Supercooling was far more easily observed than superheating but, in every case, the width of the hysteretic cycle was far from the theoretical limit of metastability for superheated and supercooled states. The Orsay group of superconductivity had the idea to try the same experiment with superconducting microspheres. The idea of using mercury came almost immediately, but the very clever trick was to remember that a long time ago mercury salts were prescribed to cure syphilitic chancre. In fact, the ointment was a poison because it also contained metallic mercury, and had been finally discarded. Orsay at the time being still a rural little town, would it be possible that the local pharmacy still had the drug? Such was the case. A small nut of pomade filling the interior of a tiny cylindrical coil which was part of a resonant LC circuit was plunged into a liquid helium bath under reduced pressure. The long awaited result was there: superheated and supercooled states were immediatly observed as predicted by theory. A conversation between P.G. de Gennes and G.
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Charpak launched the idea of overcoming the metastability barrier by X-irradiation. The path for more mundane experiments was open. In 1975 at DESY, with a 6 GeV pure electron beam, a single channel transition radiation detector provided a direct proof of transition radiation theory thanks to the wide energy band response of the SSG detector. Real-time read-out of a single superheated grain transiting to the normal state was realized at the same time. More recently a 16 channel device was operated at 100 mK was operated at CERN [9]. For rare event experiments, one of the drawbacks of SSG detectors is the need of a quiet electromagnetic environment. Zero Gauss chambers are useless since a magnetic field is mandatory to get superheated states. This difficulty is now overcome at the Laboratoire Souterrain Bas Bruit de Rustrel-Pays d’Apt (50 km east of Avignon). In this low noise underground laboratory below 1500 mwe, in a volume of 1250 m3 without m-metal, the noise level above 10 Hz is better than 2 fT/Hz1/2, less than a hundred times the magnetic noise of your sleeping brain in its cooler phase! (for more details see Ref. [10]). In the early 1980s Raghavan proposed an experiment to detect solar neutrinos with a lowenergy threshold, 128 KeV. The target was indium and besides X’s and g’s the product was tin, both superconductors! Evidently, it had to be largescale experiment, 4 tons of indium being required for a rate of one event/day. Because of their massive nature and easy pixellization, SSG were an evident candidate. To check the interest of this idea, together with Fran@ois Vanucci, a highenergy physicist from Paris 7, we decided to organize an informal meeting at Groupe de Physique des Solides of University Paris-7 to see what could be the response of particle physicists to such an idea.
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little bit more than 20 scientists from a dozen of solid state groups and high-energy physics laboratories actually participated to the meeting. After an introduction to SSG, the state of the art for the read-out electronics was presented by A. Hrisoho (Orsay), and for transition radiation detection by D. Perret-Gallix (Annecy). The Josephson effects were discussed by C. Vanneste (Nice), non-equilibrium superconductivity by N. Perrin (Paris). F. Celani (Frascati) presented electronics read-out for tunnel junctions detectors to introduce indeed a round table about Josephson devices for SSG. The second day R.S. Raghavan (Bell Labs.) presented his indium solar neutrino capture proposal and Leo Stodolsky (Max Planck Munich) described the application of SSG as a neutral current detector for neutrino physics and astronomy. Of course it ended by a round table... after many informal discussions in the cafe! s surrounding Jussieu and lively meals taken at near-by restaurant of cuisine lyonnaise... ). The overall budget for all that was less than 1500 French francs (230 euros). One outcome of all this is still alive: LTD meetings.
Acknowledgements I thank N. Coron (Orsay), V.L. Ginzburg (Lebedev), T.A. Girard (Lisboa), Ch. Glasshauser (Rutgers & Livingston), the late N. Kurti (Oxford), J.M. Kantor (Math Paris 7), P. de Marcillac (Orsay), M. Ribeiro Gomes (Lisboa) and Jean Matricon (GPS-Paris 7) co-author of Cold Wars, A History of Superconductivity (Rutgers University Press, August 2003). They gave to me various helps, discussions, interviews and documentations. The mistakes, if any, are mine, of course.
References 7. LTD zero The small poster for the meeting (a single A4 sheet of paper) announced a ‘‘Workshop on Metastable Superconductors in Particle Physics’’ on 14–15 April 1983. At the opening of the workshop, 33 participants had registered and a
[1] F. Gatti, et al., Nature 397 (1999) 137. [2] E. Rutherford, F. Soddy, Philos. Mag. 4 (1902) 582. [3] Victor Ya. Frenkel Yakov Ilitch Frenkel, His Work, Life and Letters, Birkh.auser Verlag, Basel, 1996, p. 141. [4] Jean Matricon, Georges Waysand, La guerre du Froid, une histoire de la supraconductivit!e, e! ditions du Seuil, Paris, 1994, p. 147 (ISBN 2.02.021792.9 and also in the
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[5] [6] [7] [8]
G. Waysand / Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10 Anglo-American updated version, Cold Wars, A History of Superconductivity, Rutgers University Press, 2003, p. 93). A. Goetz, Phys. Rev. 55 (1939) 1270. S.P. Langley, Proc. Natl. Acad. Arts Sci. 16 (1881) 342. A.A. Penzias, R.W. Wilson, Astrophys. J. 142 (1965) 419. F.J. Low, in: W.H. Hogan, T. S. Moss (Eds. ), Cryogenicsz and Infrared Detection, Proceedings of a Technical
Colloquim on Cryogenics and Infrared Detection Systems, April 17–18, 1969, Frankfurt-am-Main, West-Germany. Boston Technical Publishers Inc, Boston, 1969, p. 21. [9] L.C.L. Yuan, C.P. Chen, C.Y. Huang, S.C. Lee, G. Waysand, P. Perrier, D. Limagne, V. Jeudy, T. Girard, Nucl. Instr. and Meth. A 441 (2000) 479. [10] http://www.Isbb.univ-avignon.fr.
Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10
A modest prehistory of low-temperature detectors Georges Waysand* Groupe de Physique des Solides, Universit!e Paris 6, Campus Boucicaut 140 rue de Lourmel, 75015 Paris, France Laboratoire Souterrain Bas Bruit de Rustrel, Pays d’Apt Universite! d’Avignon et des Pays du Vaucluse, Rustrel 84400, France Dedicated to the memory of Sandro Vitale
Abstract The early days of low temperature detectors are an entanglement between particle physics, astronomy and lowtemperature physics. They are traced from 1903 to the first of the LTD meetings, ‘‘LTD-zero’’, which took place at the Groupe de Physique des Solides in Paris, in April 1983. r 2003 Published by Elsevier B.V. PACS: 29.40; 64.60; 95.55; 01.65; 01.75 Keywords: Detectors; Metastable states; Space telescope; History of sciences; Sciences and society
1. Introduction This gathering being the 10th session of the LTD meetings, I have been asked by the organizing committee to present their prehistory. Indeed, they are the outcome of a very modest encounter, now nicknamed ‘‘LTD-zero’’. LTD-zero took place at the Groupe de Physique des Solides, at that time associated with Universite! Paris 7, just 20 years ago. It was organized by Fran@ois Vanucci and myself. Sandro Vitale, Director of the School of Medical Physics in Genoa, was one of the speakers. Sandro is best known to our community *Corresponding author. Groupe de Physique des Solides, Universit!e Paris 6, Campus Boucicaut 140 rue de Lourmel, 75015 Paris, France. Tel.: +33-1-43-25-66-40; fax: +33-1-4354-28-78. E-mail address: [email protected] (G. Waysand). URL: http://www.elsevier.nl/inca/publications/store/5/0/5/ 7/0/1. 0168-9002/$ - see front matter r 2003 Published by Elsevier B.V. doi:10.1016/j.nima.2003.11.208
by his elegant experiment on rhenium to demonstrate the X emission fine structure [1]. It was the result of a long race in low-temperature detection. Registering for LTD-zero, he explained in his short letter: ‘‘Presently, I am interested in Josephson tunnel detectors for low energy spectroscopy’’.1 Sandro passed two years ago. This talk is dedicated to his memory. I would like to place our activity in a larger frame, hence the title of this talk: modest prehistory. To explore the entanglement between particle physics, astronomy and low temperatures, my starting point for this sketchy perspective will be 1903, just a century ago: in 28 min from now (and a few pages ahead for the reader), let us hope that we will reach our common LTD birth date: 1983. 1 Sandro Vitale to Fran@ois Vanucci , March 14, 1983 (my archives).
ARTICLE IN PRESS G. Waysand / Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10
This centennial choice is more than a calendar coincidence. In 1903, physicists were not many. However, the variety of their interests led to a curious situation which somehow is at the origin of the present division of physics in different fields, each with its own tradition—a division which we feel so strongly in low-temperature detectors.
2. a rays, ‘‘emanations’’yand helium On June 25, 1903 (thus almost day for day a century ago), Marie Sklodowska Curie presented the findings of her work about a rays in her doctoral thesis. For her, a rays were already particles electrically charged and projected at high speeds2 but nobody was certain that their nature was independent of the emitting element. A little celebration in Marie’s honour, was arranged in the evening by Paul Langevin. Ernest Rutherford was among the guests. He was then working in Canada but temporarily in Paris and anxious to meet Marie Curie. He had good reason. His study of the deflection of radiation in magnetic fields had not met with success until he had been sent a strongly radioactive preparation by the Curies. a rays were recognized to be emitted by minerals each time they contained uranium or thorium, but their nature was unclear since gaseous radioactive ‘‘emanations’’ as they were called by Rutherford were also noticed. The most advanced view towards the solution of this problem was indeed put forward by Rutherford and Soddy just a year before:
And again in this year 1903: ‘‘y possibly helium is an ultimate product of the disintegration of one of the radioactive elements, since it is only found in radioactive minerals.’’ Rutherford based his conviction upon an approximate measure of e/m=5000 electromagnetic units against 9650 for hydrogen atom (this one provided by water electrolysis).3 This straightforward method of identification by a crude mass spectrography experiment was at odds with the usual chemical method of analysis of the period: optical spectroscopy. In fact, helium had been discovered by optical spectroscopy. During the solar eclipse of 1868 P.J.C. Janssen, sent to India for observation of the solar spectrum, noticed a new yellow spectral line in the sun. ‘‘It was suspected by Frankland and Lockyer that the line was due to hydrogen; but no means was found of causing that element to show such a line. They therefore came to the conclusion that it must be due to the presence in the solar atmosphere of an element unknown on the earth; and they gave it the name ‘‘helium’’, to suggest its solar origin. Shortly afterwards, Langlet, working in Cleve’s laboratory, discovered helium independently4.’’ Helium at that time was also of interest for the completion of the periodic table which was the main interest of Ramsay. Indeed Soddy, the first of Rutherford’s students, left Canada to work with Ramsay. According to Ramsay (in his Nobel speech for chemistry the next year):
‘‘ythe speculation naturally arises whether the presence of helium in minerals and its invariable association with uranium and thorium, may not be connected with their radioactivity [2].’’
‘‘...we at once began to investigate the properties of the radium emanation; for its life is so much longer than that of the thorium emanation (in the proportion 463,000 to 87) that it is possible to deal with it by ordinary physical methods. The emanation from about 60 milligrams of radium bromide was collected during 8 days; it was introduced into a minute
2
‘‘It was not till 1900 that Madame Curie threw out the suggestion that the a-rays, which were stopped by small thicknesses of metal or glass, proceeding from polonium, might be of the nature of small particles, projected with great velocity, but which lost their energy in passing through matter.’’ William Ramsay (Nobel Lecture for chemistry 1904). Ramsay followed Rutherford and named ‘‘a rays’’ what we call nowadays a rays.
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E. Rutherford, Nobel Lecture. W. Ramsay, Nobel Lecture.
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measuring tube, and its volume determined; it was found to be a self-luminous gas, obeying Boyle’s law; and its volume slowly contracted during four weeks, until at the end of that time only the smallest visible bubble remained, which nevertheless still appeared as a brilliant speck of light; and on heating the tube which had contained the gas, a gas was evolved from the walls, possessing three and a half times the volume of the emanation, which showed the spectrum of helium. It had doubtless been projected with a velocity considerable enough to cause the molecules to imbed themselves in the glass of tube, from which they were expelled at a red heat. Other experiments showed that it is easy, by heating a radium salt which has been prepared for some time, to expel the helium which has accumulated; this result has been repeatedly confirmed, not only by Soddy and myself, but also by other observers.’’ Rutherford and Geiger had calculated, on the assumption that the ‘‘a-particle’’ was a helium atom, that 1 g of radium in equilibrium should produce a volume of 158 mm3 of helium per year. With the exception of the recipe to get helium, these preoccupations were secondary for James Dewar and Kamerlingh Onnes. They were competitors for its liquefaction. Dewar, enjoyed making a show of presenting during his public lectures at the Royal Institution the last experiments he had built. He insisted on using glass, contrary to the advice of his assistants who were aware that presumably at low temperature, radiation heat cannot be neglected. In the end, Dewar’s obstinance resulted in helium being liquified for the first time, not at the Royal Institution in London but at the Natuurkunde Laboratory in Leiden.
3. The golden age of physics The mystery of the emanation was not totally solved. The ‘‘self-luminous gas’’ was evidently not only composed of helium. After many years, in the twenties, it was recognized that the radioactive part of the emanation was a single element
unknown up to then: radon. But that was already the golden (and still innocent) age of physics. Physicists were not many, but each of them could # dream to get his baton de Mar!echal as we say in French. A group photograph of smiling physicists from Leningrad, published in a recent biography of Yacob Frenkel, is a good evidence of this: L. Gurevitch, L. Landau, L. Rosenkevitch, A. Arsenieva, Ya. Frenkel, G. Gamow, M. Manchinskii, D. Ivanenko and G. Mandel are in front of a blackboard upon which someone has written with a piece of chalk: ‘‘ANNO QUANTI XXIX’’ as if it was engraved above the pediment of a temple [3]. Of course, all the achievements of the 1920s and 1930s are our daily tools. But the discovery of the neutron and the positron, the extensive use of the tunnel effect formalism for the description of the a ray emission, and the superfluidity of helium are of extreme importance for what will be low-temperature particle detection. If the late 1920s and 1930s were the golden age of physics, they were also a dark time for societies. Let us just recall the words of the late Nicolas Kurti at the banquet talk of LTD4: ‘‘An important event in the history of the Clarendon was Hitler’s coming to power in Germany in 1933 which resulted in an influx of German academic refugeesy .’’ Let us also remind ourselves of the fate of those in a picture taken on the steps of the lowtemperature laboratory of Kharkov in the Soviet Union in 1934. Seated on a sunny day in the front row are: Shubnikov (shot in 38), Leipunski (jailed, then freed to become a leader of the atomic program), Landau (jailed and according to him saved from a certain death by Kapitza), and finally Kapitza who was denied to return to his Mond Laboratory while he was on vacation in the Soviet Union [4]. The combination of scientific and political factors at the end of the 1930s had created a double movement: *
an internal movement: some physicists faced the emerging division of physics by moving from one field to another: Kapitza was hired by
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Rutherford mostly for doing nuclear physics, but he moved towards low temperatures, contrary to Kurchatov, who started in semiconductors but switched to nuclear physics. an exile movement, mostly from the third Reich, Austria and Italy, because of the nazi antisemitic laws, which created a deep modification of the repartition of the scientific workforce within Europe, and between Europe and the United States.
This scientifico-political context had two important consequences for low-temperature detectors: *
*
the first particle detection at low temperature was performed in Oxford by Nicolas Kurti when he brought (without safety precautions!) a 1.5 g radium source near his adiabatic demagnetization cryostat, and watched the temperature elevation in order to evaluate its cooling power. With Simon and Mendelssohn, he had just arrived from Breslau (nowadays Wroclaw) a few years before. superfluid helium was discovered in Cambridge by Allen and Misener in spite of Stalin y and in Moscow by Kapitza thanks to Stalin.
However low-temperature as a specific field of activity was still in its infancy. There were only around 10 low-temperature laboratories world wide. The first suggestion of a superconducting bolometer was published on the eve of the war [5]. These early developments were almost totally stopped during WWII.
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Schrieffer had provided the microscopic theory, are still not fully appreciated nowadays. The isotope effect (giving an immediate proof of the electron–phonon interaction), the concept of electron pairing, the utilization of many-body problem techniques, and the later direct measurement of the energy gap by tunnel effect are direct importations into condensed matter physics of products, tools and concepts from nuclear and particle physics. However, in the reverse direction, superconductivity is the field from which in 1963 Brian Josephson gave to the notion of the phase of the wave function a physical meaning. Particle theoreticians were happy to describe the vacuum of the Standard Model by analogy with the electromagnetic vacuum inside a superconductor, and more generally enjoyed the concepts of broken symmetries and phase transitions a" la Ginzburg-Landau. In the same way our present description of neutron star is a byproduct of the microscopic understanding of superconductivity. Of course, we should not forget, less mundane but not less important, the numerous utilizations of superconductivity, either already or potentially in use: transition edge sensors, superheated superconducting grains, tunnel and Josephson junctions and more generally all the devices in which a spatial modulation of the order parameter allows the trapping of quasiparticles. This is evident if now we have a look at the main driving force for the development of low-temperature detectors: observational astronomy.
5. Cosmic microwave background and infrared astronomy 4. A new knot between particle physics, cosmology and low-temperature physics: superconductivity After WWII, physics was booming. As a result of specialization, the borders between fields were less permeable. Superconductivity, unexpectedly, was to be an exception for a small number of people. The intertwining between nuclear techniques and theory leading to the breakthrough of the microscopic theory, as well as the feedback on particle physics after Bardeen, Cooper and
The bolometer was invented by Langley in 1881 and presented in its original publication with some verbosity: ‘‘I had flattered myself with the hope of succeeding better than my predecessors. I found however, that though I got results, they were too obscure to be of any great value, and that science possessed no instrument that could deal successfully with quantity of radiant heat so minute.
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I have entered into these preliminary remarks as an explanation of the necessity of such an instrument as that which I have called the Bolometer (bolZ,metron), or Actinic Balance, to the cost of whose construction I have meant to devote the sum the Rumsford Committee did me the honor of proposing that the Academy appropriate. Impelled by the pressure of this actual necessity, I therefore tried to invent something more sensitive than the thermopile, which could be at the same time equally accurate, which should, I mean, be essentially a ‘‘meter’’ and not a mere indicator of the presence of a feeble radiation. This distinction is a radical one [6].’’ In the late 1950s, Scovil and his associates at Bell Labs were building the world’s lowest-noise microwave amplifiers, ruby travelling wave masers. These amplifiers were cooled to 4.2 K or less by liquid helium. They were used by Penzias and Wilson behind a 20-ft horn-reflector and the reference noise source was also cooled at 4.2 K in a separate cryostat. With this combination of instruments the spectrum of the cosmic microwave background, was discovered and measured at that time estimated to be a 3 K black body spectrum [7]. Since then, the study of the cosmic microwave background has been linked to low temperature detection. Infrared spectroscopy was a child of this evolution. Low, one of its pioneers was in 1969 reporting on the state of the art of germanium bolometers. At that time the operating temperature of the typical detector was 2 K, with an area of 1 1 mm2, a focal ratio of f/15 and range of sensitivity from 7 to 14 mm, a background power of Q=2 107 W with a thermal conductance G=10 6 W/K, and a noise equivalent power of 3 10 14 W/Hz1/2. Contrary to most of us in our proposals for new funding, Low was apparently not an optimist, in his conclusion asking himself: ‘‘The questions arise: ‘‘What of the future?’’, as detector sensitivity increases through future developments, can we expect an ever increasing observational sensitivity? It is clear that the answer is negative unless the background power can be reduced...’’
But Low also saw clearly the solution: ‘‘By refrigerating the entire telescope and placing it in space, it should be possible to extend the observational capability by several orders of magnitude [8].’’ That has been done.
6. The background of LTD zero: superheated superconducting grains Simultaneous with Low’s efforts in infrared detection, specialists in superconductivity and theoreticians of phase transitions were puzzled by an irritating issue: Why hysteretic behavior was not observed in type I superconductors in spite of their first order phase transition in a magnetic field? Of course, it was a minor issue, but the understanding of superconductivity has more than once been changed drastically by unexpected experimental facts. Carefully metallurgically prepared pure type I crystals, cylinders, and whiskers were tested in magnetic fields. If their transitions in a magnetic field were hysteretic, it was almost negligible. Supercooling was far more easily observed than superheating but, in every case, the width of the hysteretic cycle was far from the theoretical limit of metastability for superheated and supercooled states. The Orsay group of superconductivity had the idea to try the same experiment with superconducting microspheres. The idea of using mercury came almost immediately, but the very clever trick was to remember that a long time ago mercury salts were prescribed to cure syphilitic chancre. In fact, the ointment was a poison because it also contained metallic mercury, and had been finally discarded. Orsay at the time being still a rural little town, would it be possible that the local pharmacy still had the drug? Such was the case. A small nut of pomade filling the interior of a tiny cylindrical coil which was part of a resonant LC circuit was plunged into a liquid helium bath under reduced pressure. The long awaited result was there: superheated and supercooled states were immediatly observed as predicted by theory. A conversation between P.G. de Gennes and G.
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Charpak launched the idea of overcoming the metastability barrier by X-irradiation. The path for more mundane experiments was open. In 1975 at DESY, with a 6 GeV pure electron beam, a single channel transition radiation detector provided a direct proof of transition radiation theory thanks to the wide energy band response of the SSG detector. Real-time read-out of a single superheated grain transiting to the normal state was realized at the same time. More recently a 16 channel device was operated at 100 mK was operated at CERN [9]. For rare event experiments, one of the drawbacks of SSG detectors is the need of a quiet electromagnetic environment. Zero Gauss chambers are useless since a magnetic field is mandatory to get superheated states. This difficulty is now overcome at the Laboratoire Souterrain Bas Bruit de Rustrel-Pays d’Apt (50 km east of Avignon). In this low noise underground laboratory below 1500 mwe, in a volume of 1250 m3 without m-metal, the noise level above 10 Hz is better than 2 fT/Hz1/2, less than a hundred times the magnetic noise of your sleeping brain in its cooler phase! (for more details see Ref. [10]). In the early 1980s Raghavan proposed an experiment to detect solar neutrinos with a lowenergy threshold, 128 KeV. The target was indium and besides X’s and g’s the product was tin, both superconductors! Evidently, it had to be largescale experiment, 4 tons of indium being required for a rate of one event/day. Because of their massive nature and easy pixellization, SSG were an evident candidate. To check the interest of this idea, together with Fran@ois Vanucci, a highenergy physicist from Paris 7, we decided to organize an informal meeting at Groupe de Physique des Solides of University Paris-7 to see what could be the response of particle physicists to such an idea.
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little bit more than 20 scientists from a dozen of solid state groups and high-energy physics laboratories actually participated to the meeting. After an introduction to SSG, the state of the art for the read-out electronics was presented by A. Hrisoho (Orsay), and for transition radiation detection by D. Perret-Gallix (Annecy). The Josephson effects were discussed by C. Vanneste (Nice), non-equilibrium superconductivity by N. Perrin (Paris). F. Celani (Frascati) presented electronics read-out for tunnel junctions detectors to introduce indeed a round table about Josephson devices for SSG. The second day R.S. Raghavan (Bell Labs.) presented his indium solar neutrino capture proposal and Leo Stodolsky (Max Planck Munich) described the application of SSG as a neutral current detector for neutrino physics and astronomy. Of course it ended by a round table... after many informal discussions in the cafe! s surrounding Jussieu and lively meals taken at near-by restaurant of cuisine lyonnaise... ). The overall budget for all that was less than 1500 French francs (230 euros). One outcome of all this is still alive: LTD meetings.
Acknowledgements I thank N. Coron (Orsay), V.L. Ginzburg (Lebedev), T.A. Girard (Lisboa), Ch. Glasshauser (Rutgers & Livingston), the late N. Kurti (Oxford), J.M. Kantor (Math Paris 7), P. de Marcillac (Orsay), M. Ribeiro Gomes (Lisboa) and Jean Matricon (GPS-Paris 7) co-author of Cold Wars, A History of Superconductivity (Rutgers University Press, August 2003). They gave to me various helps, discussions, interviews and documentations. The mistakes, if any, are mine, of course.
References 7. LTD zero The small poster for the meeting (a single A4 sheet of paper) announced a ‘‘Workshop on Metastable Superconductors in Particle Physics’’ on 14–15 April 1983. At the opening of the workshop, 33 participants had registered and a
[1] F. Gatti, et al., Nature 397 (1999) 137. [2] E. Rutherford, F. Soddy, Philos. Mag. 4 (1902) 582. [3] Victor Ya. Frenkel Yakov Ilitch Frenkel, His Work, Life and Letters, Birkh.auser Verlag, Basel, 1996, p. 141. [4] Jean Matricon, Georges Waysand, La guerre du Froid, une histoire de la supraconductivit!e, e! ditions du Seuil, Paris, 1994, p. 147 (ISBN 2.02.021792.9 and also in the
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G. Waysand / Nuclear Instruments and Methods in Physics Research A 520 (2004) 4–10 Anglo-American updated version, Cold Wars, A History of Superconductivity, Rutgers University Press, 2003, p. 93). A. Goetz, Phys. Rev. 55 (1939) 1270. S.P. Langley, Proc. Natl. Acad. Arts Sci. 16 (1881) 342. A.A. Penzias, R.W. Wilson, Astrophys. J. 142 (1965) 419. F.J. Low, in: W.H. Hogan, T. S. Moss (Eds. ), Cryogenicsz and Infrared Detection, Proceedings of a Technical
Colloquim on Cryogenics and Infrared Detection Systems, April 17–18, 1969, Frankfurt-am-Main, West-Germany. Boston Technical Publishers Inc, Boston, 1969, p. 21. [9] L.C.L. Yuan, C.P. Chen, C.Y. Huang, S.C. Lee, G. Waysand, P. Perrier, D. Limagne, V. Jeudy, T. Girard, Nucl. Instr. and Meth. A 441 (2000) 479. [10] http://www.Isbb.univ-avignon.fr.