A few months after celebrating his 90th birthday, Willibald Jentschke passed away on 11 March 2002. With him we lost a charming person who has left remarkable footprints in European and international science. Without him, DESY in Hamburg would not exist and as director-general of CERN he guided the laboratory through difficult waters.

I consider it a privilege to have been asked to remember him at this sad occasion since I owe him much gratitude. When, during my early career, I wanted to change from nuclear to particle physics he arranged for me a one-year stay at Cornell University with Robert R Wilson. Destiny decreed that later I followed him in various functions - as director of DESY, as director-general of CERN and others.

First scientific successes (Vienna 1935-1946)

Willibald Jentschke (known as Willi by his friends) was born in Vienna on 6 December 1911. He studied at the University of his hometown where he received a PhD in 1935 and, working in the II. Physikalische Institute, he became docent in 1942. He published several papers with his teacher Georg Stetter on alpha radioactivity and on a precise determination of the neutron mass using the photoeffect on heavy water.

In 1939, Jentschke got into the epicentre of the discovery of nuclear fission whose story is largely known. But let me report a less well known detail, which illustrates the importance of Jentschke's work. In my story a man called Paul Rosbaud played an essential role. He was scientific adviser to Springer Verlag and quite influential. Indeed, Otto Hahn and Rosbaud had conspired to save Lise Meitner from arrest by the Gestapo. In the autumn of 1938, Otto Hahn and Fritz Strassmann discovered barium nuclei after the bombardment of uranium by neutrons. On the night of 22 December 1938 Hahn phoned Rosbaud with the news that he had just finished writing a paper describing the experiments that they had performed. That evening Rosbaud arranged for one of the articles in the Naturwissenschaften, which had already been typeset for the next issue, to be pulled out in order to make room for the Hahn and Strassmann paper. Rosbaud probably had, earlier than any scientist, imagined the destructive potential of uranium fission and wanted to alert the world community of physicists as soon as possible.

How does Jentschke come in? At the moment when fission was discovered, Britain's Secret Intelligence Service was not the least bit interested in such esoteric subjects as atomic energy, in spite of the imminent war. But a number of British scientists were, among them John Cockcroft who had built the first atom-smashing machine with Ernest Walton in 1931. Consequently, Cockcroft had a proprietary interest in the new work on smashing the heaviest element known - uranium. He obtained from Lise Meitner a detailed account of her interpretation, but Cockcroft wanted to know more, especially about what was happening experimentally in Germany. A few months before the war, Rosbaud was a willing courier.

Cockcroft and Rosbaud met for lunch on 10 March 1939. Rosbaud's summary of the experimental results on nuclear fission in Germany (including annexed Austria) impressed Cockcroft, particularly Rosbaud's accounts of the experiments of Willibald Jentschke and Friedrich Prankl. Jentschke's experiments were not only among the first to corroborate the results of Hahn and Strassmann but they were beginning to demonstrate how the energy of nuclear fission might be harnessed by investigating details that were published in several papers during 1939. In an interview which Jentschke gave in 1997, he was asked what his most important work had been and his answer was "the detection of uranium fragments after the irradiation of uranium by neutrons".

During the war Jentschke continued to work at the University of Vienna with Georg Stetter, Josef Schintlmeister and Friedrich Prankl. Using a Cockcroft-Walton accelerator with an energy of 1 MeV they produced neutrons, determined the cross-sections for neutron resonance absorption and continued their investigations of nuclear fission.

The American years (1946-1956)

Like many other German and Austrian scientists, Willi Jentschke went to the USA in 1946, landing at the University of Illinois at Urbana where eventually he climbed the academic ladder by becoming consecutively research assistant, associate professor and full professor. His activities at Urbana fall into four groups.

He performed considerable work on the response of scintillation counters, both on sodium iodide and anthracene crystals. Secondly, he returned to nuclear physics using a low-energy cyclotron to investigate nuclear reactions, mainly few-nucleon reactions. In 1951 he was appointed director of the cyclotron laboratory and the cyclotron was transformed under his guidance into a strong focusing "spiral ridge" variable-energy accelerator. Thirdly, with his friend Hans Frauenfelder, he measured angular correlations of gamma rays to determine magnetic and electric moments of excited nuclear states. Quite important also were the results he obtained with D R Maxson and J S Allen in 1955 on electron-neutrino angular correlation in the beta decay of neon-19, which helped to clarify the V-A nature of the weak interaction.

Jentschke's ten years in the US can certainly be considered as a most fruitful scientific period, earning him a reputation as an excellent physicist worldwide.

The founding of DESY

It was not a big surprise that in 1956 Jentschke was offered the vacant chair of physics at the University of Hamburg. At the Physikalische Staatsinstitut, as it was called, nuclear research had started thanks to the efforts of Rudolf Fleischmann, Hugo Neuert and Erich Bagge, but the activities were restricted because of the meagre financial situation and until 1955 nuclear research was forbidden in Germany by the Allied authorities. On one hand Jentschke considered it a challenge to change this situation, but on the other he was really not very keen to leave Urbana. Therefore he made somewhat unusual financial requests during the negotiations at Hamburg, which he continuously increased every time they were granted. In the end, he asked for DM 7.5 million - an incredibly large sum in those days - for the construction of a proton synchrotron with an energy of 2 GeV. To Jentschke's surprise Hamburg approved this request and hence, as he himself said later, he was trapped and had no choice but to accept. His Austrian charm was certainly not a negligible factor during these negotiations and one of the senators of Hamburg said to Jentschke: "Your dialect alone is worth DM 2 million."

This success triggered intensive discussions among German physicists, including Gentner, Paul, Schmelzer, Walcher and Brix, and the question was raised as to whether this money should not be used for a larger national facility. This was the beginning of DESY with an electron synchrotron of 7.5 GeV, which was complementary to the facilities at CERN. In the end it cost about DM 100 million, mainly financed by the Federal Government - a good bargain for Hamburg.

The synchrotron, similar to the one at Cambridge in the US, was built in a record time thanks to the help of American colleagues, in particular Stanley Livingston, who had become a friend of Willi Jentschke. DESY's first steps were also strongly influenced by several German physicists who had spent some time in the US and who Jentschke had brought back with him. These included Erich Lohrmann, Peter Stähelin and Martin Teucher - who also played an important role in the realization of BEBC, the big bubble chamber at CERN.

A first beam in DESY was obtained in 1964 after two years of construction. When necessary, Jentschke could be very courageous. During a ceremony celebrating the start up of DESY attended by ministers, senators and other VIPs, a FAX several metres long was handed to Jentschke in which the Federal Audit Office complained that many rules and regulations had been disregarded in establishing DESY. Jentschke remained cool and employing his charm was able to straighten out the problems. Thanks to Jentschke, DESY became one of the most vigorously exploited electron accelerators in Europe, used by scientists from all over the world.

However, Jentschke did not spend much time basking in this success, he was thinking about the future. Soon discussions started about the next step and two alternatives were considered: a larger electron synchrotron or an electron-positron storage ring. With today's knowledge the decision in favour of a storage ring seems obvious. However, in 1966/7 quarks were still considered as figments of mathematical imagination, and just to test QED and study the hadron form factors in the time-like region did not look like a challenging programme for the future. The choice of energy was another difficult problem. Indeed, most of the criticism came from the theorists. They had good arguments that an energy above 2 GeV would be unjustified. The reasons were that the quantum-mechanical point cross-section drops with the square of the energy and all form factors also fall with energy. With the luminosities expected, the number of events would be so small that no relevant results would be obtained.

How could Jentschke decide? Of course, there was the official channel of the Scientific Council and the scientists of DESY could also express their opinion. Jentschke also consulted the international community of high-energy physics, in particular Pief Panofsky at SLAC. In the end, however, opinions were balanced between the two options. At that moment Jentschke took the decision to go for a storage ring, a decision that later turned out to be crucial for the future development of DESY.

Planning started in 1968 and the DORIS storage ring was approved in 1970. Fortunately Jentschke did not listen to the theorists but insisted that the energy should be as high as 3 GeV and he even made sure that the magnetic rings would go to 5 GeV. This decision seemed minor at the time but had very beneficial consequences. Experiments at DORIS started in November 1974. The same month marked the November revolution in particle physics with the discovery of the J/Ψ particle. Hence DORIS was just in time to make important contributions to the rich exploration of the world of the charm quark. DORIS missed the discovery of the upsilon particle found at Fermilab. But thanks to the far-sighted earlier decision of Jentschke, the ring was pushed to 5 GeV and immediately demonstrated that this resonance really consisted of two well separated states. This opened the way to a decade of a most successful programme of b-quark physics, carried out above all by the ARGUS collaboration.

Willi Jentschke, however, did not stay to see the completion of DORIS and the beautiful physics results. Instead, he moved to CERN.

Director-general of CERN

As successor to Bernard Gregory, Jentschke was appointed director-general of CERN for the period of 1971-75 in somewhat strange circumstances. CERN's Council had decided to split CERN into two laboratories, CERN I (Meyrin) with Jentschke as its director-general and CERN II (Prévessin) under John Adams. Having two director-generals in adjacent laboratories was an unusual situation. The reason was that John Adams had been appointed as director-general for the construction of the Super Proton Synchrotron before its site had been decided and when in the end CERN was chosen, his appointment could not be reversed. Jentschke and Adams handled the delicate situation very well and Jentschke's charm helped without doubt to overcome any differences.

One of the reasons for the success of CERN is the fact that the transitions from one director-general to the next are achieved in a smooth overlap, so that each can build on the achievements of his predecessors and also lay the ground for his successors. Thus during Jentschke's mandate the Intersecting Storage Rings (ISR), which had been started under Viki Weisskopf, were inaugurated in October 1971 and became a fertile and unique research instrument. Before becoming director-general, Jentschke had served from 1969 to 1970 as chairman of the ISR Experiments Committee where he played a key role in the selection of the first experiments.

Among the most important results obtained with the ISR was the rising total cross-section for proton-proton collisions; the diffraction measurements showing that the proton was apparently increasing in size when observed at higher energies; and above all the unexpected production of pions and kaons with high transverse momenta providing a first indication of the existence of quarks inside the proton. On the other hand, at that time the importance of detectors covering the full solid angle around the interaction point was not yet appreciated, so the ISR missed the discovery of the J/Ψ particle, leading to some criticism of Jentschke.

The other physics highlight during Jentschke's mandate was the discovery of the neutral currents of the weak interaction in 1973 by the Gargamelle heavy-liquid bubble chamber. This was the first great discovery at CERN and was worthy of the Nobel Prize. Jack Steinberger once said: "In order to get this prize you must have done something, but you must also live long enough." Unfortunately André Lagarrigue, leader of the Gargamelle collaboration, did not fulfil the second criterion.

The publication of the Gargamelle results had an epilogue that required Jentschke's intervention. CERN had to stand its ground against a group at Fermilab with their conflicting, and ironically named, "alternating currents". It was typical for Jentschke that he went to the Gargamelle group, discussed with the people who had done the work, formed his own opinion and defended the results as correct.

Although the total CERN budget reached its all-time peak during this extremely fertile period for CERN, mainly due to additional funds for the SPS, the first signs of financial limitations imposed by the member states appeared on the horizon indicating the end of the laboratory's honeymoon period. Jentschke, responsible for Lab. I, had to cope with a more or less constant budget - a new situation at CERN. Nevertheless, he managed to sustain an excellent programme and good relations with the member states.

In his final report to CERN Council at the end of 1975, Jentschke said: "I also believe that we must follow the lesson from CERN's success and base our future plans on international collaboration, certainly within Europe or, perhaps, if conditions eventually permit, within a wider framework." Fortunately this advice was followed by all his successors and is one of the main reasons for CERN's prominence today. Indeed, throughout his whole career Jentschke had always been an advocate of international collaboration. Although DESY had been founded as a national laboratory, Jentschke made sure that it was open to scientists from the whole world right from the beginning. At CERN he intensified collaboration with the US and he put the still-young co-operation with the Soviet Union on firmer ground. A radio-frequency particle beam separator and a fast ejection scheme that had been built by CERN were delivered and inaugurated at the Institute of High-Energy Physics at Protvino on 2 June 1972 in his presence, and several extensions of the agreement between CERN and the Soviet Union were signed. He also established contacts with China when he visited with a delegation in 1975. Over the years a strong Chinese participation in the CERN programme resulted from these first contacts, above all in the LEP experiments.

The CERN I and CERN II laboratories were unified formally on 1 January 1976 when Jentschke left, but they continued to exist covertly under two director-generals (John Adams and Leon van Hove) until the end of 1980 when I was appointed as sole director-general, and thus the real grand-unification was established for the construction of LEP.

After CERN

After his return to Hamburg in 1976, Jentschke went back to physics. Taking a sabbatical year he went to SLAC and joined an experiment investigating the deep inelastic scattering of polarized electrons from deuterium. This experiment became one of the cornerstones of the Standard Model and established the most accurate value of the Weinberg mixing angle for some time. Jentschke was an essential member of the collaboration since he was the only one who could read the classical publications in the German journals of the 19th century, for example on the Pockel cells that were essential for producing a circularly polarized laser beam.

After his sabbatical year he returned to Hamburg, participating in the life of DESY by giving advice whenever required and enjoyed scientific successes or special events such as anniversaries and birthdays.

The person

We all remember Willibald Jentschke as a warm-hearted person, full of charm and a fatherly personality open to problems of all kinds concerning his collaborators. He never behaved as a big boss but had a special way of involving collaborators in discussions in order to guide them in the proper direction by asking pointed questions. He walked at all hours of day and night through the experimental halls, control rooms or the canteen always looking for opportunities to talk to people. He particularly cared about young scientists and their many worries.

His deep engagement for human problems and sufferings became perhaps most obvious when two theorists had an accident in the mountains in January 1973 and disappeared. Although very busy with CERN affairs, Jentschke immediately left for the French Alps and surveyed for several days at the location of the search operations carried out by professionals and other CERN staff. Unfortunately neither theorist survived.

Those who knew Willi Jentschke only superficially might have got the impression that he had a rather soft character yielding easily to pressure. This gave rise to the humorous saying, accepted by him with a laugh, "Willy the driver and Willy the driven", which referred to the driver Willy Aigner. However, knowing Jentschke closely it was obvious that underneath that kid glove there was, if necessary, an iron fist. He was able to take difficult far-reaching decisions with great determination and he could display a tenacious attitude in negotiations.

We physicists are lucky because for most of us our profession is also our hobby. This was certainly true for Jentschke. But he loved his family and was always available when his children needed him.

Suffering for many years from an illness that severely restricted his mobility, he nevertheless followed developments at DESY and CERN for as long as possible. He attended the "old boys" meetings of the SPC and he enjoyed the colloquium that CERN organized at the occasion of his 80th birthday. His 90th birthday last December was celebrated at DESY, still in his presence. A few months later he passed away.

Jentschke received a number of distinctions, for example the Österreichische Ehrenzeichen für Wissenschaft und Kunst in 1983 and in 1996 the John Tate Award of the American Institute of Physics, which is awarded only every few years to foreign nationals "for distinguished service to the profession of physics". But he always was and remained a modest person. Indeed he did not like so much celebrations in his honour and he was always a little embarrassed at such occasions. However, I believe that if he can look down today on our assembly from a white cloud up there he would enjoy it.

Herwig Schopper, CERN.