1. The First Fifty Years
Daniele Bergesio, TERA Foundation
It was snowing heavily when, at the beginning of 1960, I passed through the CERN entrance gate, which was then always open and practically unattended, for the first time. The road which ran from Geneva to the village of Meyrin, where the research centre is located was then quite narrow with little traffic. The laboratories and offices, constructed in the architectural style of the day, were neat, with aromas of wood and coffee.
Today the same road is often congested with traffic, despite being much wider and definitely improved by tramways going to the city, while on the main part of the site large and small buildings are crowded together in a disorderly way. When I arrive by car at the labs and offices used by the TERA Foundation - which was created twenty years ago to promote research into tumour therapy by means of hadron irradiation I recognise them one by one like old friends, arranged along a network of streets whose names are distributed somewhat haphazardly.
The CERN roads are in fact named after great physicists of the past and to wander along them is to be reminded of the history of physics, jumping from one century to another, from a great discovery to an invention which changed our history.
Our story starts at the CERN main building , designed originally by the architects Peter and Rudolf Steiger, which hosts the main auditorium, post office, bank, main restaurant, newsagent, and travel agency. Leaving the restaurant behind us from which on clear days you can glimpse views of Mont Blanc we descend along Route Marie Curie, running along the site boundary. Route Rntgen opens on the right, close to one of the secondary entrances to CERN, where the fence ends the world of particle physics and long rows of vines extend.
A Mysterious Radiation
The physics we will talk about came into being on the evening of Friday 9 November 1895, when Mrs Rntgen found the dinner getting cold because her husband had not come up from his laboratory, located on the lower floor of the house put at his disposal by the University of Wrzburg. That day Wilhelm Rntgen had actually observed a phenomenon missed by his many colleagues, who had for years used similar, but less performing, instruments; electrons, accelerated by a potential difference of some ten thousand volts, produced a new, very penetrating radiation when they struck the base of a glass tube and the positive electrode.
The new invisible radiations so mysterious that the discoverer named them X-rays were electrically neutral, hence very different from a bunch of electrons (which is negatively charged, because every electron carries an elementary negative electric charge).
The X-ray particles, as were later shown, are in fact packets of electromagnetic energy similar to the photons which make up every beam of light. But a Rntgen photon carries a thousand times more energy than a photon of visible light and is therefore much more penetrating when it encounters matter. Mrs Rntgen could verify this when she saw the bones of her own left hand, with the ring she wore on her finger, on a photographic plate recently developed by her husband, which is shown in Fig..
Fig. 1.1
( a ) Apparatus used to make the first radiograph in history, on 22 December 1895 (Science Photo Library). ( b ) The flux of X rays was very small and the exposures were lengthy: Mrs Rntgen had to keep her hand immobile for 15 min (Courtesy Archive Deutsches Roentgen-Museum, Remscheid)
Rntgens Accelerator and Its Effects
Wilhelm Conrad Rntgen, born in Holland in 1845, was tall, reserved and quite shy, but with a lively character (Fig. ); he and his wife were bound by a great affection, strengthened by a shared passion for sailing and the mountains. As a scientist, he preferred to work alone, constructing his instruments on his own, so that he had no real need of an assistant, and he continued in that way at the University of Wrzburg, after he was appointed director of the new institute of physics at the age of 43.
On the 8 November 1895, Rntgen began a series of experiments in which a beam of electrons, accelerated by a potential difference of around 20,000 V in a glass tube evacuated of air, struck the base of the container, covered externally by black cardboard. This was therefore an electrostatic accelerator , in which charged particles are accelerated by a constant electric field produced between two electrodes. Under the action of this potential the electrons acquired a very high energy for that time: 20,000 eV.
In the darkness, Rntgen noticed by chance a glimmer originating from a bench a metre away, where a fluorescent sheet had been placed; on the sheet a weak luminescence appeared each time the electrons were accelerated.
Having made several trials, after a few minutes Rntgen concluded that a previously unknown radiation was being emitted from the point at which the electrons struck the glass. In the paper On a new kind of rays, submitted on December 28 to the Proceedings of the Wrzburg Physical-Medical Society , Rntgen described his many experiments with the following words:
The tube is surrounded by a fairly close-fitting shield of black paper; it is then possible to see, in a completely darkened room, that paper covered on one side with barium platinocyanide light up with brilliant fluorescence when brought into the neighbourhood of the tube. The fluorescence is still visible at two metres distance. It is seen, therefore, that some agent is capable of penetrating a black cardboard which is quite opaque to ultra-violet light, sunlight, or arc-light. It is readily shown that all bodies possess this same transparency, but in varying degrees.
For example the fluorescent screen will light up when placed behind a book of a thousand pages. Similarly the fluorescence shows behind two packs of cards. Thick blocks of wood are still transparent. A piece of sheet aluminium, 15 mm thick, still allowed the X-rays (as I will call the rays, for the sake of brevity) to pass, but greatly reduced the fluorescence. If the hand be held before the fluorescent screen, the shadow shows the bones darkly, with only faint outlines of the surrounding tissues. Lead 1.5 mm thick is practically opaque. The salts of the metal, either solid or in solution, behave generally as the metals themselves. The preceding experiments lead to the conclusion that the density of the bodies is the property whose variation mainly affects their permeability. (Rntgen )
Fig. 1.2
Wilhelm Conrad Rntgen (18451923) (Courtesy Archive Deutsches Roentgen-Museum, Remscheid)
The speed with which Rntgen reached these conclusions was a consequence of his skill as an experimenter and the amount of time he devoted, over a few days, to the most varied experiments; so dedicated was he that he moved his bed to the laboratory. Referring to the first time he had observed the unexpected glimmer in the darkness, a journalist enquired: And what did you think? . Rntgen replied: I didnt think, I investigated (Dam ).
