In August 1955 the Bariloche Atomic Center (CAB) and Balseiro Institute (IB) was initiated as an Institution for Research and High Learning in Physics.

Whereas from the very start teaching activities were realized with top efficiency, implementation of efficient activities in research was only possible after a couple of years during which some tentative projects were undertaken, until, approximately in 1961, the different Divisions of Research in Physics started to crystallize themselves and continued to develop in a successful manner. Here we describe the initiation and early evolution of one of them:

THE ATOMIC COLLISION DIVISION

In 1960 the CAB-IB received as a visitor Professor Samuel King Allison, Director of the Enrico Fermi Institute of the University of Chicago, an investigator of the highest reputation in different fields of physics. At that time in the CAB a source of 14 MeV neutrons, produced by the reaction T(D,n)He, had been constructed. It consisted of an accelerator of about 100 kV, provided with an ion source delivering a deuterium beam of about 20 mA [1]. Furthermore the construction of a second accelerator, with an acceleration voltage of up to 300 kV, had been initiated, the destination of which was to facilitate also the use of the D(D,n)He-reaction. The initial purpose of the visit of Prof. Allison was to instruct us about the use of these machines for research in neutron physics.

As Allison was one of the first promoters of Research in Atomic Collisions, which then gave rise to the spectacular resurrection of Atomic Physics happening in those years, he also gave us a seminar about this topic, dealing in particular with collisions of capture an loss of electrons by atomic projectiles. When, after his exposition, I asked him if it would not be more advantageous if we dedicated ourselves to the study and investigation in atomic collisions, the answer was terminative, he said:

"You are damned right,- -
why don't you come to Chicago to introduce yourself in that field working in my laboratory at the Enrico Fermi Institute".

This visit,of a duration of about 1 1/2 years, which took place in 1961/62, lead to the performance and publication of an experimental study of the effective charge of a helium beam traversing a gaseous and solid cadmium target [2], for which a new method of fabricating thin metal foils was developed [3]. With the help of Prof. Allison, a grant of U$ 66.000,- was obtained from the US National Science Foundation, destined for the first installation of the Atomic Collisions Laboratory in Bariloche.

The collaboration with the Enrico Fermi Institute continued. Other members of the Bariloche group visited Chicago. Also a second visit of Prof. Allison to our laboratory took place, when in Bariloche the first experiments concerned with the measurent of charge equilibrium fractions of He-beams traversing different gaseous targets [4,5] were initiated.

It was very lamentable that, already in 1965, happened the sudden death of Prof. Allison, with whom we also were united by a beautiful relation of friendship. But our research in atomic collision physics had gained sufficient stability to progress, with the tradition of the laboratory at the Enrico Fermi Institute, which was dissolved. Our accelerator of 300 kV inherited the name "Kevatron" from that of Allison's laboratory, which he used to call "a big machine for a low voltage", a nickname also applicable to our modest home made accelerator, which up to the present has served to realize 75 research projects, published in international refereed journals and presented in international conferences. It is perhaps not useless to say, that this represents an example for the fact that the value of an activity in research should not be judged by its cost but by its scientific output.

In 1964 the construction of a smaller accelerator of up to 70 keV was undertaken, which received the name "Kevatrito". This machine, put into operation in 1966, also facilitated the realization of an ample spectrum of scientific production, the first of which dealt with the determination of cross sections of collisional charge exchange and the non existence of an isotope effect in charge changing collisions [6].

In 1968 a scientific contact with the J. J. Hopkins Laboratory of Pure and Applied Science, Gulf General Atomic in San Diego was established. There Victor Hugo Ponce, a distinguished graduate of the Balseiro Institute, had the opportunity to realize his doctoral thesis in a theoretical topic of atomic collisions [7]. His Director of thesis, Prof. J. C. Chen, used to comment that not even of a Chinese such an intense dedication to work could be expected. At his return Dr. Ponce was the initiator of research activities in atomic collision theory in Bariloche, most of them being closely connected with the topics being, or to be developed experimentally in the Laboratory.

In 1968 a project of measurements of stopping powers of atomic projectiles in solid targets was started. Measurements of the energy loss of hydrogen projectiles as a function of the atomic number of the target, resulted in one of the first doctoral thesis works, of A. Valenzuela [8], performed in the Division. Subsequently Dr. G. Lantschner, and Dr. J. C.Eckardt continued forming a stable group, dedicated to the study of stopping powers, which is active up to today. The fabrication of extremely thin metal foils [3,9] made possible experimental results that otherwise would not have been accessible.

In 1968 I was invited by the Ministry for Scientific Research of the Federal Republic of Germany, to visit different German Universities and Research Centers. This visit gave rise to joint research projects, in the field of Electron Emission Induced by Atomic Collisions, with the Group of Prof. K. O. Groeneveld at the Institute for Nuclear Physics of the University of Frankfurt/Main. This cooperation continued in a fruitful manner until the present.

Starting in 1970 more new activities were incorporated in the research program of the Atomic Collision Division, mainly as the result of the initiative of Dr. R. A. Baragiola. A new laboratory, occupied with the interaction of atomic and electronic projectiles with solid surfaces, was installed.

The purpose of the present exposition was to inform only about the initiation of research in atomic collisions in the CAB-IB, until a branching off into the different groups and laboratories happened, which today continue in full activity in this beautiful field of science.

References

1. Design and performance of a hot cathode magnetically collimated arc discharge ion source
   M. Abele and W. Meckbach
   Review of Scientific Instruments 30, 335 (1959).
2. Ratio of the effective charge of He beams traversing gaseous and metallic cadmiun
   W. Meckbach and S. K. Allison
   Physical Review 132, 290 (1963).
3. Preparation of unbacked cadmiun foils of approximately 50 ug/cm²
   W. Meckbach
   Review of Scientific Instruments 34, 188 (1963).
4. Charge equilibrium of helium ions in helium gas from 60 to 840 keV
   W. Meckbach and I. Nemirovsky
   Physical Review 153, 13 (1967).
5. Charge equilibrium of a helium beam in hydrogen, nitrogen, neon and argon from 50 to 850 keV
   P. J. Torres, W. Meckbach and A. Valenzuela
   Physical Review 183, 216 (1969).
6. Search for a possible isotope effect in charge changing collisions involving hydrogen and deuterium
   E. R. Salvatelli, G. Lantschner and W. Meckbach
   Journal of Physics B 2, 772 (1969).
7. Teoría de colisiones atómicas a bajas energías para el sistema protón - átomo de hidrógeno
   V. H. Ponce
8. Stopping power of some pure metals for 25-250 keV hydrogen ions
   A. Valenzuela, W. Meckbach, A. J. Kestelman and J. C. Eckardt
   Physical Review B 6, 95 (1972).
9. Preparation of extremely thin self supporting metal foils
   A. Valenzuela and J. C. Eckardt
   Review of Scientific Instruments 42, 127 (1971).