(image: ISOLDE experimental hall. The magnet of the ISOTOPE separator, the collection chamber and the control desk were placed in the same area as most of the experiments.)

The underground hall for ISOLDE is ready in 1967 and the first proton beam bombards the target on October 16. The first experiments are successful and prove that the online technique meets the expectations of the experimentalists. During the next year, a number of experiments produce short-lived isotopes of a several elements. The first paper is published early in 1969 and presents results for short-lived isotopes of the noble gases Ar, Kr, Xe and Rn and several other elements like Ag, Cd, I, Pt, Au, Hg, Po and Fr.

(image: excavation work for ISOLDE underground hall in 1966)

On 8 May 1966, the CERN Synchrocyclotron begins a long shutdown until mid-July. During this time major modifications are carried out as part of a programme to improve the capacity of the machine and its associated facilities. One of the main items of work during the shutdown is the construction of a new tunnel for an external proton beam line to the new underground hall for the ISOLDE experiments. This tunnel is constructed underground to keep external radiation levels down and the existing proton room is kept for experiments that use beams of lower intensity.

On 10 April 1963, a number of European nuclear physicists meet at CERN to discuss the isotope separator project. A first outline is presented in an internal nuclear physics division report.

A Working Party is set up and a series of meetings are held from May to September. In a memorandum dated 26 October 1964 the chairman of the Nuclear Structure Committee Torleif Ericson recommends the on-line isotope separator project to CERN and on 9 November the Working Party submit a formal proposal.

On 17 December 1964 the Director-General gives formal permission to the groups behind the proposal to carry out the experiment.

(image: The isotope separator in 1960)

Plans for an isotope separator are published in the proceedings of the International Symposium held in Vienna, May 1960. This isotope separator is built by CERN's Nuclear Chemistry Group (NCG) and used to measure the production rate of radionuclides produced in different targets irradiated with 600 MeV protons from a CERN Synchrocyclotron (SC) beam. Researchers observe high production rates showing that the SC would be the ideal machine for setting up a dedicated experiment for on-line production of rare isotopes. 

First experiment at the ISOLDE Proton-Synchrotron Booster.

The first experiment was carried out on June 26, where the beta-proton decay of the neon isotope with mass number 17 was studied. This experiment was relevant for the understanding of nuclear halo structure, first proposed at ISOLDE.

Danish physicists Otto Kofoed-Hansen and Karl-Ove Nielsen, working at the Institute for Theoretical Physics at the University of Copenhagen, are first to demonstrate how to produce radioisotopes with an on-line technique. In a paper entitled Short-lived Krypton isotopes and their daughter substances Kofoed-Hansen and Nielsen demonstrate the feasibility of on-line production of short-lived radioactive isotopes.

They used fast neutrons, produced in the Copenhagen cyclotron in an internal Be target, to bombard a uranium oxide target. The produced fission products arre swept directly into the ion source of an isotope separator. This direct coupling of the accelerator, target and separator gives access to isotopes with shorter half-lives than any earlier indirect production method.