Early in November, the first run was carried out at CERN's proton synchrotron on an experiment to determine the parity of the negative xi. This experiment relies on an important and interesting new piece of equipment, the polarized-proton target, brought into use through the fruitful collaboration of groups at Saclay (Centre d'Études Nucléaires) and CERN.

One of the fundamental properties of both atomic nuclei and sub-nuclear particles is their "spin", a quantum-mechanical concept best imagined as the amount of rotation (angular momentum) about an axis in the particle. Spin is related to "parity", another quantum-mechanical property that determines whether a particle is, or is not, indistinguishable from its mirror image, and measurements of both play an important role in high-energy physics research.

Such measurements involve the interaction between a beam of incoming particles and the nuclei (at low energy) or nucleons (at high energy) of a target. It is a fact of everyday experience that the direction taken by a ball after bouncing from a flat surface depends on the way the ball is spinning. Similarly, a non-spinning ball bounced off a revolving globe will have a preferred direction of flight, and repeated throws of an arbitrarily spinning ball will show a specific pattern according to the sense and speed of rotation of the globe. In most of the corresponding experiments with particles, although both the beam and target particles have a specific magnitude of spin, the direction is in both cases arbitrary and the resulting patterns are difficult to analyse. For this reason, attention has turned to the production of sources and targets of polarized particles in which an enhanced proportion of the particles not only have their spin axes parallel to a given direction but also spin in the same sense.

The new target uses the principle of "dynamic polarization", in which a paramagnetic crystal is cooled to below liquid-helium temperature in a strong magnetic field and subjected to radio-frequency radiation of a particular (very high) frequency. It consists of four main parts: the cryogenic apparatus for producing the low temperature; the magnet, which must provide an extremely uniform field; the microwave system, which polarizes the protons; and the high-frequency system, which measures the sign and amount of the polarization. Except for the magnet, which was designed and made at CERN, the target was developed at Saclay.

• Compiled from the article on pp168–172.