Design of Permanent Magnets for Cloud‐Chamber Work

For the investigation of radiations of high energies, one can place a magnetic field between two cloud chambers. For a given flux of radiation to be observed, the air gap of the magnet in this arrangement can be made much smaller than when a cloud chamber is mounted between the pole pieces of a magnet. For small gap lengths, a permanent magnet is capable of producing a strong magnetic field. In order to assure most efficient distribution of the magnetic alloy used, model experiments were performed. A calculation shows that, if the variables are chosen appropriately, a single constant can be adjusted so that all the experimental results can be fitted to a universal function within a few percent. By means of a coordinate transformation of the universal function, one can predict field intensities or determine optimum constructions of a large variety of permanent magnets. Reasonable accuracy can be expected as long as the ratio of gap length to linear dimension of the pole faces is less than 1/4. The method has been applied to the construction of a large permanent magnet to be used for a study of the anomalous scattering of cosmic‐ray mesons.