The energy loss of penetrating cosmic-ray particles in copper

Absorption measurements for cosmic-ray particles by the cloud chamber method have been made in heavy metals by Anderson and Neddermeyer (1936), Crussard and Leprince Ringuet (1937), Blackett and Wilson (1937) and by Neddermeyer and Anderson (1937). Anderson and Neddermeyer have confined their attention to particles of low energy and give (1937) reasons for supposing that particles of differing absorption properties exist in this region (E < 4 × 108 e-volts). This result is only partially confirmed by more recent work (Blackett 1938) which shows that forE < 2 × 108 e-volts the mean energy loss of all particles and the distribution of losses among the particles are in accord with the predicted behaviour of electrons, and that there is no appreciable number of particles at this energy with non-electronic absorption properties. It is only for energies above 2 × 108 e-volts that two different kinds of particle are found. In this region the very few absorbable particles are probably normal electrons, while the penetrating particles differ in some way from normal electrons but apparently become indistinguishable from them when the energy falls below about 2 × 108 e-volts. Measurements of the absorption of the particles in the region where penetrating particles predominate have been made by Blackett and Wilson over an extended range, while Crussard and Leprince Ringuet have measured the energy loss of particles of a mean energy about 8 × 108 e-volts and report a mean loss which is in accord with the measurements of Blackett and Wilson. Upon the nature of these penetrating particles there is not at present complete agreement. It is now generally believed that the particles are more massive than electrons and that they radiate according to the classical (Bethe-Heitler) formula appropriate to their mass.