Decay and Capture of Slow Mesons in Dielectrics

Abstract

Conversi, Pancini and Piccioni¹, and others², observed decay electrons from positive mesons coming to rest in solids of either light or heavy elements. For negative mesons, however, decay electrons were found in light elements only ; for heavy elements it is generally assumed that negative mesons are captured by atomic nuclei before they can decay. The absence of capture of positive mesons can be understood as being due to the influence of Coulomb repulsion³ ; its absence for negative mesons in light nuclei has led Fermi, Teller and Weisskopf⁴ to the conclusion that the interaction between nuclei and mesons is much weaker than was assumed hitherto. These authors show that it takes less than 10^-12 sec. for a meson to reach an energy of about 1,000 eV., where its velocity is about equal to that of electrons in outer orbits, that is, 10⁸ cm./sec. They then consider that the meson quickly loses its remaining energy, reaching the K-orbit of an atomic nucleus in about 10^-12 sec. It should then be captured by the nucleus in about 10^-18 sec. if current ideas of interaction between mesons and nuclei are correct. In doing so they have, however, considerably overestimated the energy transfer from slow mesons to electrons⁵. In the present communication reasons are given for believing that in dielectrics the time required by a meson to reach a K-orbit is longer than estimated by Fermi et al., but that it would be very difficult to decide from theoretical considerations whether this time may be of the same order as the decay time ( 2 10⁶ sec.).