Abundance of lithium, beryllium, boron, and other light nuclei in the primary cosmic radiation and the problem of cosmic-ray origin

Abstract

A combination of sensitive and insensitive photographic emulsions is used to improve the accuracy of measurement of the specific energy loss of relativistic nuclei. The method is applied to the determination of the charge spectrum of the primary cosmic radiation at geomagnetic latitude λ=30° and results in nearly complete resolution between neighboring elements up to Z∼14. It is shown that lithium, beryllium, and boron nuclei are almost or entirely absent in the primary cosmic ray beam. Since nuclear disintegrations of energetic heavy ions frequently lead to fragments of 3<∼Z<∼5 it is concluded that most heavy primary nuclei do not suffer nuclear collisions between the time of acceleration and arrival and that this time must be less than 10⁶/ρ years, where ρ is the density of atoms along the trajectory. This result seems to be in disagreement with several recent theories on the origin of cosmic rays and raises some general difficulties for theories assuming galactic origin.