Highly ionizing cosmic rays at mountain altitude

Large arrays of CR-39 plastic track detectors are being used at various depths in the atmosphere to study energetic, highly ionizing particles. The first measurements are made of the energy spectra of He and Li nuclei at mountain altitude (603 g/sq cm) and the first observations of relativistic heavy nuclei (Z/beta greater than or equal to 12; Z ranging from 8 to 14) at subsonic aircraft altitude (186 g/sq cm). A 95 percent CL upper limit of 0.4/sq m-yr was determined for the flux at 603 g/sq cm of particles with Z/beta greater than or equal to 30 and of monopoles with velocity as low as 0.01 c.