Abundance of Lithium, Beryllium, and Boron in the Primary Cosmic Radiation

The flux of nuclei of charge greater than two of the primary cosmic radiation has been measured at 41° and 55° geomagnetic latitudes with photographic emulsions flown in "Sky Hook" balloons. The technique used at the lower latitude is similar in principle to that employed originally by Bradt and Peters, while that used at the higher latitude is the method of Dainton, Fowler, and Kent. The different experimental methods are discussed and the latter is found more satisfactory for the light-element problem. Primary flux values are reported for the medium nuclei ($6<~Z<~10$) and the heavy nuclei ($Z>\mathrm{}10\mathrm{}$) at the two latitudes. It is concluded that there exists a finite primary flux of the light nuclei ($3<~Z<~5$) and the most reliable value from these experiments of the ratio of the primary light-nuclei flux ${N_L}^0$ to the primary medium-nuclei flux ${N_M}^0$ at the top of the atmosphere is found to be 0.46±0.15.