On the Mechanism of Production of the Neutron Component of the Cosmic Radiation

Experiments have been performed on the neutron component of the cosmic radiation, with a system of B${\mathrm{F}}_{3}$ proportional counters embedded in paraffin, capable of recording neutrons in the energy range between \ensuremath{\sim}2 and \ensuremath{\sim}15 Mev. The neutron rate recorded with such a detector is due to both neutrons locally produced inside the detector and neutrons produced outside the detector, i.e., in the surroundings and in the atmosphere.The local neutron production is due to a radiation which in the great majority does not consist either of photons or $\ensuremath{\mu}$-mesons.The intensity of such a radiation increases with altitude with a mean free path in air of 120-130 g/${\mathrm{cm}}^{2}$, which is confirmed by the fact that it shows a barometric coefficient \ensuremath{\cong} -11 percent per cm Hg. At mountain elevation (4000 m) the intensity of this radiation is close to that of the total ionizing cosmic radiation. This suggests that it consists principally of fast neutrons.The locally produced neutrons are mostly produced in multiples, with multipliticy depending upon the material. In lead the average multiplicity observed was close to 8, in carbon smaller than 2.The rates of neutron production in different materials are satisfactorily described by a cross section proportional to the ⅔ power of the mass number of the material.The results indicate that the main source of all the neutrons present in the cosmic radiation are "stars," though high energy processes like penetrating and extensive showers do contribute to neutron production.