Primary alpha particles in the cosmic radiation near the geomagnetic equator

Abstract

An apparatus consisting of a G-M counter coincidence train in which is interposed a high-pressure ionization chamber has been utilized to obtain measurements of the flux of primary helium nuclei during a series of balloon-flights in India.The instrument records relativistic particles characterized by a specific ionization at least as great as that of an alpha particle. The experiments were conducted at Aligarh, Uttar Pradesh (geomagnetic latitude 18° N) and Bangalore, Mysore (geomagnetic latitude 3° N). At each station, the intensity N( I > 3.2 I min) of particles producing ionization chamber pulses exceeding the bias setting corresponding to 3.2 I min plotted on a logarithmic scale as a function of atmospheric depth, follows a straight line. The intensity N total was also measured by removing the criterion I > 3.2 I min. Taking into account local nuclear interactions initiated by protons, knockon electrons accompanying protons, and slow protons (albedo) which actuate the apparatus, the alpha-particle flux is determined from the extrapolated values of N total and N( I > 3.2 I min) at the “top of the atmosphere.” The results are: 49 ± 13 particles m −2 sec -1 sterad-1 at λ = 3° N, and 81 ± 22 particles M −2 sect sterad-1 at λ = 18° N. The qualitative effect of the presumably small systematic uncertainties is generally in the direction of making these values low. Both protons and helium nuclei can be represented by an integral energy distribution of the form: N(> E) = k(1 + E) −1.2, where E is kinetic energy per nucleon; k = 4000 and 1.5 < E < 15 Bev for protons; k = 450 and 0.3 < E < 7 Bev per nucleon for alpha particles. The composition of the primary cosmic radiation is not drastically different at λ = 3° and λ = 18°, although the total intensity is anomalously high at the latter station.