Specific Excitation of N2 (C3πu) and Specific Ionization by 4.3-MeV α Particles

Abstract

In this paper, specific excitation, dN* / dx (the number of excited molecules per millimeter) is compared with specific ionization, dN + /dx (the number of ions created per millimeter) along the track of 4.3-MeV α particles in nitrogen at atmospheric pressure. The knowledge of the ratio of the collisional to the radiative rate constants allows one to calculate the specific excitation from measurements of specific luminescence. In this way, the specific excitation and specific ionization at atmospheric pressure have been calculated from measurements of specific luminescence and ionization at eight pressures ranging from 23–253 torr. It is assumed that the comparison along the entire track concerns ionization and excitation leading to the state C 3πu. The excitation is found to be nearly proportional to the ionization along most of the α track. Beyond the average range of the α particles, however, excitation seems to become much more likely than ionization. This could be simply the result of a higher efficiency for excitation, compared with ionization, when the secondary electrons are formed with lower velocities. In addition, it may partly result from the appearance of another type of excitation of N2 ( C3πu), namely excitation by He+ ions.