Atomic Excitation and Ionization by Neutrons

ABSTRACT Atomic excitation and ionization processes by neutron impact have been studied for K‐shell electrons in the sudden approximation. The electron transition is considered to be induced by the recoil of the target nucleus during neutron‐atom collisions. The matrix elements for excitation and ionization due to the nuclear recoil effect are calculated using nonrelativistic hydrogenic wave functions. The general expression of matrix elements for K‐shell electron excitation is obtained analytically in terms of Gauss‐type hypergeometric functions. On the other hand, the matrix element for ionization is given with simple analytical functions. The K‐shell excitation and ionization probabilities are expressed in the universal form as a function of the reduced recoil momentum transfer. The validity of the dipole approximation for the ionization process is discussed. Rough estimations of K‐shell excitation and ionization cross sections by neutrons are made.