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We demonstrate that the angular distribution of electrons knocked out from anatom by a fast charge particle is determined not only by dipole but also byquadrupole transitions, the contribution of which can be considerably enhancedas compared to the case of photoionization. To obtain these matrix elements onehas to study the angular distribution of electrons emitted by the atom in itscollision with a fast charged particle. The distribution has to be measuredrelative to the momentum q transferred from the projectile to the target atom.The situation is similar, but not identical to the photoionization studies,where the matrix elements of continuous spectrum atomic quadrupole transitionscan be determined by measuring the so-called non-dipole angular anisotropyparameters of photoelectrons. However, they are strongly suppressed as comparedto the dipole matrix elements by small ratio of atomic size to the photonwavelength. This suppression is controlled in fast electron-atom collisions,where it can be much less than in photoionization since the respective virtualphoton wavelength can be much smaller than in photoionization. We present notonly general formulas, but also concrete results of calculations for noble gasatoms He, Ar and Xe. We have investigated their outer and subvalent subshells,as well as strongly collectivized 4d10 subshell in Xe. It appeared that evenfor the case of very small transferred momentum q, i.e. in the so-calledoptical limit the deviation from photoionization case is prominent.

Non-dipole effects in angular distributions of secondary electrons in fast particle-atom scattering