Polarization fraction ofP1line radiation in helium

A cascade-free determination of the polarization fraction of $2{}_{}{}^1{}_{}{}^{}P$ line radiation excited by electrons in the energy range from 30 to 500 eV has been made from electron-photon angular-correlation and differential-cross-section data. The present results are, in general, larger than previous results and are in good agreement with Glauber-approximation calculations. Evidence is also given to show that the polarization fraction of the $3{}_{}{}^1{}_{}{}^{}P$ state is larger than that of the $2{}_{}{}^1{}_{}{}^{}P$ state at 80 and 100 eV.