Polarization of K-shell x-ray transitions of Ti19+ and Ti20+ excited by anelectron beam

The x-ray spectrum of heliumlike Ti20+ excited by a monoenergetic electron beam was measured at an energy just above the electron-impact excitation th reshold (4800 eV) with a. pair of polarization-sensitive spectrometers. Val ues for the linear polarization were inferred for the 1s2p P-1(1)--> 1s(2 1 )S(0) resonance line, the 1s2p P-3(1) --> 1s(2) S-1(0) intercombination lin e, the 1s2p P-3(2) --> 1s(2) S-1(0) magnetic quadrupole line, and the ls2s S-3(1) --> 1s(2) S-1(0) forbidden line, as well as for the ls2s2p P-2(3/2)- -> 1s(2)2s S-2(1/2) resonance line in Ti19+ Relativistic distorted-wave cal culations of the magnetic sublevel-specific electron-impact excitation cros s sections are presented for comparison. Combined with earlier measurements of iron, the results confirm the predicted Z dependence of the polarizatio n. [S1050-2947(99)07611-8].