Determination of the ion yield and the electron lifetime in TMS by a pulse method

A long term stability of the signal was realized: the decreasing in the pulse height was less than 10% over one year. The peak position of the pulse height spectra due to 976 keV electrons is plotted versus electric field in fig.1, after charge calibration. Gf´(E), the ion yield measured by this method, can be related with the free ion yield, Gf(E), by equation where F(E, π) is the reduction due to positive ion effect and to electron attachment to electronegative impurities and π is the electron lifetime. F(E, π) was calculated under three assumptions: (1) the spatial distribution of the ion pairs produced by a 976 keV conversion electron can be approximated to a linear track uniformly ionized and with a length equal to the extrapolated range of that electron; (2) the peak of the pulse height distribution can be identified with the pulse height corresponding to a conversion electron emitted at the mean value of the emission angle; (3) the effective electron lifetime π is constant within the electric field range used. With these assumptions and taking the pulse shape in the presence of impurities according to ref.[4], F(E, π) comes out to be equation where R is the extrapolated range of a 976 keV electron in TMS, π is the electron lifetime, T is the maximum electron drift time ( T=x/(μE) where E is the electric field and μ is the electron mobility ) and x is the distance between the electrodes in the chamber. The free ion yield is predict by Onsager´s theory [5].