Radiative lifetimes Hanle effect

From the measured halfwidth AB /2 the product gjTeff of Lande factor g/ of the excited level 2) times its effective lifetime teff can be derived. For atomic states the Lande factor gj is generally known, and the measured value of A i/2 determines the lifetime teff. Measurements of teff (p) as a function of pressure in the sample cell then yield by extrapolation p 0 the radiative lifetime (Sect. 6.3). The Hanle effect therefore offers, like other Doppler-free techniques, an alternative method for the measurement of atomic lifetimes from the width AB /2 of the signal [832]. 

We have shown in previous chapters that the -values of spectral lines are important fundamental data which must be known before detailed calculations of the behaviour of gas discharges, plasmas, or stellar atmospheres can be undertaken. Since it is difficult, in many cases, to make theoretical calculations of f-values to an accuracy of better than 20 per cent, experimental measurements of these quantities are essential. A considerable number of different techniques have been developed for this purpose, many of them involving the determination of radiative lifetimes. In this chapter we discuss two such techniques, namely the beam-foil and the delayed-coincidence methods. In Chapter 8 we shall discuss the determination of the f-values of resonance lines by studies of the profiles of spectral lines and in Chapters 15 and 16 the use of the Hanle effect and optical double resonance methods. 

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