All the levels are excited at a precise position (& time) when the ions of a fast monoenergetic beam pass through a thin foil.

By recording the decay of a line intensity after the foil it is possible to extract the lifetime of the upper level of the line.

The cascading effect (repopulation of the upper level during the decay - green dots) make the measurement more difficult!


Typical CCD spectrum

Decay curve in Xe (measured with a CCD-UV detector - work in progress):