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Calculate the mean lifetime of excited atoms if it is known that the intensity of the spectral line appering due to transition to the ground state diminishes by a factor eta=25 over a distance l=2.5mm along the stream of atoms whose velocity is v=600m//s. |
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Answer» Solution :Let `T=` mean life time of the EXCITED atoms. Then the number of exicted atoms will DECREASE with time as `E^(-t//T)`. In time `t` the atom travels a distance `vt` so `t=(l)/(v)`. Thus the number of excited atoms a in a beam that has travesed a distance `l` has decreased by `e^(-l//vT)` The INTENSITY of the line is proportional to the number of excited atoms in the beam. Thus `e^(-l//vtau)=(1)/(eta) or TAU=(l)/(V i n eta)=1.29xx10^(-16)` second. |
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