Doppler broadening
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Transcript of Doppler broadening
Doppler Broadening
M.Zeeshan Khalid
09050610-039
Introduction
• It is the broadening of the spectral line due to Doppler
Effect of the random thermal motion of the molecules.
• Lack of sharpness in the spectrum line causes the
broadening and is related to the distribution of velocities
of the atoms or molecules.
• Causes red shifted and blue shifted wavelengths
• Emitting atoms are in motion with a range of speeds Δν along the line of sight to the observer then Doppler Broadening is given as
• For a gas of atoms of mass m at a temperature T, the velocity dispersion is given by
where k is the Boltzmann constant (1.38 × 10−23 J K−1)
Thermal Doppler broadening
• Atoms and molecules move in a haphazard direction with average velocity is given as (1/2mv2 )= 3/2kT
• The spreading of the spectral line due to the temperature of the emitting medium is called as thermal Doppler broadening.
• Spreading of the spectral line depends on the frequency, mass of the emitting particles and the temperature.
Doppler broadening on nuclear reactors
• The Doppler effect arises when the temperature of the fuel changes.
• When the uranium is heated, its nuclei move more rapidly in random directions, and therefore generate a wider range of relative neutron speeds.
• Pebble bed nuclear reactors
Doppler Broadening Applications and other causes
• Thermal Doppler broadening
• Causes of velocity distribution
Turbulent motion Accretion disc
• Stark broadening