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The use of Mössbauer spectroscopy in chemistry


The Doppler effect in Mössbauer spectroscopy
Norman Greenwood Scientist
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You know that if you hear an ambulance siren pass you on the road. Bzzzz as it goes past. Or a train whistle, when it’s blowing. That is the Doppler effect, because when a sound emitter, in this case, is moving towards you, the sound waves are compressed, so that the pitch of the tone rises. When it’s disappearing away from you, it is attenuated, and the note drops in tone.

The gamma ray is also electromagnetic radiation, like light, but of a very much shorter wavelength, very much more energetic, in fact. And so you can get devices which move backwards and forwards with particular wave shapes, and they will be a Doppler velocity which gives more and less energy, just around the absorption energy. So one gets a curve, or perhaps I’ll start this way… there is the baseline, comes down like that.

And magically, that works… well, Mössbauer found it first in iridium. It turns out that iron is by far the easiest, the 57 isotope of iron is the pre-eminent Mössbauer absorber, and that’s of course the one that we started on as well, when I’d heard about this.

Norman Greenwood (1925-2012) was born in Australia and graduated from Melbourne University before going to Cambridge. His wide-ranging research in inorganic and structural chemistry made major advances in the chemistry of boron hydrides and other main-group element compounds. He also pioneered the application of Mössbauer spectroscopy to problems in chemistry. He was a prolific writer and inspirational lecturer on chemical and educational themes, and held numerous visiting professorships throughout the world.

Listeners: Brian Johnson

Professor Brian FG Johnson FRS, FRSE, FRS Chem, FAcad Eu, FAS. Professor of Inorganic Chemistry University of Edinburgh 1991-1995, Professor of Inorganic Chemistry University of Cambridge 1995-2005, Master Fitzwilliam College Cambridge 1999-2005. Research interests include studies of transition metal carbonyls, organometallic chemistry, nano- particles and homogeneous catalysis. Professor Johnson is the author of over 1000 research articles and papers.

Tags: Mössbauer spectroscopy, Rudolf Mössbauer

Duration: 1 minute, 27 seconds

Date story recorded: May 2011

Date story went live: 25 November 2011