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USGS CMG InfoBank: Mass Spectrometer

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Comment: 23:19 - 24:58 (01:39)
Source: Annenberg/CPB Resources - Earth Revealed - 10. Geologic Time
Keywords: "Jason Saleeby", "mass spectrometer", isotope, element, "absolute age dating"

Our transcription: The mass spectrometer accelerates the ions or charged atoms of an element, so that they form a beam which is then spread out into a succession of points, a mass spectrum.
From the position and intensity of the points, the mass and relative abundance of individual isotopes can be determined.
Once the element that we're going to measure is loaded in the mass spectrometer it's ionized at a temperature of between a 1,000 and 2,000 degrees centigrade depending on what element it is.
The ions are then accelerated by a 8,000 to 10,000 volt drop down the tube which is a high vacuum tube.
And as they're being accelerated, they're focused into a very fine beam.
Once they enter the tube as a fine beam, they move through a magnetic field.
The magnetic field puts a drag on the ion beam, which causes the heavy isotopes to bend along the outer part of the tube and the lighter ones into the inner part of the tube.
By the time the beam comes out of the magnetic part of the tube, it's broken into its various isotopes.
And at the far end of the tube we count the ions of each isotope, which ultimately gives us our isotopic ratio.

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