Zircon has been widely used as a geochronometer with the U—Pb decay system but rarely with the Th—Pb system. As a one-dimensional system, a series of consistent Th—Pb ages can be used to date a geological event. In contrast, a wide variation in Th—Pb ages could result from Pb loss or multiple growth events, making it difficult to link to specific geological events. The results demonstrated that these seven U—Pb zircon standards have similar absolute concentrations of common lead.
Accelerator Mass Spectrometry (AMS) Dating
What is AMS? (Accelerator Mass Spectrometry)
Mass spectrometry MS is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum , a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures. A mass spectrum is a plot of the ion signal as a function of the mass-to-charge ratio.
A TIMS is an instrument that measures isotopic ratios that are used in geochemistry, geochronology, and cosmochemistry. A TIMS is a magnetic sector mass spectrometer that is capable of making very precise measurements of isotope ratios of elements that can be ionized thermally, usually by passing a current through a thin metal ribbon or ribbons under vacuum. The ions created on the ribbon s are accelerated across an electrical potential gradient up to 10 KV and focused into a beam via a series of slits and electrostatically charged plates. This ion beam then passes through a magnetic field and the original ion beam is dispersed into separate beams on the basis of their mass to charge ratio. These mass-resolved beams are then directed into collectors where the ion beam is converted into voltage.
When interpreting fragmentation patterns, you may find it helpful to know that, as you might expect, the weakest carbon-carbon bonds are the ones most likely to break. You might wish to refer to the table of bond dissociation energies when attempting problems involving the interpretation of mass spectra. This page looks at how fragmentation patterns are formed when organic molecules are fed into a mass spectrometer, and how you can get information from the mass spectrum. When the vaporized organic sample passes into the ionization chamber of a mass spectrometer, it is bombarded by a stream of electrons. These electrons have a high enough energy to knock an electron off an organic molecule to form a positive ion.