Radioactive dating mass spectrometer
The standard gas may be measured before and after the sample or after a series of sample measurements.While continuous-flow IRMS instruments can achieve higher sample throughput and are more convenient to use than dual inlet instruments, the yielded data is of approximately 10-fold lower precision.The disadvantages of this method stem from the maximum temperature achieved in thermal ionization.The hot filament reaches a temperature of less than 2500 degrees Celsius, leading to the inability to create atomic ions of species with a high ionization potential, such as Osmium (Os), and Tungsten (Hf-W).These methods include rubidium–strontium dating, uranium–lead dating, lead–lead dating and samarium–neodymium dating.When these isotope ratios are measured by TIMS, mass-dependent fractionation occurs as species are emitted by the hot filament.Beams with lighter ions bend at a smaller radius than beams with heavier ions.The current of each ion beam is then measured using a 'Faraday cup' or multiplier detector.
In continuous flow IRMS, sample preparation occurs immediately before introduction to the IRMS, and the purified gas produced from the sample is measured just once.
Many radiogenic isotope measurements are made by ionization of a solid source, whereas stable isotope measurements of light elements (e.g.
H, C, O) are usually made in an instrument with a gas source.
This field is of interest because the differences in mass between different isotopes leads to isotope fractionation, causing measurable effects on the isotopic composition of samples, characteristic of their biological or physical history.
As a specific example, the hydrogen isotope deuterium (heavy hydrogen) is almost double the mass of the common hydrogen isotope.