If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusionsetting the isotopic "clock" to zero. However, many objects were found in caves, frozen in iceor in other areas whose ages were not known; in these cases, it was clear that a method for dating the actual object was necessary. The uranium content of the material can then be calculated from the number of tracks and the neutron flux. Planetary Sciencespage Any 14 C signal from the machine background blank is likely to be caused either by beams of ions that have not followed the expected path inside the detector, or by carbon hydrides such as 12 CH 2 or 13 CH. Wilson; R. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization.
The carbon isotope would vanish from Earth's atmosphere in less than a million years were it not for the constant influx of cosmic rays interacting with atmospheric nitrogen.
Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. Carbon has a relatively short half-life of 5, years, meaning that the fraction of carbon in a sample is halved over the course of 5, years due to radioactive decay to nitrogen The fission tracks produced by this process are recorded in the plastic film. This means that after 5, years, only half of the initial 14 C will remain; a quarter will remain after 11, years; an eighth after 17, years; and so on.