Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.

In contrast, methane made from petroleum products had no measurable radioactivity.

The collagen fraction usually yields more reliable dates than the apatite fraction (see Dates on bones).

In addition to various pre-treatments, the sample must be burned and converted to a form suitable for the counter.

The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere.

The sample is converted to graphite and mounted in an ion source from which it is sputtered and accelerated through a magnetic field.AMS technology has allowed us to date very small samples (such as seeds) that were previously undatable.Since there are practical limits to the age range of the method, most samples must be younger than 50,000 years and older than 100 years.Any organic material that is available in sufficient quantity can be prepared for radiocarbon dating.Modern AMS (accelerator mass spectroscopy) methods require tiny amounts, about 50 mg.Libby calculated the half-life of c14 as 5568 ± 30 years.This means that half of the c14 has decayed by the time an organism has been dead for 5568 years, and half of the remainder has decayed by 11,136 years after death, etc.