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.
Most samples require chemical pre-treatment to ensure their purity or to recover particular components of the material.
The objective of pre-treatment is to ensure that the carbon being analyzed is native to the sample submitted for dating.
The sample must be destroyed in order to measure its c14 content.
The first measurements of radiocarbon were made in screen-walled Geiger counters with the sample prepared for measurement in a solid form.
The diminishing levels via decay means that the effective limit for using c14 to estimate time is about 50,000 years. Subsequent work has shown that the half-life of radiocarbon is actually 5730 ± 40 years, a difference of 3% compared to the Libby half-life.