This resemblance is used in chemical and biological research, in a technique called carbon labeling: carbon-14 atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions involving carbon atoms from any given organic compound.
These are relatively low energies; the maximum distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue.
Although one can simply measure older samples for longer times, there are practical limits to the minimum sample activity that can be measured.
At the present time, for a 1 milligram sample of graphite, this limiting age is about ten half-lives, or 60,000 years, if set only by the sample size.
It should be noted that a BP notation is also used in other dating techniques but is defined differently, as in the case of thermoluminescence dating wherein BP is defined as AD 1980.Organic materials, which require the most processing, are limited to younger ages by their corresponding process blank.Due to counting and measurement errors for the blanks and samples, statistical errors are higher for very old samples.Results of carbon-14 dating are reported in radiocarbon years, and calibration is needed to convert radiocarbon years into calendar years.Uncalibrated radiocarbon measurements are usually reported in years BP where 0 (zero) BP is defined as AD 1950.