Detail of one type of sample-counting tube for carbon-14 work. Carbon-14 in benzene gas molecules is placed in the central cell and mixed with a fluid that scintillates, or emits light flashes, when exposed to radiation. Photomultiplier tubes convert the flashes to electric signals.
The radiocarbon-bearing gas is pumped into the sample counter through the filling tube, and all the counts resulting from its disintegrations are recorded electronically. The age of the sample is calculated from the [NET COUNTING RATE] (the sample counting rate minus the background); the lower the counting rate the higher the age. The upper limit of the age that can be measured is determined by the [STATISTICAL ERROR] (that is, by the measure of the instrument accuracy) in the net count. In very old samples this error may be great enough so that the calculated age of the sample may have little or no meaning.
Carbon-14 Results
OBJECTS DATED BY RADIOCARBON
Hair of an Egyptian woman. 5020 ± 290 years old.
Linen wrapping from the Dead Sea Scroll containing the Book of Isaiah. 1917 ± 200 years old.
Peruvian rope. 2632 ± 200 years old.