De stands for ‘equivalent dose’ and stems from the fact that the laboratory procedures utilize gamma sources, whereas the dose the sample has received in the past is the sum of multi-energetic alpha, beta, gamma, and cosmic rays (see below). Thus, the experimentally determined dose value is the gamma equivalent of the naturally received dose, which is frequently called ‘paleodose’, P. The SI unit for absorbed dose is Gray (Gy).
The measured ESR signal must have the following properties to provide reliable results:
• The signal intensity grows in proportion to the dose received.
• The signals have a stability, which is at least one order of magnitude higher than the age of the sample.
• The number of traps is constant or changes in a predictable manner, provided recrystallization, crystal growth, or phase transitions have not occurred.
• The signals should not show anomalous fading.
• The signal is not influenced by sample preparation (grinding, exposure to laboratory light, etc.).
For the measurement of the DE value, the sample is irradiated in the laboratory with increasing dose steps from a calibrated gamma source (these are, e. g., used in hospitals where they are used for cancer treatment or sterilization). The irradiation process generates more trapped electrons; consequently, the measured ESR signals increase. A dose response curve can be established by plotting the signal intensity against the applied dose (Figure 3). This data set allows extrapolation to zero ESR intensity and the DE value results from the intersection of the best fit of the data with the dose axis. The dose response curve of tooth enamel is not linear, but is most often described by a single saturating function.
World History
