Prior to the final depositional episode it is necessary that any previously acquired TL is removed by exposure to sunlight.After burial the TL begins to build up again at a rate dependent upon the radiation flux delivered by long-lived isotopes of uranium, thorium and potassium.
In the absence of a field gamma spectrometer this is extremely important as the presence of rock or any other dissimilar material within this distance may have an effect upon the radiation dose received by the sample.
This effect cannot be determined in the laboratory from the sample submitted.
Both specimens are carefully sieved to separate the 90-125 micrometre grain size fraction, chemically cleansed in dilute HCl,etched in 40% w/w HF and finally subjected to heavy liquid separation.
The sample so prepared consists of better than 99% pure quartz grains.
The exposed material at either end of the tube is used in the determination of the annual radiation dose and the internal unexposed portion for the palaeodose determination.
The sample collected should be taken from the centre of a homogenous sphere of 30cm radius.In the case of an older sample this correction may only represent a small proportion of the total age.The radiation dose received annually by the sample is measured by means of calibrated thick source alpha counting which determines the specific activity of the uranium and thorium decay chains assuming that secular equilibrium exists.If a field gamma spectrometer is available measurements should be made in the field by placing the gamma probe into the hole from which the sample has been removed.This correction will subsequently be applied to the laboratory measured radiation dose value.TL Age = Palaeodose (P) _____________ (ARD) TL samples may be collected in open ended or opaque PVC tubes approximately 12cm in length and 6cm in diameter.