It is always advisable to contact the laboratory before collecting samples to discuss environmental complications and the probability for successful dating. Any such treatment can reduce the luminescence signal and produce too young ages. Airport and postal inspection X-rays are usually not of significant dosage, but avoid them if possible. Do not perform any unnecessary treatment of the samples. Supply a list of treatments that have been applied.
Contaminants can affect both the luminescence signal and the radioactive assay.
Washing with distilled water is okay. At least 100 g of sediment representing that in which the sample was buried, or on which it was resting in the case of surface items, should be supplied in a plastic bag. Care should be taken to avoid any sorting as different size fractions will typically differ in composition as well. Exposure of the soil to sunlight, ultraviolet, x-rays, etc., does not matter. The sediment should come from within 30 cm of the sample but will be representative of the full environment of the sample only to the extend the latter is homogeneous.