Gamma spectroscopy


 Professor Rainer Grün

Dating studies on palaoeanthropological sites is usually carried out on material associated with the human remains, such as the sediment, charcoal or other fauna rather than the human specimen itself. The reason lies in the fact that most dating techniques are destructive and because the hominid remains are too rare to be sacrificed for dating. This indirect dating approach is in many cases not satisfactory, because:

  • the human remains are often buried into the sediments and the association with other materials is uncertain (e.g. Skhul, Qafzeh, etc.);
  • faunal remains or minerals from the sediment are re-worked from older deposits.
  • the hominid specimen was discovered at a time when no careful excavations were carried out and it is impossible to correlate the specimen with other datable material (which applies to nearly 90% of all palaeoanthropological specimens).

Until recently, hominid fossils could only be dated by radiocarbon. This method reaches back to about 40,000 years. As a consequence, all the older fossils could not be analysed and many important questions in our understanding of human evolution could not be addressed. Large bone samples can be measured in our non-destructive gamma ray facility.

Although gamma spectrometry is the least efficient method for measuring isotopes of the U-decay chains, it is completely non-destructive. Furthermore, all isotopes of the U-238 and U-235 decay chains are measured at the same time, so that Th/U - Pa/U open system modelling can be carried out (see Simpson & Grün 1988).

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