英语论文网

results from three parameters: the strength of the radioactivity (dose rate), the number of traps (sensitivity), and the duration of radiation exposure (age) (Bahn 2008: 158-159; Greene 2002:173; Rink 1998).

The third radiocarbon revolution, 1980 to Present

Thermoluminescence and Infrared/Optical Stimulated Luminescence:

Optical dating was discovered by David Huntley and his associates in 1984, whilst at the Physics Department at Simon Fraser University, British Columbia, Canada. Thermoluminescence and Infrared/Optical Stimulated Luminescence dating can now be applied with a high degree of accuracy to sediments ranging from 100 BP to about 350,000 BP however, ages as young as 7 BP and as old as 800,000 BP have been reported (Aitken, 1998: 6-36).

Thermoluminescence and Infrared/Optical Stimulated Luminescence are the three common methods for dating soil sediments and heated objects such as pottery, and for environmental dosimetry. Sediments and some archaeological artefacts contain poly minerals composed of crystal structure, when these minerals extracted from a buried material are subjected to ionizing radiation, (alpha, beta, gamma), from radio nuclei (i.e. Uranium, Thorium, Potassium) in the surrounding soil, this natural irradiation causes ionization of valance electrons and creates electron/hole pairs. Then these free electrons and holes are trapped at pre-existing lattice defects, within the crystal structure of the mineral (Bahn 2008: 154-158; Greene 2002:171-173; Aitken, 1998: 6-36).

When this crystal is subsequently excited by heating or by exposure to light electrons, (infrared for feldspar or silt, blue or green for quartz), the are released from the traps and recombine with the holes. The recombination energy is emitted as thermoluminescence and infrared stimulated/optical luminescence respectively. The absorbed dose by the buried material is proportional to luminescence quantity that is proportional to trapped charge concentration; this can be related to the time in which the crystal is subjected to ionizing radiation and called equivalent dose (ED), dose rate (DR) is the dose that sample received per unit time (a or ka) (Bahn 2008: 154-158; Greene 2002:171-173; Aitken, 1998: 6-36).

This dose rate is calculated from measurements of the radioactive elements (Potassium, Uranium, Thorium) within the material and its surroundings, and from the radiation dose rate from cosmic rays. The age of the material can be calculated by the equivalent dose (ED) divided by the annual dose rate (DR) (Bahn 2008: 154-158; Greene 2002:171-173; Aitken, 1998: 6-36).

In Conclusion:

“What Have Been the Most Important Advances in Scientific Dating Since the 1950s?” There have been significant changes to scientific dating since BP 1950, which have introduced a wide variety of natural, electro-magnetic, chemical, and radio-metric dating methodologies to today's archaeologists. This has increased the archaeologist’s ability to date objects that are just a few hundred years old, to objects that are millions of years old.

However, having said this one would like to put forward an observation, that during his research it was mentioned on numerous occasions within (credible literature), that the varieties of dating methods used by archaeologists to determine dates all have one thing in common