Thermoluminescence is used on sediment 'grains', which function as natural radiation dosimeters when buried with defects or impurities, to determine age. The valid range is 1,000 to 500,000 years and the technique is used extensively in archeology and earth sciences to date artifacts and rocks.
When exposed to radiation, quartz emits light proportional to the energy it absorbs. Replicating the very low dose of background radiation from natural sources present in quartz is a key precondition for precise and accurate dating results. Italian scientists have now developed a method to control the accuracy of the dose calibrations delivered to the samples during laboratory irradiation with heavy particles, replicating natural radiation exposure. Using oxygen and lithium ions from the Tandem accelerator at the National Institute of Nuclear Physics (INFN) in Florence, researchers found that their measurements were accurate to within 1%, despite large fluctuations in the irradiation beam.
In this study, the authors improve on previous calibration measurement techniques. To do so, they employ a pulsed ion beam that produces ion bunches, and rely on a system combining an aluminium foil and an electron detector, dubbed the MicroChannelPlate (MCP). When the ion bunches pass through the aluminium foil some electrons are emitted and detected by the MCP.
The MCP's energy resolution is not sufficient to count the number of ions constituting the bunch. However, Palla and colleagues have found they can perform the calibration by comparing the response of the MCP with that of a silicon detector, which offers extremely good energy resolution.
They show that it is possible to precisely evaluate the number of ions within each bunch crossing the foil and reaching the target to be irradiated.
Citation: L. Palla, C. Czelusniak, F. Taccetti, L. Carraresi, L. Castelli, M.E. Fedi, L. Giuntini, P. R. Maurenzig, L. Sottili, and N.Taccetti (2015), Accurate on line measurements of low fluences of charged particles, European Physical Journal Plus 130: 39, DOI 10.1140/epjp/i2015-15039-y
Accurate Thermoluminescence Dating - Calibration Down To The Last Ion
By News Staff | April 15th 2015 07:26 AM | Print | E-mail