Description
Authors (affiliation): 1. M. Hult (EC-JRC), 2. J. Qiao (DTU, Denmark), 3. Ransby (AWI, Germany), 4. Lindahl (Sweden), 5. Lutter (DTU, Denmark), 6. Marissens (EC-JRC), 7. Stroh (EC-JRC)
The study of natural archives like tree rings, ice cores and corals is a field that increases in importance. It can teach us a lot about the Earth's history like past changes in climate. Improved low-level radioactivity measurement techniques can be used for measuring radionuclides in natural archives that were not accessible for study before.
For underground gamma-ray spectrometry, a critical aspect is the optimisation of the sample geometry and the selection of detector. Today, the detector manufacturers have a wide range of HPGe-detectors to choose from and selecting the best detector for a given sample/radionuclide combination is not straightforward, especially when coincidence summing is involved. In this paper, the focus is on describing metrological tools for measuring gamma-ray emitting radionuclides in natural archives. A few specific cases will be presented in detail: tropical corals, cold water corals, and Greenland ice cores.
The coral samples were meticulously prepared to enable study of individual years. The tropical corals weighed 7-10 g and were measured in a well detector and on a BEGe-detector. The cold water coral samples weighed 0.4-2.2 g and were measured in a SAGe-well detector. The objective of the gamma-ray spectrometry was to detect 210Pb and 226Ra to perform nuclear dating. This will support subsequent destructive measurements performed using radiochemical methods to measure anthropogenic radionuclides including plutonium, uranium and iodine. The cold water corals provide information of deeper ocean processes and unlike tropical corals, also from temperate to high latitude regions.
The Greenland ice core samples were collected from the vicinity of the Camp Century where a PM-2A nuclear reactor once was in operation. The ice core was cut in 1 cm thick slabs. Each melted ice sample weighed about 300 g. The objective was to detect 137Cs which will help to define a depth–scale in years.
