Researcher Mayank Jain from DTU Nutech at a TL/OSL reader. Photo: MIkal Schlosser.

The apparatus geologists love

Geology Climate change
DTU Nutech has for more than three decades developed, designed and sold an apparatus, which is especially popular among geologists worldwide for the dating of sediments.. The 400th such unit was shipped just before Christmas last year.

DTU Nutech has for more than three decades developed, designed and sold an apparatus, which is especially popular among geologists worldwide for the dating of sediments.

DTU Risø Campus is home to an authentic export success known only to a few people. Since 1982, engineers and researchers from DTU Nutech have developed and produced the so-called TL/OSL readers.

TL stands for ‘Thermoluminescence’, while OSL is the short form for ‘Optically Stimulated Luminescence’, and these are methods that can be used, for example, to reveal when a grain of sand last saw the daylight. This is information that geologists and archaeologists all over the world use in their work to investigate issues such as landscape evolution, climate change, and human evolution.

Foto: Mikal Schlosser
Research Technician Per Günther Sørensen is part of the 10-strong team at DTU Nutech, which develops, assembles, tests, and sells the readers used by researchers for their measurements. Photo: Mikal Schlosser. 

At the end of 2015, DTU Nutech shipped its 400th TL/OSL reader from Risø. The department sells around 20 units annually, and the advanced piece of equipment has currently made its way into more than 40 laboratories around the globe. The reason why the units are made at Risø is that the equipment involves the use of radioactive sources (alpha and beta sources).

DTU Nutech maintains close ties with international researchers who visit the centre to carry out research or to receive instruction in using the TL/OSL reader. DTU’s research into—and development of—the reader is also making a significant mark on the world of research. At the most recent international conference on research into luminescence dating, 90 per cent of the presentations were based on equipment or methods developed by the University.

The first TL/OSL reader was made in 1982, and today, the production, development and sale of the unit provides work for around 10 employees at DTU.

Explore the apparatus here

Foto: Mikal Schlosser Photo: Mikal Schlosser

1. Merry-go-round

The materials that are to be examined are placed in a ‘sample wheel’ which rotates around inside the TL/OSL reader. Here, the samples are exposed to a cycle of operations: heating, lighting, and exposure to beta particles. In a standard dating of a mineral, the wheel carrying the materials runs through approximately 12 such cycles. Each sample wheel has room for 48 samples, and each sample can consist of a single or up to several thousand grains of sand.  

2. Detection- and stimulation head

Light sources used for optical stimulation of the samples are usually blue, green, and infrared LEDs or lasers. The luminescence—that is the light, which grains of sand emit after having been (optically) stimulated—is so weak that a number of filters are required to measure it accurately it. It is critical to filter away the stimulation light from the detection, as it is about 1018 times stronger than the actual luminescence.

3. PM tube or EMCCD camera

The released luminescence is measured by either a so-called PM tube (Photomultiplier tube) or an EMCCD camera (Electron Multiplying Charge Coupled Device). In 2014, DTU Nutech was the first to deliver a fully functional camera to the TL/OSL reader.

4. Radioactive source

Irradiation of the samples is a precondition for being able to date them. Based on the luminescence (i.e. the light the material emits during stimulation) signal intensity, researchers obtain a precise age determination of the samples. The source is typically a beta source (strontium), but it is also possible to install other sources in the TL/OSL reader, for example, an X-ray source or an alfa source.