Radioactive Fossils!

Last week one of our engineers took a trip down to Moab, Utah which is about a 4 hour drive south from our facility. For those of you who have never visited southern Utah, Moab is a world-famous mountain biking destination. It’s also known for dinosaur bones – the bright red sandstone in the area has produced some amazing ancient remains. While checking out one of the shops in town, our engineer noticed that the MiniRad-D (a portable radiation detector) he brought with him alarmed when he passed a row of fossils. I was surprised to find that this isn’t an anomaly: fossils often have radiation levels much higher than the environment around them. Robert Bekker, a world famous paleontologist, referred to this phenomenon when he said "you wouldn't want to leave some bone fragments in your pocket all day long."

An enthusiast checks the radiation levels of a dinosaur bone near Denver (source).

So why are fossils so ‘hot’? The reasons for this are not completely known, but one possible reason is that naturally-occurring radiation tends to concentrate in the living tissue of plants and animals. This is especially true with ocean-dwelling creatures such as shellfish and snails. Particles containing  isotopes such as U-238 and Th-232 and other isotopes often coalesce on the seafloor where the living organisms are exposed to them. Over long periods of time, the collected isotopes decay into other radioactive isotopes, making even small concentrations stand out. Also, In a process known as permineralization, living materials are replaced at times by deposits of denser materials with greater concentrations of radioactive isotopes.

These concentrations are usually fairly low, however, and it’s easy to see why people miss them. There’s often no visual difference between a rock containing a fossil and other ancient rocks. And because Geiger counters respond slowly to radiation, they would be ineffective at finding radiation at such low levels unless the operator knows what they are looking for. Scintillation detectors like the Cesium Iodide crystal used in the MiniRad-D will have a much better chance of finding these materials because they react quickly to radiation and can be up to 100 times more sensitive to radiation.

Also found in southern Utah, this rock contains measurable levels of Th-232.

Has anyone else had luck finding fossils or bones with a radiation detector? All this talk has made me want to get out into the late-spring sunshine and go searching. Who knows how many hot dino bones are still down there?  

D-tect Systems is supplier of advanced radiation and chemical detection equipment sold around the world. www.dtectsystems.com.