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.

My Trip to Japan

While in Japan, I was paired with a group that was sent to check on the structural integrity of several church buildings in several cities. My role was to show them how to use the equipment and gauge the levels of radiation at each site. To check on these levels I went armed with two different radiation detectors: the MiniRad-D (a small, pager-sized detector) and the Rad-ID (a portable radiation identifier).

In my visits to cities from Tokyo to Iwaki I checked radiation levels and talked with the local church officials about what those levels meant. Radiation levels in downtown Tokyo were near natural background levels but the closer I got to Fukushima, the higher the radiation levels rose. The cities I visited showed readings of anywhere from 0.35 µSv/hr to 2 µSv/hr above background radiation, which are elevated levels, but definitely not dangerous. Using the Rad-ID, I found out that most of the radiation came from the radioactive isotopes Co-60, I-131, I-132, and Cs-137, which are commonly given off in nuclear processes.


An interesting observation that I made was that storm drains in the areas I visited showed higher levels of radiation than the surrounding areas. I surmised that rainfall had carried down and collected some of the radioactive dust in the air and deposited the contamination as it flowed down these drains.


Although the Japanese have shown amazing resilience and are working as hard as they can to solve these enormous problems, there is still much uncertainty about health risks and what the future will bring. We’ll be back soon to check on the radiation levels again. If you’d like to brush up on your radiation basics, you can check out this sheet we’ve complied. It has basic conversions, safety levels, and doses to put radiation exposure in perspective. An interesting chart on radiation dose rates can be found here.

Radiation Detector Overview

“The only thing constant in life is change.” -  François de la Rochefoucauld

Although they report on thousands of different stories each day, the covers of newspapers in recent weeks have all carried a similar theme – instability.  On-going political changes in many parts of the world, as well as the rapid power transfers and challenges in the Egypt, Yemen, Libya, and many bordering countries have made it clear that political unrest is on the rise.  Recent upheavals have also made it clear that finding security in an increasingly unstable world is a difficult task. 

Adding to political turmoil, terrorist organizations have become increasingly aggressive in both their tactics and technology.   The release of diplomatic cables lays bare new plans by terrorist organizations, such as the Taliban, to construct ‘dirty bombs’ – weapons designed to spread radioactive material over large areas.  We here at D-tect Systems focus on this increasingly relevant area of that security effort: radiation detection. 

With dozens of detector types utilized of literally thousands of radiation detection products, matching the right technology to a threat is a daunting task.  To make this search a little easier, we’ve compiled a general overview of some of the main radiation detectors currently in use.

Geiger-Mueller Tubes, with low sensitivity and a wide range, are the most commonly used detectors on the market.  Available in sizes from ring-worn dosimeters to giant cargo scanners, Geiger-Mueller detectors can pick up certain types of alpha, beta, and gamma radiation.  The downside to these kind of detectors is that they are much less sensitive to radiation than other detector types and cannot differentiate between radiation types.  They are also too slow to detect moving radiation, but are cheap and durable.

Sodium Iodide (NaI(Tl)) and Cesium Iodide (CsI(Tl)) are among the most common gamma radiation detectors.  These two types of materials are commonly referred to as inorganic scintillators because of their composition and method for detecting radiation.  Unlike Geiger-Mueller Tubes, they are fast, sensitive, and can measure the actual energy of gamma rays.  D-tect Systems’ MiniRad-D and MiniRad-V devices uses CsI(Tl) detectors equipped with photo-multiplier tubes that allow the operator to detect radiation from tens of meters away.  

CsI(Tl) detectors, like those used in the MiniRad-D, can detect gamma radiation from even some shielded sources.

Plastic Scintillators (PVT) use the same detection method as NaI(Tl) and CsI(Tl) detectors but usually require much larger detector sizes the achieve the same sensitivity.  They are commonly used in high-volume portal monitors and come in a variety of shapes and sizes.

Lanthanum Bromide (LaBr3) detectors are capable of finding energy peaks more quickly (known as detector efficiency) than a corresponding NaI(Tl) detector, but LaBr3 detectors exhibit internal radioactivity that reduces its spectral resolution at energies below 100 keV.  The current cost of LaBr3 detectors is generally much higher than that of comparable NaI(Tl) detectors. 

 

High Purity Geranium (HPGe) detectors figure into the top end of radiation detection and identification.  Devices using HPGe detectors are able to identify isotopes 2-3 more quickly than NaI(Tl) partly because they need sense far less radiation to come up with an identification.  The downside to this type of detectors is that HPGe detectors must be cooled with liquid nitrogen to operate, which makes HPGe devices bulky and much more expensive than scintillator units.

Cadmium Zinc Telluride (CZT) detectors have higher resolution and stability (for gamma rays and x-rays) than NaI(Tl), but are expensive in large crystal volumes.  Many CZT systems contain arrays of multiple small CZT detectors because the detection sensitivity increases with volume and some directionality can be established this way.  The Rad-ID device by D-tect Systems is available in configurations that contain four or eight CZT crystals, as well as a large NaI(Tl) detector. The combination of multiple detector types allows the Rad-ID to quickly and accurately identify over 110 radioactive isotopes.

Detection systems for neutron radiation (extremely high-energy radiation produced by elements such as Uranium and Plutonium) are also critical for security.  This type of radiation only comes from a few highly-controlled materials. The most commonly used neutron radiation technology involves the use of He3 tubes and requires relatively large volumes.  D-tect Systems’ Rad-ID device has neutron radiation detection capabilities with an optional He3 tube.

So whatever kind of radiation detection you need, we hope this short overview allows you to make informed decisions to help ensure security in an unstable world.