Answer to Question #6506 Submitted to "Ask the Experts"

Q

My husband is a geologist. I am concerned about the types of materials (rocks) he comes in contact with/or brings home to the family. I would like to buy an easy-to-use radiation detector so that I can monitor the safety of materials/exposure. What type of radiation detector should I buy? Can this detector also detect any radiation from dust on boots/clothes that he may encounter if he is walking in certain areas? He once told me that he did bring home a rock of radioactive origin when he was young, and I am concerned about anything else he may come in contact with. Please provide a recommendation about a general purpose, easy-to-use radiation detector that would allow me to detect radiation on rock samples/dust on clothes/boots etc. I have young children and am concerned about his occupational exposure.

A

First, I would not expect that rocks brought home by your husband would pose a health threat to him, you, or your family, although some may show evidence of radioactivity. In particular, rocks that contain significant amounts of uranium may exhibit signs of radioactivity associated with the naturally occurring uranium and some of the progeny that the uranium produces in its radioactive decay. If he deals routinely with uranium ores then some of your concern may be justified in that some high-uranium-content ores when handled may release some uranium if the ore surface has degraded and the uranium oxide is at the surface.
Such loose material could get transferred to one's hands and possibly end up getting ingested or, in some instances, get airborne and be inhaled. It is unlikely that enough material could be taken in as to present a health concern, but it represents unnecessary exposure that one should avoid. If your husband does deal with such high-uranium-content rocks, he should store them in a closed plastic bag or other reasonably leak-tight container to avoid spreading any loose material around the house or other locations. Such ores do emit radiations that can often be detected with a simple Geiger detector (also called a Geiger-Mueller detector or GM detector). Geiger detector-based handheld instruments are among the lowest-cost radiation detection/measurement instruments that are routinely used and available. In its decay, uranium and its progeny emit alpha particles, beta particles, and gamma radiation. If the uranium is close to the surface of the rock, one may be able to detect the low-penetrating alpha radiation, the more penetrating beta radiation, and small amounts of the high-penetrating gamma radiation with a GM detector that is equipped with a thin window that will allow penetration of the lower-penetrating radiations. These detectors are also capable of monitoring any significant radioactive dust/contamination that might be present on surfaces, skin, shoes, etc.

There are numerous manufacturers/suppliers that provide such thin-window GM detectors for sale; their prices vary a fair amount depending on the manufacturer and the instrument characteristics. Here are a few links to some providers; one is supplied by Topac and is called the Monitor 5; the second is the Model TBM-3 from Technical Associates; the third is the Inspector, also from Topac; and the last is the Ludlum Model 14 ratemeter with the 44-9 thin window probe (I have shown the instrument being supplied by Biodex, but you can find the components and others on Ludlum's site). You can find other providers by searching the internet for Geiger detectors.

For your intended purposes I believe one of the least expensive models would be adequate. There are also used GM detectors commonly sold on eBay (search for Geiger detector) that may be purchased often at a considerable discount from new instruments, although there is always a chance that the instrument may not function properly. You must also be able to assess whether a particular instrument will fill your needs.

While, as I have stated, I do not believe that the typical rocks that most geologists deal with are a hazard from a radioactivity standpoint, the use of a radiation detector to survey the rocks may alleviate your apprehension and may prove to be an interesting activity and could turn into a possibly good science project if you have any students in your home. Good luck.

George Chabot, PhD, CHP