Answer to Question #10792 Submitted to "Ask the Experts"

I plan to buy a used vehicle from Japan. As I am going to drive the car daily and am currently three months pregnant, I intend to buy a Geiger Müller-type detector to monitor the car (interior/and air conditioning system) for contamination by radioactivity. Some detectors mentioned can detect alpha, beta, gamma, and x radiation. Some more affordable detectors can only detect beta and gamma radiation. Please advise which one is more suitable for my objective.

If you were buying a new car from Japan I would not recommend that you invest in a radiation detector since imported new cars from Japan are monitored for radioactivity and, to my knowledge, no significant radiation has been detected. Used cars may be somewhat of a different story, and contamination with radioactivity from the Fukushima accident is more likely. According to the Japan Used Motor Vehicle Exporters' Association, all used vehicles being exported overseas are monitored for radioactivity/radiation and must meet a recommended limit of 0.3 µSv per hour. Among countries that import used vehicles from Japan, Russia is the most dominant, having imported more than 132,000 used cars in 2012. All such vehicles imported into Russia have been monitored (by Russians) and out of the 132,000 (according to Japanese Ministry of Finance), about 300 were found to be contaminated to a level in excess of the Russian acceptance level of 0.2 µSv per hour. This is a small fraction (0.0023 or 0.23 percent) of the number imported, but provides some evidence that some used cars are contaminated to some extent.

I do not believe that any car that you might receive from Japan would be contaminated to a degree that would present a health hazard to you or to your unborn child, but I can understand your possible concern and your desire to verify that your car is not contaminated to an unacceptable extent. If you are going to invest in a Geiger detector I would recommend the detector that is sensitive to alpha radiation as well as to beta and gamma/x-ray radiations.

The alpha-sensitive detector has not only the added sensitivity to alpha radiation but also a significantly increased sensitivity to relatively low-energy beta radiation because of the thinner entrance window that is used on the detector. This increases the likelihood of being able to detect smaller quantities of radioactivity possibly associated with releases from the Fukushima event (e.g., the beta radiation from ¹³⁷Cs and ¹³⁴Cs). While it is extremely unlikely that there would be any detectable alpha-emitting radionuclides that originated from the Fukushima incident, it is possible that in your measurement you might detect some alpha radiation, depending on the operating history of the vehicle and the specific measurements you make. The alpha radiation would likely be associated with some of the naturally occurring radioactive progeny of airborne gaseous ²²²Rn. While vehicle surfaces may accumulate some of these progeny, their presence is greatly enhanced in systems that concentrate them from large volumes of air. The classic example of this is the buildup of these radon progeny on the air filter used in the automobile. If the automobile has been operating within several hours of the measurements made, the natural radioactivity may be especially noticeable. Most of such radioactivity decays with a short half-life (less than one hour), but there are some components, which would likely be present at much reduced levels that have longer half-lives and would build up on the filter over long periods of operation.

I mention this in the event that you observe elevated measurements and want possibly to rule out natural radioactivity. The presence of significant alpha radiation can often be inferred by making a measurement at a specific location with the bare radiation detector and then making a subsequent measurement at the same location with the detector face covered by a regular sheet of paper. The paper is sufficient to stop virtually all of the alpha radiation but will allow most of the beta and gamma radiation to penetrate to the detector. If the measurement with the paper is markedly lower than that without the paper, you might suspect that naturally occurring radon progeny are present.

I will not go into much detail here about how you should interpret readings and at what levels you might want to take actions to reduce/eliminate exposure, but I will note a couple of points. The first is that the level that the Russians have used of 0.2 µSv per hour is well below any level that should cause any concern on your part for the health of you or your child-to-be. Even if you drove four hours per day every day of the remaining six months of your pregnancy in a vehicle that delivered such a dose rate to you/your fetus, the total dose accrued would be about 150 µSv, about 5% of the typical annual dose from radiation background received by an individual in the United States and not sufficient to produce any adverse impact. The general consensus among experts (The National Council on Radiation Protection and Measurements and the American College of Obstetricians and Gynecologists) is that doses below 50,000 µSv are not likely to be injurious to the developing fetus for most situations; this level is greatly in excess of any level I could realistically project for your situation.

I hope this is helpful to you and that you are not unduly concerned about the extremely low likelihood of any significant dose coming from the automobile you obtain. I hope that your remaining pregnancy is pleasant and that before long you will enjoy a wonderful and healthy new child. If you have additional questions or concerns, please contact us again.

George Chabot, PhD