Answer to Question #9974 Submitted to "Ask the Experts"

Category: Nuclear Accidents — Fukushima

The following question was answered by an expert in the appropriate field:


What type of device would you recommend for someone traveling to Japan to determine if an item (e.g., food or an object) is emitting harmful radiation (alpha, beta, or gamma) and for assessing his overall exposure to radiation during the visit? For example, are the commercially available Geiger counters (e.g., Inspector + or Gamma Scout) suitable for these applications? Is a dosimeter also necessary? Are these devices useful in determining if Japanese products entering the United States (e.g., cars) are radioactive? Would such Geiger counters and/or dosimeters be useful to carry around on a daily basis so that the user could be alerted to a nuclear event (i.e., an accident or terrorist act)? Finally, do these Geiger counters and/or dosimeters require regular calibration to remain accurate? If so, how often?

The kinds of Geiger detector-based instruments to which you refer are suitable for assessing significant changes from typical ambient background radiation levels. They have been used by numerous groups and individuals to detect elevations in background radiation levels from contamination on various surfaces in the vicinity of the Fukushima event. Also, however, there have been numerous erroneous measurements made as a consequence of using inappropriate radiation-detection instruments or instruments that have not been properly calibrated and/or not been properly used.

If you do obtain a Geiger-type (or other) survey meter, make sure that it has been calibrated for the kinds of readings you will be taking (e.g., exposure rate or dose rate). Get familiar with how the instrument operates and use it in a variety of locations to see how normal background radiation levels appear and how much variability you might expect in the readings. For routine use, it is generally recommended that instruments be calibrated at least once per year. If you have a radiation check source available, it can also be very helpful in confirming proper operation (such a source does not necessarily have to be a source purchased specifically for this purpose; it could be something like a piece of old Fiesta® dishware that used uranium in the glaze). A Geiger detector with a thin window, as in both the detectors that you cited, when placed at a relatively close distance from the surface of such an item, will yield a significant dose rate that is easy to read on the meter. Using this source with the instrument always positioned in the same fashion with respect to the source allows a check as to whether the detector appears to be behaving in a consistent fashion. This does not substitute for calibration, but it does provide some assurance of suitable operation between calibrations.

The thin-window Geiger detector, such as that available on the instruments you mention and on many others, is sensitive to the three major radiations—alpha, beta, and gamma. When placed close to the surface of markedly contaminated materials, you would expect a response. If you were in an area close to the Fukushima site where some significant levels of ground and other surface contamination may be present, you may obtain readings above background levels when the detector is close to a surface, but the readings may not be easily interpretable because you would not necessarily know what radiations were contributing to the readings. Often the detector will have been calibrated to read exposure rate or dose rate from gamma radiation; when response is to beta or alpha radiation from surface contamination, the readings will not make physical sense if interpreted as exposure or dose rates. As I understand it, there have been cases in which detectors of the type being discussed have been used to detect radioactive contamination from Fukushima on automobiles.* Again, elevated readings might indicate the presence of contamination, but one may not be able to say much beyond that.

You should keep in mind, also, that if you use the detector to attempt to measure radiations being emitted from food products, there could be activity present in amounts that might be considered inappropriate for regular human consumption, but you may not be able to distinguish radiation levels different from natural background in the area. Meaningful analysis of radioactivity in food products generally requires sophisticated laboratory techniques in which rather large amounts of food products are treated to concentrate and separate the radioactivity; chemical separations are performed as needed, and emitted radiations are measured with specialized detection systems.

There are various types of personal dosimetry devices that have been and are worn when individuals are in areas where significant radiation exposure is a concern. The use of such devices has been most dominant among individuals classified as radiation workers. If you hold such a position that you would be frequenting areas of the Fukushima reactor accident site during your trip, then the use of personal dosimetry would be desirable and probably required by radiation-control officials. Otherwise I see no need for use of such dosimetry, except perhaps to satisfy your own concerns or curiosity.

Regarding your question as to whether Geiger detectors or dosimeters should be carried around on a daily basis, I assume you are referring to daily life outside of Japan. While engaging in such actions might be informative because you might observe fluctuations in radiation levels associated with different locations and different activities, and such information will provide you a good perspective on what your normal radiation environment looks like, I do not feel there is a need for such action. I suspect that use of such devices by large numbers of members of the public may lead to a lot of unwarranted concern because of improperly used and/or uncalibrated instruments and spurious responses to nonionizing radiation sources (e.g., radiofrequency radiation) and normal but unexpected fluctuations in background radiation levels. If you and other individuals have instruments and/or dosimeters available, they could be helpful if there were a situation or threat that involved potential exposure to measurable radiation sources, and you might elect to use the devices at such times.

If you get to Japan, I hope you enjoy your trip.

George Chabot, PhD

*Editor’s Note: See answer to Q9993.

Answer posted on 23 November 2011. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.