Answer to Question #13002 Submitted to "Ask the Experts"
Category: Radiation Basics
The following question was answered by an expert in the appropriate field:
I have a body scanner which is based on non-x-ray technology, it is millimeter wave technology and it radiates in the frequency range of 70–80 GHz only for 64ms (whenever a scan is provoked) with peak power around 1 mW.
I wish to demonstrate that my unit is not producing any x rays. So, with which equipment can I demonstrate that my unit is a non-x-ray scanner? Please suggest an easy and cost friendly way.
I should note something up front of which you may already be aware—that is, in order to produce x rays you would have to have an x-ray tube or some other evacuated tube containing an anode and cathode sustaining an applied potential of several thousand volts. For most glass-encapsulated tubes a voltage close to 10,000 volts is necessary to produce x rays of sufficient energy to penetrate the glass wall of the tube. If you can demonstrate that your system incorporates no such x-ray generating capability that might be sufficient for some inquisitors. For others, unwilling or otherwise unable to accept such evidence, I can understand why you might want to provide an actual physical detection system to show the lack of emitted x rays.
There are a variety of radiation detectors that might suffice for your purposes, but all cost some money and you are looking for an inexpensive solution. Since I believe all you require is a yes-or-no answer as to whether x rays are being produced there are some rather simple things that can be done but you will still require access to certain facilities and/or equipment. One of the least expensive approaches would be to expose a piece of x-ray film (in its light-shielded covering) for several minutes at the typical exposure distance from your scanner. This, however, requires equipment to process the film. If you do not have access to any facility that could do this, it would probably not be practical. There are other inexpensive devices that might be used, again somewhat dependent on your particular capabilities and connections. If you work for or have connections to a facility that uses personal dosimetry devices to measure doses from ionizing radiation, some such devices would be adequate for your intended use. For example, a thermoluminescent dosimeter (TLD) with a thin covering material (such as the skin dose-sensing element in a typical personal dosimeter) could be exposed in a similar fashion as would be used for the film and then read out by the provider. Here again, if you have any professional contacts in this area, you might be successful. The film and the TLD themselves each cost only a few dollars, but the readout would be expensive if you had to provide your own equipment,
If these solutions are untenable, the next most affordable possible solution would be to build or purchase a low-cost real-time radiation detection instrument. Most inexpensive commercial detectors use Geiger Mueller (GM) detectors as their sensors. In order to be able to detect, or demonstrate that you can detect, low energy x-rays (I specify low energy because people familiar with whole-body scanners will likely be aware that such scanners often use low energy x rays in a backscatter imaging process), the GM probe should have a thin window (typically between about 2–4 mg cm-2). The cheapest of such detectors is in the range from about $250 to $350. You can find several such detectors by searching for low cost GM detectors on the internet. You can also find information for building your own detector. A very inexpensive version shown in the following link is one based on a silicon pin diode, rather than a GM tube. I have no experience with this particular system, although I have used commercial versions of silicon diode-based radiation detectors. Of course, one of the additional demands you would encounter if you built your own system is that you would have to demonstrate that it was capable of detecting low energy x rays, and this could be a problem if you do not have access to such a source.
I should warn you that one of the commonly encountered difficulties with using many ionizing radiation detectors around radio frequency (RF) fields is the potential interference caused by RF-induced currents in the circuitry of the radiation detecting instrument, leading to false readings. This is especially common with inexpensive instruments and there is often a need to provide RF shielding around the instrument to inhibit such effects. It would likely be necessary in your situation. Such RF shielding, normally a good electrical conductor, should be thin, preferably only a few mg cm-2 to allow penetration of the (nonexistent) x rays.
George Chabot, PhD