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Monitoring Times Reviews

June 2004



Monitor 4 Geiger Counter Kit

By Bob Grove


            As international fear grows with the threat of terrorism, more and more civilians feel vulnerable. Words like “dirty bomb” get tossed about with few Americans really knowing what they mean. A few have some notion that it refers to radioactivity, but that’s about it. And what if such a device does go off? How would we know if there’s a danger to us?

            It’s questions like this that led me to research a bit about such nuclear threats and to see what I could do to prepare myself without becoming a wide-eyed zealot.

            Basically, a dirty bomb is a conventional explosive (gunpowder, dynamite, ammonium nitrate slurry) which has been laced with radioactive waste collected from a variety of sources.

            What kinds of waste, you ask? Well, up until the 1970s, glow-in-the-dark watch, clock and instrument dials contained radium chloride; dust-static eliminators for record players contained radioactive polonium; and red-orange glazing in the pottery industry was likely to contain uranium oxide.

            More recently, hospitals are using increasing amounts of radioactive isotopes in diagnosis and treatment; smoke detectors utilize a pellet of americium oxide to ionize air particles; the mining and hydrology industry employ radioactive tracers to subterranean mapping; radioactive mineral specimens are widely available on the Internet; and even some gas mantles for portable lanterns are impregnated with radioactive thorium to improve its incandescence lifetime.

            Can such constituents of a dirty bomb be deadly? It all depends upon its contents and the resourcefulness of the terrorist in accumulating the load. And what happens when eruptions on our sun send massive clouds of energetic particles into our atmosphere? I’d like to know if there’s nuclear activity around me, wouldn’t you?


Affordable and Available Protection


            About two decades ago, the now-defunct Heathkit Company of Benton Harbor, Michigan, offered an inexpensive Geiger counter kit, a radiation detector that would show the relative presence of the most common types of nuclear energy – alpha and beta particles, gamma rays, and the ever-present cosmic radiation as well as X-rays.

            It just so happens that the kit, known as the Monitor 4, is still available, both as a kit and fully factory assembled and tested. The pocket-size detector is powered by a standard nine-volt battery and is entirely self-contained.

            A two-inch meter reports in two scales – counts per minute (CPM) and milliroentgens per hour (mR/hr). A sensitivity switch can elect any of three positions to accommodate various field intensity levels; it also allows measurement of the battery voltage status. Another switch permits selection of the silent meter and blinking LED only, or the added activation of an internal piezo speaker to render the familiar audible clicks traditionally associated with Geiger counters.


Let’s Build One


            The kit arrived promptly and securely; parts were carefully packaged and a handy inventory allowed confirmation of its contents. A substantial zipper case is included, as is the solder for the job.

            Two manuals accompanied the kit; one for step-by-step assembly and final alignment and operation, the other to pictorially identify components and circuit-board locations and procedures. But this wasn’t just any old manual – all of the resistors, capacitors and diodes were carefully held in position with transparent tape alongside their part numbers and values!

            Not only that, but a vial of conformal compound is provided to coat the high-voltage components to prevent humidity failure. These are examples of extraordinary service for a kit company to provide, and they made a big difference during assembly. They give the impression that this Geiger counter means business.


No Real Problems


            An experienced, skilled kit assembler should be able to do the soldering in two hours with an extra hour for final fiddling and pruning. We found the manual easy to follow, and only experienced problems when we decided to ignore the schedule and fly by the seat of our pants! As tempting as this is for Type A personalities (I speak from experience!), it’s not a good idea. There’s a reason for the manual.

            Over the years, as parts become obsolete or hard to find, substitutions are made. These usually, but don’t always, get into the manual. This was the only problem I encountered and it was immediately and courteously resolved by a phone call to the factory. The very last step, closing the clam-shell case, was delayed by a persistent resistance that wouldn’t allow the two halves to mate properly.

            It turned out that a small, plastic icicle left over by the injection-molding process wasn’t actually supposed to be there (it looked like a support for the circuit board). Snip, problem solved.


Let’s Try it Out


            Inserting the nine-volt battery into its snap and switching the unit on, I immediately had the pleasure of hearing the clicks, watching the meter and seeing the LED flash – what a rush! First time and no errors! Without any calibration procedure, the unit has 20% accuracy, improved to 10% with appropriate alignment tools.

            But most of us are well satisfied with seeing the meter hang low, not caring how many mR/hr that means. It’s when the needle dances off the scale, the LED seems to come on solid without blinking, and the clicks become a buzz that we become understandably alarmed!

            I tested the Monitor 4 on an array of household sources that I have accumulated – old radium-dial paint chips, smoke detector pellets, gas-lantern mantles, even my microwave oven. They were all “hot” except for the microwave oven; I guess they’ve made substantial improvements in X-ray shielding over the years!


A Final Look


            I’m very pleased with my Monitor 4. Over the years this model has given reliable service. (I still have my original Heathkit and it’s never had any attention but occasional battery replacement.) It was like meeting an old friend to see the new kit come in, and it was a pleasurable experience building it.

            The Monitor 4 is available from the manufacturer, S.E. International (web site for $170 plus shipping. S.E. International, Inc. P.O. Box 39, 436 Farm Rd. Summertown, TN 38483-0039: 1-800-293-5759 Fax: 931-964-3564;


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