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Quick Radon Detector For The Student Fabrication Tool

  • Listed: April 3, 2019 12:48 am


Despite the extreme simplicity, the chamber can detect surprisingly low levels of radon by detecting the radioactive “radon daughters” produced when radon gas decays. How well do various radon mitigation techniques work?

Are some dust collecting materials better for accumulating radon daughters?

Illustrate the concept of equilibrium and demonstrate the curves associated with a system reaching equilibrium. But these radioactive materials “decay” into lighter elements, emitting energetic sub-atomic particles in the process.Since radon is a noble gas, it is chemically inert and doesn’t stay bound in the solid the way it’s parent did.

These radon “daughters” are not noble gasses like radon, they are usually ionized when they are produced, and they will readily stick to anything nearby, like healthy lung tissue. This unfortunate chain of events is due to the decay chain including a noble gas!

Applying a positive voltage on the outer can relative to the internal wire, causes these ions to be attracted to the wire and the free electrons to be attracted to the interior wall of the can. The simple chamber described below is capable of detecting extremely tiny currents. It is necessary to shield the circuit from external electric fields.Find the center of the bottom of the ionization chamber can. Now, use a fingernail pressed against a ruler to establish the radius, press the fingernail against the can, and draw a few lines from different directions to mark the center. It can be difficult to drill a clean hole in the thin metal and a satisfactory alternative is to drill a smaller hole and use a hand reamer to widen the hole to about 1/2 inch diameter. Cut the bare wire to be shorter than the ion chamber can by 3/4 inch. Apply a small amount of epoxy to the top end of the transistor, keeping the epoxy well away from the leads.

You may solder a temporary wire to the can to help hold the transistor while the epoxy cures. This resistor may be left out, but accidentally shorting the transistor base lead to the can will destroy the transistor. Apply some double-sided foam tape to the edge of a 9 volt rectangular battery on the side that will result in the wires from the battery snap coming out on top. This should be a thin, flexible wire so that it doesn’t pull on the transistor very hard as you move things around. So, optionally, snug it up reasonably tightly and solder the nut to the can and threads to keep it in position. Simply running the wire through the hole is adequate, but you will need an additional wire for the can connection.

Position the two cans together making sure the connector doesn’t hit the battery and the wire stays away from the center lead of the transistor. Sand off the finish on both cans near the marks with fine sand paper. Connect the battery snap to the battery, and tack solder the two cans together, using plenty of heat and solder. When soldering the cans together, let the iron sit several seconds to heat both cans. Find a circular object with a slightly larger diameter than the ion chamber can and use it to draw a circle on a piece of aluminum foil.

You may try to use a rubber band or tape to affix the foil but it is difficult to let go of the band without destroying the foil. Make sure the foil is pulled tight against the sanded lip of the can so that electrical contact is made. Add rubber feet to whichever side looks like the bottom (not critical). In the cool laboratory, the background reading is 19 millivolts. Simply draw air through some sort of material and they will rapidly collect. Plug in the power supply and find the two thicker wires that have the power supply’s rated voltage across them. Strip those two wires and connect them to the fan with red going to positive and black going to negative. For the supply shown, the blue wire from the supply was positive and goes to the red wire of the fan and the black wire from the supply was negative and goes to the black wire of the fan.

Connect the wires by twisting them together and soldering or securing with wire nuts or electrical tape. Add some feet to the bottom of the fan so that it can stand vertically. Now, unplug the fan and tip the collector over to the horizontal position. If all goes well, some radon daughters should have been detected as an increased voltage reading. Thicker materials like ordinary paper towels will collect more efficiently but the airflow is greatly reduced. The radiation will drop exponentially as the various isotopes decay. This time is the approximate average half-life of the collected isotopes. Different locations are likely to exhibit different levels of radiation due to different levels of radon gas. If you happen to live in an area with unusually high radon levels in the soil, it might be possible to detect radon gas in the city water. Pitch a plastic tent with no floor, seal it as well as possible, and see if radon builds up inside from the earth below. It may prove difficult to achieve sufficiently low air flow in and out of the tent.

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A hefty 12 volt battery will be needed for running the fan for extended periods. The more advanced experimenter could replace the voltmeter with a computer data taker for automatically making plots. Outside air would be drawn in via the 3″ pipe, approaching the temperature of the surrounding air in the 4″ pipe as it goes. Since the air coming into the room is already near room temperature and the air going outside is near the outside temperature due to the heat exchange, the head exchanger greatly reduces the energy cost associated with bringing fresh air directly into the house. Do various stone materials stored in a basement raise the radon levels?

What effect does smoke have on the levels of radon daughters in the air. Can radon gas be detected seeping through the ground or a wall?

Demonstrate the half-life or radon gas by trapping a volume of air in a sealed box and plotting the drop in radioactivity over time.

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Demonstrate how various materials will block radiation, using the collected radon daughters as a radioactive test source. One of the lighter elements in the chain of decay is radon, a radioactive, noble gas. It diffuses right through solids and ends up floating freely in the air.

You breath in some radon with every breath but then you breath it right back out, since it isn’t chemically active or electrically charged. Those isotopes keep decaying, until a stable isotope of lead is reached. They typically have an even shorter half-life than radon and quickly decay inside the lung, kicking out energetic alpha and beta particles that can cause tissue damage and potentially trigger lung cancer. The deceivingly simple ion chamber is quite sensitive and can detect radon daughters in buildings with radon concentrations below the “action level” recommended by health authorities. When a radioactive particle passes through the air in the chamber, many of the molecules of air are ionized, having electrons knocked loose from the outer atomic shells. This movement of charge is a tiny current that may be amplified to detect the rate at which ions are being generated, and thereby the rate that radioactive particles are passing through the can. There’s quite a lot of activity going on in that small volume of air when you place the radioactive sample in front of the foil window and the reading climbs several tens of millivolts. Alpha particles can’t make it through the aluminum foil window.Typical cans include a small coffee can, a baby formula can, or a holiday snack tin. Possible cans for the ionization chamber and electronics shield. A simple way to find the center is to measure the diameter and divide by 2 to determine the radius. The excess metal will form a short, ragged tube extending into the can instead of breaking off in bits but the hole will be smooth and round on the outside. Pass the long wire into the can and press the flat side of the transistor against the outside bottom of the can, allowing the epoxy to spread onto the can. Solder a 1k resistor in series with the positive (red) battery snap lead and cover it with heat shrink tubing or electrical tape.

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Stick the battery to the bottom of the ion chamber can near the hole. Connect the negative battery lead (black) to the emitter of the transistor (left lead with the flat face down and the leads pointing away from you). Drill a 1/4 inch hole in the bottom of the short can near the edge. Use fine sandpaper or a rotary tool to remove the enamel coating around the hole on the inside of the can so that the washer will make electrical contact. It is hard to tighten such a connector in thin metal without damaging the connector or bending the can. Holding the two together with a good orientation, mark across them with a marker in two or three locations.

You just need to expose the bare metal so that solder will adhere. The circuit draws virtually no power so the battery will last many years, essentially its shelf life. Right before removing the heat, add a little more solder and the fresh flux will brighten the joint. Tack soldering holds cans together and makes electrical contact. Sand the paint off the lip of the can so that the aluminum foil will make electrical contact. After you destroy a few pieces and learn a few new words, try a large pipe clamp. The reading should drop to a few tens of millivolts, depending on the room temperature.The photo below shows a simple collector that is easy to build. Often the unused colors will pull right out of the cut off connector, but the most reliable way to find the right two wires is with a voltmeter. Rubber feet will keep the assembly from moving around due to the fan’s vibration. Well ventilated homes may have few radon daughters in the air and it may be necessary to repeat the test in an older building with lots of masonry, or in a basement. Basements in some parts of the country may require the meter be switched to a less sensitive range!

To proceed, a simple set of experiments could be to try different collection materials to find the most effective. Thin materials will have greater air flow, but may let the radon daughters slip by. Find the point where the meter reading has dropped half way to the background reading and record the time. Run the fan in different rooms or other locations for a specific time, perhaps an hour, and measure the resulting radiation. Can you map the levels and make an educated guess as to the source of the radon?

It can take nearly a week for the level to stabilize, so use a guest bathroom!

City water tends to be exposed to the air for long periods and the radon gas has time to escape or decay. And, it might be interesting to see if one can determine how long the water has been in the system by comparing the levels at the home tap to levels at the source, say a lake feeding the treatment plant. Remember, the half-life of radon is 4 days, so it will take at least that long for the level to stabilize. Remember, the radioactivity on the collection cloth decays quite rapidly, so you don’t have a lot of time from when the collector fan is turned off to when the measurement is made. The gap allows air to sneak in around the edges so you can plot the radon level continuously. But there is nothing wrong with the manual labor approach!

It may take several hours for a small fan or open window to make a noticeable effect. The 4″ pipe would lead outside and air from the house would approach the outside temperature as heat is exchanged through the wall of the 3″ pipe. The 3″ pipe should extend a few yards past the ends of the 4″ pipe on both ends so that the same air isn’t simply travelling in a circle. Turn on the fan for an hour or two to collect the radioactive isotopes and use the ion chamber to make a measurement.

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fabrication tool Quick Radon Detector for the Student Fabrication Tool

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