Aware V-TAC

While testing different procedures for collecting Radon decay product from various rock samples, we noticed the "plating out" of decay product onto a metal plate was greatly enhanced if a negative charge was applied to the plate, indicating the decay product is positively charged.

We employed one of our highly efficient minus 1000 VDC H.V. power supplies to supply the voltage. We connected, by way of alligator clip leads, the ground pole from the power supply to a coffee can body, and the negative pole to a metal washer mounted in the middle of the plastic coffee can top, by way of a screw and nut.

We placed the rock in the can and applied the lid then energized the power supply. After approx. 2 hours, we removed the coffee can lid and placed it on an RM-60 such that the metal washer was right above the Alpha-Beta window. The increase in count rate was very much higher than that generated by the same experiment without the H.V. applied.

The electrostatic field is very effective at attracting freshly generated Radon decay product, so much so that perhaps most, if not all, Radon decay product collects on the negatively charged plate. Since essential all the decay product generated migrates to the charged plate, Radon equilibrium within the sealed can is not necessary to achieve maximal decay product collection, given the short half-life of the decay products of interest (20 to 40 minutes) as compared to the half-life of Radon (3.8 days).

The limiting factor in this case is the rate of Radon generation and liberation from the rock sample, therefore one would expect the metal plate to reach equilibrium within perhaps 2 hours (based on the half-life of the decay products of interest), instead of perhaps 2 to 4 weeks (based on the half life of Radon), and this indeed seems to be the case.

Perhaps one does not need the coffee can and washer, but perhaps one could attach the ground and negative leads from the power supply to a double sided PC board. (One can purchase double sided blank PC boards from Radio Shack). First, use a scissor to cut a piece of PC board, larger then the Alpha-Beta window of your RM-60, 70 or 80. Next solder hookup wire to each side of the PC board. Inspect the PC board edge to make sure no bits of copper plate short from one side of the board to the other. Perhaps add a bead of glue or hot melt around the edge of the board to insure against a short developing at the edge. Next, place the double sided PC board within a container (perhaps a plastic bag or small jar) with the rock sample, and connect the wire leads to the power supply. After a period of time (perhaps 30 minutes to 2 hours), disconnect the power supply, remove the PC board, and place it right over the RM-60, 70, or 80 Alpha-Beta window. Notice only the negative side of the board is very radioactive. (Since one would be detecting primarily Alpha and Beta, the PC board would shield the other side).

Another option, connect the minus 1000 VDC output pole of the V-TAC to the screen covering the window of an RM-70 or RM-80, and the ground pole from the V-TAC to a ground, for example, the building ground, PC case or container. The -1000 VDC charge on the screen will attract decay product to the screen above the detector window, and thereby increase the sensitivity to airborne decay product. In an open room type environment, the increase in sensitivity to decay product will not be as great as with the Fan-Filter option (see description of Fan-Filter elsewhere), but in a closed environment, such as an underground covered hole, closed container, etc., the collection efficiency could be equal to or even greater than the Fan-Filter option.

We have not put together a complete kit of parts but we do have available, for those who are interested, the minus 1000 Volt DC power supply (V-TAC power supply).

The V-TAC power supply is an ABS box, the same size as the RM-60 (4.4" x 2.44" x 1.06"). The box has two clips mounted on the lid, onto which one can attach alligator clip leads. The V-TAC also has a standard 2.1 mm DC power jack into which one can plug the leads from an external power supply with a voltage between 4 and 25 volts DC, for supplying power to the V-TAC. We include a nine volt battery clip to 2.1 mm power plug, allowing one to use a standard nine volt battery to supply the power for the V-TAC. The V-TAC consumes approx. 0.2 ma so a nine volt battery should last well over 500 hours.

The V-TAC contains a fully regulated switching H.V. section. We include a 4.7 million ohm resistor in-line with the negative pole output (impedance: 4.7m ohms), to avoid shock hazard. The ground output is connected to the minus input.

The V-TAC power supply plus the nine volt battery clip to 2.1 mm power plug is $99. To order, just write V-TAC on the order form.


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