Jochen's High Voltage Page

Commonly available radioactive sources

Radium paintRa 226

This luminous paint contains a radium salt and some scintillating (fluorescing) substance, which makes it "glow in the dark". It was used until the 1950s on the hands and faces of clocks and watches, as well as in instruments and meters that had to be read in darkness. Its use was banned, mainly because of the danger for the workers handling it.

Radium and its decay products emit alpha-, beta- and gamma radiation. The activity of radium dials can be astonishingly high. Typical figures are 0.1 to 1µCi (1µCi = 1e-6 Curie = 37kBq)

Items with radium paint are frequently found on flea markets and in antiques shops. Two examples are shown in the pictures to the right.

Top: watch from the 1950s, radium paint marks on face and hands. Count rate at 5cm distance 400/min with front glass, 1000/min without.

Bottom: luminous badge from WW II, diameter ca. 6cm. Estimated activity in the radium paint 70kBq. Count rate at 5cm distance 20,000/min. (!)

Gas lantern mantlesTh (nat)

Gas lantern mantles used to be impregnated with thorium salts. Old radioactive lantern mantels can still be found in camping supply stores, but new ones are no longer radioactive. Activity and penetration power are comparable to radium dials or somewhat lower. Both alpha and beta (plus accompanying gamma) radiation is emitted. The example shown was found on a flea market.

Gas lantern mantle, thorium impragnated. Count rate at 5cm distance 400/min.

Uranium colored glassU (nat)

Uranium was used in former times to make colored glass (greenish or yellowish) that fluoresces under UV light or just bright sunlight. This stuff is only sold at antiques stores or markets nowadays, and it's usually expensive.

The image shows three examples collected from flea and antiques markets.

  • green-yellow bottle 250ml (top left) 400/min @ 5cm distance
  • pale greenish drinking glass (top right) 40/min @ 5cm distance
  • green flask (bottom) 200/min @ 5cm distance

Uranium glazed pottery U (nat)

Certain kinds of orange glaze ("fiesta ware") owe its bright color to uranium. This stuff is only sold at antiques stores nowadays, and it's expensive.

Thorium doped opticsTh (nat?)

Thorium was reportedly used to increase the index of refraction of glass. As usual, applications seem to be mostly military. Nowadays, these things are antiquities (WW II).

Rocks and mineralsU,Th (nat)

The most obvious source of natural radioactivity. The best known probably is pitchblende, from which the first pure radium was extracted. Radioactive rocks and minerals can be bought or found.

Pieces of Uranotile, Si2O7Ca(UO2)26H2O, from Caceres, Spain. (Many thanks Gerardo!) The rocks produce 5000/min (!) @ 5cm distance.

Radioactive chemicalsU (dep), Th (nat?)

Uranium and thorium salts, e.g. uranyl nitrate, are used for chemical analysis, and are available from chemical supply stores. Viewed as natural radioactivity, certain quantities may be freely available (not subject to the procedures usually required for radioactice sources). Uranium is expensive and very poisonous, thorium nitrate is more reasonable. As an example, 50g have a nominal activity of 165kBq. The small container (see picture) measures 800 counts/min at 5cm distance.

The uranium available this way is usually depleted of U 235, i.e. it's a waste product of the uranium enrichment process for reactors or weapons.

Ionization smoke detectorsAm 241

Most ionisation smoke detectors contain Am 241 (an alpha emitter), for home purposes usually 1µCi or 37kBq. Industrial units may contain even more. However, the radiation is nearly pure alpha, and so is not easily detected by cheap (non-window type) geiger counter tubes. This type of smoke detector used to be (and probably still is) widely available in Great Britain (e.g. in DIY stores for around £ 10).

The pictures shows such a smoke detector in different stages of disassembly. After the black plastic cage with the metal cap (top right in left picture) is removed, the radioactive source can be seen and accessed (center in right picture).

Voltage regulation tubesKr 85

Some old voltage regulation tubes contain radioactive krypton to lower the breakdown voltage. Single tubes may radiate too weakly to detect, but a whole box full pf them is quite detectable.

Cesium doped spark gapsCs 137

Reportedly available surplus (at least in the US), and labeled as containing Cesium 137.

Luminous plastic etc.H 3

The modern substitute for radium paint is tritium (H 3). Together with a suitable phospor it is used in all kinds of "glow in the dark" stuff: luminous paint, plastic, glass vials etc. Some watches reportedly contain or contained tritium. Military instruments and emergency exit signs are other common applications.

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