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Formation and growth of tracks in nuclear track materials

“…decay chain of 222 Rn, three groups of alpha particles are emitted, namely, the alpha particles with energies of 5.49 MeV emitted from 222 Rn, those with energies of 6 MeV from 218 Po and those with the most energetic 7.69 MeV from 214 Po. Other radon isotopes, such as 220 Rn (often referred to as thoron) can also be present in air and emit alpha particles that may be detected by track detectors.…”

“…The first mode employs ''open'' or bare detectors where the detectors are simply immersed in the air at the location where the measurements are conducted. Alpha particles emitted by 222 Rn and its progeny strike the detectors and leave latent tracks in it. The exposure time t is known and depends on the radon and progeny concentrations as well as the desired uncertainties of the measurements.…”

“…In addition to 222 Rn and its progeny, many different species like dust particles, water vapor, etc. are also present in the air.…”

“…The second problem is more fundamental than the previous one, namely, 222 Rn in air is always accompanied by its short-lived progeny that are also alpha emitters. As the track detectors register alpha particles from radon itself as well as those from its progeny, this technique measures both radon and its progeny.…”

“…Although the concentration of 220 Rn is usually small, and on average amounts to about only 5% of the 222 Rn concentration, under some circumstances the 220 Rn concentrations may be much larger. An example can be found in buildings in Hong Kong [113][114][115], where high concentration of 220 Rn can be found due to the relatively high concentrations of 232 Th in the building materials [116].…”