Radon decay scheme

The radioactive decay schemes of radon and thoron are shown in Fig. 1.1. The old generic nomenclature (RaA, ThB etc.) is now superseded by the isotopic designation (218Po, 212Pb etc.), but where necessary for clarity the old designation will be added. 

Pb, Ra is produced, and it decays by a emission to produce Rn that has a half-life of 3.825 days. Although the entire decay schemes will not be shown, the relevant steps that lead to the production of radon can be summarized as follows ... 

Evidence for the second viewpoint comes from measurements of longer-lived radionucleides within the radium decay sequence, specifically bismuth-210 and lead-210. The major routes for nuclei conversion within the radium decay scheme are shown in Fig. 7-27. The direct decay product of radium-226, an alpha-emitter, is radon-222, which escapes the Earth surface. Only the continents are a source the contribution from the oceans is negligible. Since the half-life time of radon-222 is only 3.8 days, its distribution in the troposphere is rather uneven. Over the continents the mixing ratio declines with increasing altitude (see Fig. 1-9). Over the oceans, the vertical gradient is reversed, as the oceans act as a sink and the zonal circulation keeps supplying material from the middle and upper troposphere. The immediate... 

A method for estimating the residence time of tropospheric aerosol particles associated with radon decay product radionuclides is based on the radioactivity of a pair of genetically related radioisobars, such as Pb, Bi or Pb, Po according to the sequential disintegrations in the beta decay scheme, as... 

The residence time, xr, can also be determined through the ratio of activities of radon, 222Rn, Xr AiRn, and Opb, A,pb Alpb, in air according to the sequential disintegrations in the alpha and beta decay scheme as... 

Using the data on radon decay product aerosols, Papastefanou and Bondietti (1991) reported a mean residence time, xr, of 8 days for aerosols of 0.3-pm activity median aerodynamic diameter (AMAD) size as determined from Bi/ Pb activity ratios. From the decay scheme of 2 Po T /2 = 3.05 min), because of the relatively short half-lives of the product radionuclides after two a-decays and two /S-decays, Pb-aerosols are produced. From 32 experiments for radon decay product aerosols ( °Pb-aerosols), Papastefanou and Bondietti (1991) calculated average values of fractions F and F2 of about 76.11 and 21.32, respectively. From 12 measurements of sulfate aerosols, Bondietti and Papastefanou (1993) calculated in the same manner average values of fractions F and F2 of about 68.67 and 12.63, respectively. According to Equation (4.12) and the above mentioned data, a mean residence time, xr, SO , of about 12 days would apply to sulfate aerosols of 0.3-pm mass median aerodynamic diameter (MMAD) size. 

In today s parlance, we call the radium emanation radon-222. (Like radium, the word radon comes from the Latin radius, for ray or beam. ) The alpha decay of radium-226 produces radon-222 and helium-4. The thorium emanation is radon-220, but the decay scheme from thorium-232 is more involved (see Problem 19.11). Rn-222 and Rn-220 are the two longest-lived isotopes of radon, the heaviest and rarest of the noble gases. (There are now 36 known isotopes of radon with mass numbers ranging from 193 to 228.) For many years, Dorn was generally credited as the sole discoverer of radon. However, as noted above, Ernest Rutherford and his co-workers, particularly Frederick Soddy, should be given at least equal billing. 

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