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Radon-222 (222 Rn, Rn-222, historically radium emanation or radon) is the most stable isotope of radon, with a half-life of approximately 3.8 days. It is transient in the decay chain of primordial uranium-238 and is the immediate decay product of radium-226 .
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
Radium (88 Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226 Ra with a half-life of 1600 years. 226 Ra occurs in the decay chain of 238 U (often referred to as the radium series). Radium has 34 known isotopes from 201 Ra to 234 Ra.
All other 27 known radium isotopes have half-lives under two hours, and the majority have half-lives under a minute. [2] Of these, 221 Ra (half-life 28 s) also occurs as a 237 Np daughter, and 220 Ra and 222 Ra would be produced by the still-unobserved double beta decay of natural radon isotopes. [13]
Radium-226 decays by alpha-particle emission, producing radon that collects over samples of radium-226 at a rate of about 1 mm 3 /day per gram of radium; equilibrium is quickly achieved and radon is produced in a steady flow, with an activity equal to that of the radium (50 Bq). Gaseous 222 Rn (half-life of about four days) escapes from the ...
The most stable isotope is 222 Rn with a half-life of 3.8235 days, which decays into 218 Po. Six isotopes of radon, ... 217 At, 218 At, 223 Ra, 224 Ra, 225 Ra, ...
222 Rn: Decay modes; Decay mode: Decay energy : alpha decay: 4.870 [1] ... Radium-226 (226 Ra) is the longest-lived isotope of radium, with a half-life of 1600 years.
A naturally-occurring gas formed as a decay product of radium, radon is one of the densest substances that remains a gas under normal conditions, and is considered to be a health hazard due to its radioactivity. Its most stable isotope, radon-222, has a half-life of 3.8 days.