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The decay-chain of uranium-238, which contains radium-226 as an intermediate decay product. 226 Ra occurs in the decay chain of uranium-238 (238 U), which is the most common naturally occurring isotope of uranium. It undergoes alpha decay to radon-222, which is also radioactive; the decay chain ultimately terminates at lead-206.
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.
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.
The most stable isotope is 222 Rn (half-life 3.82 days), which is a decay product of 226 Ra, the latter being itself a decay product of 238 U. [41] A trace amount of the (highly unstable) isotope 218 Rn (half-life about 35 milliseconds) is also among the daughters of 222 Rn.
The activity of a sample decreases with time because of decay. The rules of radioactive decay may be used to convert activity to an actual number of atoms. They state that 1 Ci of radioactive atoms would follow the expression N (atoms) × λ (s −1) = 1 Ci = 3.7 × 10 10 Bq, and so N = 3.7 × 10 10 Bq / λ, where λ is the decay constant in s ...
The unit of activity is the becquerel (symbol Bq), which is defined equivalent to reciprocal seconds (symbol s −1). The older, non-SI unit of activity is the curie (Ci), which is 3.7 × 10 10 radioactive decays per second. Another unit of activity is the rutherford, which is defined as 1 × 10 6 radioactive decays per second.
This radiation is a small portion of the total emitted during radium 226 decay. Radium 228 emits beta particles, and is also a concern for human health through inhalation and ingestion. The gamma rays emitted from radium 226, accounting for 4% of the radiation, are harmful to humans with sufficient exposure.
Radiative decay occurs with a half-life 8.4 orders of magnitude longer, in excess of 1000 seconds. [ 25 ] [ 26 ] Embedded in ionic crystals , ionization is not quite 100%, so a small amount of internal conversion occurs, leading to a recently measured lifetime of ≈ 600 s , [ 6 ] [ 14 ] which can be extrapolated to a lifetime for isolated ions ...