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Specific activity (symbol a) is the activity per unit mass of a radionuclide and is a physical property of that radionuclide. [ 1 ] [ 2 ] It is usually given in units of becquerel per kilogram (Bq/kg), but another commonly used unit of specific activity is the curie per gram (Ci/g).
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.
The general historical unit for radioactivity, the curie, is based on the radioactivity of 226 Ra. it was originally defined as the radioactivity of one gram of radium-226, [42] but the definition was later refined to be 3.7 × 10 10 disintegrations per second. [43]
The becquerel succeeded the curie (Ci), [12] an older, non-SI unit of radioactivity based on the activity of 1 gram of radium-226. The curie is defined as 3.7 × 10 10 s −1 , or 37 GBq. [ 4 ] [ 13 ]
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.
It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)", [1] but is currently defined as 1 Ci = 3.7 × 10 10 decays per second [4] after more accurate measurements of the activity of 226 Ra (which has a specific activity of 3.66 × 10 10 Bq/g [5]).
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).
The following are among the principal radioactive materials known to emit alpha particles.. 209 Bi, 211 Bi, 212 Bi, 213 Bi; 210 Po, 211 Po, 212 Po, 214 Po, 215 Po, 216 Po, 218 Po; 215 At, 217 At, 218 At