Radioactive Decay and the Band of Stability

Schematic diagram of a mass spectrometer. [Blatt Communications.] 

The atomic mass of an element as listed in the periodic table Is a weighted average of all the known Isotopes having the same atomic number, as shown by Equation (2.6), where f) is the decimal percentage of the naturally occurring abundance of an isotope and m, is its atomic mass and the sum is for all the known isotopes having atomic number Z  

The masses and natural abundances of every known isotope have been tabulated by the National Nuclear Data Center in a booklet known as the Nuclear Wallet Cards. An electronic version of the nuclear wallet cards can be found at http //vmw.nndc.bnl.gov/wallet/wccurrent.html. The mass excess (A = M — A) in this table is given in units of megaelectronvolts and needs to be converted into amu for all practical calculations (recall that I amu = 931.494 MeV). 

Solution. The two stable Isotopes of chlorine have the following natural abundances and masses  

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