Atomic Weights and Isotopic Compositions for Potassium
 Isotope   Relative
Atomic Mass 		    Isotopic
  Composition  		 Standard
Atomic Weight 		  Notes 
 
19 K 39   38.963 706 4864(49)   0.932 581(44)    39.0983(1)  
40   39.963 998 166(60)   0.000 117(1)
41   40.961 825 2579(41)   0.067 302(44)

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