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neutron-proton mass difference energy equivalent  Numerical value  2.072 146 89 x 10-13 J  Standard uncertainty  0.000 000 74 x 10-13 J   Relative standard uncertainty  3.5 x 10-7  Concise form  2.072 146 89(74) x 10-13 J       Click here for correlation coefficient of this constant with other constants Source: 2018 CODATA      recommended values  Definition of uncertainty       Correlation coefficient with any other constant