Nuclear Masses Don’t Add Up

In 2015 Edmund Myers at Florida State University in Tallahassee and colleagues reported measurements of atomic mass ratios that left researchers puzzled. Their data implied that the sum of the masses of the proton and deuteron minus the mass of the helium-3 nucleus, that is,mp+md−mh, was much smaller—by more than 4 standard deviations—than the value deduced by combining accepted values of the individual masses. Something didn’t add up. Either the Myers team’s measurements or the individual mass values were off. A subsequent measurement of the proton mass was made by other researchers, implying that the accepted proton mass had indeed been too large (see 18 July 2017 Synopsis). However, the discrepancy remained at more than 3 standard deviations. Now, in a rerun of their experiment, Myers and co-workers confirm their 2015 result with improved precision.