318 BELL SYSTEM TECHNICAL JOURNAL 



of atoms there are curiosities enough to keep theorists busy, one guesses. 

 for years. I leave this for the future, and close by speaking briefly of 

 the magnetic moments, which by themselves suffice to show that the 

 task will not be easy. 



For the magnetic moments attributable to extra-nuclear electrons 

 (or rather to their projections upon the direction of the angular mo- 

 mentum corresponding), we found by theory and by experiment values 

 which we wrote as g^ejlmc) ^n{n -\r 1) A/2x; here m stands for the 

 mass of the electron; g is 1 for the orbital motion of a single electron, 

 is 2 for the spin of a single electron, and has calculable values not 

 greater than a very few units for the extra-nuclear electron-system as a 

 whole; n is the quantum-number of the associated angular momentum, 

 and is 1/2 for the spin of a single electron and has various values for 

 the other cases. 



If now a proton be a simple particle with a spin 1/2, one would 

 expect for its magnetic moment a value differing from that of the 

 electron-spin only by the substitution of nip the proton-mass for m, 

 therefore about 1840 times smaller. The actual value (page 313) 

 is about three times as great as the expected one, so that the analogy 

 with the electron is good enough to predict the order of magnitude, 

 but is not perfect. This is as surprising a discovery as any that has 

 cropped up in the last several years in the field of atomic physics, and 

 shows that even the supposedly elementary particles still have mys- 

 teries for us. The value for the deuteron is a good deal smaller, which 

 with the proton-neutron scheme implies that the neutron has a mag- 

 netic moment pointing in the opposite direction to that of the proton. 

 The spins of proton and neutron must, however, be parallel, else 

 their resultant could not be unity, which is the value of / for the 

 deuteron. This brings up a new point: I have not yet said whether 

 magnetic moment and angular momentum should be visualized as 

 parallel or anti-parallel, or better, whether the component of the 

 former along the direction of the latter should be taken as positive or 

 negative. The qualities of the deuteron indicate that whichever is the 

 case with the proton, the opposite is the case with the neutron. Ac- 

 tually it is often possible to tell, from features of hyperfine-structure 

 of which I have said little (cf. footnote 5, p. 302), which of the cases is 

 realized for the nucleus as a whole. For the proton and the deuteron 

 these features are unhappily either absent or inaccessible, and the 

 question remains open. For most of the others which have been 

 analyzed, the magnetic moment is said to be positive, meaning that 

 it is of the sign which one expects, considering the nucleus as a whirling 

 positive charge. For a few nuclei, however, it appears to be negative 



