MAGNETIC RESONANCE. II 397 



nance). Therefore there are eight resonance-peaks for the electrons in 

 the atoms of the isotope 143, and eight more for the electrons in the atoms 

 of the isotope 145. This is the key to the remarkable pattern shown in 

 the curve at the bottom of Fig. 3. 



In the middle of the pattern is the stump of a tall peak. This is the 

 unperturbed peak due to the electrons in the atoms of even isotopes, 

 those of which the nuclei have no magnetic moment. Whether it is at 

 the position corresponding to g = 2.00 will depend on whether the dis- 

 placement due to electric fields in the crystalline salt of neodymium, 

 with which these data were obtained, is negligible or is not. Then, there 

 are eight much shorter peaks. These are due to the electrons in the atoms 



Nd EVEN 



Nd 143 I I \ I \ [ 



Nd 145 I \ \ I \ \ I I 



Fig. 3. — Hyperfine-structure pattern of the electron resonance of neodymium 

 in a salt of the metal, showing that the nuclei of each of the odd isotopes of neo- 

 dymium have eight orientations and therefore a spin of 7/2, and that the even 

 isotopes do not affect the resonance. (Courtesy of B. Bleaney). 



of the more abundant of the two odd isotopes. Then, there are eight still 

 shorter peaks (provided we count one which is merged with one of the 

 other group of eight) . These are due to the electrons in the atoms of the 

 less abundant of the two odd isotopes. This is beautifully confirmed by 

 the fact that the statures of the two groups of peaks stand to one another 

 in the ratio of the abundances of the two isotopes! Further, the spacings 

 within the two groups stand to one another in the ratio of the magnetic 

 moments of the nuclei of the two isotopes. As for the two combs that 

 stand above the curves, they are markers to identify for the onlooker 

 the members of the two groups of peaks. 



Observations on the similar pattern of a (rare) isotope of vanadium 

 — vanadium 50 — have led to the inference that this nucleus possesses 

 a non-zero magnetic moment and a spin equal to 6 (the highest value 

 so far known). This may seem surprising, since I have implied that nuclei 

 of even mass-number have neither spin nor magnetic moment. Vanadium 



