PAIRING IN NUCLEI 
 
 
  
 That has to do with nuclear pairing. As I mentioned before, nuclei 
with even N and even Z are more stable than others. Pairs of neutrons 
and also pairs of protons like to couple to total spin 0, with a little 
extra binding. That feature, which accounts for the fact that all known 
even-even nuclei have ground state angular momentum of 0, is due to
the basically attractive nature of the nuclear force. Now Maria Mayer 
had shown that one can get some of the qualitative effects of pairing 
with a very simple model of nuclear forces, namely one with zero range 
interactions. There are also some very interesting mathematical 
regularities which show up in this model, which Maria Mayer and her
student Dieter Kurath found by detailed calculations. Soon afterwards, 
it was shown by Racah and Talmi that a model with zero range 
interactions has some interesting group symmetries, known as 
seniority, and later as quasispin. This aroused my own interest, and
while I did not work on the subject for a while, in the 1960's I 
discovered a very interesting generalization of Maria Mayer's scheme, 
the so called Surface Delta Interaction. That's what I was really excited 
bout when I last saw Maria in 1965. It was not until 25 years later that
I began to understand the physical origin of all this, including why 
such a crude model of zero range interactions makes any physical 
sense, given the fact that everybody knows that nuclear forces are 
finite ranged, due to exchange of mesons. 
 
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