🚀 go-pugleaf

I'm trying to write a macro that will output nuclear physics symbols
as shown in the summary line, namely a superscript mass number
followed by the letter abbreviation.  What I use now is 

\def\Ni#1 {\ifmmode {}^{#1}\rm{Ni} \else ${}^{#1}\rm{Ni}$ \fi}

which is fine when typing a symbol in the middle of text, e.g.

"... one of the interesting properties of \Ni64 lies in ..."

but is a nuissance when writing a reaction in the standard form

"... We have examined the reaction \Ni64(\O16,\O18)\Ni62 at ..."

Note that TeX chokes on the above line (the \O macro is defined the
same way as the \Ni).  Admittedly, the extra spaces that have to be
added to the above line for it to work are only a nuissance, but I'm
wondering if there is a way to avoid needing them.  

I'm thinking of playing around with changing the catcode for the
digits to be able to distinguish them from the `(' and `)', but am not
sure if it will get me anywhere.  Any help is appreciated!
 -- 
Roland Roberts                      BITNET: roberts@uornsrl
  Nuclear Structure Research Lab  INTERNET: rbr4@uhura.cc.rochester.edu
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