@property<EOL><INDENT>@memoize<EOL>def s1n(self):<DEDENT>
M_N = <NUM_LIT>         <EOL>f = lambda parent, daugther: -parent + daugther + M_N<EOL>return self.derived('<STR_LIT>', (<NUM_LIT:0>, -<NUM_LIT:1>), f)<EOL>
Return 1 neutron separation energy