15. Use the semiempirical mass formula to obtain an expression for the two-neutron separation energy when A » 1. (Hint: A differential method is far easier than an algebraic one for this problem.) Estimate the size of the various terms and discuss the A dependence. Compare with the following data for Al and Te: 25 Al 31.82 MeV 117 Te 18.89 MeV 124 Te 16.36 MeV 26 Al 28.30 MeV 118 Te 18.45 MeV 125 Te 16.00 MeV 27 Al 24.42 MeV 119 Te 18.17 MeV 126 Te 15.69 MeV 28 Al 20.78 MeV 120 Te 17.88 MeV 127 Te 15.41 MeV 29 Al 17.16 MeV 121 Te 17.46 MeV 128 Te 15.07 MeV 30 Al 15.19 MeV 122 Te 17.04 MeV 129 Te 14.86 MeV 31 Al 13.03 MeV 123 Te 16.80 MeV 130 Te 14.50 MeV Why do we choose two-neutron, rather than one-neutron, separation en- ergies for this comparison?