Chapter 30 - Nuclear Reactions and Elementary Particles - Learning Path Questions and Exercises - Conceptual Questions - Page 1029: 3

$Mg^{25}$ would have a larger capture cross-section because it has an odd neutron number and thus the likelihood of neutron capture (so as to create a neutron pair in the nucleus) is higher. An atom nucleus is more stable with if neutrons are in pairs.

$Mg^{25}$ would have a larger capture cross-section because it has an odd neutron number and thus the likelihood of neutron capture (so as to create a neutron pair in the nucleus) is higher. An atom nucleus is more stable with if neutrons are in pairs.