Why is Silver-108 unstable?

Question

Why is Silver-108 unstable if silver-107 and silver-109 are stable? I found it on crash course but no answer was given.

Answer 1

The hand-waving answer is nuclear pairing energy. Protons and neutrons prefer to move in pairs in the nucleus, and they prefer to pair like-to-like rather than one to another. This means that, for the most part, nuclei with odd proton number and odd neutron number ("odd-odd nuclei") are less tightly bound than "even-even nuclei," and the odd-odd nuclei tend to turn into even-even nuclei by a weak decay.

In fact, there are only eight naturally-occurring odd-odd isotopes: four light isotopes which are actually stable (deuterium, lithium-6, boron-10, and nitrogen-14) and four with lifetimes comparable to the age of the earth (potassium-40, vanadium-50, lanthanum-158, and lutetium-176). The pattern on the chart of nuclides is quite striking: for instance, tin ($Z=50$) has ten stable isotopes, while its odd-$Z$ neighbors indium and antimony have only two each, both with even neutron numbers.