Radioactive decay is not affected by the conditions around the nucleus. It doesn't matter what the temperature is, or whether the atom is bonded to a molecule, or even how long the nucleus has existed. What does affect the rate of radioactive decay is the interaction between the strong and weak nuclear forces. This interaction is unique to each isotope. Therefore, Uranium 238 (92 protons, 146 neutrons) has a half-life of 4.5 billion years whereas Uranium 234 (92 protons, 142 protons) has a half-life of 245,500 years. In this way, we can say that Uranium 238 is less likely to undergo radioactive decay than Uranium 234, but that's only because we know the half life of Uranium 238 is longer than Uranium 234.