Wow, here we have the resources to figure out what it really takes to blow up a planet. The 'death star' beam is stoopid, of course. It takes enough energy to accelerate the planet's
entire mass to its own escape velocity to make it explode. For an earth-sized planet this is equivalent to several months output by our sun. (!) A simple 'beam' cannot possibly deliver this much energy. And anyway, if it's delivered from outside, it just burns away one side of the planet, sending the rest spinning away somewhere. The only practical way to really
explode a planet is to deliver enough anti-matter to the core to make an explosion big enough to shatter the planet.
So, if someone can figure out how much energy is needed to accelerate the earth's mass to it's own escape velocity, then back-convert that to matter/anti-matter reaction, we would then know how much anti-matter a super-high-tech ablative delivery device (the 'bunker buster' is a toy compared to this problem...
) has to deliver to the planet's core.