Heat will do the trick too, but indirectly. It makes atoms move quickly and hit each other. Each successive electron tends to be harder to strip, as it sees itself as part of an object with an increasingly greater positive charge. After all the electrons are gone, you're left with nothing but a nucleus. Because the strong force holding the protons and neutrons together is stronger than the electromagnetic one, knocking the nucleus apart into pieces demands more energy than removing the electrons.
Neutrons are particularly useful because they have no electric charge.
Thus, they can cruise straight into a nucleus, unimpeded by electromagnetic forces. Typically it takes about a million times as much energy to get stuff out of a nucleus as it does to strip an electron from an atom. Two more points are probably worth covering while we're at it. The first is that if you hit protons and neutrons hard enough, you find that they in turn are made of even smaller pieces, called quarks . So far, we have no evidence that electrons have anything smaller rattling around inside them.