Cn you me with this question?

That period of time is called the "half-life" of that particular isotope,
because that's how long it takes for ONE-HALF of it to decay and
turn into some other substance.

So, however much you start out with, you can expect that after one
half-life of time has passed, half of the total amount (50%) has decayed
and turned into other substances, and the other half (50%) remains.

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -