1-Half life is the time it takes for half of the nuclei in a sample of radioactive material to decay(Am I right?). Why does the first nucleas that decays,decay first and the one that decays in the end, decay in the end? What's the difference between the two nuclei or what causes this the nuclei to decay in different times? 2-Also if radioactivity occurs randomly in time and space (according to my book) then why does every radioactive isotope has its own constant half-life? Thanks in advance for the answer.