Simple Nature - Light and Matter

Discussion QuestionsA In the reactions n → p + e − + ¯ν and p → n + e + + ν, verify thatcharge is conserved. In beta decay, when one of these reactions happensto a neutron or proton within a nucleus, one or more gamma rays mayalso be emitted. Does this affect conservation of charge? Would it bepossible for some extra electrons to be released without violating chargeconservation?B When an antielectron and an electron annihilate each other, theyproduce two gamma rays. Is charge conserved in this reaction?8.3 FusionAs we have seen, heavy nuclei tend to fly apart because each protonis being repelled by every other proton in the nucleus, but is onlyattracted by its nearest neighbors. The nucleus splits up into twoparts, and as soon as those two parts are more than about 1 fmapart, the strong nuclear force no longer causes the two fragmentsto attract each other. The electrical repulsion then accelerates them,causing them to gain a large amount of kinetic energy. This releaseof kinetic energy is what powers nuclear reactors and fission bombs.It might seem, then, that the lightest nuclei would be the moststable, but that is not the case. Let’s compare an extremely lightnucleus like 4 He with a somewhat heavier one, 16 O. A neutron orproton in 4 He can be attracted by the three others, but in 16 O, itmight have five or six neighbors attracting it. The 16 O nucleus istherefore more stable.It turns out that the most stable nuclei of all are those aroundnickel and iron, having about 30 protons and 30 neutrons. Just as anucleus that is too heavy to be stable can release energy by splittingapart into pieces that are closer to the most stable size, light nucleican release energy if you stick them together to make bigger nucleithat are closer to the most stable size. Fusing one nucleus withanother is called nuclear fusion. Nuclear fusion is what powers oursun and other stars.Section 8.3 Fusion 495