|MadSci Network: Physics|
Dear Pat, You asked why one needs to use a neutron to split an atom, rather than a proton. What makes up an atom? In this case, we're really only concerned with the nucleus-- the electrons swirling around the nucleus are not involved at all. The nucleus is made of protons and neutrons, packed together quite tightly. What are the differences between a proton and a neutron? If you find a high school physics book, you will see that they have the same mass, and the same size, and even the same spin. In fact, as far as we're concerned, the only difference is that the proton has a positive electric charge and the neutron has no electric charge. What happens when you put two charged objects near each other? If they have opposite charge (one positive and one negative) they are attracted to each other. If they have the same charge (either both positive or both negative) then they are repelled by each other. That means the closer they are to each other, the harder you have to push to get them to stay that close. Since the nucleus is made of protons and neutrons, it has a positive charge. (The electrons have a negative electric charge, so the total charge of an atom is zero since the number of protons and electrons is the same.) Thus, if we shoot a proton (with its postive charge) at a nucleus, it will be repelled and will most likely not strike the nucleus. However, the neutron has no charge and will not be repelled. It can enter the nucleus and cause it to break apart. We can also use electrons (since they have negative charge) to probe the internal structure of nuclei and of protons and neutrons themselves!
Try the links in the MadSci Library for more information on Physics.