MadSci Network: Physics

Re: Why do you need a nuetron to split an atom? Why can't you use a proton?

Date: Thu Apr 13 11:15:41 2000
Posted By: Benn Tannenbaum, Post-doc/Fellow, Physics and Astronomy, University of California, Los Angeles
Area of science: Physics
ID: 955381011.Ph

Dear Pat,

You asked why one needs to use a neutron to split an atom, rather than a

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

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!

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