...measures
If the anthropomorphism of billiard balls bothers you, please imagine that these are very large ``billiard balls'' with cabins occupied by Physicists who make all these observations and calculations.
...Galileo.
It had better! The behaviour of slow-moving objects did not undergo some sudden retroactive change the day Einstein wrote down these equations!
...them.
This is, after all, the most ubiquitous instinct of Physicists and perhaps the main æsthetic foundation of Physics. It is certainly what I mean by ``Physics as Poetry!''
...components.
I know I haven't explained what I mean by a ``nucleus'' yet, or even an ``atom;'' but here I will suspend rigourous sequence and ``preview'' this subject. The details are not important for this description.
...bombs.]
The name, `` atomic bomb,'' is a frightful misnomer; the atoms have nothing whatsoever to do with the process involved in such horrible weapons of destruction, except insofar as their nuclei are the active ingredients. The correct name for the ``atomic'' bomb is the nuclear fission bomb.
...neutrons.
The notation used here is 104#104 El, where the atomic weight A of an element is the total number of neutrons (uncharged nucleons) and protons (positively charged nucleons) in the nucleus and El is the chemical symbol for the element in question. ``Nucleon'' is just a generic name for either protons or neutrons, which have about the same mass [the neutron is slightly heavier] and the number of protons in a nucleus [called its atomic number Z] determines its net electrical charge, which in turn must be balanced by an equal number of negatively charged electrons in orbit about the nucleus to make up the atom. The atomic number Z therefore determines all the chemical properties of the atom and so defines which element it is. We could just specify Z in addition to A to know everything we need to know about the specific nucleus in question [which we call an isotope], but names are more appealing than numbers [even to Physicists!] so we use the chemical symbol [, U = Uranium, Mo = Molybdenum, La = Lanthanum, H = Hydrogen, He = Helium and Li = Lithium] as an abbreviation for the name of the element. Sometimes you will see Z as a subscript on the left of the chemical symbol, as in 105#105U, but this is not the only convention for isotopic notation and I see no reason to confuse matters any further. There --- a micro-introduction to nuclear, atomic and chemical terminology!
...Chernobyl.
There is an interesting history to the American [and presumably the Soviet] reactor design: the original version was built on a small scale to go into nuclear submarines, where it worked quite well (and was comparatively safe, considering the unlimited supply of coolant!). However, the successful submarine reactor design was simply scaled up to make the big land-based power reactors, a thoroughly dumb and lazy man132#132uver by the power industry that has led to a long series of unnecessary troubles. If the world had standardized on the CANDU design, nuclear power would have a much better reputation today, except for the irreducible (though undeserved) taint of psychological association with nuclear weapons, which has even prompted doctors to change the name of NMR (nuclear magnetic resonance) imaging machines --- probably the most harmless and beneficial devices ever created by modern technology --- to ``MRI'' (for Magnetic Resonance Imaging) just so their patients wouldn't be spooked by the boogey-word ``nuclear.''
...nucleus.
Note how extensively we rely on this gravitational metaphor! This is partly because we don't know any more compelling poetic technique and partly because it works so well --- it is a ``good'' metaphor!
...hill.
If you think about it some more, you will realize that such a situation usually constitutes unstable equilibrium: the tiniest push will set the ball rolling downhill, never to return of its own accord. In this case (carrying the nice metaphor a little further) there is actually a slight depression at the top of the hill, so that the ball can rest easy in metastable equilibrium: as long as it doesn't get to rolling around too energetically [enough to roll up over the edge of the depression], the ball will stay where it is; but if we ``tickle'' it enough [in this case, by dropping in a neutron] it will bounce out and from there it is all downhill again. This picture works almost perfectly in developing your intuition about metastable nuclei, except for the peculiar prediction of quantum mechanics that the ball can get through the ``barrier'' without ever having enough kinetic energy to make it up over the ridge! But that's another story....
...thermonuclear
We call such processes thermonuclear because the positively charged nuclei don't ``like'' to get close enough to each other for the strong, short-range nuclear force to take over (they repell each other electrically), and to overcome this ``Coulomb barrier'' they are heated to such enormous temperatures that their kinetic energy is high enough to get them together and then ... bang! The heating is usually done by means of a very small fission bomb, from what I understand.
...bomb.''
Once again, the popular terminology ``H bomb'' is completely misleading. The first thermonuclear bombs used a mixture of deuterium (135#135H) and tritium (136#136H) --- two isotopes of hydrogen --- as the components that fused to form heavier products, hence the name; but modern thermonuclear bombs use (I think) deuterium and lithium, which can be combined chemically into a solid form that is relatively easy to handle and not spontaneously radioactive.
...triumf
The acronym triumf stands for tri- university meson facility, in recognition of the three B.C. Universities that originally founded to project [there are now several more, but we don't change the cute name] and the main product of the cyclotron.
...diagrams
This is basically what won Feynman his Nobel Prize; these simple diagrams are rigourously equivalent to great hairy contour integrals that you would not really want to see! Thus Feynman brought the Right Hemisphere to bear on elementary particle physics. Without this simple tool I wonder how far we would have come by now....
...electrons.
Note that gamma particles [photons] are not conserved --- they are always being created or destroyed!
...theory.
Of course, if you are interested now and just can't wait, I can recommend some good reading....
...intensity
The intensity of an accelerated particle beam can be measured in particles per unit time [ triumf has about 153#153 protons/sec] or, if the particles carry electric charge, in amperes of electrical current [ triumf has about 140 154#154A (microamperes)].
...Nature.
The real surprises come when we find heavy particles that don't decay into lighter ones [or at least not right away]; this always means some hitherto unsuspected conserved property like ``strangeness'' or ``charm'' --- but now I really am getting too far ahead!
...shown
Don't you hate that phrase? Me too, but for now I have to resort to it.
...out
Ouch! There's another one.
...particles.
This is also a preview of topics to come; as we shall see later, Newton was quite right! Light does come in well-defined quanta known as photons, particles of zero rest mass that always propagate at the speed of you-know-what!

Jess Brewer
Fri Sep 13 11:17:01 PDT 1996