A chemical element consists of atoms all of which have the same number of protons in the nucleus. That's the "atomic number" of the material: hydrogen has 1 proton, helium has 2, and so forth to uranium with 92 protons (and on to elements beyond).

But atoms also contain neutrons to help bind their nuclei together without (much) affecting the element's chemical properties. Variant numbers of neutrons make variant isotopes of the same element. "Atomic weight" is the total number of protons and neutrons. The usual form of hydrogen is 1 proton and 0 neutrons; heavy hydrogen (deuterium) has 1 proton and 1 neutron, for an atomic weight of 2; fissionable uranium has 92 protons and 143 neutrons and since 92+143=235 it's called U-235; and the commonest uranium variant has 92 protons and 146 neutrons, aka U-238.

Now plot a graph with atomic number on one axis and atomic weight on the other. Show how stable an atom is by the height at every point in the graph. The isotopes found in nature fall along a zig-zag line slanting out and up from the origin of the graph. What you've got is like a map of a peninsula, an irregular ridge rising up above the surface of the ocean, extending towards the northwest.

It's a magical map, with gaps in places where there are no stable elements due to the vagaries of nuclear structure, with snaky sandbars along the shore, with treacherous reefs hidden just below the waterline, and with surprising islands of stability popping up far from the mainland.

This image of the nuclides comes to mind sometimes in the context of people and their stability (or lack thereof). At summer music camp last year my daughter (GD) was complimented by her cabin counselor, who described her as a "defuser", someone who reduced tensions and restored peace in potentially explosive situations.

In my youth I flattered myself by imagining I was a rock of stability, an immovable mountain of calm. Now I know I'm not; I have had far too many sad experiences of unreason. Only in a few lucky instances have I had the wit to (try to) refocus and recenter myself out of a crisis. It helps me to remember certain fictional or real-world heroes — immovable objects, masters of that hardest challenge: themselves.

(see InStability (20 Aug 1999), BeyondTheInnerCitadel (26 Sep 1999), StandingWaves (21 Aug 2000), LensManic (16 Jul 2001), ...)

TopicScience - 2002-04-28

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