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Strong Nuclear Force

The strong nuclear force holds particles together in atomic nuclei. It must be stronger than the electromagnetic force because it is able to overcome the repulsion that occurs between protons in the nucleus because of their positive charge – like charges repel.

Demonstration: Magnetic force

Protons are positively charged and should fly apart. A pair of small magnets arranged with similar poles together, simulating He with 2 proton. When we have ten magnets (2 stacks of 5), simulating Ne with 10 protons, the force between the two stacks of magnets is much stronger. There must be a stonger force than electromagnetism overcoming the electromagnetic force trying to drive the protons apart.


Electron shells and neon.

Why this electron arrangement is significant is that all the inert gases have the outmost shell "full" with 8 electrons. It is possible to "excite" one of their outer electrons to a higher electron shell than it normally resides in. For example, neon has electrons arranged 2, 8. If we use an electric field to excite an electron so they're arranged 2, 7, 1 then when the electron drops back to its normal location it gives off a photon (light). This is very basically how neon lights work. (I mentioned I'd say more about neon and electron shells later. I'll mention it again in Module 15 – Light.)

Neon is found in the air (1 part in 65,000) and is produced by liquid air fractional distillation. Neon (average atomic mass 20.18) has three isotopes, all stable:

20Ne – 90.48% – 10 neutrons
21Ne – 0.27% – 11 neutrons
22Ne – 9.25% – 12 neutrons


As the periodic table shows, all americium (the c has a "sh" sound) isotopes (of which there are 18) are radioactive and artificially made. Americium-243 has the longest half life of 7,370 years (or 7,950 years), while americium-241 used in smoke detectors has a half life of 432.2 years and "is easily prepared in a fairly pure form" in kilogram quantities. As expected, it's a source of alpha particles, decaying to neptunium-237, but Am-241 is also used as a portable source of gamma radiation.

Separate page dealing with the Chernobyl meltdown.


Periodic Table: PDF of detailed color printable periodic table (broken link). It includes electron shell configurations.

Note that two element symbols are white text on white background (117 = Uus, 118 = Uuo). I've mentioned it to him. This has since been fixed. Update: And updated, since those elements have been named. Update: And it's now on a new website, PTable.

In the Chemistry section on this site there is also a periodic table.

The Radioactive Boy Scout (short version) is a cautionary tale of American teenager David Hahn who used lots of smoke detectors to make his own nuclear reactor.

... June 26, 1995, was not a typical day.

... Three [men], in respirators and white moon suits, were dismantling her next-door neighbor's shed with electric saws, stuffing the pieces into large steel drums emblazoned with radioactive warning signs.

... David Hahn. He had attempted to build a nuclear reactor in his mother's shed following a Boy Scout merit-badge project.

... When David's Geiger counter began picking up radiation five doors from his mom's house, he decided that he had "too much radioactive stuff in one place" and began to disassemble the reactor.

... At 2:40 a.m. on August 31, 1994, Clinton Township police responded to a call concerning a young man who had been apparently stealing tires from a car.

... David Hahn is now in the Navy, where he reads about steroids, melanin, genetic codes, prototype reactors, amino acids and criminal law. "I wanted to make a scratch in life," he explains now. "I've still got time." Of his exposure to radioactivity he says, "I don't believe I took more than five years off my life."

What's up with those dates? ABC in Australia has The Radioactive Boy Scout listed in their Great Moments in Science...

And David? Well, while he was a whiz at science, he never was much good with maths and English. So today, he’s a junior sailor/deckhand on the aircraft carrier, USS Enterprise, which has 8 nuclear reactors.

A long version of The Radioactive Boy Scout is available which gives interesting insight into why David did it, but be warned – some of it makes scary reading.

Wikipedia also lists David Hahn (1976 – 2016). I guess he's famous.