06 February, 2007

Nuclear Fission - Ping Pong Ball Experiment

Before the Super-Bowl there was an ad on about the propagation of ideas that I really liked (though it failed in its marketing because I cannot remember who it was for).

The narrator of the ad held a ping pong ball over a basketball court covered with mousetraps with ping pong balls on them. When he dropped the ball on one it went off and launched its ball in the air which landed on several others which launched theirs and so on.

This struck me as an awesome way to display the principles behind nuclear fission chain reactions.

It hits all of the key concepts.

Neutron absorption cross section is simulated by the relative size of the traps and the balls. Fuel density by how close the traps are to each other. Neutron escape by the proximity to the edge of the court. Balls that are launched too energetically bounce fewer times so they display absorption resonance zones and fast neutron escape. If you wanted to simulate thermalizing effects on the probability of absorption you could place curtains or sheets to knock energetic ones back into the field of traps. Poisons could be simulated by pillows or sticky mats to stop or slow down the bouncing balls. Try different shapes to see how geometry affects the likelihood of escape.

You could judge efficiency of the designs based on how many traps are left unsprung and how fast or slow the entire reaction takes to finish.

Of course it is all two dimensional but it still gives a good idea of what happens.

All in all a pretty good science experiment for someone who wants to do it. Of course you probably want to replace the mouse traps with something less likely to break a student’s fingers. Has anyone done this this way before?

This commercial demonstates an old science experiment I once saw on PBS and on a science video shown in a science classroom. It goes back 20 years I think. Todd

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