Posts Tagged ‘physics demonstration’

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Neutron Experiments on Video

January 10, 2010

Here are my inaugural YouTube offerings treating neutron production, detection, and use for producing radioisotopes in the home laboratory.  See an americium-beryllium neutron source (made from smoke detectors) in action!  I hope to make more such videos in the future.

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Hand-Cranked X-Rays

September 8, 2009

xray_apparatus A hand-cranked Wimshurst static generator, coupled with a modern-production “magnetic effect” Crookes tube, can produce just enough x-rays to make useful digital radiographs and excite Geiger counters.  The Wimshurst machine and the discharge tube can be readily obtained from online retailers in educational science apparatus for as little as $120.  To make radiographs, I employed a 6-inch fluoroscopy image intensifier tube with a custom mount for my Canon S3 IS digital camera.  All photos in the following gallery were 15-second exposures with moderate hand cranking.

Magnetic-effect tubes contain a slotted cathode that allows a beam of electrons, formed in a high-vacuum glow discharge, to impinge upon a phosphor screen at near-anode potential.  In the classic usage, the experimenter observes deflection of the electron beam when a magnet is brought near the tube.  The only contemporary American manufacturer of a magnetic-effect demo tube, Electro-Technic Products Inc., was enjoined from offering the product on the domestic market precisely because of x-rays.  So tubes of this type available in the US are invariably of Chinese or Indian manufacture—all the better because they’re cheap.  I bought mine from www.sci-supply.com for $79.95.

So what’s the possible utility of this?  Radiography in third-world outposts with no electrical supply?  Hardly…the image quality is too poor, 15 seconds too long for practical exposures, and ever since the vacuum tube went the way of the dinosaur it’s been easy to get enough power from batteries to energize small, intense, pulsed cold-cathode x-ray machines.  But the novelty factor is nice, and in museums or other didactic settings, the literal hands-on nature of this x-ray apparatus should be appealing.

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Fingers of a 28-year-old male hominid.  This hominid’s other hand was busy cranking the Wimshurst to power the tube for the exposure.  Field uniformity is poor, and the source-to-detector distance is a mere six inches–but contrast is OK and this is a perfectly serviceable human radiograph.  Exposure was approximately 100 μR.

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PVC and polyethylene hoses of the same size (left and right, respectively), vividly illustrating the x-ray attenuating power of the chlorine in PVC.

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Electronic stopwatch. Decent detail, including individual wires, can be discerned.  Remember, the x-ray source is a Crookes tube, not a modern line-focus x-ray tube!

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Iodine tincture (a few percent iodine in alcohol) from the drugstore is black to x-rays.

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Geiger tube from a CDV-700 civil-defense Geiger counter.  Prominent features visible by x-ray include the thin beta window in the middle of the tube’s active region, and the thin anode wire running down its axis.

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A hand tap set contained in a plastic box. No big surprises, but the taps are slightly magnetized and some resulting warpage of the image-intensifier output can be seen.

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The handle of a cheap steak knife, showing how the blade is anchored into the plastic.

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Package of “AA” lithium batteries.

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