Archive for the ‘Just Fooling Around’ Category

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Trick or Treat!

October 30, 2011

What lurks inside these beguiling treats?

A razorblade, perhaps?

Or a sewing needle?

Time for another Halloween in America, and you know what that means: some good ol’ fearmongering about dangerous strangers who are hell-bent on kidnapping, raping, and chainsaw-murdering your darling little moppets! Oh joy. Perhaps no trope of the “stranger danger” variety is more firmly ensconced in the contemporary American Halloween lore than the idea of the devious misanthrope who slips razor blades into apples or needles into candy bars before passing them out to trick-or-treaters.  Concern persists despite scant evidence for such activity.  The fear had reached its zenith by the mid-’80s following the Chicago Tylenol Murders of ’82.  By 1988, the city of Reno, NV was spending about $1630 per annum to x-ray trick-or-treaters’ loot in the radiology wards of its three hospitals, as an article by J. Calvanese in Veterinary and Human Toxicology reported. “No films were positive for radio-opaque foreign bodies.” Despite a near-zero incidence of such tampering, it is still common for establishments with x-ray equipment to operate it for paranoid Halloweeners.

Tonight I offer you a couple low-energy radiographs of compromised “treats” prepared with great care in my kitchen (click any image for a high-res version). Typical dental and medical x-ray equipment operating in the 80-120 kVp range has difficulty producing high contrast for the objects pictured here, so I recommend a mammography or extremity type of tube operated at a low voltage. These photos were taken at 26 kVp with the tube and screen shown.  The screen was 5 feet downstream of the tube, where the exposure rate was about 100 roentgen / hour. The photos of the screen were made with my Panasonic LX5 point-and-shoot at ISO200 / f2.1 / 30-40 seconds. Happy Halloween…and remember, your kids are far more likely meet a grisly end in a traffic accident driving to the hospital / police station / courthouse to x-ray their candy, than they are from the candy itself.

At top: beryllium-window x-ray tube used in these images.

At bottom: the diverging x-ray beam from the tube’s window impinges on the CdZnS fluoroscopy screen used to take these images.

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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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Cheap Chinese Induction Coils

March 31, 2009

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The induction coil, once an essential tool of modern physics that lay behind the discovery of the electron, x-rays and radio, has been relegated to the toybin.  Most of the modern ones are made in China like the rest of our toys.  While the coils of yore were mahogany-cased artisanal masterpieces destined for the most prestigious laboratories, today’s product is pitched at the Wal-Mart Shopper: sloppy mass production and everyday low prices.  I recently bought one such coil for use in an outreach program at Albuquerque’s Explora museum.  Billed as a 60-kV Ruhmkorff coil, the same product seems to have several outlets in the US.  This is a quick review.  Click below for more… Read the rest of this entry ?

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Scintillation Crystals and X-Rays

May 7, 2008

Here are a few photos of inorganic scintillators glowing from exposure to a ~ 300 R / hr x-ray field. These were all long digital exposures, 5-15 seconds, taken last year, and all had to be de-speckled extensively due to radiation noise on the camera CCD.

Bismuth germanate (BGO) crystals from a PET scanner. Lovely cyan glow, not particularly well-matched to photomultiplier tubes but gorgeous to the human eye. Dense, and a wicked photoabsorber of gamma rays, BGO is well-suited to portable homebrew scintillation detectors.

Barium fluoride, a material of choice for fast pulse-mode gamma detectors. Much of the light emission is in the ultraviolet, and to the eye the glow appears a deep purple color. Perhaps there’s a use for this in fast neutron detectors based on inelastic scattering on F-19?

Sodium iodide doped with thallium (NaI:Tl), the old standard for gamma spectrometry and high-class uranium prospecting. This 3″ x 1″ crystal is hermetically sealed because the NaI is hygroscopic. The rich blue glow resulting from exposure to a 60 microcurie radium source is literally bright enough to read by. Next to the x-ray machine, it shines like a spotlight!

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X-rays Cure Snow Globe of “Static Cling”

March 16, 2008

Snow globe and x-ray machineClick here to watch the demo (1:40, AVI format, 4 MB). The forced-air snow globe has become a popular piece of holiday decor in recent years. But, as the Wikipedia article mentions, this toy is menaced by static cling: “snow” adheres to the inside of the plastic globe and refuses to fall. (Presumably, the globe and the snow become triboelectrically charged during operation.) So how do you instantly exorcise this static cling from your snow globe? Simple. You expose your snow globe to a powerful beam of ionizing radiation.

The video available here depicts a snow globe suffering from extreme static cling being treated with an 80 kVp / 3 mA portable x-ray machine that produces about 300 R / hr near the midpoint of the globe. The x-rays create ions in the air that rapidly discharge the plastic “snow” and globe, eliminating the electrostatic forces trapping the snow against the globe. This is a variant on the radiation-discharging-electroscope demo commonly practiced in physics lectures in the early part of the 20th century. A good example can be found in Sutton RM, ed., Demonstration Experiments in Physics, New York: McGraw-Hill (1938.):

“Three rubber balloons filled with hydrogen or illuminating gas and attached to a common point on the table by silk threads make an effective large-scale electroscope. When charged, they will stand far apart but will come together promptly when an x-ray beam is turned on them.” (p. 497-498.)

This genre of demonstration is rarely performed today for safety and liability reasons. In 1938, folks were aware that radiation had its hazards but were pretty casual about controlling exposure. Sutton’s words of caution prefacing the above excerpt embody this attitude perfectly:

Caution: Prolonged exposure to x-rays may produce bad burns. Do not expose any part of the body for more than a few minutes.”
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