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.


  1. Carl, Where can I obtain one of these tubes for my tube collection? And how did you hook it up and also protect yourself from the radiation. The bottom of the tube where the window is looks like a heat sink, and how long can these tubes run without burning out?

  2. Hi Steve, my tube came from an extremity x-ray machine in the “Surplus City” boneyard here in ABQ. I don’t have any leads on other similar ones I’m sorry to say. For similar capability I would recommend any mammograph tube or one of the analytical tubes with a beryllium window, which do make regular eBay appearances. Hookup was simple: I apply 2.2VDC to heat the filament, which is at ground potential, and I bring 0-30kVDC to the anode from a little RF-driven C-W multiplier. Rad protection is mostly by distance and by staying out of the direct beam. These low-E x-rays don’t have much penetrating power and the tube was run nowhere near its capabilities. I can’t estimate lifetime…it probably depends heavily on treating the filament carefully. Hope you’re doing well! -Carl

  3. I first heard about the razor blade in the apple myth from my mother, who was warned of it it as a child by my grandmother, likely back in the 1950s. I have never heard the story about people sticking sewing needles inside chocolate bars, or similar candy. I think that these are one of those urban myths, much like Chinese restaurants using stray cats as a source of meat, I suppose it’s possible, but it seems unlikely given the effort involved. I never could figure out how one would get a razor blade in an apple without it showing a slit through the skin. In both cases wouldn’t it have been more practical for the city of Reno to have supplied metal detectors for the purpose rather then tying up hospital x-ray machines?

  4. Carl, do you know how well a tube like this would work at making short pulses of x-rays? I’m wondering if you could pulse the high voltage then could some kind of time of flight ranging be done from reflected x-rays. I saw where NASA developed a Miniaturized High-Speed Modulated X-Ray Source (MXS), but I don’t understand what keeps a Coolidge tube like yours from being modulated at high speed as well.

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