I have been scouring the Internet for some time, looking for any examples of what I remember seeing when I was quite a bit younger, and looking at a WESTCLOX radium clock face. Not just observing the glow of the zinc sulphide paint with the radium in it, but looking at the paint at a microscopic level. One might assume you would just see a green glow, constant and unremarkable. That is not what I observed.
Zinc Sulfide Fluorescence Microscopy
With about 30-60x magnification, I was able to see individual flashes of light that occur when the radium, a radioactive element, emits alpha particles that strike the zinc sulfide (ZnS), causing it to fluoresce. The phenomenon is known as radioluminescence. It reminded me of a tiny lightning storm as viewed from orbit above the Earth. At the time, though, we didn’t know what actual lightning storms looked like from space. Now we have that luxury.
Enter the Spintherascope
A spinthariscope (from the Greek spintharis, meaning “spark”) is a fascinating early-20th-century scientific instrument that allows you to visually observe the invisible world of radioactive decay. Invented in 1903 by British physicist William Crookes, it’s often called the “first radiation detector” or even the “ultimate atomic toy” because it turns nuclear events into tiny, sparkling light shows.
Microscopic Radium Glow
UPDATE: I recently found this on YouTube. It is a demonstration of radioluminescence caused by a polonium 210 sample impinging on silver-activated zinc sulfide paper.
How It Works
At its core, a spinthariscope is a simple handheld device—essentially a short tube or eyepiece—that lets you peer into the quantum chaos of radioactivity:
- Radioactive source: A speck of radium (or a safer modern equivalent like americium from smoke detectors) emits alpha particles (helium nuclei).
- Scintillator screen: At the other end, a phosphor-coated surface (typically zinc sulfide) captures these particles.
- The magic: When an alpha particle slams into the screen, it excites the phosphor atoms, causing brief flashes of light called scintillations. Through a magnifying lens, you can see these sparks twinkling like stars in a night sky—each one representing a single atomic disintegration.
In a dark room, after your eyes adjust (it takes about 10-20 minutes), you’ll spot 10-100 scintillations per minute, depending on the source strength. It’s mesmerizing but a reminder of radiation’s dual nature: wondrous and hazardous.
Crookes unveiled the spinthariscope at a lecture to the Royal Institution, captivating audiences and popularizing the idea of “seeing atoms dance.” It played a key role in early nuclear physics, helping scientists like Ernest Rutherford quantify alpha decay rates. By the 1920s, it became a novelty item sold in toy stores and science kits, complete with warnings about the radium inside. (Yes, people back then handled it casually—radiation safety was a work in progress.)
Today, vintage spinthariscopes are museum pieces (like at the Smithsonian), and replicas use low-level sources for education. You can even DIY one with household items, though I’d recommend buying a safe kit from places like United Nuclear to avoid any glow-in-the-dark mishaps. I’d love to learn how to make one of my own.
If you’re into hands-on science, it’s a poetic way to witness the universe’s randomness—proof that even atoms know how to throw a sparkler party. Got a specific angle, like building one or physics deeper dive? Let me know!
My experience aligns with the physics of radioluminescence: radium decays, emitting alpha particles that excite the ZnS molecules, which then release photons as they return to their ground state. This creates the scintillating effect I saw, rather than a uniform glow.
Today, all the radium dials from the past have degraded over time due to alpha particle bombardment, resulting in a reduction in luminescence. Many surviving radium-painted items (e.g., Westclox dials) no longer glow brightly, making the scintillation effect faint and hard to capture on video.
