Dynodra

Dynodra, a hooded tube-wizard, sends a single spark up a staircase of glowing steps, and it grows brighter at every step.

The Physics

A photomultiplier tube turns one photon into a measurable pulse. The photon frees an electron from the photocathode. It is then accelerated onto the first dynode, where it knocks out several secondary electrons. Each of those is accelerated onto the next dynode, and so on. With δ secondaries per electron at each of N stages, the gain multiplies.

G = δ^N, so ln G = N ln δ

• G: overall electron gain
• δ: secondary-emission ratio per dynode
• N: number of dynodes

With δ = 4 and N = 10, G = 4¹⁰ = 1,048,576, about 10⁶ electrons from one. That is enough to make a pulse from a single photon.

Honest caveat: It multiplies electrons, not photons: only the first step involves light, and many photons free no electron at all. δ is an average that depends on the voltage at each stage, so the real gain fluctuates from pulse to pulse.

On the sticker

Dynodra raises a hand as a cyan spark climbs a glowing staircase of dynode steps. Printed text: DYNODRA with the line ln G = N ln δ. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.