Photomultiplier Tubes (PMTs)
Hold it to a light and look at the photocathode window — a healthy tube shows a smooth semi-transparent gold-brown or blue-grey mirror film; a tube gone to air has a chalky white getter and a patchy cathode, and is worth nothing to anyone.
How to spot it
Evacuated glass cylinder or bulb 10–500 mm in diameter with a flat or hemispherical optical window, an internal stack of curved dynode vanes, a getter mirror patch, and a 10–21 pin base or flying leads. Markings: Hamamatsu R-numbers (R928, R6231, R7600), RCA/Burle (931A, 8575), EMI/ET 9xxx (9266B), Philips XP-series, Amperex. Often inside a mu-metal shield with a potted divider base. Found in scintillation counters, gamma cameras, well-logging tools, flow cytometers, spectrophotometers and LiDAR.
Metal content
| Metal | Quantity | Notes |
|---|---|---|
| Silver | 0.1–2 g per tube | AgMg dynode alloys in some designs; estimate |
| Gold | 0–20 mg per tube | Occasional plating on anode/pin leads, not economically recoverable |
| Base metal | BeCu dynodes with an activated BeO surface | This is the hazard, not the value. Total PM under $1–4 per tube |
At 4 Aug 2026 spot prices that works out to $1.90 per pound of contained metal — Silver 1 g = $1.90. A refiner paying $0 returns about 0% of that, which is normal: refining costs money and the buyer takes a margin.
Safe removal
Working temperature: Gentle warming 40–50 °C maximum
De-energise and wait at least five minutes for divider capacitors to bleed. PMTs are usually optically coupled to a scintillator with silicone grease inside a mu-metal can: warm gently to 40–50 °C and twist rather than pry, because thermal or mechanical shock cracks the glass-to-metal seal and destroys the tube. Keep it dark, short the leads, ship double-boxed.
Hazards
NEVER blow on, wipe with bare fingers, or brush away cut optical fibre.
NEVER grind, sand, file, saw, drill, abrasive-cut, sandblast, hammer, crush, shred, torch, melt or incinerate anything that might contain BeO. Sell or dispose of suspect parts intact. Broken beryllium parts are worth nothing; your lungs are worth everything.
NEVER short a large capacitor with a screwdriver. It welds the tip, blasts molten metal at your face, and can rupture the can.
NEVER grind, sand, saw or incinerate anything that might contain thorium or radium. Sealed sources stay sealed.
NEVER dry sweep or use compressed air on a scrapping bench. HEPA-vac or wet-wipe only.
Before you scrap it
The common trap
Questions
How much gold is in photomultiplier tubes (pmts)?
Silver: 0.1–2 g per tube. Gold: 0–20 mg per tube. At current spot that is about $1.90 of contained metal per pound.
How do you identify photomultiplier tubes (pmts)?
Hold it to a light and look at the photocathode window — a healthy tube shows a smooth semi-transparent gold-brown or blue-grey mirror film ; a tube gone to air has a chalky white getter and a patchy cathode, and is worth nothing to anyone.
How do you remove photomultiplier tubes (pmts) safely?
De-energise and wait at least five minutes for divider capacitors to bleed. PMTs are usually optically coupled to a scintillator with silicone grease inside a mu-metal can: warm gently to 40–50 °C and twist rather than pry, because thermal or mechanical shock cracks the glass-to-metal seal and destroys the tube. Keep it dark, short the leads, ship double-boxed.
Is photomultiplier tubes (pmts) worth more working than as scrap?
100% of the value is resale — the ratio is infinite because scrap value is zero. Working dark-current-tested tubes sell $25–3,000; large-format 5 in+ and multianode/PSPMT types are the money. Even untested, vacuum intact, getter bright listings sell well.
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