white
nav_bg
top_gradient
home
About
experiments
museum items
banner_gen
logo3
Tube Schematic
Tube Schematic
Accelerating Anode'
utube_button
facebook
flickr_button
X
Lighting Gallery
PMT
Odysee

Radiation Detectors



One of the most common radiation detectors is the Geiger-Muller tube (G-M) This operates by detecting the current through a rarefied gas mixture including neon and argon. There is a voltage present between the cathode and anode but only when localised ionisation occurs due to radiation a cascade of ion charge occurs and is detected as a small current pulse. These can detect Gamma, Beta and Alpha particles if a mica window is present on the tube. The image shown is of the window end of a GM tube and also the ionisation appearance. This is normally a short dim flash and almost invisible to the eye.


Another method is a simple spark gap arrangement with fine meshed wires.

Scintillator detectors are also very popular they have some advantages over G-M and 'spark' counters but are a little more complicated. Various crystals or plastics scintillator are used in these, but they are mostly used in conjunction with a photomultiplier tube (PMT). These are incredibly sensitive detectors but work with visible light. The scintillator is therefore used to convert the radiation into small bursts of visible light, most commonly blue. A blue emitting plastic scintillator is shown here. PMT tubes require a voltage divider to supply the dynodes with a voltage cascade. This is used to amplify any photocathode emitted electron into a larger signal that can be externally amplified and detected.

The required electrical connections are shown in the diagram on the right.


The detector starts detecting particles with an anode voltage of around 850V but only seems to detect high energy particles. With an operating voltage of 1.1kV the sensitivity is similar to my G-M counter.

Two GM detectors are used in coincident here, and in conjunction with a lead shield. This arrangement discriminates between particles from different angles, only counting where coincidence occurs from high energy particles from above, and excluding other natural background occurrence. In this way we can say that the unit detects cosmic radiation.

base_gradient
logo3
Copyright 2025 tuopeek.com