The Geiger-Müller Detector (Drift Chamber)

The detector is pretty straightforward. It consists of 4 plastic plates (21x21x1cm), some aluminium foil and wire.

Construction of the high-voltage grid:

Take a piece of hefty solid copper wire without insulation and bend it to a U. That will be the 'bus wire' for the grid. Use a square piece of wood and carve 19 small notches spaced precisely half a centimeter apart at 2 opposite borders. Secure the bus wire with some adhesive tape on the wooden square.

Take some 'sense wire' (bare copper wire only 250(!)μm thick) and secure it with tape at the first notch. The thin wire is needed to produce a large enough electric field.
Now wrap this wire around the wooden square and use the notches to align the wire parallel to the previous winding.

Solder the sense wire to the bus wire everywhere they touch. Also solder the high-voltage supply wire to the bus wire. Carefully snip the sense wire outside the bus wire and glue the sensing grid to the sense square (3.) by using slow-setting (24-hour) epoxy.

Notes:

While the detector in the SciAm article is made airtight, I will run the detectors at normal pressure with plain air. Furthermore I don't use aluminium foil, but tinplate (see below).

UPDATE: 03-APR-2006: About 2.5 years after I started this project I've finally started to assemble the prototypes of the flat detectors.

UPDATE: 18-JAN-2006: Finally I got some 50μm bare copper wire and I started to construct the final detectors.

The thick frame wire mounted on some piece of wood, already with the sense wire wrapped around.

A close up - notice the notches for the sense wire guidance/spacing

Make sure you have a powerful soldering iron (I use a 30W type) - the thick frame wire (2.8mm in diameter) absorbs a lot of heat. Such a thick copper wire is not the best solution, since it's pretty tough to get it straight. Better use some thin copper pipe (round, square or rectangle profile) available in hobby stores, most likely in stores for model railway building and/or modeling stores in general. Cut 4 pieces of equal length, mount them on the piece of wood and solder those together. Then wrap the sense wire around the wood and proceed as described above.

UPDATE: 14-MAR-2004: I wasn't able to find bare sense wire in the desired diameter, so I removed the insulation of a wire made up of fine strands of bare wire for the sense wire. To give you an idea about the wire: the wire with the insulation has a diameter of 1.7mm and there are 64(!) very thin bare wires in it.

Read more at:
http://www.sas.org/E-Bulletin/2002-10-04/labNotes/body.html
http://www.sas.org/E-Bulletin/2002-10-18/labNotes/body.html

UPDATE: 19-SEP-2004: While talking to a physicists at the ECRS 2004, he mentioned that it should be possible to retrieve energy information of the incoming particle with the flat detectors. The detectors need to be operated at a voltage high enough that the particle is stripping electrons from the gas inside, but low enough that no saturating electron avalanche is triggered. Then the signal can be sampled and integrated. Such pulses have a high bandwidth (up to ~200MHz), so some sort of low pass filter will be necessary to avoid complicated high speed ADC hardware. More information when I get to this point of experimentation.
Note: Only energy information can be retrieved (if at all), but no information about the type of particle causing the event!

Professional detectors use the scintillation principle for determining the energy. There are several layers of scintillation material stacked upon each other and depending on the number of layers the particle is penetrating, the energy information in retrieved. The more scintillation layers the particle is flying thru, the more the energy of the particle.

Be very careful when handling high voltages!
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