High Voltage Forum

Ionizing radiation => Detection, Counting and Measurements => Topic started by: pentode on April 24, 2019, 05:41:07 PM

Title: Now building a spark chamber
Post by: pentode on April 24, 2019, 05:41:07 PM
I don't suppose anyone is interested in dated spark chambers but...….
I have started building a circular one using Argon gas.
Circular is much easier to seal to ensure it's gas tight.

10 Aluminium plates 200mm dia spaced at 20mm giving a 180mm high display.
Adjustable 25kV DC across alternate plates, non pulsed.

Non pulsed HV was used in the very early spark chambers but one gets spurious discharges.

If my non pulsed system doesn't work I shall have to spend, spend, spend on scintillators and
photo multiplier tubes, amps and timing extras.
Title: Re: Now building a spark chamber
Post by: pentode on April 27, 2019, 12:56:40 PM

Here's the 10 aluminium  discs with 20mm nylon spacers and nylon bolts.
Each alternate one to be connected for HV supply.
This is just a mock up to ensure everything fits together.   :)

Plates must be even to each other within about 1% so that's .2mm in this case.

Acrylic enclosure shown to have top and bottom plates attached, gas proof
with valves to supply argon and drain chamber of air.

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Title: Re: Now building a spark chamber
Post by: Mads Barnkob on April 27, 2019, 08:55:23 PM
You have me following your build process :)

Nothing wrong with dated and old school scientific equipment as they are often the basic principles that more modern and complex equipment is build upon, looking forward to see your results.
Title: Re: Now building a spark chamber
Post by: pentode on April 30, 2019, 02:19:21 PM
I hunted around for some small valves for gas inlet/air outlet.
As the whole rig is only 200mm dia x 250mm high I didn't
wish for large ones, so I bought two model railway engine valves. (60mm high)

Both mounted on the top acrylic plate where the argon gas is not inclined to escape
anyway as it is heavier than air.

The rig will be tilted to one side to fill the chamber, argon pushing the air up
and out.....I hope. :)  If a problem I shall have to  pipe the gas to the bottom of the chamber.

Now how to know when the chamber is full?
I shall use a lighted match burning at the exit valve and when it goes out
I should be nearly there !

Is there a better way?

Title: Re: Now building a spark chamber
Post by: pentode on May 01, 2019, 09:42:26 PM
Whilst waiting for more parts I built the power supply on the acrylic base mounted under the base. (It will be covered for safety as the voltage will be up to 25kV.  )
Initially the supply will be from a 15kV 30m/a  NST I stripped from an old SGTC I once built.

Nothing unusual in the power supply, just series HV diodes in a bridge with smoothing caps and bleeders wound around a piece of acrylic tube.
I always use nylon bolts, super glued to bases etc  to make cheap stand off HV insulators.


Title: Re: Now building a spark chamber
Post by: pentode on May 03, 2019, 09:11:42 AM
I thought about pressure build up in the chamber as sparking will warm up the Argon gas
and so pressure build up.

To keep an eye on this in a very cheap way I will fit a thin sheet of neoprene
onto a 60mm dia neoprene flat washer.  This will be fitted to the top
acrylic plate with a small hole drilled through it.

In this way any pressure increase or decrease will immediately show as a
depression or bulge in the neoprene. (dotted lines)
It will be interesting to watch this as sparking occurs.
I may put a position sensor on it too.

So I can keep an eye on pressure and cut the HV if too much.

Title: Re: Now building a spark chamber
Post by: pentode on May 05, 2019, 11:13:20 AM
When a partical passing through my chamber ionises the Argon, ( I hope  ),
the spark created will continue so I need to cut the HV after some
short time. As I am finding, switching 20kV plus HV is rather costly so I will make a short period timer to cut the mains supply to the NST, if I can
detect when a spark has been triggered by a partical and not spurious.

This is all a new ball game for me and the next part of the game is ordering
a small cylinder of Argon and a regulator.
to suit. I think these will fit the bill from Machine Mart who is near to me...……..


Maybe I ought to train up as a gas engineer. ;D
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