The Spark Chamber

A spark chamber is a device used for detecting electrically charged particles. Widely used in the 1970s as a research tool, its main purpose today is to demonstrate cosmic rays for educational purposes. It is well suited to this as it is highly visual and can also be transported to public events and schools. This web page provides general information about spark chambers. You could also visit:

  • NEW Discovering Particles, our recently-developed, integrated outreach programme. Includes short video clips explaining how a spark chamber works.

A cosmic ray path in the chamber

The Birmingham portable spark chamber
Cosmic ray track in the chamber

What Does it Detect?

The main use now of spark chambers is to detect secondary cosmic rays. These are charged particles produced by the collision of highly energetic particles from outer space with nuclei in the upper atmosphere. So-called primary cosmic rays typically have energies ranging from 106 to 1020 eV. Through Einstein's equation E=mc2 this energy is converted into mass, so the atmospheric collisions form showers of particles, mainly muons, neutrinos and highly energetic photons in the form of gamma rays (For more on cosmic rays, see QuarkNet page). Nearly all the particles detected by spark chambers are muons or electrons that a muon has decayed into, because of the particles in a cosmic ray shower muons are the most penetrating charged particleas they do not interact much with other particles. Other particles that could be detected would be kaons or pions; these, along with positrons, were first detected by studying cosmic ray (in cloud chambers though, not spark chambers).

How Does it Work?

A spark chamber is a collection of parallel plates (modules) arranged in to a stack with gaps between the plates that allow you to see the visible sparks. Each module is made from a perspex "picture frame" (as shown) with an aluminium plate placed on either side of it.

The gap between the plates in each module is filled with a noble gas mixture (70% Neon and 30% Helium). On the top and bottom of the spark chamber are two scintillation detectors. When a charged particle passes through these, a short pulse of visible light is produced, which is converted into an electrical signal by a phototube. This is then turned into a digital signal by a discriminator. When the cosmic ray has passed through the spark chamber, the same process takes place at the second scintillation detector.

The digital signal from the first scintillation detector is sent to a coincidence unit and if this arrives at the same time as the digital signal from the second scintillator detector, a high voltage is applied across all of the pairs of aluminium plates by the trigger unit. This large voltage difference between each of the pairs of plates is unstable and will try to discharge by the easiest path available. Usually this is along the path of the cosmic ray, as they leave a trail of ionisation within the gas in a module. With this the plates discharge with a furious crack and a spark. As there are many modules arranged in a stack, it is easy to join the dots between the individual sparks, and so show the path where the cosmic ray passed through the spark chamber.

Randomnormal

Sometimes the result from the spark chamber is that shown on the left, as opposed to the normal clear path shown on the right. The random scattered affect occurs when something other than a cosmic ray, such as a defect in the chamber, causes the trigger unit to be activated, putting a high voltage across the aluminium plates. As in the case outlined above this voltage is unstable and wants to discharge to earth; however, there is no clear ionisation trail for it to follow, as it was not caused by a cosmic ray. The path of least resistance which the charge will follow is now completely random, so the scattered affect above is seen.

Another feature that arises from the spark chamber's design is how the cosmic rays appear to be regular occurences; the cracks and discharges seen have a roughly equal time spacing, as the video at the top shows. Yet this is not the case, as the particle showers in the atmosphere are completely random events. The regularity arises because it takes a certain set period of time for the spark chamber to build up another high voltage to discharge after the previous detection; if this time could be minimised completely then the appearance of cosmic ray events would be found to be random.

Development of the Spark Chamber

Below follows a brief description of the events that lead to the spark chamber as we know it today

Year Development
1949 Keuffel observed that discharge between parallel plates occurred along the path of cosmic rays
1953 Bella and Frazinetti took photos of sparks discharging along these cosmic ray tracks
1955 Hennings and Bagge improve the chamber further by:
-using several parallel plate counters
-enhancing the spark with a triggered condenser discharge (alcohol or argon-based)
-taking stereo photos
1957 Harwell, Cranshaw and de Beer looked into applying the voltage immediately after the particle had passed through the chamber and developed the accompanying trigger mechanism
1959 Fukui and Migamoto introduced the idea of observing multiple particles at once and using a noble gas in the chamber, as well as applying the voltage across the plates even more rapidly
1963 Alikhanian proposed leaving enough space between the plates so a spark could be observed
1970 The spark chamber was one of the principal detectors used for experiments. It was replaced by newer detectors such as the bubble chamber, drift chamber, time projection chamber and silicon detectors.

What do particle physicists use now?

In current research, the spark chamber is redundant, as it has been replaced by faster and much more sophisticated particle detectors with better time and spatial resolution. For example, in the 1990's, the OPAL experiment at the Large Electron-Positron (LEP) accelerator at CERN used drift chambers, while LHC experiments such as ATLAS, CMS and LHCb make extensive use of silicon detectors

Gallery of videos

We have some videos and many still images individual event pictures from studies by Jessica and James.

We have also collected together some of the unusual looking events which were a surprise to see. Ideas welcome!

persons Credits

The spark chamber web pages were originally written by Stephen Bull and remain contact point for schools. James Fleming and Jessica Cuttriss improved these as part of work experience placements mid-July 2010. They were reviewed by Ben Maybee and Megan Hopton in July 2012.

Further Reading

Topic attachments
I Attachment Action Size Date WhoSorted ascending Comment
pdfpdf sparkchambers.pdf manage 782.1 K 23 Sep 2013 - 15:13 NathanaelASFarley  
jpgJPG DSC00110.JPG manage 283.6 K 06 Sep 2010 - 11:15 NigelWatson test
pngpng TwikiFinal2.png manage 129.0 K 26 Oct 2010 - 08:57 NigelWatson Updated header images
gifgif sparkmodule1.gif manage 53.4 K 01 May 2012 - 09:44 NigelWatson  
gifgif sparkmodule2.gif manage 52.8 K 01 May 2012 - 09:44 NigelWatson  
Topic revision: r47 - 23 Sep 2013 - 15:15:25 - NathanaelASFarley
General.SparkChamber moved from Publish.SparkChamber on 23 Jun 2011 - 07:51 by NigelWatson - put it back
 
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