(r46) SparkChamber < General

General Web>OutReach>SparkChamber (revision 46) (raw view)~~EditAttach~~
---+ The Spark Chamber

A spark chamber is a device used for [[http://public.web.cern.ch/public/en/Research/Detector-en.html][detecting]] electrically charged particles. Widely used in the 1970s as a research tool, its main purpose today is to demonstrate [[General.CosmicRays][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:
   * %N% [[http://www.ep.ph.bham.ac.uk/general/outreach/DiscoveringParticles/detection/spark-chamber/][Discovering Particles]], our recently-developed, integrated outreach programme. Includes short video clips explaining how a spark chamber works. 

<table width="23" cellspacing="10" style="height: 35px" border="0"><tbody><tr><td>

<img width="268" alt="" src="http://www.hep.ph.bham.ac.uk/general/outreach/SparkChamber2/sparkchamber1.gif" height="136" />
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---+++ <img width="215" alt="A cosmic ray path in the chamber" src="%PUBURL%/General/WeirdEvents/MVI_7572_0031.jpg" height="156" />
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<iframe width="300" height="200" src="http://www.youtube.com/embed/nvvW9chTxH4?rel=0" frameborder="0" allowfullscreen></iframe>
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</td></tr><tr><td> The Birmingham portable spark chamber<br /></td><td>Cosmic ray track in the chamber</td></tr></tbody></table>

---+++ 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 10<sup>6</sup> to 10<sup>20</sup> eV. Through Einstein's equation E=mc<sup>2</sup> 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 [[http://www.ep.ph.bham.ac.uk/twiki/bin/view/General/QuarkNet][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 [[https://www.ep.ph.bham.ac.uk/twiki/bin/view/General/CloudChamber][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.

%TABLE{tableborder="20" cellborder="20" cellspacing="20" cellpadding="20" databg="none" tableframe="void" tablerules="none"}%
|  <img width="200" alt="" src="https://www.ep.ph.bham.ac.uk/twiki/pub/General/SparkChamber/sparkmodule1.gif" title="perspex frame of a module." /> | <img width="200" alt="" src="https://www.ep.ph.bham.ac.uk/twiki/pub/General/SparkChamber/sparkmodule2.gif" title="aluminium plate of a module" />  |

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.

<table width="512" cellspacing="1" style="height: 202px" cellpadding="0" border="0"> <tbody><tr><td><img width="237" alt="Random" src="http://www.ep.ph.bham.ac.uk/twiki/pub/General/WeirdEvents/MVI_7571_0016.jpg" height="177" /></td><td><img width="230" alt="normal" src="http://www.ep.ph.bham.ac.uk/twiki/pub/General/WeirdEvents/MVI_7571_0029.jpg" height="177" /></td></tr> </tbody></table>

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 <br />%TABLE{ sort="on" ="1" cellpadding="0" cellspacing="0" cellborder="0" headerbg="#D5CCB1" headercolor="#666666" databg="#FAF0D4, #F3DFA8" headerrows="1" footerrows="1" }%

| *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 [[General.DeteCtors][detectors]] such as the [[General.BubbleChamber][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 [[http://public.web.cern.ch/public/en/Research/Detector-en.html][particle detectors]] with better time and spatial resolution. For example, in the 1990's, the [[http://opal.web.cern.ch/Opal/welcome.html][OPAL]] experiment at the [[http://public.web.cern.ch/public/en/research/lep-en.html][Large Electron-Positron (LEP)]] accelerator at [[http://public.web.cern.ch/public/en/About/About-en.html][CERN]] used drift chambers, while [[http://public.web.cern.ch/public/en/lhc/LHCExperiments-en.html][LHC experiments]] such as [[http://atlas.ch/][ATLAS]], [[http://cms.cern.ch][CMS]] and [[http://lhcb-public.web.cern.ch/][LHCb]] make extensive use of silicon detectors

---+ 
---+++ Gallery of videos
 We have some [[http://www.hep.ph.bham.ac.uk/general/outreach/SparkChamber2/videos][videos]] and many still images [[http://www.hep.ph.bham.ac.uk/general/outreach/SparkChamber2/events][individual event pictures]] from studies by Jessica and James.

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

---+++ %ICON{persons}% Credits
 The [[http://www.hep.ph.bham.ac.uk/general/outreach/SparkChamber2/][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
   * http://www.physics.mcgill.ca/~arobic/Sparkchamber/Spark_Chamber.html 
   * [[http://www.hep.ph.bham.ac.uk/general/outreach/SparkChamber2/][A more detailed description of the spark chamber built in Birmingham]] 
   * http://www.ep.ph.bham.ac.uk/general/outreach/DiscoveringParticles/detection/spark-chamber/
Attachments
Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
gif	sparkmodule1.gif	r1	manage	53.4 K	01 May 2012 - 09:44	UnknownUser
gif	sparkmodule2.gif	r1	manage	52.8 K	01 May 2012 - 09:44	UnknownUser
jpg	DSC00110.JPG	r1	manage	283.6 K	06 Sep 2010 - 11:15	UnknownUser	test
png	TwikiFinal2.png	r1	manage	129.0 K	26 Oct 2010 - 08:57	UnknownUser	Updated header images
Topic revision: r46 - 06 Jul 2012 - _47C_61UK_47O_61eScience_47OU_61Birmingham_47L_61ParticlePhysics_47CN_61nigel_32watson?
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