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What is a Spark Chamber?

A spark chamber is a stack of conducting plates separated by a gas gap. When an energetic ionising particle passes through the device, a control circuit applies a high voltage between each pair of neighbouring plates. The voltage generates a spark between each of the plates. The spark prefers to form at the spot where the particle passed through, due to the ionisation trail left by the particle. The path of the traversing particle is thus revealed by the array or line of sparks, which may be seen or photographed through the side of the device. They hey-day of the spark chamber as a research tool for detecting high energy cosmic rays came to an end in the 1960s when it was replaced by better techniques (drift chambers, bubble chambers, silicon detectors etc). Nevertheless, spark chambers are still designed for museums and used in education as they are an exciting, visually direct and simple way of demonstrating cosmic rays to an audience.

Find pictures in the Gallery

Sparks in the Birmingham spark chamber on which ours will be based The Birmingham spark chamber on which ours will be based

Intended impact

When a member of the public first sees a spark chamber in action, they are usually astonished. Although they may have heard of "Cosmic Rays" and "sub-atomic particles", they usually believe that these are ephemeral things that have nothing to do with reality.

A working spark chamber demolishes this notion instantly, demonstrating that each person is being "stabbed" in every minute of every day by a "cosmic rain" made of the same subatomic particles we observe in CERN. Adults and school children alike are astounded to learn that some of the particles generating the rays come from cataclysmic events in or outside the galaxy that are not yet understood by the science of today.

In two minutes, this piece of apparatus can:

(1) demonstrate the "reality" of particle physics,

(2) show the existence of sub-atomic particles,

(3) visualise real Cosmic Rays in real time,

(4) link particle physics "on earth" to astrophysics and astronomy "in space",

(5) excite people with the revelation that the source/existence of the highest energy cosmic rays is still a major topic of cutting-edge research, and remains largely unknown,

(6) encourage further discussion between demonstrators and the public on the work of CERN, astrophysicists and other STFC research areas.

Phases of project development

(1) The first objectve is to evaluate the best design for the chamber. To first order we aim to build a transportable spark-chamber identical to the one built and run successfully by Birmingham University for almost ten years (also supported by Small Award Funding). Their chamber has seen much use in the midlands. We hope to be able to make use of advances in technology since the Birmingam chamber was built to reduce weight, reliance on HV, improve reliability, and perhaps reduce cost. Some test pieces will have to be built in order to determine the optimal design - and large fraction of the money requested accounts for this. CHaOS and the Cambridge HEP group will work together on the design at all times to ensure the transportability and safety of the chamber.

(2) Having finalized the chamber design, we will build it.

(3) Exploitation phase: Once built, the chamber will be used in four areas:

(3a) The chamber will become a part of the CHaOS Road-Show (a multi-week summer event) and other CHaOS events throughout the year will take the chamber into schools, town halls and county shows around the country. To give an example of audience numbers: the 2007 "Road-Show" reached over 4000 people, and was accomplished over 20 days of demonstrating over a 4 week tour, and exhibited in Devon, Milton Keynes, Oxford, Nottinghamshire, Suffolk, Monmouthshire, Herefordshire and Lincolnshire. The annual "Crash Bang Squelch" event in Cambridge draws in a further crowd of 1000.

(3b) The chamber will form the centre-piece of the Particle Physics contribution to "The Physics at Work outreach programme" which gains an annual attendance of 2100 school children, as well as any other smaller outreach days.

(3c) The chamber will make its way to schools as a demo to support "schools talks" requested of suitably trained members of the Particle Physics staff.


The spark chamber itself will (subject to changes in the design that may be determined during the development phase) be modelled on the one successfully operated by Birmingham University. This will make it likely to be a sandwich of aluminuim plates held at alternating high voltage, separated by gaps (in which the sparks will appear) containing a re-fillable Helium-Neon gas mixture. The gas to be retained behind transparent windows also acting as insualtors for the aluminum plates. Above and below, scintilators and photomultipliers or silicon avalance photo diodes (APDs) to trigger the HV supply to the plates on passage of a cosmic ray. The chamber and any necessary electrical apparatus to be contained within a Faraday cage to reduce unwanted EM-interference, and the whole to be sufficiently enclosed/insulated such that the unit presents no HV risk to viewers or demonstrators. The unit to be constructed to survive up to two weeks off-site in a "back of the van" environment were access to maintenance facilities will be limited. This will place particular constraints on mechanical integrity, weight, packaging, and how to ensure gas-tightness or refillability. Once built the project will progress to an exploitation phase where the emphasis will be on providing support, such as (but not limited to): maintenance, availability of consumables (eg gases), training for demonstrators, and production of associated publicity material, eg posters, which may be used to accompany the unit.

Who is funding the programme? Can students be funded?

The Science and Technology Facilities Council (STFC) have agreed to fund the initial equipment, travel and consumables costs associated with the building of a Transportable Spark Chamber for the East of England. The STFC funding does not (regrettably!) stretch to include susbsistence for summer students and similar. Prospective summer students will therefore have to investigate other sources of maintenace, such as College funding, if they want to be paid the going rate of 200 pounds per week. Fortunately, any such funding a student does find will be matched by a Newton Trust bursary up to a total of 1000 pounds. In other words, if a student find a college that will pay then 100 pounds per week, the Newton trust will match that amount with their own 100 pounds per week, and will continue to match that funding for up to ten weeks. (see details in the Undergraduate Research Opportunities Programme (UROP)) The STFC grant was made under the Small Awards Scheme which funds projects related to the public understanding of science and outreach.

Who will build/operate the Spark Chamber?

The Chamber will be built and operated by a joint venture between the High Energy Physics group of the Cavendish Laboratory of the University of Cambridge and the CHaOS Science Roadshow (Cambrige Hands-On Science Roadshow).

The Particle Physics group will supply the know-how, workshops, technicians, experience with HV safety, etc, to build the chamber, and is visited by 2100 school children annually in the "Physics at Work" events, thus guaranteeing at least this many visitors per year.

CHaOS has nearly ten years worth of experience of how to take scientific exhibits into schools, how to ensure safety, and most importantly knows how to construct something that can survive two weeks transport in the back of a van during a "CHaOS road show". Last year's "road show" visited eight counties and reach in excess of 4000 people.

Dr Lester (Cavendish Particle Physics) and Mr Ansell (CHaOS) will jointly "steer" the project over its lifetime. In addition many other people will be involved in a variety of stages: providing advice, building it, demonstrating it, and providing training in demonsration.

Dr Lester will co-ordinate physics input to the design, liaise with experts in the Birmingham group, provide workshop space in which to build / store the detector, access to lab infrastructure and access to the experienced electrical/mechanical technicians and/or willing student labour. He also will demonstrate the chamber in Phyiscs at Work days and on his own schools visits, and will train others in the use of the chamber. As an active member of the ATLAS experiment at the LHC he will use the interest which spark chamber generates among members of the public to promote further discussion on particle physics, leading to further discussion of ATLAS and other LHC experiments.

Mr Ansell will provide input to the design, particularly regarding safety, tranportability and accessability. He will ensure that the chamber forms a key part of CHaOS events like the "road show" which will ensure the chamber gets to other parts of the country regularly. He will provide access to willing student demonstrators and science communicators, and provide training services to them. He may also put together smaller exhibits (e.g. geiger counter + natural sources of radioactivity) that would complement the chamber and allow discusision of one to lead into the other - relating radio activity, nuclear physics and particle physics.

Staff in the Cavendish will provide mechanical and electrical skills.

Students, members of staff and members of CHaOS will contribute to research, design, running, demonstrating and building the chamber.

Contact details

Dr Christopher Lester (for Cambridge University High Energy Physics).
David Ansell (for the CHaOS Science Roadshow and The Naked Scientist).
Dr Bart Hommels (for Cambridge University High Energy Physics).
Maurice Goodrick (for Cambridge University High Energy Physics).

Outreach / publicity

Once the chamber is complete Mr Anselll, in his role as a presenter of the "Naked Scientists Radio Show", will produce a short radio programme on the chamber (and an associated podcast). A typical "Naked Scientist" podcast is downloaded by 40,000 people, and the radio programme audience-size is in the region of 100,000.

A web-site to go with the chamber will be produced which would (1) inform other potential science communicators of a project that could be within their reach, and (2) communicate the aims of the project listed in section "9" above to audience members who might never see the chamber in person.

Members of the local and/or national press are often invited to key outreach events at which the chamber will be present.

We do not expect to have to advertize the chamber *itself* within the target audience in order to gain audience numbers: the Physics at Work events and CHaOS "road-shows" are usually over-subscribed or fully booked, having been advertised by other organisations or by word of mouth via previous years.