Faster than light at Kenyatta University: The Water Cerenkov Counter


Schematic diagram of the water Cerenkov counter illustrating the emission of Cerenkov radiation when a cosmic ray muon enters the steel tank filled with water.

The Department of Physics at Kenyatta University has received a donation of a water Cerenkov counter from Prof. Dr. Claus Grupen, Siegen University, Germany. The equipment comprises of a steel tank,photo-multiplier tubes, scintillation detectors and the associated electronics. This is used for the detection and measurement of cosmic ray muons using the Cerenkov radiation technique – emission of faint blue light when a charged particle travels faster than light in a medium.

The speed of light in vacuum has the value c = 3 × 108 m/s. Nothing can travel faster than this speed. However, light slows down when it travels through an optically dense medium (refractive index n > 1).The speed of light in a medium reduces to c/n. When a charged particle travels in a medium at a speedgreater than this reduced speed of light, the particle sends out electromagnetic shock waves and the medium emits faint blue light called Cerenkov radiation – named after Pavel Cerenkov (Physics Nobel Prize 1958 together with Frank and Tamm) who first observed this light experimentally.

The water Cerenkov counter is designed to detect and measure cosmic ray muons produced by the interaction of primary cosmic rays with the atmosphere. The muons travel at high speeds in the atmosphere, close to the speed of light. The steel tank of the water Cerenkov counter is filled with water during operation. The passage of cosmic ray muons at speeds greater than the speed of light in water causes the emission of the Cerenkov radiation. The faint blue light is detected by the photo-multiplier tubes in coincidence with the scintillators for processing by the electronic modules. The electronic modules include a power supply, power distributor and signal processing units – amplifier, discriminator,delays, coincidence and counter.

For the first time in Kenya and the east and central African region, students are going to observe particles – cosmic ray muons – travelling at speeds greater than that of light in a medium – water. This is a great facility that will expose our students to an important technique in experimental physics – namely the Cerenkov technique. This is widely used in world's leading experiments in particle and astro-particle physics. The quipment is currently being prepared for launch and commissioning by Prof. Olive Mugenda, Vice-Chancellor, Kenyatta University

The steel tank and photo-multiplier tubes for the water Cerenkov counter
The electronic modules for the water Cerenkov counter – power supply, power distributor and signal processing units – amplifier, discriminator, delays, coincidence and counter.

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