GRAPES 3 Moun Telescope

For the first time in the world, researchers at the GRAPES-3 muon telescope facility in Ooty have measured the electrical potential, size and height of a thundercloud that passed overhead on December 1, 2014.

More on news

• At 1.3 gigavolts (GV), this cloud had 10 times higher potential than the previous record in a cloud.
• This is not because clouds with such high potentials are a rarity, but rather, because the methods of detection have not been successful so far.
• Clouds have negative charges along their lower side and positive charges on top and can be several kilometres thick.
• Using a computer simulation and the observed muon intensity variations, the group worked out the relationship with the electric potential of the cloud.
• Scientists calculated that the potential of the cloud they were studying was approximately 1.3 GV.
• Until now, no one has ever measured potential, size and height of a thundercloud simultaneously. That is the reason for all the excitement.

What is GRAPES 3 Experiment?

• The GRAPES-3 experiment located at Ooty in India started as a collaboration of the Tata Institute of Fundamental Research, Mumbai, India and the Osaka City University, Osaka, Japan.
• At present many institutions from India and Japan are in collaboration.
• GRAPES-3 (Gamma Ray Astronomy PeV EnergieS phase-3) is designed to study cosmic rays with an array of air shower detectors and a large area muon detector.
• It aims to probe acceleration of cosmic rays in the following four astrophysical settings. These include acceleration of particles to, (i) ~100 MeV in atmospheric electric fields through muons, (ii) ~10 GeV in Solar system through muons, (iii) ~1 PeV in our galaxy through nuclear composition of cosmic rays, (iv) ~100 EeV in nearby universe through measurement of diffuse γ-ray flux.
• The GRAPES-3 is located at N11.4o, E76.7o, and 2200m above mean sea level. The observations began with 217 plastic scintillators and a 560 m² area muon detector in 2000.
• The scintillators detect charged particles contained in extensive air showers produced by interaction of high energy cosmic rays in the atmosphere.
• At present the array is operating with ~400 scintillators that are spread over an area of 25,000 m². The energy threshold of muon detectors is 1 GeV.
  
  

  Mouns Muons and other particles are produced when cosmic rays bombard air particles surrounding the earth. The muons produced can have positive or negative charge. When a positively charged muon falls through a cloud, it loses energy. If its energy falls below 1 giga electron volt (GeV), which is the threshold of detection of the GRAPES-3 muon telescope, it goes undetected. On the contrary, a negatively charged muon gains energy when falling through the cloud and gets detected. Since there are more positive than negative muons produced in nature, the two effects don’t cancel out, and a net change in intensity is detected.