GRAPES 3 EXPERIMENT

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Context

• The GRAPES-3 experiment has discovered a new feature in the cosmic-ray proton spectrum at about 166 tera-electron-volt (TeV) energy.
• The observed feature suggests a potential re-evaluation of our understanding of cosmic-ray sources, acceleration mechanisms, and their propagation within our galaxy.

Details

• Cosmic rays, discovered over a century ago, are the most energetic particles observed in the universe.
• They continuously bombard Earth's atmosphere from outer space, displaying a uniform distribution from all directions.
• Upon entering the atmosphere, cosmic rays initiate a cascade of particles, including electrons, photons, muons, protons, and neutrons, which travel to Earth's surface at speeds close to that of light.
• The observation of cosmic rays spans a wide energy spectrum, ranging from 10^8 to 10^20 electron volts (eV), with the flux decreasing steeply with increasing energy, following a power law distribution.
• The "Knee," a notable deviation in the cosmic-ray proton spectrum around 3 peta-electron-volts (PeV), has been recognized for nearly seven decades, indicating the presumed upper limit of energy for cosmic-ray acceleration within Galactic sources.
• However, the recent revelation by the GRAPES-3 experiment unveils a new feature in the cosmic-ray spectrum exceeding 100 TeV but remaining below the Knee.
• This observation challenges the previously accepted hypothesis proposing a single power law representation of the spectrum up to the Knee energy threshold, prompting a re-evaluation of existing theoretical models.

About GRAPES-3

• The GRAPES-3 experiment, also known as the Gamma Ray Astronomy PeV EnergieS phase-3, is a collaborative effort between the Indian Tata Institute of Fundamental Research, the Japanese Osaka City University, and the Japanese Nagoya Women's University.
• Located in Ooty, GRAPES-3 aims to study cosmic rays using an array of air shower detectors and a large-area muon detector.

Objectives:

• Acceleration of Cosmic Rays: Investigate the origin, acceleration, and propagation of cosmic rays with energies exceeding 10^14 eV in the galaxy and beyond.
• Knee in Energy Spectrum: Determine the existence and characteristics of the "knee" in the energy spectrum of cosmic rays.
• High-Energy Cosmic Rays: Study the production and acceleration mechanisms of the highest energy cosmic rays, reaching energies around 10^20 eV, in the universe.
• Gamma-Ray Astronomy: Explore the astronomy of multi-TeV gamma rays emitted from neutron stars and other compact objects.
• Solar Effects: Investigate the Sun as the closest astrophysical object, its role as an accelerator of energetic particles, and its effects on Earth.

Overview:

• The history of cosmic ray research in Ooty dates back to 1955 when B. V. Sreekantan initiated the first experiments using cloud chambers at the Cosmic Ray Laboratory (CRL).
• Over the years, various experiments were conducted at the CRL, including studies on high-energy interactions, extensive air showers, and high-energy nuclear interactions.
• The GRAPES-1 experiment was subsequently upgraded to GRAPES-2 before the establishment of GRAPES-3 at a new site called the RAC site, 8 km away from the old site, due to technical and administrative constraints.
• GRAPES-3 currently operates with approximately 400 plastic scintillator detectors, each covering an area of 1 m^2, with a separation of 8 meters between detectors.
• The experiment aims to record the density and arrival time of particles in cosmic ray showers continuously.
• GRAPES-3 boasts the highest density conventional Extensive Air Shower (EAS) array globally and includes a massive 560 m^2 area tracking muon detector, making it the largest area tracking detector in the world.

Conclusion

In summary, the GRAPES-3 experiment represents a significant endeavor in the field of cosmic ray research, aiming to unravel the mysteries surrounding the origin, acceleration, and properties of cosmic rays across different astrophysical settings.

PRACTICE QUESTION Q. Discuss the significance of the GRAPES-3 experiment conducted by the Tata Institute of Fundamental Research in advancing our understanding of cosmic-ray physics. (250 Words)