India-based Neutrino Observatory (INO)

The India-based Neutrino Observatory (INO) is a proposed underground research facility dedicated to the study of neutrinos, one of the most fundamental and elusive particles in physics. Located in the Bodi West Hills near Theni district in Tamil Nadu, the project represents one of India’s most ambitious scientific undertakings in the field of high-energy physics. It aims to advance the understanding of neutrino properties, their interactions with matter, and their role in the evolution of the universe.

Background and Scientific Rationale

Neutrinos are electrically neutral, nearly massless subatomic particles that interact only through weak nuclear forces and gravity. They are produced in vast quantities in nuclear reactions such as those occurring in the Sun, stars, supernovae, and nuclear reactors. Despite their abundance, neutrinos are extremely difficult to detect because they pass through matter almost undisturbed.
The study of neutrinos is crucial for understanding key questions in particle physics and cosmology, such as:

• Why neutrinos have mass, contrary to predictions of the original Standard Model.
• The role of neutrinos in the evolution of the universe.
• Matter–antimatter asymmetry and its implications for the existence of the universe.

India has a historical connection with neutrino research: the first detection of atmospheric neutrinos occurred in 1965 at the Kolar Gold Fields (KGF) experiment, making India one of the earliest contributors to neutrino physics. The closure of KGF in the 1990s prompted the scientific community to seek a new site for continued research, which led to the proposal of the INO project in the early 2000s.

Location and Design of the Observatory

The chosen site for INO lies near Pottipuram village in Bodi West Hills, approximately 1,200 metres underground, beneath a solid rock cover. The underground setting is essential to shield the detector from cosmic radiation and other background noise, allowing for the detection of rare neutrino interactions.
The main facility will include:

• Underground Laboratory Complex: Situated under a 1.3 km high mountain, accessed via a horizontal tunnel approximately 2 km long.
• Surface Laboratory and Administrative Complex: Located nearby for data processing, storage, and technical operations.
• Detector Cavern: The central hall housing the Iron Calorimeter (ICAL) detector, which is the core experimental apparatus of the observatory.

The Iron Calorimeter (ICAL) Detector

The ICAL detector is designed to study atmospheric neutrinos produced when cosmic rays interact with the Earth’s atmosphere. It consists of three modules, each measuring about 16 metres in height, 16 metres in width, and 48 metres in length.
Key features of the detector include:

• Magnetised Iron Plates: About 50,000 tonnes of iron stacked in layers to create a magnetic field that allows the distinction between neutrinos and antineutrinos.
• Resistive Plate Chambers (RPCs): Sensitive detector units interleaved between iron plates to record the passage of charged particles produced during neutrino interactions.
• Precision Measurement Capability: Designed to track and measure the momentum and charge of muons, which are secondary particles produced by neutrino interactions.

The ICAL detector will primarily investigate the neutrino mass hierarchy the ordering of neutrino masses which remains one of the most significant unsolved problems in modern particle physics.

Objectives and Research Focus

The India-based Neutrino Observatory aims to address several scientific objectives:

• Determine Neutrino Mass Hierarchy: Understanding whether the three known neutrino types (electron, muon, and tau neutrinos) follow a normal or inverted mass order.
• Study of Atmospheric Neutrinos: Analysing the properties and oscillations of neutrinos as they travel through the Earth.
• Magnetic Effects on Neutrino Oscillation: Investigating how magnetic fields influence neutrino trajectories and properties.
• Support for Future Experiments: Providing crucial data that can complement results from other international neutrino observatories, such as Japan’s Super-Kamiokande and the United States’ DUNE project.

In addition to neutrino studies, the INO facility could also be used for research in geophysics, cosmic ray physics, and radiation shielding technology.

Institutional Collaboration and Management

The project is coordinated by the Institute of Mathematical Sciences (IMSc), Chennai, with participation from more than twenty Indian institutions, including the Tata Institute of Fundamental Research (TIFR), Mumbai, the Bhabha Atomic Research Centre (BARC), Mumbai, and several Indian Institutes of Technology (IITs).
The Department of Atomic Energy (DAE) and the Department of Science and Technology (DST), Government of India, are the primary funding agencies. The INO collaboration includes over 100 scientists from various disciplines, ranging from particle physics and materials science to computer simulation and electronics engineering.

Challenges and Controversies

Since its proposal, the INO project has encountered several delays and controversies, primarily due to environmental and administrative concerns.
Key challenges include:

• Environmental Clearance: Concerns have been raised regarding potential ecological impacts on the Western Ghats, a recognised biodiversity hotspot. The requirement for multiple environmental and forest clearances has led to protracted legal and bureaucratic delays.
• Local Opposition: Certain groups and local residents have expressed apprehension about tunnelling operations and radiation risks, despite official clarifications that the observatory poses no nuclear hazard.
• Regulatory Delays: Shifting environmental policies and state-level permissions have repeatedly stalled construction work since approval was first granted in 2009.

Despite these hurdles, the scientific community continues to advocate for the project, emphasising its importance for India’s advancement in fundamental physics research.

International Context and Comparison

Globally, neutrino observatories such as Super-Kamiokande in Japan, Sudbury Neutrino Observatory (SNO) in Canada, and IceCube in Antarctica have made significant contributions to neutrino physics, including the discovery of neutrino oscillation a phenomenon that confirms neutrinos have mass.
The INO, when operational, would join this elite group, providing complementary data due to its geographical location. Its position near the equator allows unique observation angles for atmospheric neutrinos traversing different Earth path lengths, offering advantages in studying oscillation parameters.

Scientific and National Significance

The establishment of the India-based Neutrino Observatory carries immense significance for Indian and global science:

• Scientific Leadership: It would re-establish India as a major contributor to experimental particle physics, building on the legacy of Kolar Gold Fields.
• Technological Advancement: The project promotes the development of indigenous technologies in areas such as detector fabrication, data acquisition systems, and large-scale magnet design.
• Capacity Building: INO is expected to nurture a new generation of Indian researchers, engineers, and technicians through training and academic collaboration.
• Strategic Value: By fostering expertise in advanced instrumentation, computation, and data analysis, the project enhances India’s capacity to participate in global scientific collaborations.

When completed, the INO will serve as a landmark facility for the exploration of fundamental particles, enriching scientific understanding of the universe’s most basic constituents.