The proposed ICAL detector at INO is a large sized underground magnetized iron detector. ICAL is designed to reconstruct muon momentum using magnetic spectrometers. Energy measurement using magnets fail for muons in TeV range, since the angular deflection of the muon in the magnetic field is negligible and the muon tracks become nearly straight. A new technique for measuring the energy of muons in the TeV range is used by the CCFR neutrino detector, known as the Pair-Meter technique. This technique estimates muon energy from measurements of the energy deposited by the muon in many layers of an iron-calorimeter through e$^+$ and e$^-$ pair production. In this work we have performed Geant4 based preliminary analysis for iron plates and have demonstrated the observational feasibility of very high energy muons (1TeV-1000TeV) in a large mass underground detector operating as a pair-meter. This wide range of energy spectrum will be helpful for studying the cosmic rays in the Knee region and an understanding of the atmospheric neutrino flux for the present and future ultra high-energy atmospheric neutrino experiments.
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