Dr. Raju Kumar
Post-doctoral Researcher
University of Oxford, United Kingdom
Current research
Multi-Spectroscopy/Microscopy and Luminescence Physics
Low-temperature spectroscopic studies of natural aluminosilicates (feldspar, KAlSi3O8), quartz, Al2O3:C, Mg and Mn2+ doped metal oxides. Investigations on feldspar reveal
An excited state in the conduction band (CB).
Before trapping, electrons undergo thermalisation into the band-tail states.
Occurrence of the same defect in different crystal fields; this was further supported by scanning electron microscope- cathodoluminescence (SEM-CL) based imaging.
Two electron acceptors (traps) in close proximity can interact and compete.
Nuclear Physics & Quantum Imaging Radiation Dosimetry (QIRD)
A timepix detector can measure the energy of each interacting quantum of ionizing radiation and is even capable of distinguishing between them from their track/footprint visualization.
Different types of particles/rays interact with the chip differently and, thereby, leave distinguishable footprints.
The higher the energy, the higher would be the ToT (Time over Threshold).
Cosmic makes straight marks/paths on the chip.
Through energy-ToT calibration, one can find the energy of unknown interacting particles.
Evaluating energy of the particle can be used to track the radionuclide from which it emitted.
Gamma spectrometry to determine K, U, and Th concentrations.
Luminescence Dosimetry
It is a method to quantify the absorbed dose of radiation in a dosimetric material. Here is how?
Some defects (naturally or synthetically doped) form metastable states by capturing electrons or holes upon interaction with ionizing radiation.
The concentration of these metastable states can be measured in terms of luminescence. With the help of calibration, the resulting luminescence intensity can be turned into the absorbed dose.
The figure shows radio-photoluminescence (RPL) signals/spectra originating from a natural dosimeter for increasing x-ray exposure times.
Luminescence Dating
This is an application of Luminescence Dosimetry, widely used in geo-archaeological sciences to study the past.
Optically stimulated luminescence (OSL) techniques are widely used.
Preferred materials are quartz and feldspar.
Other techniques using feldspar are Infrared photoluminescence (IRPL), Infrared radioluminescence (IR-RL), and Thermoluminescence (TL).
Can be used to study past up to 0.5 Ma.
Latest Publications
Site-selective mapping of metastable states using electron-beam induced luminescence microscopy
Metastable states created by electron or hole capture in crystal defects are widely used in dosimetry and photonic applications. Feldspar, the most abundant mineral in the Earth’s crust (> 50%), generates metastable states with lifetimes of millions of years upon exposure to ionizing radiation....Access the full article from here.
Site-selective characterisation of electron trapping centres in relation to chemistry, structural state and mineral phases present in single crystal alkali feldspars
Feldspars are ubiquitous natural dosimeters widely used in luminescence dating.... Access the full article from here.