Department of Nuclear and Atomic Physics

Transcription

1 Department of Nuclear and Atomic Physics Welcome to the Department of Nuclear and Atomic Physics! Our department boasts of a vast and diverse canvas of experimental and theoretical research activities ranging from nuclear structure and emergent nuclear properties, ionatom collisions, molecular dynamics, intense light-matter interactions, physicsbiology interfaces, and nano-optics. The DNAP is equipped with several state-ofthe-art equipment and facilities that enable even the obscurest of studies easily accessible in the lab. We do take a lot of pride in building our instruments ourselves! Given the multitude of high-profile research publications routinely emanating from the department, you surely can expect an inspiring and a rewarding research career in the DNAP. Browse through the following pages to acquaint yourselves with our researchers and their interests. We are also at Faculty members Prof S N Mishra (Chair) Prof E Krishnakumar Prof M Krishnamurthy Prof S V K Kumar Prof G Ravindra Kumar Prof Deepak Mathur Prof Indranil Mazumdar Dr Deepankar Misra Prof Sushil Mujumdar Prof Vandana Nanal Prof Subrata Pal Prof Rudrajyoti Palit Prof R G Pillay Dr Vaibhav Prabhudesai Prof Lokesh Tribedi

2 Molecular Dynamics and Control Laboratory We aim to study the structure and dynamics of negative ion states of molecules, which are formed under low energy electron-molecule interactions. These states, which generally have lifetimes of picosecond or lower are ideal to study the mixing between electronic and nuclear degrees of freedom, conical intersections of molecular potential energy surfaces, the role of symmetry in orientation specific electron attachment, site specific cleavage of molecular bonds and control of electron induced chemistry. We probe these states by selectively preparing them at different points on their potential energy surfaces using electron beam of variable energy or in combination with coherent population transfer technique using nanosecond or femtosecond lasers. In addition to their very fundamental nature, these studies have important consequences to other areas of science, technology and medicine like planetary and space science, astrochemistry, plasma devices, nanolithography and radiation therapy. We use mass spectrometry along with a very versatile ion momentum imaging spectrometry developed by us. UV to visible tunable nanosecond lasers and a femtosecond laser system with pulse shaping and wavelength changing capability are used for population transfer to specific states. A pulsed supersonic beam, specially built effusive molecular beams, custom designed electron guns, a FTIR spectrometer and closed cycle He cryo head are other tools that we use for probing the negative ion states in gas phase as well condensed phase. Control of molecular dissociation using low energy electrons: First demonstration of selective breaking of O-H, C-H, and N-H bonds in simple organic molecules using electron energy as a control parameter. Unravelling the structure and dynamics of transient molecular negative ions: Developed the very first ion momentum imaging technique to study the dynamics of transient molecular anions formed in low energy electron molecule interaction. Catalytic action of low energy electrons: Demonstrated the catalytic action of low energy electron in chemical transformation of simple molecules by studying the resonant CO 2 formation from condensed formic acid on interaction with low energy electrons Electron interaction with crystalline v/s amorphous CO 2 films. Sub-ionization low energy electrons break DNA, & protein Momentum distribution of Cl - from Cl 2 produced by (a) 2.5eV (b) 4.5 ev and (c) 6.5 ev electron impact. The arrow indicates the direction of the electron beam. Current Members: E. Krishnakumar, S. V. K. Kumar, Vaibhav S. Prabhudesai, Vishvesh Tadsare, Krishnendu Gope, Sramana Kundu, Atiq-ur- Rahman, Yogesh Upalekar, Satej Tare, Julia Chellia, Thupten Tsering Location and Contact Details: Room W145 (Prof. E. Krishnakumar) Extn: 2502 Room W144 (Prof. S. V. K. Kumar) Extn: 2400 Room P309 (Dr. Vaibhav S. Prabhudesai) Extn: 2821 Room W140 (Lab) Extn: 2729/2401/2043; PhD positions available

3 Ultrashort Pulse High Intensity Laser Laboratory (UPHILL) Imagine the earth as a giant lens, focusing the solar energy it receives on the tip of a pencil! Such gargantuan light intensities can be reproduced in our laboratory by a femtosecond laser pulse. We work at the frontier of intense laser-matter interactions by exciting matter with intense femtosecond laser pulses of terawatt peak powers. Facilities and Equipments 20 terawatt, 30 femtosecond Ti-sapphire laser 100 terawatt, 25 femtosecond, ultrahigh contrast Ti-sapphire laser Peak intensities up to W/cm 2 that can drive electrons to relativistic speeds. State of the art 100 TW laser that can produce stellar conditions in laboratory Some recent publications Generation of picosecond-bursts of the largest terrestrial magnetic fields, nearly a billion times that of the earth, with far-reaching implications in inertial confinement fusion and laboratory astrophysics (Sandhu PRL 2002, Mondal PNAS 2012, Chatterjee PRL 2012). Table-top acceleration of neutral atoms to mega-electronvolt energies (Rajeev Nature Phys. 2013) as a result of the interaction of intense lasers with cluster nanoplasmas (Trivikram PRL 2013). Generation of hard x-ray pulses from nanostructures (Rajeev PRL 2003) and even bacterial cells (Krishnamurthy Opt. Exp. 2012). Mechanism of charge transfer in the generation of MeV neutrals Current members: G. Ravindra Kumar, M. Krishnamurthy Prashant Kumar Singh, Amitava Adak, Amit D. Lad, P. Brijesh, Malay Dalui, Sheroy Tata, Jagannath Jha, Moniruzzaman Shaikh, Deep Sarkar, Soubhik Sarkar Location and Contact details: Room B133 (Prof. G. Ravindra Kumar) Extn: 2381 Room B114 (Prof. M. Krishnamurthy) Extn: 2685 Room B136/137 (Lab) Extn: 2650 Room B122 (Office) Extn: 2745 URL: PhD positions available

4 Ion yield (arb.units) fs 22 fs fs m/q Atomic and Molecular Sciences group Our experiments focus on ultrafast phenomena in atoms, molecules, clusters in the gas-phase as well as atoms, molecules and biological entities in the condensed phase. ultrafast laser pulses.. they are on for only 5 fs: lasting for barely 2 optical cycles of 800 nm light! optical traps.. using tightly focused laser beams to create a dipole trap we work on LIVE single cells! spectroscopy integrated with traps Raman Tweezers! time-of-flight spectrometry... looking at SINGLE ions! IR & fibre lasers for photonics; nonlinear optics. We create plasma channels in condensed media for basic studies (like DNA damage caused plasma constituents) and applications, like writing waveguides and photonic structures within glasses and other bulk materials. With only 2 optical cycles, the carrier envelope phase (CEP) within a pulse becomes important: we stabilize and control it! This allows us to explore how ionization and dissociation of molecules depend on CEP opens new vistas for attosecond dynamics. [Mathur et al., Phys. Rev. Lett. 110 (2013) ] We ve shown that ultrafast molecular rearrangements, like proton migration, can occur on timescales of only one vibrational period! [Garg et al., J. Chem. Phys. 136 (2012) ] By created hot plasma in water containing DNA we ve shown that DNA damage can be induced by very low-energy electrons and by OH-radicals. [D Souza et al., Phys. Rev. Lett. 106 (2011) ] We trap healthy and malaria-infected red blood cells to probe changes in cell membrane elasticity and birefringence. [Dharmadhikari et al., J. Biomed. Opt. 18 (2013) ] We also use tightly-focused laser beams to generate nano-bubbles encrusted with carbon nanotubes (CNT); these generate broadband radiation and open new possibilities of highly-localized whitelight therapy in biomedical environments. Defeating Jahn Teller instability in a polyatomic molecule, tetramethylsilane, using intense laser pulses lasting only 5 fs, much shorter than typical vibrational times in this molecule. As a result, the TMS molecular ion, which is normally not seen, now becomes visible in our mass spectrum! [Dota et al., Phys. Rev. Lett. 108 (2012) ] a) b) c) Folding of a single red blood cell under the influence of our dipole optical trap: the folding dynamics depends on the extent of malarial infection! Current members: Deepak Mathur Aditya Dharmadhikari, Rodney Bernard, Vijay Pawaskar Location: B-124; also labs in SAMEER, IIT-B as well as at Manipal Univ. URL: Research positions available

5 Counts High-energy gamma-ray lab The major activities are centred around two broad topics. To study the real time response of the nuclear many-body system at finite temperature and angular momentum. This is achieved through exclusive measurements of high energy Giant Dipole Resonance (GDR) gamma-rays. The measurements are carried out at TIFR, Mumbai and IUAC, Delhi using state-of-the art detection facilities, namely, large volume NaI(Tl) and LaBr 3 :Ce detectors, a 4p sum-spin spectrometer, and gas-filled magnetic spectrometer. Our primary goal is to search for very rare quantum shape-phase transitions and discovering higher order giant multipole oscillations in hot nuclei. Detailed theoretical investigations of the structural properties of newly discovered light neutron-rich halo nuclei using full three-body Faddeev calculations. We search for the elusive and fascinating Efimov effect in nuclei like, 11 Li, 14 Be, 20 C, 36 Ne, 38 Mg etc. The TIFR 4p Spin-Spectrometer and high energy g-ray setup. The large volume LaBr 3 :Ce g-ray detectors 2000 E = 30 MeV Measured Simulated First measurement of the linear response of large volume LaBr 3 :Ce up to 22.5 MeV monochromatic g-rays Energy (kev) First measurement of monochromatic 30 MeV photons in the large cylindrical LaBr 3 :Ce compared with the GEANT4 simulation Current members: Indranil Mazumdar, S. Roy, P. B. Chavan, S.M. Patel Contact Details: Prof. Indranil Mazumdar indra@tifr.res.in PhD positions available

6 Accelerator-based Condensed Matter Physics We study solid state phenomenon at short length and time scales using high energy heavy-ion accelerator and hyperfine interactions as tools. A range of nuclei produced by nuclear reaction are used to probe solid state properties at a microscopic level. The spin of these nuclei precesses under the influence of the fields produced by the atoms of the solid (hyperfine fields) and modulate the γ-ray intensity emitted by them. By measuring the spin precession we obtain information regarding properties of the material. We are currently engaged in studies of narrow band phenomenon like, magnetism and Kondo interaction, correlated electrons, nano-metals, critical phenomenon, charge and spin fluctuation etc. We also perform band structure calculations to support our experiments. Measurement of nuclear moments is another area of our research activities. Magnetism and Kondo interaction in small solids. Atoms of transition and f-block elements carry magnetic moments described by Hund s rule. Solids formed from these atoms, especially the 3d metals like Cr, Mn, Fe, Co, Ni and f-block metals (rare earth and actinide) and their alloys often show long range magnetic ordering ferro-, antiferro or complex. When dilute concentrations of these atoms are placed inside a nonmagnetic solid (host), the moment may or may not survive. If it survives in an infinite solid, will it remain intact in small solids (nano- metals)? For the last few years we have been asking these questions and carrying out experimental and theoretical studies to find some answers. For example, using hyperfine interaction technique we have shown conclusive evidence that lattice size plays a decisive role not only on the formation of local moment but also on the Kondo interaction which is directly linked to spin fluctuations. Evidence for size induced localization of 4f electrons have also been observed in strongly correlated electron systems. Spin precession of 54Fe nuclei in nano-nb Recent Publications: Phys. Rev. Lett., 85, 1978 (2000); Phys. Rev. Lett., 105, (2010); Phys. Rev. B, 71, (2005); Phys. Rev. B, 87, (2013) A 7T; K experimental set up for accelerator based hyperfine interaction studies. Current Members: S. N. Mishra, S K Mohanta, S M Davane Location and Contact Details: Room P114. (Lab) - Extn: 2344 Prof. S. N. Mishra mishra@tifr.res.in Ph.D positions available

7 First Hit Accelerator-based Atomic Physics Laboratory We, at the Accelerator Based Atomic Physics lab, mostly focus on the study of Interaction of highly charged ions and fast electrons with simple atomic and molecular systems like H, He, H 2, complex molecular systems like C 60 and large bio-molecules. We address questions related to the quantum mechanical interference in ionization of molecules like H 2, N 2 and O 2 etc. Also we study the collective behaviour of electrons in large molecules like C 60. Recently, we have also been interested in the study of fragmentation dynamics of small di- and tri-atomic molecular systems in collisions with highly charged ions from ECRIA. We carry out our experiments with slow and highly charged ion beams from an ECR based ion accelerator facility (ECRIA) as well as fast highly charged ion beams from the BARC-TIFR 14 MV tandem Pelletron-Linac accelerator facility at TIFR. We use different measurement techniques such as electron spectroscopy, time-of-flight mass spectrometry and high resolution x-ray spectrometry. Recently we have developed a Recoil Ion Momentum Spectrometer (RIMS) to study the fragmentation dynamics of small molecular systems. Radiative decay of auto ionizing doubly excited states in He like highly charged ions. First observation of the fluorescence-active doubly excited states in He-like Si, S, and Cl ions measured using a bent crystal x-ray spectrometer. Total ionization cross section of Uracil in collisions with highly charged ions from ECRIA and Pelletron. A comparative study of total ionization cross sections measured over a wide range of energies which covers the Bragg peak region in hadron therapy. ECR based Ion Accelerator at TIFR Second Hit Fragmentation of N 2 : Momentum Distribution Current Members Lokesh C. Tribedi, Deepankar Misra, W. A. Fernandes, K. V. Thulasiram, Nilesh Mhatre, S. Manjrekar, A. H. Kelkar, M. Rundhe, S. Nandi, A. Khan, S. Biswas, S. Bhattacharjee Location and Contact Details: Room: PG-06/W-134 Extn: 2465 Prof. Lokesh Tribedi lokesh@tifr.res.in; Dr. Deepankar Misra dmisra@tifr.res.in URL: Ph.D positions available

8 Nano-optics and Mesoscopic Optics Laboratory We study the transport of optical waves through media which have a variation in the refractive index over length scales comparable to the wavelength. These experiments deal with visible or near infrared radiation. The structure can be ordered, disordered or even a combination of both. Given that light can experience amplification and nonlinear effects, fascinating phenomena, hitherto unpredicted by theory, are unravelled in these systems. Sophisticated laser sources, ultrasensitive detectors, and nanofabrication techniques makes it possible to observe even the most elusive of phenomena! Anderson localization: A most exotic optical phenomenon, realized by disorder-induced interferences, directly observed in the lab. Anderson-localized mode (exponentially decaying wings) in an array of amplifying microresonators. The lab is equipped with several laser sources, sensitive spectral and temporal detectors at various wavelengths, sample making facilities etc. Thin metal-film plasmonic media are fabricated inhouse, while nanostructured lowdimensional semiconductor membranes are obtained from collaborators. Sub-wavelength topographic and optical measurements can be made using an indigenous near-field scanning optical microscope. Schematic of a near-field measurement. Simultaneous topographic and near-field optical measurement of a plasmonic nanowire, showing decaying fronts of intensity. Exponentially tempered Levy sums, Phys. Rev. Lett., (2015) Super critical angle fluorescence, App. Opt., (2015) Super reflection from a random laser, Phys. Rev. A (2014) Gap state random lasing, Phys. Rev. Lett., (2013) Current Members: Sushil Mujumdar, Randhir Kumar, Tajinder Singh, Shadak Alee, Arpit Rawankar, Sreeman Kumar. Location and Contact Details: Room AB101 (Lab) - Extn Room P109 (Prof. Sushil Mujumdar) - Extn 2459 Prof. Sushil Mujumdar mujumdar@tifr.res.in URL: Ph.D positions available

9 Nuclear Physics Laboratory Search for Neutrinoless Double Beta Decay (0νββ): The mass and nature of neutrinos play an important role in theories beyond the standard model. Presently, 0νββ, which can occur if neutrinos have mass and are their own antiparticles, is perhaps the only experiment that can tell us whether the neutrino is a Dirac or a Majorana particle. Further, 0νββ can provide the information on absolute effective mass of the neutrinos. In India, a feasibility study to search for 0νββ in 124 Sn has been initiated. The TIN.TIN experiment (The INdia s TIN detector) will be housed at The India-based Neutrino Observatory (INO), an underground facility with ~1000 m rock cover all around. Development of cryogenic bolometer of 124 Sn operating around 10 mk is in progress Nuclear structure studies with GDR: The Giant Dipole Resonance (GDR) gamma rays provide a very unique probe to study structure of excited nuclei at high angular momentum. Study of the shape evolution of nuclei with angular momentum in A~160 region, has been the main focus in recent years. The group is actively engaged in the development of a novel detector array comprising LaBr3(Ce)+ NaI Phoswich as a part of PARIS (Photon Array for studies with Radioactive Ion and Stable beams) collaboration, for studying GDR in highly unstable nuclei. Energy spectra with 241 Am- 9 Be source with PARIS prototype detector Reactions with Weakly Bound nuclei: Reactions with weakly bound stable and unstable nuclei provide opportunities to explore unusual features of nuclei like halo/skin structures, extended shapes and large breakup probabilities. We study this with experiments using stable beams like 6,7 Li at PLF, Mumbai and using Radioactive ion beams like 6,8 He at GANIL (France). Current Members: V. Nanal, R.G. Pillay Chandan Ghosh, Abhijit Garai, Harisree, Ghanshyam Gupta and Balaram Dey Location and Contact Details: Room P106 (Lab) - Extn: 2511/2333 Prof. V. Nanal nanal@tifr.res.in Prof. R. G. Pillay pillay@tifr.res.in Ph.D positions available

10 Theoretical Physics The theoretical physics program focuses on the development of fundamental and phenomenological models to identify various new phases of dense nuclear matter with an emphasis to study the:(i) Equation of state of neutron-rich asymmetric nuclear matter formed at intermediate energy heavy ion collisions,(ii) Properties of the novel state of matter viz. the Quark-Gluon Plasma formed at ultra-relativistic energy heavy ion collisions at RHIC/BNL and LHC/CERN. Density dependence of symmetry energy: The density dependence of asymmetry energy has wide-ranging implications for the physics with radioactive ion beams to neutron stars. However, it is poorly known. Our group has developed relativistic mean-field and transport models that could constrain the asymmetry energy over wide density range by comparison with measurements of: neutron skin of various nuclei at subsaturation nuclear densities and mass-radius of neutrons stars at supranormal densities. The Quark-Gluon Plasma: In ultra-relativistic heavy-ion collisions high temperature and density are reached. The quarks and gluons confined within the atomic nuclei are liberated to form the Quark- Gluon Plasma (QGP). Our group has developed very sophisticated transport models that encompasses all stages of the collision. Within this model, we have shown that the QGP formed at RHIC and LHC is a (strongly coupled) near perfect fluid that has large anisotropic collective flow and long range dihadron correlations. We have also formulated relativistic dissipative fluid dynamics from kinetic theory which could explain the observed femtoscopic radii of emerging particles from QGP. Nuclear Matter Phase diagram Current Members: Subrata Pal, Sreemoyee Sarkar, Ananta Mishra, Chandrodoy Chattopadhyay Room P309 (Prof. Subrata Pal) Extn 2820 Prof. Subrata Pal spal@tifr.res.in Ph.D positions available

11 Discrete Gamma Spectroscopy of Atomic Nuclei We investigate the low energy response of atomic nuclei to rotational stress using a powerful femtoscope consisting of segmented high purity Germanium detectors. The nuclei are prepared in excited states (with rotations per second) using energetic beams from the heavy ion accelerators. The fast rotating nucleus decays to its ground state, through the intermediate excited states, emitting copious gamma rays that are measured by the femtoscope. By casting the nuclei to various shapes and studying their decays, the emergent properties of complex nuclear many-body system are elucidated. The Quest How does a simple pattern emerge in excitation of complex nuclei? How are the patterns of the excited states related with symmetry and shape of nuclei? What are the different correlations present in the nuclei? Members in the group are involved in the simulation, design and testing of state-of-the-art radiation detectors required for the investigation of nuclear structure. The young investigators in the group get the opportunities to work on advanced digital signal processing scheme and data analysis. Current Members: Rudrajyoti Palit B.S. Naidu, R. Donthi, S. Jadhav, S. Saha, J. Sethi, S. Biswas, D. Choudhury, P. Singh Location and Contact Details: Room: P309 (Prof. Rudrajyoti Palit) Extn 2562 URL: PhD positions available

12 Facilities The Pelletron LINAC facility, a joint venture of TIFR and BARC, has been a major research centre for the heavy ion accelerator based research in India. The Pelletron accelerator was inaugurated on 30th December 1988 and marked an important milestone in nuclear physics research in India. The facility was augmented in July 2007 with the indigenously developed superconducting LINAC booster to enhance the energy of the accelerated beams. A number of state-of-the-art experimental facilities have been developed at this centre to pursue frontier research in nuclear, atomic, condensed matter and bio-environmental physics. Experiment hall LINAC hall Joint TIFR-BARC Facility