Inter University Accelerator Center

Delhi, India

Inter University Accelerator Center

Delhi, India
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Sharma P.,Inter University Accelerator Center | Nandi T.,Inter University Accelerator Center
Physics of Plasmas | Year: 2016

Charge state evolution of the energetic projectile ions during the passage through thin carbon foils has been revisited using the X-ray spectroscopy technique. Contributions from the bulk and the solid surface in the charge changing processes have been segregated by measuring the charge state distribution of the projectile ions in the bulk of the target during the ion-solid interaction. Interestingly, the charge state distribution measured in the bulk exhibits Lorentzian profile in contrast to the well-known Gaussian structure observed using the electromagnetic methods and the theoretical predictions. The occurrence of such behavior is a direct consequence of the imbalance between charge changing processes, which has been seen in various cases of the laboratory plasma. It suggests that the ion-solid collisions constitute high-density, localized plasma in the bulk of the solid target, called the beam-foil plasma. This condensed beam-foil plasma is similar to the high-density solar and stellar plasma which may have practical implementations in various fields, in particular, plasma physics and nuclear astrophysics. The present work suggests further modification in the theoretical charge state distribution calculations by incorporating the plasma coupling effects during the ion-solid interactions. Moreover, the multi-electron capture from the target exit surface has been confirmed through comparison between experimentally measured and theoretically predicted values of the mean charge state of the projectile ions. © 2016 Author(s).

Pullanhiotan S.,Inter University Accelerator Center
Journal of Physics: Conference Series | Year: 2016

Several properties observed in heavy ion induced fission led to the conclusion that fission is not always originated from fully equilibrated compound nucleus. Soon after the collision of two nuclei, it forms a di-nuclear system than can fission before a compound nucleus is formed. This process termed quasi-fission is a major hurdle to the formation of heavier elements by fusion. Fission originated before complete equilibration showed anomalously large angular anisotropy and mass distribution wider than what is expected from compound nucleus fission. The standard statistical model fails to predict the outcome of quasi-fission and currently no dynamical model is fully developed to predict all the features of quasi-fission. Though much progress has been made in recent times, a full understanding of the fission dynamics is still missing. Experiments identifying the influence of entrance channel parameters on dynamics of fusion-fission showed contrasting results. At IUAC accelerator facility many experiments have been performed to make a systematic study of fission dynamics using mass distribution, angular distribution and neutron multiplicity measurements in mass region around A ∼ 200. Recent measurement on mass distribution of fission fragment from reaction 19 F +206,208 Pb around fusion barrier energy showed the influence of multi-mode fission in enhancing the mass variance at low excitation energy. In this talk I will present some of these results. © Published under licence by IOP Publishing Ltd.

Sharma P.,Inter University Accelerator Center
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2016

A theoretical study on the shaking process accompanying swift heavy ion-atom collisions is presented. Using the nonrelativistic hydrogenic wavefunctions, analytical expressions for the survival and shakeup/shakedown probability have been derived for the K-,L- and M-shell electrons of hydrogen-like atomic systems. The resulting expressions are used to calculate the shaking and shakeup/shakedown probability in the typical case of the recoiling nucleus of the multielectron (63Cu+) and hydrogen-like (63Cu28+) atomic systems, respectively. Interestingly, it is found that the requirement of the high colliding energy for the suddenness of the perturbation, can well fulfill the limiting condition of the necessary nuclear recoil for finite electron shaking during the ion-atom collisions. Further, the dependence of the shaking probability on atomic number has been depicted, and it has emerged that for a particular value of the recoil energy per nucleon, the shaking processes are more significant in the lower atomic number region. © 2017 Elsevier B.V.

Kumar S.,Inter University Accelerator Center
6th International Particle Accelerator Conference, IPAC 2015 | Year: 2015

High Current Injector (HCI) is an alternate injector to superconducting linac at IUAC in addition to pelletron. It consists mainly of high temperature superconducting ECR ion source (PKDELIS), radio frequency quadrupole (RFQ) and a drift tube linac (DTL). The ions of mass to charge (A/q) ratio of 6 are analysed initially and accelerated through RFQ and DTL to a total energy of 1.8 MeV/u. The different energy regimes connecting the accelerating stages are named as low, medium and high energy beam transport section (LEBT, MEBT and HEBT). The energy spread of beam increases from 0.02% at ECR source to 0.5% at the LINAC entrance. An ion beam of normalized transverse and longitudinal emittance of 0.3 pi mm-mrad and 3 keV/u-ns has been considered at the start for the simulation of ion optics using TRACEWIN code. The whole beam transport system has been designed using GICOSY, TRANSPORT and TRACE 3D codes piecewise and TRACEWIN code is used to simulate whole ion optics from start to end including acceleration stages such as RFQ and DTL. Simulation results shows that beam can be injected through LEBT, MEBT and HEBT into LINAC without significant emittance growth and beam loss. Copyright © 2015 CC-BY-3.0 and by the respective authors.

Som S.,Indian School of Mines | Sharma S.K.,Indian School of Mines | Lochab S.P.,Inter University Accelerator Center
Materials Research Bulletin | Year: 2013

This paper reports the structural and optical modifications of Y 2O3:Eu3+ nanophosphor induced by 150 MeV Ni7+ swift heavy ions (SHI) in the fluence range 1 × 10 11 to 1 × 1013 ions/cm2. The XRD, TEM and FTIR studies confirm the loss of crystallinity of the nanophosphors after ion irradiation. Diffuse reflectance spectrum shows a blue shift in the absorption band for SHI induced nanophosphors. An increase in the intensity of photoluminescence peaks without any shift in the peak positions was observed. © 2012 Elsevier Ltd.

Mal S.,North Carolina State University | Nori S.,North Carolina State University | Narayan J.,North Carolina State University | Prater J.T.,U.S. Army | Avasthi D.K.,Inter University Accelerator Center
Acta Materialia | Year: 2013

We have introduced defects in ZnO epitaxial thin films by swift heavy 107Ag9+ ion irradiation and investigated systematically their magnetic, electrical and optical properties. Oxygen annealed ZnO films are epitaxial single crystals that exhibit no long-range magnetic order. However, in this paper it is shown that room-temperature ferromagnetism (RTFM) can be introduced in a controlled manner in these films using ion irradiation and that the magnetization increases with ion dose. This qualitatively agrees with earlier studies which showed that RTFM could be induced in ZnO films through either vacuum thermal annealing or pulsed laser annealing below energy densities that lead to melting. Raman studies of the ion irradiated samples revealed dramatic changes in the vibration modes that correlated with increases in the carrier concentration, indicative of lattice disorder and defect creation. We compare these results with those observed in laser irradiated and vacuum annealed samples, and then discuss these findings in the context of defects and defect complexes created during the high-energy heavy ion irradiation process. We propose a unified mechanism to explain RTFM and n-type conductivity enhancements during irradiation, and laser and vacuum annealing. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Sultan K.,National Institute of Technology Srinagar | Ikram M.,National Institute of Technology Srinagar | Asokan K.,Inter University Accelerator Center
Vacuum | Year: 2014

Polycrystalline bulk samples of PrFe1-xMnxO 3 (x = 0.0, 0.1, 0.3, 0.5) were synthesized by solid state reaction method to understand their structural, optical and dielectric properties. X-ray diffraction (XRD) and Raman spectroscopy were investigated to confirm chemical phase and the orthorhombic pbnm structure. As the concentration of Mn increases, the lattice parameter b increases while the lattice parameters a and c/√2 decrease but the change of former is less than later. PrFe1-xMn xO3 exhibits O-type (a < c/√2 < b) orthorhombic pbnm structure upto x = 0.5. From XRD it is also evident that the peaks shift towards higher 2θ values with increase in Mn content indicating the development of strain in the crystal structure possibly due to Jahn-Teller distortion after the incorporation of Mn3+ ions in the parent compound PrFeO3. From the Raman study, the modes exhibit a blue shift with broadening of spectral features in the doped samples. The observed shift in wave number with doping clearly indicates change in the bond lengths of Fe-O/Mn-O as well as their impact on FeO6/MnO6 octahedra. The dielectric constant (É′) and dielectric loss (tan δ) are also studied as a function of frequency and temperature. The dielectric constant and ac conductivity increases with Mn doping. The variation of dielectric properties such as ac conductivity, tan δ and É′ suggests that small polarons contribute to the conduction mechanism. Activation energy (Eσ) and optical band gap (E g) decreases with the concentration of Mn. The observed higher values of these quantities reveals that there is hopping between Mn3+ to Mn4+ and Fe3+ to Fe2+ at the octahedral sites of the compound. Possible mechanism contributing to these processes has been discussed. © 2013 Elsevier Ltd. All rights reserved.

Kumar V.V.S.,Inter University Accelerator Center
Applied Surface Science | Year: 2015

Nanocomposite (nc) ZnO-SiOx thin films were grown using rf magnetron sputter deposition technique and post-deposition annealing at 750 °C. These films were irradiated with 750 keV Argon ions at fluences in the range from 1 × 1015 to 1 × 1017 ions/cm2, using Low Energy Ion Beam Facility (LEIBF) at IUAC. X-ray diffraction (XRD) patterns of the as-deposited irradiated films show decrease in intensity of ZnO peaks relative to pristine film. Fourier transform infrared (FT-IR) spectroscopy measurements of the as-deposited irradiated films indicate the breakage of Zn-O, Zn-O-Si and Si-O-Si bonds in them, which is substantiated by FT-IR measurements of 750 °C annealed films that were irradiated at a fluence of 1016 ions/cm2. Photoluminescence (PL) measurements show drastic decrease of visible PL emission from as-deposited irradiated films. Current-Voltage (I-V) measurements show decrease in surface resistance of irradiated films by three orders of magnitude. The results suggest that 750 keV argon ion irradiation of nc ZnO-SiOx films has resulted in the formation of non-radiative defects in ZnO phase and damage in SiOx, and amorphization in Zinc silicate phase. These results are explained on the basis of the dominant energy loss mechanism of low energy ions in materials. © 2015 Elsevier B.V.

Siva Kumar V.V.,Inter University Accelerator Center
Vacuum | Year: 2016

We report studies on growth of nanocrystalline diamond films by electron cyclotron resonance chemical vapour deposition (ECR CVD) and their structural and photoconduction properties. Bias enhanced nucleation (BEN) under higher methane partial pressure has been used to grow diamond nanocrystals with sp2 carbon clusters at grain boundaries in an amorphous carbon matrix. Structural studies indicate the size of diamond nanocrystals decreased and sp2 content increased in the films with increase in methane partial pressure, which is explained using subplantation model. Current- Voltage (I-V) measurements under dark and deep ultraviolet (DUV) light illumination conditions showed higher photocurrent in films with smaller sized diamond nanocrystals (3 nm–8 nm) compared to films having diamond nanocrystals of larger size (∼15 nm). The results indicates that the photocurrent generated in the films has major contributions from photoexcited electrons in diamond nanocrystals and sp2 carbon nanoclusters, with minor contribution from amorphous carbon phase. © 2016 Elsevier Ltd

Muralithar S.,Inter University Accelerator Center
Pramana - Journal of Physics | Year: 2014

A multidetector gamma array (GDA), for studying nuclear structure was built with ancillary devices namely gamma multiplicity filter and charged particle detector array. This facility was designed for in-beam gamma spectroscopy measurements in fusion evaporation reactions at Inter-University Accelerator Centre, New Delhi. Description of the facility and in-beam performance with two experimental studies done are presented. This array was used in a number of nuclear spectroscopic and reaction investigations. © Indian Academy of Sciences.

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