Nirankar Nath

Protons, helium and heavy ions in backscattering analysis of high-Tc superconductors

Abstract Ion backscattering spectra for 1 H, 4 He, 7 Li, 12 C, 16 O and 28 Si ions incident on thin and thick superconductor samples in the energy range 2–28 MeV have been measured. The spectra are analyzed by using a computer program package for ion backscattering data analysis. The general characteristics of the ion beams for the backscattering analysis of high- T c superconductors both in the Rutherford and non-Rutherford energy regime are discussed. The advantages and disadvantages of using proton and heavy ion beams are compared to those of conventional 4 He ion backscattering.

Stopping power of Mylar for heavy ions up to copper

Abstract The stopping powers of Mylar for several heavy ions covering Z =11 to 29 in the energy range ∼0.3 to 2.3 MeV/n have been measured using the elastic recoil detection technique and twin detector system. The technique provided a unique method to generate a variety of variable energy ion species utilizing a fixed energy 140 MeV Ag 13+ primary beam from the Pelletron accelerator facility at Nuclear Science Center, New Delhi, India. Most of these measurements are new. The experimentally measured stopping power values have been compared with those calculated using LSS theory, Ziegler et al. formulation and Northcliffe and Schilling tabulations. Merits and demerits of these formulations are highlighted. Stopping power calculations using the Hubert et al. formulation have been extended successfully beyond its recommended range of validity, i.e. 2.5–500 MeV/n down to energies as low as 0.5 MeV/n.

Energy loss of MeV heavy ions in carbon

Abstract A novel technique, using secondary forward recoil ions generated in thin standard targets by energetic very heavy primany ion beam, has been employed to measure energy loss of several ion species (Z1 = 8 to 29) covering energies between 0.1 and 1.0 MeV/u. Energy variation was simp y affected by changing the detector angle between 35° to 70°, avording the dominant elastic scattering of the primary beam. A twin detector permitted simultaneous measurement of both unabsorted and absorbed spectra. The experimental data on stopping power are compared with evaluated values using LSS theory and TRIM. A better understanding of the validity of available theoretical evaluations has become possible, with a need for higher precision in experimental data in some cases.

An experimental study of stopping power for MeV heavy ions

A 60 MeV Ag primary ion beam was used to generate secondary recoil ion beams of Cl, K, Ca, Sc, Ti, V, Mn and Cu in the energy range 0.1-0.6 MeV . The stopping power in the carbon absorber was measured and compared with Lindhard, Scharff and Schiott (LSS) theory, the Northcliffe and Schilling model and semiempirical estimates of Ziegler et al (1985). Data for heavier ions of Ag, I and Au from other sources was also considered in order to extend the scope of such a comparison. LSS theory was found to satisfy the data within a narrow mid-velocity range (-, where is Bohr velocity). Estimates made by Ziegler et al were seen to generally agree to within a few per cent except for energies below 0.2 MeV , where deviations as high as 25% were seen. Expected oscillations could not be discerned down to the lowest ion velocities so far attempted.

Stopping power of carbon for heavy ions upto copper

Abstract Stopping powers for ions of O, Cl, Sc, Ti, Cr, Mn, Fe and Cu in the energy range 0.2–1.0 MeV/n have been measured in carbon foils using the elastic recoil ion technique and a twin detector system. Very heavy ions of Gold and Iodine of energy around 100 MeV have been employed to generate the various recoil ions using pure thin (≈ 1000A) elemental/compound targets. The data have an overall average accuracy of 6%. The stopping power for Sc, Mn and Fe ions in the energy region 0.2–1.0 MeV/n as well as those for Ti and Cu ions in the energy region below 0.45 MeV/n are perhaps the first such measurements. The limitations of LSS theory even within the range of its applicability has been demonstrated. Varelas and Biersack estimates agree well in the region of their applicability lying above the ion velocity limit set for LSS theory. Northcliffe and Schilling predictions as well as the TRIM estimates provide the best fit with data. However, one does notice variations upto 25% for some ions at lower energi...

MeV heavy ion stopping power measurements using NSC Pelletron

Abstract Surface modification and characterization are being undertaken increasingly using the MeV heavy ion beams. Interpretation of such data requires reliable and precise values of stopping powers involved. Sufficient data exists above 2.5 MeV/n but less information is available at lower energies. The present series of experiments report the results of stopping power measurements for various ion species between Z = 8 and 29, covering the energy range ∼ 0.2–1.0 MeV/n in carbon. The elastic recoil ion detection system provided a unique method to generate variety of variable energy ion species utilising a fixed energy heavy (Z = 47, 53, 79) projectile beam from the NSC Delhi 15 MV Pelletron facility. The data has been compared with available theoretical and semiempirical fitting treatments. Relative merits and demerits of these formulations have been highlighted. Future projections to our line of investigation have been indicated in the light of some recent innovative theoretical predictions.

Thermal oxidation of nickel following cerium and platinum implantations

Abstract The study of thermal oxidation of polycrystalline nickel and Ni-20Cr samples was made following cerium ion implantation. Samples were vacuum-annealed (up to 850°C) and subsequently oxidised (up to 1000°C) at different temperatures. RBS and 16O(d, p) reaction analysis was made to estimate cerium and amount of oxidation, respectively. A few selected samples were subjected to SIMS analysis to ascertain the double Ce-peaking effect observed at high oxidation temperature. Platinum ion implantation has been tried to get an idea of the oxidation mechanism, since it is not known to have any degrees of mobility in Nickel relative to Cerium. A preliminary report on the various results obtained will be presented.