Showing papers by "Anindya Sarkar published in 2012"
TL;DR: In this paper, the authors report results from new positron-argon total cross-section (TCS) measurements, which are very good, except at the lowest energies of common measurement.
Abstract: We report results from new positron–argon total cross-section (TCS) measurements. Agreement with the corresponding recent data of Jones et al (2011 Phys. Rev. A 83 032701) is found to be very good, except at the lowest energies of common measurement. Excellent qualitative agreement is also found between our measurements and an improved convergent close-coupling (CCC) calculation which was undertaken as a part of this study. This level of accord between our experimental and theoretical TCSs has enabled us to determine an experimental scattering length (a) of a = −4.9 ± 0.7 au for the positron–argon system. That value is in excellent agreement with the relativistic polarized orbital optical potential approach result of Jones et al (a = −4.7 au) and our CCC result of a = −4.3 au.
34 citations
TL;DR: In this article, a systematic study on the modification of optical properties in mechanically milled ZnO powder has been reported, where the average grain size of the powder becomes ∼20nm within 4h of milling.
32 citations
TL;DR: In this paper, the authors report on measurements of total cross sections for positron scattering from the fundamental organic molecule methane (CH${}_{4}$), and the energy range of these measurements was 0.1 -50 eV.
Abstract: We report on measurements of total cross sections for positron scattering from the fundamental organic molecule methane (CH${}_{4}$). The energy range of these measurements was 0.1--50 eV, whereas the energy resolution was $\ensuremath{\sim}$100 meV when our Ni moderator was used and $\ensuremath{\sim}$260 meV when the W moderator was employed. To assist us in interpreting these data, Schwinger multichannel calculations were performed at both static and static plus polarization levels of approximation for elastic positron scattering from 0.001 to 10 eV. These calculations are found to be in quite good qualitative agreement with our measured data, and they clearly educe the crucial role played by the target polarization in the low energy positron--CH${}_{4}$ scattering dynamics.
24 citations
TL;DR: Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6 MeV H(+) ions in a hydrothermally grown ZnO single crystal and reveals a single component lifetime spectrum for both the unirradiated and irradiated crystal.
Abstract: Low temperature photoluminescence and room temperature positron annihilation spectroscopy have been employed to investigate the defects incorporated by 6?MeV H+ ions in a hydrothermally grown ZnO single crystal Prior to irradiation, the emission from donor bound excitons is at 3378?eV (10?K) The irradiation creates an intense and narrow emission at 3368?eV (10?K) The intensity of this peak is nearly four times that of the dominant near band edge peak of the pristine crystal The characteristic features of the 3368?eV emission indicate its origin as a ?hydrogen at oxygen vacancy? type defect The positron annihilation lifetime measurement reveals a single component lifetime spectrum for both the unirradiated (164???1?ps) and irradiated crystal (175???1?ps) It reflects the fact that the positron lifetime and intensity of the new irradiation driven defect species are a little higher compared to those in the unirradiated crystal However, the estimated defect concentration, even considering the high dynamic defect annihilation rate in ZnO, comes out to be ?4???1017?cm?3 (using SRIM software) This is a very high defect concentration compared to the defect sensitivity of positron annihilation spectroscopy A probable reason is the partial filling of the incorporated vacancies (positron traps), which in ZnO are zinc vacancies The positron lifetime of ?175?ps (in irradiated ZnO) is consistent with recent theoretical calculations for partially hydrogen-filled zinc vacancies in ZnO Passivation of oxygen vacancies by hydrogen is also reflected in the photoluminescence results A possible reason for such vacancy filling (at both Zn and O sites) due to irradiation has also been discussed
13 citations