G.L.N. Reddy

Effect of Fe layer thickness and Fe/Co intermixing on the magnetic properties of Sm–Co/Fe bilayer exchange-spring magnets

Sm?Co(20?nm)/Fe(tFe) bilayers are fabricated with different Fe layer thicknesses (tFe?=?0, 2, 4, 6 and 8?nm) in order to systematically investigate the intermixing effect between Fe and Sm?Co layers and its influence on the magnetic properties. X-ray diffraction analysis indicates that the deposition of soft layer (Fe) promotes crystallization of hard layer (Sm?Co) at a low annealing temperature (400??C). The annealed films consist of hexagonal Sm2Co7, Sm2Co17 and SmCo5 phases in the hard layer and bcc-structured Fe(Co) in the soft layer. Rutherford backscattering is employed to investigate the atomic composition of the individual layers and thereby the extent of diffusion of Co atoms into the Fe layer. The estimated Co content is higher for lower tFe. The magnetic properties of the bilayers very close to the interface are analysed by the magneto-optical Kerr effect. The calculated Kerr intensities (which represent the magnetization process) are significantly affected by the extent of diffused Co in the Fe layer. Superconducting quantum interference device magnetic measurements demonstrate smooth and single-phase magnetic behaviour for tFe up to 6?nm and a good combination of high coercivity (6.5?kOe) and high magnetic remanence (834?emu?cm?3) is obtained for tFe?=?4?nm.

MEASUREMENT OF GERMANIUM ESCAPE PEAKS IN PIXE SPECTRA RECORDED USING HIGH PURITY Ge (HPGe) DETECTOR

This paper deals with studies on Ge Kα and Kβ escape peaks in particle induced X-ray emission (PIXE) spectra recorded by a high purity germanium (HPGe) detector. A knowledge of the energies and intensities of these escape peaks is desirable for accurate qualitative as well as quantitative analysis of elements by PIXE. The spectral interferences caused by Ge K escape peaks in the determination of Fe in U by PIXE are highlighted for illustration. A simple theoretical approach based on the production of Ge K X-rays inside the Ge crystal of the detector during the process of detection of the incident characteristic X-rays and the subsequent escape of a fraction of the produced radiations from the crystal, is described to calculate the intensity ratio of the Ge escape peak to its parent characteristic X-rays. The calculated values are in agreement with the experimental values and those estimated using the formulation provided in GUPIX software for PIXE. The Ge K escape peaks are very prominent; the intensities of Ge Kα escape peaks, from bromine to silver, range from 15% to 6% of those of their respective Kα X-rays. These intensities are, in general, considerably higher compared to those of Si escape peaks in spectra recorded by Si(Li) detector. Ge K escape peaks therefore may give rise to severe interferences. The present approach provides a precise (~8%) determination of the intensity of an escape peak and thereby facilitates a reliable PIXE analysis.

Pick up of cesium and cobalt activity by oxide sludge in steam generator

A pinhole developed near the tube sheet in the steam generator (SG) tube of a pressurised heavy water reactor (PHWR) caused leak of primary coolant containing radioactive contaminants (137Cs, 134Cs and 60Co) to the shell side. The sludge collected from the tube sheet region was found to have adsorbed these radionuclides at the high temperature (230-240 °C) that prevailed in the SG. An attempt has been made to evaluate the quantity of activity retained in the various oxide phases that constitute the sludge and their mode of pick-up. The sludge was characterized by XRD and XPS, which showed the presence of various oxides of iron, copper and nickel along with the silicates of calcium, magnesium and aluminum. Gamma-spectrometry of the sludge confirmed the presence of 137Cs134Cs and 60Co to an extent of 7.6, 1.3 and 0.9 mCi/g of sludge, respectively. Selective dissolution in various EDTA based formulations and equilibration with nitric acid and magnesium chloride solutions helped to understand the quantity of activity adsorbed by various constituents of the sludge. It was concluded that a major portion of cesium was picked up by a reversible ion exchange process on various oxide constituents and about 10% by an irreversible specific adsorption process on insoluble silicates. Also, it was proved that 60Co was specifically adsorbed over the oxides of iron and nickel.