[en] A high energy resolution Compton camera consisting of position-sensitive germanium detectors is proposed for multitracer imaging. The distributions of the number of gamma-ray interaction points in both detectors are calculated by the Monte Carlo simulations. The effects of multiple scattering on the performance of the Compton camera are discussed. A gamma-ray tracking algorithm is used to determine the first interaction point in the second detector. The efficiency and spatial resolution of a Compton camera for gamma rays of different energies, emitted from different positions are also simulated

[en] A small addition (≤0.5 wt%) of cerium silicide (CeSi₂) to powder metallurgy (PM) commercially pure Ti (CP-Ti), Ti–6Al–4V and Ti–10V–2Fe–3Al (all in wt%) results in substantial microstructural refinement and noticeably improved ductility with marginally improved sintered density. CeSi₂ is unstable and decomposes between 1423 K and 1473 K. The Si goes into solid solution in β-Ti and is responsible for the improved sintered density while the Ce scavenges both oxygen (O) and chlorine (Cl) from the Ti powder and therefore improves tensile ductility. The resulting CeO₂ and CeCl_xO_y particles generally exist along or close to the prior-β grain boundaries. The substantial microstructural refinement in terms of both the prior-β grain size and the subsequent α-Ti lath size is attributed to the grain boundary pinning effect of the CeO₂ particles. The optimum concentration of CeSi₂ is approximately 0.5 wt%, beyond which both the sintered density and tensile elongation drop with increasing addition of CeSi₂. CeSi₂ can be a practical form of Ce addition to PM Ti alloys for impurity scavenging, microstructural refinement and tensile ductility improvement

[en] We report that pure microwave (MW) radiation, without the assistance of MW susceptors, can rapidly heat titanium hydride (TiH₂) powder to 1300 °C for isothermal sintering. The release of hydrogen, however, induces low-temperature plasmas which reflect incident MWs, leading to cyclic temperature fluctuations. Commercially pure titanium fabricated by MW radiation of TiH₂ powder exhibits much higher sintered densities, tensile strength and ductility together with finer residual pores, compared to that sintered from hydride–dehydride titanium powder

[en] Superconducting thin films of Bi-Ca-Sr-Cu oxide, with T/sub c/ onset of approximately 90K, have been prepared by rf magnetron sputtering on sapphire with and without a CaZrO/sub 3/ buffer layer, ZrO/sub 2/-coated silicon (111), as well as on single crystal MgO (100). Sintered pellets of Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+x/ (2122) and Bi/sub 4/Ca/sub 3/Sr/sub 3/Cu/sub 4/O/sub 16+x/ (4334) were employed as targets. The as-deposited films were amorphous insulators which were then annealed in various ways. Zero resistance at 72K for films on (100) MgO was achieved after annealing in air at 810⁰C for 2 hr. However, the X-ray diffraction pattern showed that two superconducting phases, i.e. Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+x/ (2122) and Bi/sub 2/Ca/sub x/Sr/sub 2-x/CuO/sub 6+y/ (2021), are present, and that films have preferred orientation with c-axis normal to the substrates

[en] A new molybdenum phosphide (MoP) catalyst was successfully synthesized for CO/sub 2/ reforming of CH/sub 4/ reaction. The catalysts were prepared by temperature-programmed reduction (TPR) of phosphomolybdate precursors which were modified by citric acid (CA) at the molar ratio of MoP:CA = 1: x (x = 0, 1.0, 2.0, 3.0), which were characterized by means of X-ray diffraction(XRD), N/sub 2/ adsorption-desorption and CO/sub 2/-TPD techniques. The results showed that the addition of citric acid can affect the catalytic activity and that the MoP catalyst had the highest catalytic activity at 1073 K and X=1. After reduced in H2 flow at 923 K, the activity of the post-reaction catalyst can be well restored, while its structure remains unchanged. In higher temperatures, the samples exhibit good anti-sintering ability and stability. (author)

[en] Three series of single-phase La-Ca-Ba-Cu-O compounds with tetragonal triple-perovskite structure and respective nominal compositions of La_4-xCa_xBa₃Cu₇O_y (LC series, 0.50< or=x< or=1.15), La₃Ca_xBa_4-xCu₇O_y (CB series, 0< or=x< or=1.25) and La_3.5-0.5xCa_xBa_3.5-0.5xCu₇O_y (LCB series, 0< or=x< or=1.25) were prepared by either a solid state reaction method or a polymeric citrate precursor method. All the single-phase materials were superconducting except for samples containing small x in the LCB series. Unit-cell parameters, such as a axes, c axes and cell volume, decreased with increasing Ca substitution. In general, the T_c and hole concentration (p) increased with increasing x form x=0 to x=1.00. In other words, evidence of hole doping was observed during Ca substitution that was the main reason for the increase of the T_c from 0 to 80 K. The optimal T_c was observed in a region close to the formula of La₃CaBa₃Cu₇O_y which had a formula per unit celt of La_1.29Ca_0.43Ba_1.29Cu₃O_z where z=7.104, p=0.308, a axis =0.3879 nm and T_c(zero) = 80 K. (author)

No abstract available

[en] SmFe_9_._3_+_xSi_0_._2B_0_._1 (x=0, 0.5, 1.0) ribbons and their nitrides were prepared by melt-spinning, followed by annealing and subsequent nitriding. The structure and magnetic properties have been investigated by means of powder X-ray diffraction, vibrating sample magnetometer and Mossbauer spectroscopy. Rietveld analysis shows that the augment of Fe content gives rise to an increase of the c/a ratio and cell volume. The increasing amount of Fe atoms occupying the 2e sites results in the change of initial structure. It is indicated that the isomer shift of 3g and 6l atom remains quasi-constant while the 2e atom shows a noticeable increase with the increase of iron content, which further conforms the preferential occupation of excessive Fe atoms at this site. Consistent with Tc, the mean hyperfine field 〈B_h_f〉 has the highest value of 25.7 T when x=0.5. The hyperfine fields at different Fe sites follow the order H2e>H3g>H6l. The highest curie temperature of 477.68 K and the hyperfine field of 25.7 T in the as-quenched ribbons were obtained when x=0.5. Meanwhile, the highest magnetic properties of H_c_j=4.31 kOe, (BH)_m=3.5 MGOe in the nitride powders were found. - Highlights: • Rietveld analysis shows that the augment of Fe content gives rise to an increase of the c/a ratio and cell volume. • The isomer shift of 2e atom shows a noticeable increase according to Fe content, which corroborates the preferential occupation of excessive Fe atoms at this site. • The hyperfine fields at various Fe sites follow the order H2e>H3g>H6l, which corresponds closely with the number of iron near neighbor of each site.

[en] A method to extract depth of interaction information for γ-rays in a segmented planar Ge detector is presented. The method is demonstrated on signals from a segmented detector which were stored by a digital oscilloscope event by event and analysed off-line. Event samples were acquired for different interaction points in the detector. A Compton scatter coincidence detection technique ensured that the event samples were highly enriched in single-interaction events. By analysing pulse shapes and the relative timing between anode pulses and the pulses from the irradiated cathode segment, a position sensitivity of 1-2 mm in the depth direction was deduced. A similar transverse position sensitivity was inferred by studying image charge pulses on neighbouring segments

[en] The nuclide ⁶⁹Kr with T_z=-3/2, A=4n+1 produced in the ⁴⁰Ca(³²S,3n) reaction has been observed via β-delayed proton emission by using pulsed-beam technique. A single proton group at a laboratory energy of 4.07±0.05 MeV with half-life of 32±10 ms was observed for the first time, corresponding to decay of the T=3/2 isobaric analog state in ⁶⁹Br to the ground state of ⁶⁸Se. Combining this result with a Coulomb displacement energy calculation yields a mass excess for ⁶⁹Kr of -32.15±0.30 MeV. The partial decay scheme of ⁶⁹Kr is proposed. copyright 1997 The American Physical Society