[en] A gamma ray scintillation camera generating (X,y) spatial coordinate and Z energy signals relative to detected radiation events. The system provides for calibration of the camera Z signal response as a function of camera face location. In addition, the camera signals are converted to their digital equivalents subsequent to which the apparent coordinate locations of detected events as determined by the camera are corrected to their true spatial coordinates based upon correction information stored in the system

[en] A system is described for improving the accuracy of a radiation transducer, such as a gamma ray scintillation camera, comprised of a transducer arranged to produce three analog signals representing X and Y position and Z energy of a detected event. The signals are converted to digital form by an analog-to-digital converter and corrected by an arithmetic unit using information stored in a translation table. The translation table is obtained by presenting the transducer with an image of accurately known dimensions and position and comparing the apparent coordinates X and Y with the true coordinates. This table may be periodically updated to account for long term changes in the apparatus. The true spatial coordinates of a detected event falling between the stored calibration points is calculated by interpolation. The system may calculate a spatially varying Z energy signal window to compensate for inherent sensitivity variations across the face of the transducer. A comparator detects whether the detected event is within the correct energy range and if so enables a gate to indicate the position of the event. (author)

[en] A microprocessor-based device has been developed to virtually eliminate the effects of nonlinearity and nonuniformity in radioisotope camera signals. Imperfections in the X and Y spatial signals or the Z energy signal can otherwise lead to spatial distortion, non-constant sensitivity, and flood non-uniformity in the resulting images. A device operates in real time on each event from the camera, and is fast enough to allow counting rates up to 120,000 per second without loss. Non-linearities in the X and Y signals are eliminated by carrying out an on-the-fly translation to corrected U and V position coordinates. The translation table is constructed based on calibration images of a parallel line phantom. Possible variations in the Z signal are accomodated by also including in the table a 64 x 64 array of spatially-depedent energy windows. These data are automatically generated based on a calibration flood image. The device operates in conjunction with an MDS Modumed Data System, and has been demonstrated using three different radioisotopes cameras. In all cases, significant improvement in image linearity and uniformity has been observed

[en] We have measured the electrical transport, heat capacity, and magnetic properties of single crystals of semiconducting PtSb₂, doped with rare earth ions. Carrier concentrations in the doped crystals range from 10¹⁷ to 10²⁰ cm^-3, and in most cases, metallic resistivity was observed. Moment densities of 10²⁰-10²³μ_B/cm³ were found for crystals doped with magnetic rare earths, and diamagnetic behavior for those doped with non-magnetic rare earths. Weak superconductivity and ferromagnetic order were observed separately in many of the doped crystals, and electron microscopy studies reveal that they likely originate with secondary surface phases. Accordingly, surface etching suppressed both the ferromagnetic and superconducting behaviors. Nonetheless, electrical transport and heat capacity measurements of the doped crystals suggest that the bulk electronic properties are modified relative to stoichiometric PtSb₂, making this a potentially interesting system for studying magnetism in a low carrier density environment

[en] We have synthesized single-crystals of Yb₂Pt₂Pb, which crystallize in the tetragonal U₂Pt₂Sn-type structure. The magnetic susceptibility χ is highly anisotropic. The χ_<100> for B-parallel <100> is 30 times larger than χ_<001> for B-parallel <001> at the lowest temperatures. Both 1/χ(T) and M(B) of Yb₂Pt₂Pb are dominated by the CEF effect. The 1/χ_<100> above 150 K is well described by the Curie-Weiss law with θ=34 K and μ_eff=4.19 μ_B, indicating well-localized Yb³⁺ ions at high temperatures. A broad maximum in χ is found around 3 K, just above antiferromagnetic transition temperature of 2 K. This suggests an important role for fluctuations in this system, due to reduced dimensionality or perhaps geometric frustration

[en] We report the synthesis and basic properties of single crystals of a new binary compound, Yb₃Pt₄. The Yb ions in this compound are fully trivalent, and heat capacity measurements show that the crystal field scheme involves a doublet ground state, well separated from the excited states, which are fully occupied above ∼150K. The heat capacity displays a large, weakly first order anomaly at 2.4 K, where a cusp is observed in the magnetic susceptibility signalling the onset of antiferromagnetic order. The entropy associated with this order is the full Rln2 of the doublet ground state, however, the magnetic susceptibility in the ordered phase is dominated by a large and temperature independent component below the Neel temperature. The heat capacity in the ordered state originates with ferromagnetic spin waves, giving evidence for the inherently local moment character of the ordered state. The electrical resistivity is unusually large, and becomes quadratic in temperature exactly at the Neel temperature. The absence of analogous Fermi liquid behavior in the heat capacity and the magnetic susceptibility implies that Yb₃Pt₄ is a low electron density system, where the Fermi surface is further gapped by the onset of magnetic order.