Bil,,~,Pb,Sn,,lSr2Ca,Cu30z (where% ranges from 0 to 0.4) have been examined via magnetization measurements, x-ray diffraction and scanning electron microprobe. In addition to observing the often reported high T, superconducting transition temperatures at 80 K (2212) and 110 K ( 2223), a range of well resolved transition temperatures have been found, implying the possible existence of new phases. The presence of Sn in these materials appeared to suppress the formation of the low T , Raveau 2201 phase. Also observed was an ordered variation in the amount of flux pinning as the Sn and Pb concentrations were changed. We suggest that Sn increases flux pinning by forming the compound Sr,Sn,O,.
The photoabsorption cross section of molecular nitrogen near 83.4 nm has been measured at room temperature. The cross sections at the wavelengths of the 2s2p 4 4p•, 4P3/: ' and 4Pin (all -2s22p34S%:) O* emission lines are measured to be 10.1 + 1.6 Mb, 0.29 _+ 0.02 Mb, and 0.049 _+ 0.008 Mb respectively. These measurements were made with an O'emission discharge source, and repeated using a synchrotron radiation source. Both measurements were made wifl'• the 0.008-nm resolution 6.65-m spectrometer at the SURF lI storage ring of the National Institute for Standards and Teclmology. INTRODUCTION The O + triplet near 83.4 nm is of great interest in ionospheric physics primm'ily for its role in remote sensing of the ionosphere. By compm'ing obse•wations of the 83.4-nm emission to the results of model calculations, the F2 region O + density and hence the electron density can be inferred (see, for example, Anderson and Meier [1985]). It has recently been pointed out [C!eaty et al., 1989] that absorption by molecular nitrogen strongly affects the intensity of this emission when observed at altitudes below 240 kin. In addition, Cleary et al. suggested that the overlap between the absorption lines of N2 and the emission lines of O* was much lower than previously indicated by Hudson and Carter[ 1969]. In this paper we report the results of a high-resolution laboratory measurement of the cross section of N2 in the vicinity of the O + 83.4-nm triplet. BACKGROUND The O + 83.4-nm emission lines are 2s 2p 4 4psa _ 2S 2 2p3 48o3a at 83.447 nm, 2s 2p 4 4P3a -2S 2 2p 3 '•Sø3,2 at 83,333 nm, and 2s 2p 4 '•P•/2 -2S 2 2p 3 •Sø3a at 83.276 nm. The source of this emission in the upper atmosphere is primarily photoionization-excitation of atomic oxygen. Below 240 km the density of molecular nitrogen is sufficiently high to cause significant absorption of the O + 83.4-nm emission. Carroll and Yoshino [1972] and Ledbetter [1972] have provided high-resolution spectrograms of the N2 absorption in this region. Although these photographic studies clearly show the complex rotational bands in the N2 spectrum, they cannot determine absolute cross section values. Previous photoelectric surveys of the N2 absorption cross section have also been made [Hudson and Carter, 1969; Carter, 1972; Gl'irtler et at., 1977]. Unfortunately, the agreement among these studies has been poor. For example, at 83.3332 nm G'drtler et al. show an N2 cross section of 19 Mb while Hudson and Carter measured a value of 3.2 Mb. According to our
The high-resolution vacuum-ultraviolet spectroscopic facility at SURF II, the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, Md., consists of a fore-optics system of three cylindrical mirrors and a 6.65-m concave grating spectrometer using the off-plane Eagle mounting. To prepare for the evaluation of the actual performance of this nationalfacility spectrometer against theoretical expectations, we computed scanning parameters, spectral resolution, and the optimum curvature and tilt of both entrance and exit slits. It is planned eventually to replace the exit slit of this instrument with a two-dimensional array detector to increase data collection efficiency. Therefore a major motivation for this work is that the results on the tilt and curvature of the exit slit can be used to maximize the resolution obtainable with the array detector through data processing.
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