Neutron polarization analysis

Fig. 101. Results from neutron-polarization analysis in CuMn 25 atom% at 7=10 K. The nonspin-flip or nuclear (in part a) and the spin-flip or magnetic (in part b) cross sections are displayed (from Cable et al. 1984).

A neutron diffraction analysis of oxymyoglobin (Phillips, 1984) located 120 water molecules at the protein surface. Peters and Peters (1986) analyzed these and earlier X-ray results (Hanson and Schoen-born, 1981 Takano, 1977a,b) and described networks formed of protein polar groups and water molecules. The network structures found for myoglobin appear to be like those for other globular proteins. 

The conventional polarized beam experiment is useful only for systems with polarization dependent cross sections. More information can often be gained if the polarization of the scattered neutrons is measured relative to the incident polarization (polarization analysis). This may be done in a triple-axis mode with a polarization sensitive analyzing crystal (Fig. 11). The technique was introduced experimentally by Moon et al. (59). In their apparatus the magnetic field at the sample may be rotated about a horizontal axis. With the sample field vertical the neutron polarization remains vertical, but with the sample field horizontal the neutron polarization at the sample becomes horizontal (a reverse rotation occurs after the sample so that the polarization at the analyzing crystal is again vertical). Thus P can be either parallel or perpendicular to the scattering vector n. 

Fig. 11. Experimental layout for polarization analysis experiments [from Ref. (59)]. The magnetic field directions sensed by the neutrons are indicated...

Accurate measurements of the concentrations of trace elements on atmospheric particulates are difiicult enough to make in polluted urban atmospheres but even more so in clean marine or polar atmospheres because of the minute quantities of material that can be collected in a reasonable time. For these measurements, one needs a sensitive analytical technique that is free from interference by other elements present. Recently, the use of lithium-drifted germanium [Ge(Li)] y-ray detectors in neutron activation analysis has greatly improved analytical sensitivities and accuracies for such studies (J). 

The determination of iodine in seawater helps in understanding the marine environment. A variety of analytical methods have been proposed for the quantitative determination of iodine in seawater. This chapter discusses the methods employed for the separation and determination of iodine in seawater. These methods include capillary electrophoresis (CE), ion chromatography (IC), high-performance hquid chromatography (HPLC), gas chromatography (GC), spectrophotometry, ion-selective electrode, polar-ography, voltammetry, atomic emission spectrometry (AES), and neutron activation analysis (NAA). The advantages and hmitations of these methods are also assessed and discussed. Since iodine is present in the ocean at trace levels and the matrices of seawater are complex, especially in estuarine and coastal waters, the methods developed for the... 

The /7-polarized IR transmission spectra (cp = 75°) for PSG layers with different phosphorns content are shown in Fig. 6.8 [36]. In addition to the Si02 bands, an intense peak at 1325 cm from P=0 bonds was observed [33-38]. The ratio of the absorbance at 1325 cm to that at 1080 or 1250 cm depends linearly on the phosphorus concentration determined by methods such as chemical or neutron activation analysis. The same dependence is observed in spectra of borosilicate glass for the ratio of the absorbance at 1350 cm to that at 1080 cm this is used for determination of the boron concentration in borosilicate glass films [38-40]. This determination of the absolute concentration of phosphorus in PSG films by IR spectra was developed in [41]. 

The objective of the worik reported herein was to assess the effect of the addition of SPS on the short-range order in PC. Short-range order was determined using wide angle neutron scattering with spin polarization analysis. 

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