Quadrupole Pairing Research Articles

Mössbauer spectroscopy of protohaem and mesohaem cytochrome c peroxidases and their fluorides

The Mössbauer spectra of cytochrome c peroxidase (CCP) containing protohaem and mesohaem have been observed in a variety of physical conditions. At very low temperature intricate paramagnetic spectra are observed, while at 195°K magnetic effects are almost completely suppressed and two quadrupole pairs appear. All spectra indicate the presence of both high- and low-spin components in agreement with susceptibility results. For the proto and meso forms in 0·2M pH 7 buffer the high-spin fractions at 4·2 °K are 0·25 and 0·4 respectively, while corresponding values at 195°K are 0·63 and 0·67. In both cases the low-spin component is in rough agreement with knowngvalues. The high-spin components are also consistent with electron spin resonance results, and the field dependence of the Mössbauer spectra indicate that the axial term in the spin Hamiltonian is 2D= 30 ± 6 cm-1. The high-spin fraction increases with increasing buffer strength, and is freezing rate dependent at very low or zero buffer strength. Fluoride complexes of both enzymes also show low-temperature paramagnetic Mössbauer spectra. These appear to be entirely high spin with 2D= 14·6±0·6 cm-1and a quadrupole interaction ½QVzz= 0·85 mm s-1. The zero-field spectra at low temperature are diffuse and consistent with the assumption of a large neighbour-nucleus interaction. At 195°K paramagnetic effects remain large and spectra are diffuse both with and without applied fields.

A Mössbauer effect study of the metallic compounds U 6 Fe and Pu 6 Fe, and the relevance of the results to theories of the behaviour of actinide metals

The intermetallic compounds U 6Fe and Pu 6 Fe were investigated using Mössbauer spectroscopy. From the Mössbauer point of view the results are straightforward; quadrupole pairs are seen in both materials at room temperature and low temperatures. Low temperature values for the splittings were 0.074 cm/sec for U 6Fe and 0.083 cm/sec for Pu 6Fe; the corresponding room temperature values were 0.069 and 0.073 cm/sec. Both quadrupole splittings and isomeric shift values are characteristic of Fe in the metallic state. Recent electrical resistivity work has established that the temperature curves for Pu 6Fe and Pu metal are qualitatively very similar. In view of this investigation and our Mössbauer results we would be inclined to reject the hypothesis that Pu undergoes an antiferromagnetic transition at low temperatures. However, the situation is complex, and some space is devoted to a review and appraisal of the theories proposed to explain the properties of this most unusual metal.

Design of a 600 MeV Superconducting Microtron

The design of a 600 MeV racetrack microtron proposed for the University of Illinois consists of a 30 MeV superconducting linac operating at 1.3 GHz between two uniform field bending magnets about 6.4 meters apart. There will be 19 parallel return paths separated by 14.7 cm. Vertical focusing is provided on each return orbit by a quadrupole pair close to each magnet. For quadrupoles 20 cm long and separated by 10 cm, the gradients required to advance the vertical oscillation phase by 90° per revolution increase monotonically from 150 to 350 gauss per centimeter. Only very weak horizontal focusing powers are needed to keep the return beams within 2 mm of linac axis. The linac itself provides some focusing but two weak quadrupole singlets on the linac axis, one near each magnet, provide additional focusing. Electron trajectories for all traversals through the linac and the magnets have been calculated in detail, by a step by step procedure where required, and are presented here. These results confirm earlier, less complete, calculations indicating that the microtron design parameters are not critical and that an output energy resolution of one part in 104 is easily obtainable.

The Oric High-Resolution Spectrograph Facility

The installation of a broad-range spectrograph system at ORIC has now been completed. The system consists of a beam analyzing magnet, two triplet quadrupole magnets, and the spectrograph magnet. These magnets are operated as a compound system to obtain optimum energy resolution. The quadrupole pair gives the system a unique flexibility in matching the properties of the beam preparation and the spectrograph magnets. Preliminary results of the operation of the system show the importance of this compound operation with obtained resolutions approaching 1 part in 2000.