Nobuhiko Sakai

An x‐ray spectrometer for Compton scattering

An x‐ray spectrometer has been designed and constructed for Compton scattering measurements using 40–70 keV x‐rays from an ellipsoid multipole wiggler (EMPW) installed in the accumulation ring of the National Laboratory for High Energy Physics at Tsukuba. The spectrometer has four sets of a Cauchois‐type energy analyzer and an imaging plate, which are arranged on the surface of a cone and share a scattering angle of 160°. In each energy‐analyzing system, to increase signal to noise ratio a set of vertical and horizontal slits are inserted between the analyzer and the imaging plate. A resolution of 0.13 a.u. in terms of electron momentum was achieved. A Compton profile of a vanadium single crystal was measured with an integrated counting rate of 400 counts/s.

Simulation of Compton Double Scatterings of Circularly Polarized γ-Rays by Magnetic Electrons

In a recent study on the magnetic-electron Compton profile measurement by the author, an important correction of the spin-dependent multiple scatterings of circularly polarized γ-rays in a specimen was made on the basis of a computer simulation of the double scattering. This paper describes the detailed procedure of its simulation. It is found that the spin-dependent double scattering intensity is about one third of the ordinary double scattering intensity, due to the mutual cancellation among the intensities of spin-dependent double scattered γ-rays themselves.

Magnetic Compton profiles of FCC-Ni, FCC-Fe50Ni50and HCP-Co

Experimental and theoretical directional magnetic Compton profiles (MCPs) of hcp-Co, fcc-Fe 50 Ni 50 and fcc-Ni are compared with each other to elucidate the difference of the electronic structure...

An X-ray spectrometer for Compton scattering experiments with synchrotron radiation

An X-ray spectrometer has been designed and constructed for Compton-scattering experiments using 29.5 keV X-rays from a vertical wiggler inserted in the 2.5 GeV storage ring of the Photon Factory at Tsukuba. It consists of a bent-crystal monochromator, a Cauchois-type bent-crystal analyzer and a position-sensitive detector. The measured incident flux on a sample is just over 1011 photons/s. An overall resolution in momentum of 0.10 atomic units (FWHM) has been achieved. The Compton profile of an aluminum single crystal was measured with a mean count rate of 28 cps. As a result of the high resolution in the measurements a sharp cutoff at the Fermi momentum was readily observed.

Measurement of the Compton Profile for Magnetic Electrons in Iron

The spin-dependent Compton scattering of circularly polarized γ-rays is applied for the first time to measure the momentum distribution of magnetic electrons in magnetized iron. The experimental techniques are described in detail. The observed profile shows a hollow around zero momentum, indicating the negative magnetization of a part of the conduction electrons. The results are discussed in comparison with the theoretical results of Wakoh, Kubo, and Yamashita.

Compton Scattering Study of Electron Momentum Density in Vanadium

The [100], [110] and [111] Compton profiles of vanadium are measured with a momentum resolution of 0.12 atomic units. The observed profiles have fine structures and directional anisotropies. Comparison of the results with the APW band theoretical predictions shows that the band theory overestimates the momentum density at low momenta and underestimates it at high momenta. The theory also overemphasizes the fine structures and the scale of the anisotropies.

Water-cooled quasi-doubly bent crystal monochromator for Compton scattering experiments

Commissioning and performance of a water‐cooled quasi doubly bent crystal monochromator for Compton scattering experiments are described. The monochromator consists of an array of twenty singly bent crystals. Each crystal is half immersed in liquid Ga‐ln alloy contained in a water‐cooled holder. This is necessary because the monochromator must be able to withstand heat load of 4 kW from synchrotron radiation from an ellipsoid multipole wiggler at the 6.5 GeV accumulation ring. The alignment procedure for twenty singly bent crystals is described in detail. Its performance is as follows; the focused beam size of 60 keV x rays is about 3 mm (vertical) and 8 mm (horizontal). The flux is 6×1012 photons/s at stored currents of 30 mA and the energy resolution is 88 eV for 60 keV x rays. Heating of various adjusting mechanisms by Compton scattered x rays from both the absorber used to suppress low energy x rays and the monochromator crystals is found to be a very serious problem for designing a high energy x‐ray ...

Electrons and Positrons in Amorphous Mg70Zn30

Measurements of the Compton profiles and angular correlations of positron annihilation radiations on the amorphous Mg 70 Zn 30 alloy are carried out. From the Compton profile measurement it is found that the valence electrons are free-electron like and the Fermi momentum is 0.77 ±0.02 atomic units ( k F =1.46 ±0.02 A -1 ) in agreement with the value calculated from a simple electron gas model. The angular correlations of positron annihilation radiations measured at 80 K and 300 K show significant smearing of the break at the Fermi momentum. The smearing at 80 K is heavier than that at 300 K. The smearing is found to be caused by localization of the positron. The potential for localization of the positron is much shallower and wider than that due to a vacancy in crystalline materials. The positrons are localized in low density dilated regions of the amorphous structure.

Application of circularly polarized x-rays to magnetic Compton-scattering experiments

Abstract Magnetic Compton-scattering experiments are successfully applied to the measurement of the electron-spin densities of Fe and Ni metals in momentum space. Circularly polarized 60-keV X-rays emitted from an elliptical multipole wiggler installed at the 6.5-GeV storage ring of National Laboratory for High Energy Physics (KEK) were used in these experiments. The highest statistical accuracy ever achieved is obtained. The results of ferromagnetic Fe and Ni are compared with recent band-theoretical magnetic Compton profiles calculated by Kubo and Asano using the full-potential linearized augumented-plane-wave method. Contrary to previous investigations, excellent agreement is found between the experiment and the theory. This paper also gives a brief introduction of the Compton profile, following the aim of the symposium.

Experimental Compton Profiles of Magnesium

Directional Compton profiles for magnesium single crystals are measured using 60 keV γ rays, and are compared with the theoretical profiles calculated by the APW method. Good agreement is found between the experimental and the theoretical Compton profiles. However, the conduction electron part of the experimental Compton profile is slightly broader than that of the theoretical one. A reason for this broadening is discussed by considering non-constant occupation probability of the conduction electrons caused by the electron-electron correlation. No crystalline anisotropy of the experimental directional profiles is found, being consistent with the theoretical results.