Tsutomu Mashimo

Gravity-induced diffusion of isotope atoms in monoatomic solid Se

A strong gravitational field resulted in the gravity-induced diffusion (sedimentation) of isotope atoms in monoatomic solid Se. The layer crystalline morphology consisting of three zones of the fine-grained crystals, the long crystals and feather-shaped crystals grown parallel to gravity direction appeared in the specimen ultracentrifuged at (0.8–1)×106 G and at 190 °C. Change in the concentration ratio 82Se/76Se of >0.8% was observed in the grown crystalline region. These results show an evidence for the sedimentation of substitutional atoms in solids via self-diffusion, and suggest the possibility of application to the control of impurity and crystalline states as well as to isotope separation.

Isotope Fluctuation in Indium-Lead Alloy Induced by Solid Centrifugation

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge experiment under conditions that a gravitational field of 0.81 × 106G for 100 hours at 150°C (solid state) in our previous study. The isotope fluctuation on this sample was measured using secondary ion mass spectrometer (SIMS). The 115In/113In isotope ratio changed with positive gradient in the direction of centrifugal force approximately 1.2%. The isotope ratio fluctuation of centrifuged sample was 4 times larger than that of starting sample (<0.3%). This showed that the isotope fractionation effect was induced by solid centrifugation in this alloy, although achieved concentration gradients were small.

Isotope Separation by Condensed Matter Centrifugation: Sedimentation of Isotope Atoms in Se

The sedimentation of isotope atoms has been realized in monoatomic liquid and solid Se. It was observed that the concentration ratio 82Se/76Se increased by % level in the specimen ultracentrifuged at 0.7–0.9 million G under liquid and solid states. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion, and suggests its possible application to isotope separation by condensed matter centrifugation.

Ultracentrifuge Experiment on an Mg‐Cd Order‐Disorder Alloy

We had previously realized atomic‐scale graded structures in several miscible alloys by an ultracentrifuge experiment. In this study, we performed an ultracentrifuge experiment on a MgCd order‐disorder alloy at disordered state of solid solution. The experimental conditions were as follows: maximum acceleration: 0.61×106 g level, temperature: 400 °C, composition: Mg:Cd = 50:50 at%, time duration: 60 h. The ultracentrifuge was stopped after cooling the sample from 400 °C (disordered state) to 100 °C (ordered state). According to the composition analysis by EPMA, the graded structure was formed in the centrifuged sample, in which Cd content continuously increased in the direction of gravitational field. We also investigated the crystal state of the centrifuged sample by XRD. It was found that there was changing of unit cell volume with composition. This result showed that the graded structure was continuous in atomic‐scale and it was formed by sedimentation of atoms. Based on the simulation of sedimentation process, the diffusion coefficient for sedimentation in this alloy was estimated to be almost the same as usual diffusion. We also found that the existence of an unusual crystal state might also be considered due to the disorder‐order transformation under the strong gravitational field.We had previously realized atomic‐scale graded structures in several miscible alloys by an ultracentrifuge experiment. In this study, we performed an ultracentrifuge experiment on a MgCd order‐disorder alloy at disordered state of solid solution. The experimental conditions were as follows: maximum acceleration: 0.61×106 g level, temperature: 400 °C, composition: Mg:Cd = 50:50 at%, time duration: 60 h. The ultracentrifuge was stopped after cooling the sample from 400 °C (disordered state) to 100 °C (ordered state). According to the composition analysis by EPMA, the graded structure was formed in the centrifuged sample, in which Cd content continuously increased in the direction of gravitational field. We also investigated the crystal state of the centrifuged sample by XRD. It was found that there was changing of unit cell volume with composition. This result showed that the graded structure was continuous in atomic‐scale and it was formed by sedimentation of atoms. Based on the simulation of sedimentation...