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The high-pressure form of cerium metal stable above 51 kbar, α'-Ce, is found to be orthorhombic with the α-uranium type of structure. At 58 kbar the cell dimensions of α'-Ce are a = 3.049, b = 5.998, c = 5.215 A. A second, metastable, phase of cerium metal, α”-Ce, has also been observed. It is monoclinic body-centered with a deformed cubic face-centered structure. The cell dimensions of α”-Ce at 56 kbar are a = 4.762, b = 3.170, c = 3.169 A, flβ = 91.73°. The volume change at the a-α' transition point is ΔV/V = 0.011. Cerium metal is fully tetravalent in both α'-Ce and α”-Ce.

The σ′ plutonium is found to be body-centered-tetragonal with two atoms per unit cell at 000 and 1/2, 1/2, 1/2. The unit cell dimensions at 477°C are α = 3.339 ± 0.003A and c = 4.446 ± 0.007A, which lead to a calculated density of 16.01 g per eu cm. Each plutonium atom is surrounded by 12 others at a mean distance of 3.275Ă. The linear coefficient of thermal expansion perpendicular to the c-axis is 106 ᾱa = 305 ±35 per °C, and parallel to the c-axis is 106 ᾱc=−659 ± 67 per °C. The average linear coefficient, (2ᾱa + ᾱc)/3, is equal to 106ᾱL = −18 ± 28 per °C. The linear coefficient of themal expansion of face-centered-cubic σ plutonium is found to be 106 ᾱL=−8.6 ± 0.3 per °C, and of body-centered-cubic ∈ plutonium 106 ᾱL = 36.5 ±1.1 per °C.

The crystal structure of americium was studied using metals produced by two different methods. The methods used in preparing the metal are described. Diffraction data are presented for the metal, comparing observed values with those calculated for crystals indexed as double hexagonal close-packed, hexagonal close-packed, and face centered cubic, and for AmO. The results are compared with results obtained previously. Magnetic susceptibility measurements and high temperature x-ray studies are in progress. (B.O.G.)

From abstract: "A compound that is shown to be KAmO₂F₂ is prepared by the addition of a saturated solution of KF to an acid solution of pentavalent americium." The report further discusses the crystal structure, lattice parameters, number of molecules per unit cell, space group, and atomic positions for the compound.