Parity violation at neutron p-wave resonances of238U and232Th and related questions

Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei²³⁸U and²³²Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for²³⁸U, respectively 1.39 (+0.35/-0.38) meV for²³²Th.     

Heat capacity of the Pb<Subscript>5</Subscript>(Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>)<Subscript>3</Subscript>O<Subscript>11</Subscript> ferroelectric system

The temperature dependences of the molar heat capacity at constant pressure, C_p, of Pb₅(Ge_1?xSi_x)₃O₁₁ crystals with x=0, 0.39, and 0.45 in the range 5–300 K, as well as of their permittivity, dielectric losses, and the pyroelectric effect, have been measured. Experimental data on the temperature behavior of the heat capacity are presented in the form of a sum of two Debye and one Einstein terms, C_p(T)=0.405C_D1(Θ_D1=160 K, T)+0.53C_D2(Θ_D2=750 K, T)+0.046C_E(Θ_E=47 K, T). Besides a peak in the region of the ferroelectric Curie point T_c=450 K for crystals with x=0, the temperature dependences of the heat capacity did not reveal any other pronounced anomalies.     

Anomalies in the physical properties of the α form of bismuth oxide

Several of the physical properties of α-Bi₂O₃ have been studied in the temperature region above room temperature: the thermal expansion, the thermally stimulated current, the permittivity, the electrical resistance, and the specific heat. X-ray diffraction measurements and a thermogravimetric analysis have also been carried out. Several unusual properties in the physical properties of bismuth oxide have been detected in the temperature interval 450–570 K: exothermic maxima on the DTA and DSC curves, a small maximum and a sharp increase of the permittivity of the single crystal, a jump and a change of sign in the thermally stimulated current, and a sharp falloff of the electrical resistance of ceramic samples. At the same time, no appreciable changes in the monoclinic structure of α-Bi₂O₃ have been recorded in the indicated temperature interval. Fiz. Tverd. Tela (St. Petersburg) 39, 865–870 (May 1997)     

Composition-induced transition of spin-modulated structure into a uniform antiferromagnetic state in a Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>x</Subscript>FeO<Subscript>3</Subscript> system studied using <Superscript>57</Superscript>Fe NMR

By analyzing the NMR line shape, the transformation of a spatially spin-modulated magnetic structure in BiFeO₃ into an ordinary spatially uniform structure of the LaFeO₃ orthoferrite in Bi_1?xLa_xFeO₃ solid solutions is studied. The measurements are made using a spin-echo technique at temperatures of 77 and 4.2 K on ceramics with compositions x=0, 0.1, 0.2, 0.61, 0.9, and 1.0 enriched by the ⁵⁷Fe isotope. It is shown that the spin-modulated structure disappears near the concentration x=0.2, which corresponds, according to the published data, to the phase transition with a change in the unit-cell symmetry R3c → C222. A formula is obtained describing the NMR absorption line shape for the spin-modulated structure with account of local line-width. Theoretical spectra adequately describe the evolution of the experimental spectrum in the concentration range 0≤x≤0.2. Highly nonuniform local magnetic fields in the intermediate compositions make it impossible to detect NMR signals in a sample with x=0.61. A uniform magnetic structure characterized by a single narrow line arises in the range of existence of a phase with the symmetry Pnma typical of the pure orthoferrite LaFeO₃.