Evidence for Magnon BEC in Superfluid <Superscript>3</Superscript>He-A

The phenomenon of phase-coherent precession of magnetization in superfluid ³He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession have been observed in ³He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and two new modes of coherent precession in compressed aerogel. Here we present evidence of magnons Bose-Einstein condensation in ³He-A in a compressed aerogel.     

Density Equation for Saturated <Superscript>3</Superscript>He

A density equation for saturated vapor and liquid ³He is presented based on 205 experimental measurements for temperatures greater than 0.2 K collected after a careful survey of the literature. The average deviation of the densities predicted by the equation against the experimental values is 0.39%. There are only 16 points with deviations larger than 1%. This equation is valid for both liquid and vapor densities of ³He up to the critical temperature of 3.3157 K. The form of the equation satisfies known scaling laws approaching the critical point, with β=0.3653. In the low-density limit, the vapor curve of our equation matches smoothly to the published virial equation density at a temperature of 1.62 K and at the saturation pressure. The rectilinear density deviates from the critical density by less than 0.28% down to 0.48 K.     

Excitation and Detection of Surface Waves on Normal and Superfluid 3He

We describe the measurement principles to excite and detect surface waves on liquid helium at very low temperatures. We excited the waves mechanically by rocking the whole cryostat with frequencies of few hertz. The waves were detected capacitively with an interdigital capacitor on a vertical wall of the cuboid experimental volume. In superfluid ³He at around 0.2 mK at least eleven surface resonances were observed below 11 Hz whereas in normal fluid only a few resonances were observable above 50 mK.     

Induced Gravity in Superfluid 3He

The gapless fermionic excitations in superfluid ³ He-A have the relativistic spectrum close to the gap nodes. This allowed us to model the modern cos-mological scenaria of baryogenesis and magnetogenesis. The same massless fermions induce another low-energy property of the quantum vacuum – the gravitation. The effective metric of the space, in which the free quasiparticles move along geodesies, is not generally flat. Different order parameter textures correspond to curved effective space and produce many different exotic metrics, which are theoretically discussed in quantum gravity and cosmology. This includes the condensed matter analog of the black hole and event horizon, which can be realized in the moving soliton. This will allow us to simulate and thus experimentally investigate such quantum phenomena as the Hawking radiation from the horizon, the Bekenstein entropy of the black hole, and the structure of the quantum vacuum behind the horizon. One can also simulate the conical singularities produced by cosmic strings and monopoles; inflation; temperature dependence of the cosmological and Newton constants, etc.     

Faraday Instability on a Free Surface of Superfluid 4He

We observed that the Faraday waves were parametrically generated on a free surface of superfluid ⁴He. Our sample cell was supported by plate springs and had a permanent magnet on the top. It was oscillated by applying oscillating current to a superconducting coil. We prepared the sample cell made of polycarbonate so as to optically observe the superfluid surface. Standing wave patterns appeared on the surface and their frequencies were one half of a driving frequency. We observed clear threshold amplitude of the oscillation for the instability. Threshold is usually determined by the viscosity of fluid and thus there must be a dissipation mechanism in superfluid for the threshold.     

Molecular analysis of isotopically enriched <Superscript>28</Superscript>SiF<Subscript>4</Subscript> and <Superscript>28</Superscript>SiH<Subscript>4</Subscript> prepared from it

We have developed analytical techniques for the determination of impurities in isotopically enriched ²⁸SiH₄ and ²⁸SiF₄. The impurities in SiF₄ were first determined by IR spectroscopy, and those in SiH₄, by gas chromatography/mass spectrometry. High-sensitivity determination of organic impurities in SiH₄ and SiF₄ was performed by gas chromatography. SiF₄ was found to contain C₁–C₄ hydrocarbons, hexafluorodisiloxane (Si₂F₆O), hydrogen fluoride, trifluorosilanol (SiF₃OH), fluorosilanes, water, and carbon oxides. The impurities identified in SiH₄ include C₁–C₄ hydrocarbons, disilane (Si₂H₆), inorganic hydrides, Si₂H₆O, alkylsilanes, and fluorinated and chlorinated organics. The detection limits of IR spectroscopy were 3 × 10^?3 to 5 × 10^?5 mol %, those of gas chromatography/mass spectrometry were 8 × 10^?6 to 10^?8 mol %, and those of gas chromatography were 6 × 10^-6 to 2 × 10^?7 mol %.     

Nonlinear Second Sound Waves and Acoustic Turbulence in Superfluid 4He

The preliminary results of an investigation of nonlinear second sound waves in a high quality resonator filled with superfluid ⁴He are presented and discussed. It is found that, for a sufficiently strong periodic driving force, a cascade of second sound waves is formed at multiple harmonics of the driving frequency over the extremely wide frequency range 1–100 kHz. It can be described by a power law A _ω =const.×ω ^−m , where the scaling index m≈1. These observation can be attributed to the formation of a Kolmogorov-like turbulent cascade in the system of second sound waves, accompanied by directed energy flux through the frequency scales. It manifests itself as a limiting of the amplitude of a standing wave, a distortion of the shape of the initially harmonic waves, and a reduction of the effective quality factor Q of the resonator.     

Isolation of <Superscript>58</Superscript>Co, <Superscript>54</Superscript>Mn,and <Superscript>86</Superscript>Rb from <Superscript>89</Superscript>Sr production wastes

Procedures for isolation of ⁵⁸Co, ⁵⁴Mn, and ⁸⁶Rb from ⁸⁹Sr production wastes are described. The production of ⁸⁹Sr was based on irradiation of natural Y in the form of oxide, placed in 1Cr18Ni10Ti stainless steel ampules, on a BR-10 fast reactor. ⁵⁸Co and ⁵⁴Mn were isolated from the casings of stainless steel ampules, and ⁸⁶Rb, from the tail solution after the isolation of ⁸⁹Sr.     

Surface hardening in N<Superscript>+</Superscript> implanted polycarbonate

The influence of low energy nitrogen ions on the surface hardness of polycarbonate has been studied by implanting some of these specimens with 100 keV N⁺ ions at a beam current of 1 μA/cm² in the dose range of 1 × 10¹⁵ to 1 × 10¹⁷ ions cm^?2. Knoop microhardness has been found to be increased nearly 24 times at a load of 9.8 mN, for the dose of 1 × 10¹⁷ ions cm^?2. The structural changes occurred in implanted specimens were studied by Raman analysis, UV–Visible spectroscopy, and X-ray diffraction techniques. Raman studies point toward the formation of a structure resembling hydrogenated amorphous carbon. Disordering in the surface structure (I _D/I _G ratio) has also been found to increase with ion fluence using Raman technique. UV–Visible spectroscopic analysis shows a clear enhancement in Urbach energy (disorder parameter) from a value of 0.61 eV (virgin sample) to 1.72 eV (at a fluence of 1 × 10¹⁷ N⁺ cm^?2) with increasing ion dose. The increase in Urbach energy has been found to be correlated linearly with the increase in Knoop microhardness number. Results of X-ray diffraction analysis also indicate disordering in implanted layers as a result of implantation. In the present work, the possible mechanism behind the formation of harder surfaces due to implantation has been discussed in detail.     

High-purity silicon isotopes <Superscript>28</Superscript>Si, <Superscript>29</Superscript>Si,and <Superscript>30</Superscript>Si

The current status of the problem of obtaining high-purity silicon isotopes ²⁸Si, ²⁹Si, and ³⁰Si is analyzed. The scheme of obtaining monoisotopic silicon includes the stages of isotope separation in the form SiF₄, synthesis and deep purification of isotopically enriched silane, obtaining polycrystalline silicon-28,-29, and-30, and growing monocrystals. The basic problems and methods of their solution in the synthesis and deep purification of silane and obtaining poly-and monocrystals of isotopically enriched silicon are discussed. Data characterizing the achieved level of chemical and isotopic purity of high-purity monocrystals of silicon-28 with a main isotope content of more than 99.99% and silicon-29 and silicon-30 with isotopic purity higher than 99% are presented. In monocrystalline ²⁸Si, the boron content was 4.5 × 10¹³, the phosphorus content was 5 × 10¹¹, the carbon and oxygen contents were <1 × 10¹⁶ at/cm³, and the specific resistance was 800 Ω cm. The results of investigation of heat capacity, heat conduction, photoluminescence, and electron paramagnetic resonance spectra for monoisotopic silicon-28 are presented. The heat conduction of monoisotopic silicon is increased considerably owing to the reduced photon scattering on isotopic inhomogeneities. In the region of 20–30 K, the heat conduction of silicon-28 with an isotopic purity of 99.98% is higher by a factor of 8 than the heat conduction of natural silicon. Investigations of photoluminescence spectra in the magnetic field in the low-temperature region demonstrated the capability of optical detection of nuclear spin states of a phosphorus admixture in high-purity silicon-28. p ]Topical questions for further investigations and possible fields of practical application of high-purity isotopically enriched silicon are discussed.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Influence of Mn<Superscript>2+</Superscript> on the up-conversion emission performance of Mn<Superscript>2+</Superscript>, Yb<Superscript>3+</Superscript>, Er<Superscript>3+</Superscript>: ZnWO<Subscript>4</Subscript> green phosphors

The Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors are synthesized successfully through the high temperature solid state reaction method. The micro-structure and morphology have been investigated by means of XRD and EDS. The doped concentrations of Mn²⁺, Yb³⁺, Er³⁺ are measured by ICP. The absorption spectra and emission spectra with different doped concentrations of Mn²⁺ are presented to reveal the influence of Mn²⁺ on the green up-conversion performance. Excited with 970 nm LED, the up-conversion emission peak at 547 nm is obtained and the CIE spectra as well as the green light photo are also presented. The results indicate that the Mn²⁺ ions play the role of the luminescence adjustment in the up-conversion process, which can improve the up-conversion green emission intensity effectively. The luminescence adjustment mechanism of Mn²⁺ ions in Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors has been discussed. The crystal parameters of Dq, B and C are calculated to evaluate the energy level split effect.     

Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

<Superscript>133</Superscript>Xe in Surface Air of St. Petersburg

In the course of testing new devices for measuring atmospheric concentrations of radioactive noble gases and also of the monitoring techniques, large number (116) of determinations of Xe in surface air of St. Petersburg was made (100 in the period from December 1997 to December 1998 and 16 in the second half of March 2000). In 1998, samples were taken at 6-h to 7-day intervals with documentation of data on the wind direction, and in 2000, at 1-day intervals, but without fixing the wind direction. Statistical treatment of data obtained in 1998 gives the mean volume activity of 2.3 ± 0.6 mBq m^?3. In 1998, this value was exceeded in three cases by a factor of 2–3 and in six cases by a factor of 5–16. In March 2000, even higher values were observed, exceeding by a factor of up to 43, which was caused essentially by releases from the Leningrad NPP. Data obtained in 1998 also show that the specific activity of ¹³³Xe depends on the wind direction.     

Behavior of Microamounts of <Superscript>22</Superscript>Na, <Superscript>85</Superscript>Sr, <Superscript>137</Superscript>Cs,and <Superscript>152</Superscript>Eu in Sorption and Coprecipitation on Mixed Potassium Neodymium Ferrocyanide from Solutions

Sorption of ⁸⁵Sr, ¹³⁷Cs, ²²Na, and ¹⁵²Eu on solid mixed potassium neodymium ferrocyanide KNd[Fe(CN)₆]·4H₂O from neutral, acidic, and alkaline media and also coprecipitation of these radionuclides with KNd[Fe(CN)₆]·4H₂O in its formation from a homogeneous solution were studied. It was found that ⁸⁵Sr and ²²Na do not noticeably coprecipitate with solid KNd[Fe(CN)₆]·4H₂O and are not sorbed by this substance. In aqueous medium, depending on the cesium concentration in solution, from 80 to 98% of ¹³⁷Cs coprecipitates with solid KNd[Fe(CN)₆]·4H₂O. In this case, the distribution coefficient K_d depends on both the cesium concentration in solution and solution pH. Within 30 min of contact of the solid and liquid phases, the degree of recovery of ¹³⁷Cs from aqueous solution with KNd[Fe(CN)₆]·4H₂O is approximately 95.0% of the initial amount. ¹⁵²Eu coprecipitates with solid KNd[Fe(CN)₆]·4H₂O during its formation from a homogeneous solution to 98–99.9%. The degree of recovery of ¹⁵²Eu from aqueous solution with KNd[Fe(CN)₆]·4H₂O precipitate within 60 min of contact of the solid and liquid phases is 70.3% of the initial amount.     

Fine purification of monoisotopic <Superscript>32</Superscript>S and <Superscript>34</Superscript>S

We have proposed and tested a combined process for ultrapurification of monoisotopic ³²S and ³⁴S sulfur, which comprises thermochemical treatment of sulfur vapor on silica and ceria packing, melting with aluminum, and distillation. The impurity composition of the purified sulfur has been determined by atomic emission and IR spectroscopy. We have obtained monoisotopic ³²S and ³⁴S sulfur samples comparable in chemical purity to high-purity sulfur of natural isotopic composition.     

Ultrapurification of <Superscript>76</Superscript>Ge-enriched GeH<Subscript>4</Subscript> by distillation

⁷⁶Ge-enriched germane has been ultrapurified by low-temperature distillation. The nature and concentration of molecular impurities in the germane samples were determined by gas chromatography/mass spectrometry, high-resolution Fourier transform IR spectroscopy, and gas chromatography. The distillate contains no more than 10⁻⁵ mol % hydrocarbons, 10⁻⁴ mol % carbon dioxide, 10⁻³ to 10⁻¹ mol % digermane and trigermane, and <3 × 10⁻⁵ mol % other impurities. A distinctive feature of the impurity composition of the isotopically enriched germane samples is the presence of silicon tetrafluoride and sulfur hexafluoride impurities.