A practical density equation for saturated vapor of helium-3 from 0.01 K to the critical point

Based on the ideal gas state equation and the saturated vapor pressure equation of helium-3, a saturated vapor density equation is proposed, which can be applied for calculating the saturated vapor density of helium-3 from 0.01 K to the critical temperature. Above 1.4 K, the average deviation between the results by this equation and experimental data is about 0.66% and the maximum is 2%. Below 1.4 K, the results of this work show a comfortable agreement with those by virial state equation (the deviations are generally within 0.1%). Based on this new vapor density equation, the compressibility factor of saturated vapor is determined and the vaporization heat is calculated.     

A small helium-3 pulse-tube refrigerator

A new three-stage pulse-tube refrigerator (PTR) is developed by scaling down a previous PTR by 50%. The new system is small in size and weight, capable of operating using little input power, and uses a small amount of working gas and regenerator material. In addition to that the system is flexible and convenient for modifications. The volume of the low-temperature part of the new PTR (pulse tubes + regenerator) is as small as 0.28 l. With ³He as a working fluid a no-load temperature of 1.73 K is reached and a cooling power of 124 mW at 4.2 K is realized.     

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.     

A generalized equation for the saturation vapor pressure of individual substances

A generalized equation for calculating the saturation vapor pressure of individual substances at temperatures from the triple to the critical point is derived. The error of the calculation is close to the error of experimental data. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 37–41, July, 2008.     

A three-stage Stirling pulse tube cryocooler operating below the critical point of helium-4

Precooled phase shifters can significantly enhance the phase shift effect and further improve the performance of pulse tube cryocoolers. A separate three-stage Stirling pulse tube cryocooler (SPTC) with a cold inertance tube was designed and fabricated. Helium-4 instead of the rare helium-3 was used as the working fluid. The cryocooler reached a bottom temperature of 4.97 K with a net cooling power of 25 mW at 6.0 K. The operating frequency was 29.9 Hz and the charging pressure was 0.91 MPa. It is the first time a refrigeration temperature below the critical point of helium-4 was obtained in a three-stage Stirling pulse tube cryocooler.     

50 mK cooling solution with an ADR precooled by a sorption cooler

CEA/SBT is currently developing a 2.5 K-50 mK cooling solution composed of a small demagnetization refrigerator (ADR) precooled by a sorption cooler, equivalent to the high temperature stage of a two-stage ADR system. Thanks to the use of this dual technology, a low weight cooler able to reach 50 mK with a heat sink up to 2.5 K can be designed. Because the sorption cooler is probably the lightest solution to produce sub-Kelvin temperatures, these developments allow us to propose a solution to face the drastic reduction in the mass budget of space missions like SPICA or IXO. The European Space Agency (ESA) is funding the development of an engineering model able to produce 1 μW net heat lift at 50 mK. It is sized so that the sorption cooler provides an additional 10 μW at 300 mK. The ESA main requirements are an autonomy of more than 24 h and a recycling time smaller than 8 h. We present the design of the system able to meet these requirements as well as the expected performances and preliminary measurements.     

0.2 K～300 K温区氦-3的p-h和T-s图

基于最新的德拜模型氦-3状态方程、氦-3饱和曲线特征方程和熔化曲线特征方程编写了氦-3热物性计算程序.在大量热物性的计算数据的基础上绘制了氦-3在0.2 K～300 K,0.000 1MPa～30 MPa范围内的p-h图和T-s图.与先前基于实验数据绘制的0.2 K～20 K温区氦-3的p-h图和T-s图相比,该图的绘制是建立在热力学理论计算的基础之上,适用温区得到了拓展,随机误差一般在2%以内.     

Efficient Bi → Nd energy transfer in Gd2O3:Bi,Nd

Bi³⁺,Nd³⁺ co-doped Gd₂O₃ were prepared by solid state reaction and the optical properties were investigated. The results show that the near-infrared emission of Nd³⁺ ions is significantly enhanced by the introducing of Bi³⁺ in co-doped samples. An efficient energy transfer from Bi³⁺ to Nd³⁺ corresponds to the near-infrared emission enhancement. The energy transfer efficiency reaches 64.1% for the sample with the strongest near-infrared emission, which has the optimized doping concentrations of 0.5% for Bi³⁺ and 2% for Nd³⁺. The interesting optical properties make Bi³⁺,Nd³⁺ co-doped Gd₂O₃ promising as the luminescent down-conversion layers in front of c-Si solar cells to enhance the performance of the solar cells.     

Realization of the 3He Melting Pressure Scale, PLTS-2000

The Provisional Low Temperature Scale of 2000, PLTS-2000, which was adopted in October 2000, uses the melting pressure of ³He to provide the basis for temperature measurement in the range from the Néel temperature of the solid, T ₂₀₀₀=0.902 mK, up to 1 K. The definition and derivation of the scale has been published, and the present paper now gives guidance on the practical methods by which the melting pressures can be measured in the laboratory. Various options are described, depending on the equipment available, and the uncertainties that may be achieved are considered.      

PIXE detection limits for dental enamel from some human teeth by excitation with protons and He ions from a 3 MeV Van der Graaff accelerator

A technique has been developed to measure elemental content in human teeth using H⁺ and ⁴He²⁺ ion beam analysis. Teeth of Oradea inhabitants were sampled in two stomatological clinics in Oradea in the period of 2004 and 2005 years. Tooth samples were irradiated in vacuum with 2 MeV proton and 3 MeV alpha beams from a Van der Graaff electrostatic accelerator of EG-5 experimental facility in FLNP, JINR. The particle induced X-ray emission (PIXE) analysis, apart from determination of Ca, allowed an optimised detection of Cr, Cu, Fe and Zn above the detection limits by the use of Al and Mylar filters. The detection limits for K_α X-rays using proton and alpha beams are determined and discussed.     

Scaling Results for Superfluid 3He in 98% Open Aerogel

We present experimental observations of the suppressed superfluid transition temperature, T _ca , superfluid fraction, ρ _s /ρ and Leggett frequency of ³He-B in aerogel, Ω _Ba . We determine T _ca from mass decoupling and the vanishing of the frequency shift away from the Larmor frequency in our different samples and different laboratories. We find that the suppressed transition temperature for ³He in aerogel occurs at a sample dependent, but approximately pressure independent, length, , where T _c and ξ ₀(P), are the transition temperature and the pressure dependent zero temperature coherence length for bulk ³He. T _ca also occurs at a pressure independent value of the Leggett frequency of bulk ³He-B. Further, we find that when the superfluid fraction and square of the Leggett frequency are plotted against T _ca −T (and not (T _ca −T)/T _ca ), the results of each measurement nearly collapse on to a pressure independent but sample dependent plot, with no further scaling. When plotted on a log–log scale, both measurements exhibit power laws in the range 1.33–1.45.      

A New Method for Precision Cold Neutron Polarimetry Using a 3He Spin Filter

We present a new method for precision measurement of the capture flux polarization of a polychromatic (white), continuous cold neutron beam, polarized by a ³He spin filter. This method allows an in situ measurement and does not require knowledge of the neutron beam wavelength distribution. We show that a polarimetry precision of 0.1 % is possible.     

Spin-Orbital Dynamics in the B-Phase of Superfluid Helium-3

We report numerical calculations on the spin–orbital dynamics of ³He-B within the formalism of Poisson brackets with the two-fluid model by Leggett and Takagi. We incorporate an additional orbital term in the equations for the spin–orbit dynamics which plays an important role at very low temperatures, when the damping of orbit dynamics is small. We also find that, under the relevant experimental conditions, the Brinkman–Smith mode is strongly modified by the orbital dynamics. The orbital momentum does not relax completely to the direction of magnetic field, but remains significantly deflected, particularly at very low temperatures, and precesses at the dipole–dipole frequency and nutate at the NMR frequency. We report numerical calculations of the spin–orbit dynamics in the spatially inhomogeneous case. We solved for the mode of precession near the walls of the experimental cell, which significantly deviates from that, obtained in theoretical calculations in previous publications. We also identified the mechanism of instability of homogeneous precession at very low temperatures, the exponential growth of textural-spin waves of the longitudinal mode of NMR.     

Luminescence excitation spectra of TbX3 (X = Cl, Br, I)

A systematic study of the excitation spectrum of TbX₃ (X = Cl⁻, Br⁻, I⁻) is presented in this work. In general, the excitation spectra of TbX₃ can be divided into three major regions: (1) the short-wave host lattice absorption region, (2) the intermediate absorption region where the Tb³⁺ 4f⁸ → 4f⁷5d¹ interconfigurational excitation transition are located, and (3) the long-wave excitation region where the Tb³⁺ 4f⁸ → 4f⁸ intraconfigurational excitation transition are located. The high spin and the low spin components of the Tb³⁺ interconfigurational excitation transition are clearly identified in the case of TbCl₃. The luminescence of TbX₃ (X = Cl⁻, Br⁻, I⁻) is dominated by emission transitions emanating from the Tb³⁺⁵D₄ state. A comparative study of the optical properties of TbX₃ (X = Cl⁻, Br⁻, I⁻) with the properties of the Tb³⁺ ion in several halide host lattices is presented. Further, a comparative study of the fundamental host lattice optical transitions in terbium halides and other halide materials is also presented.     

He and BF3 neutron detector pressure effect and model comparison

Radiation detection systems for homeland security applications must possess the capability of detecting both gamma rays and neutrons. The radiation portal monitor systems that are currently deployed use a plastic scintillator for detecting gamma rays and ³He gas-filled proportional counters for detecting neutrons. Proportional counters filled with ³He are the preferred neutron detectors for use in radiation portal monitor systems because ³He has a large neutron cross-section, is relatively insensitive to gamma-rays, is neither toxic nor corrosive, can withstand extreme environments, and can be operated at a lower voltage than some of the alternative proportional counters. The amount of ³He required for homeland security and science applications has depleted the world supply and there is no longer enough available to fill the demand. Thus, alternative neutron detectors are being explored.Two possible temporary solutions that could be utilized while a more permanent solution is being identified are reducing the ³He pressure in the proportional counters and using boron trifluoride gas-filled proportional counters. Reducing the amount of ³He required in each of the proportional counters would decrease the rate at which ³He is being used; not enough to solve the shortage, but perhaps enough to increase the amount of time available to find a working replacement. Boron trifluoride is not appropriate for all situations as these detectors are less sensitive than ³He, boron trifluoride gas is corrosive, and a much higher voltage is required than what is used with ³He detectors. Measurements of the neutron detection efficiency of ³He and boron trifluoride as a function of tube pressure were made. The experimental results were also used to validate models of the radiation portal monitor systems.     

Electrical properties of lead-free thick film NTC thermistors based on perovskite-type BaCoxCo2xBi1 − 3xO3

Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCo^II_xCo^III_2xBi_1 − 3xO₃ (x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO₃ thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity (ρ₂₃), thermistor constant (B_25/85) and activation energy are in the range of 1.995-2.975 Ω cm, 1140-1234 K and 0.102-0.111 eV, respectively.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Physical Mechanisms for Effective Mass Enhancement in 3He

We use structural information from simulations and from variational ground state calculations for calculating the effective mass of ³He at zero temperature. It is found that the relatively large effective mass is due to a combination of several physical effects: Density fluctuations cause an effective mass enhancement due to predominantly hydrodynamic backflow. This effect is, around the Fermi momentum, a smooth function of the single particle wave number; its magnitude is consistent with the effective mass of ⁴He impurities in ³He. Spin-fluctuations, on the other hand, cause a pronounced peak of the effective mass around the Fermi wave number. We also find, consistent with earlier work, an instability of the single particle spectrum at about 2.5 k _F, this is due to the coupling to density fluctuations in the maxon region.     

A generalized equation for surface tension from the triple point to the critical point

A three-parameter generalized equation is proposed for surface tension from the triple point to the critical point. This equation not only fits the data well but also is good for interpolation between the normal boiling point and the critical point. This equation is also good for extrapolation to the triple point. This equation has been tested using the surface tension of water from the triple point to the critical point. The constants of this equation obtained using orthobaric surface tensions are given for a number of compounds. The isobaric surface tensions determined at a pressure of 1 atm do not differ significantly from the orthobaric surface tensions. Such data also have been used in obtaining equations from the triple to the critical point.Nomenclature T _c Critical temperature, K - T _t Triple point, K - T _m Melting point, K - T _r Reduced temperature, K - X (T _c-T)/T _c - Surface tension, dyne · cm^–1;10^–3N · m^–1 - _m Surface tension at the melting point - _f Surface tension at T _r=0.9 - _t Surface tension at the triple point - Relative deviation 100[ _obsd– _calcd]/ _obsd - Standard deviation [( _obsd– _calcd)²/(No. points—No. parameters)]^0.5     

Growth of La0.7Sr0.3MnO3 films on Si(0 0 1) using SrMnO3 template layer

Using RF magnetron sputtering, we have successfully grown (1 1 0) orientated La_0.7Sr_0.3MnO₃ (LSMO) films on Si(0 0 1) wafers using SrMnO₃ (SMO) as a template layer. The X-ray diffraction (XRD) patterns of the SMO/Si heterostructures indicate that SMO grows along the (1 1 0) orientation, the orientation relationship between the SMO thin film and the Si (0 0 1) substrate being given by (0 1 1)_SMO∣∣(0 0 1)_Si and [01]_SMO∣∣[0 1 0]_Si. From the XRD patterns of the LSMO/SMO/Si heterostructures, we find that with an increase of substrate temperature, the required thickness of SMO, which plays an effective role of tuning the preferential orientation of LSMO, will decrease at first and then increase. It is thought that this originates from the fact that the crystallization of SMO is not perfect at low temperatures whereas too high a temperature results in reaction and diffusion at the interface of the two layers.