4He Mixtures Research Articles

Influence of acoustic modes on resonance properties of a quartz tuning fork immersed in superfluid 4He and liquid mixtures 3He–4He

The oscillating quartz tuning fork method has been used to study resonance phenomena in experimental cells of different sizes filled with superfluid 4He and concentrated liquid mixtures of 3He–4He. An analysis of the temperature dependence of the resonance frequencies of the tuning forks showed that in a number of cases, the incompressible fluid model is not sufficient to interpret the experimental results and that acoustic processes in the cell should be taken into account. The frequencies of the resonances of the first sound in cylindrical geometry are estimated and their influence on the resonant frequencies of the tuning fork is shown, which can lead to a distortion of the shape of the resonant line. A comparison is made between experimental results for superfluid 4He and mixtures of 3He-4He with light isotope concentrations of 5% and 15%. It is shown that, in contrast to pure helium, the model of a viscous incompressible fluid cannot be applied to mixtures, even in the absence of first acoustic resonances. This can be explained by the fact that, when studying concentrated solutions, the excitation of the second sound along with the first can have a noticeable effect on the resonance characteristics of the tuning fork.

Utilization of cryogenic phases of helium as “magic” working fluids in laboratory experiments: Pushing the boundaries of fluid dynamics

A surprisingly large part of the valuable scientific contributions of K. R. Sreenivasan—known to his friends and coworkers as Sreeni—to fluid dynamics is directly connected with precisely controlled benchmark experiments with cryogenic phases of helium. These experiments have been performed in a number of leading low temperature laboratories using conventional viscous 4He and 3He gases, normal liquid 4He (He I), as well as liquid 3He–4He mixtures and superfluid phases of 4He (He II) and 3He-B. We review their extraordinary physical properties and describe selected experiments, focusing on various forms of thermal convection, which push the boundaries of classical and quantum fluid dynamics.

Combustion of High-Pressure Hydrogen Diluted Mixtures in ESTHER Shock Tube

European Shock Tube for High-Enthalpy Research (ESTHER) is a new state-of-the-art combustion-driven shock tube developed for supporting future ESA planetary exploration missions. Its high-pressure combustion driver sports a unique innovative design where a mixture of He:H2:O2 or N2:H2:O2 gases, filled to pressures up to 100 bar, is ignited by a high-power Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. The qualification of this facility driver has allowed for the detailed study of laser-ignited combustion processes at high initial pressures (in the 5–100 bar range), over a series of 100 shots carried out for different configurations and gas mixtures. The influence of the oxygen-to-hydrogen ratio, filling pressure, inert gas dilution, and ignition mode have been studied and are presented in this work. The effects of nitrogen vs helium dilution are also discussed. Filling pressure and helium/nitrogen dilutions have the strongest influence in peak pressure, acoustic oscillation, and combustion velocity. The first two increase, whereas the latter strongly decreases with the filling pressure. Nitrogen diluted shots have drastically lower compression ratios and flame velocity when compared to the helium ones. Acoustic perturbations/instabilities are also found to be stronger. This test campaign allowed the definition of a large range of stable and reproducible firing conditions in deflagration mode, yielding post-combustion pressures up to 660 bar.

A Non-Matrix-Matched Calibration Method for In Situ Major and Trace Element Analysis of Scheelite by Nanosecond LA-ICP-MS.

In this work, a reliable and robust in situ non-matrix-matched calibration method is proposed for element composition determination in scheelite samples. With external calibration against the silicate glass standard reference material NIST SRM 610, the concentrations of both major elements (Ca and W) and trace elements (Si, Fe, Mo, Y, rare earth elements, etc.) in scheelite are determined using an ArF 193 nm excimer nanosecond laser ablation-inductively coupled plasma mass spectrometer (LA-ICP-MS). Here, the ablation was performed by hole drilling under a helium (He) environment using a laser spot size of 35 μm and a laser repetition of 5 Hz, and the aerosols were then transported to a quadrupole ICP-MS by a mixture of He and make-up gas argon (Ar) with a total gas flow rate of 1.6 L/min. Results showed that there was no apparent matrix effect between the NIST SRM 610 and scheelite by this proposed method. With internal standardization against W, the obtained concentrations of CaO and WO3 were found to yield an average matrix CaO/WO3 mass fraction ratio of 0.245 (2σ = 0.003, n = 19), which agreed well with the value of 0.243 (2σ = 0.002, n = 15) from electron probe microanalysis (EPMA). Furthermore, the accuracy of trace element analyses with this proposed non-matrix-matched calibration in situ method was evaluated by comparing the concentration results with those from bulk analysis by solution nebulizer ICP-MS (SN-ICP-MS). It was found that the quantification results from LA-ICP-MS and SN-ICP-MS were comparable, in particular showing a relative concentration bias of the total ∑REE+Y contents of less than 2%. This confirmed that scheelites can be accurately analyzed in situ by LA-ICP-MS without matrix-matched calibration standards. By using this developed in situ method, the element compositions in a series of scheelite samples from different W-associated deposits in China were successfully quantified, promising further genetic process investigation and associated geologic activities of the polymetallic resources.

Enhanced XUV harmonics generated in mixed noble gases using three-color laser fields.

High repetition coherent extreme ultraviolet (XUV) harmonics offer a powerful tool for investigating electron dynamics and understanding the underlying physics in a wide range of systems. We demonstrate the utilization of combined three-color (ω+2ω+3ω) laser fields in the generation of coherent extreme ultraviolet radiation in mixed noble gases. The three-color field results from the combination of fundamental, second-, and third-order harmonics of the near-infrared laser pulses in the nonlinear crystals. Different noble gases were selected as gas targets based on their ionization potentials, which are important parameters for generating higher cut-offs and intensities for the XUV harmonics. Enhanced XUV harmonic intensities were observed in the mixture of He + Kr gases when using three-color laser fields, compared to harmonics generated in the He + Kr mixture under a single-color pump. On the other hand, suppression of XUV harmonic intensity was observed in the mixture of He + Xe under the three-color pump due to the highest ionization level for these two mixed gases at similar laser conditions. Strong harmonic yields in the range of 25 to 80 eV of photon energy were observed.

VUV lasing in diffuse discharges formed by runaway electrons

The parameters of stimulated emission in diffuse discharges formed in a sharply inhomogeneous electric field by runaway electrons in mixtures of rare gases with the addition of H2 and F2 at pressures up to 10 atm are studied. Efficient VUV lasing was obtained at wavelengths from 148 to 193 nm on the transitions of H2, F2 and exciplex ArF* molecules. It was shown that the addition of He buffer gas increases the pulse duration, while Ne addition improves the output energy of the VUV laser on the H2 Lyman band. A laser pulse duration over 10 ns and an output of 0.12 mJ were obtained. The diffuse discharge in mixtures of He with F2 was found to form as a result of successive ionization waves. It was shown that the laser pulse at 157 nm has three peaks, which correspond to the maxima of the diffuse discharge current. Therewith, the first or second peak of the laser radiation has the maximum intensity, depending on the amplitude of the conduction current in the primary ionization wave. A maximal F2* laser electrical efficiency of η 0 = 0.18% and an output of Q 157 = 3.8 mJ were obtained in a He–F2 gas mixture at pressure of 10 atm, which exceeds the efficiency of lasers of this type pumped by transverse volume discharges with UV preionization. Long-pulse operation of the ArF* laser was achieved in a He–Ne–Ar–F2 gas mixture. Lasing at 193 nm continued during two periods of the diffuse discharge current. The total duration of the laser pulse was as long as 40 ns, and the radiation energy at 193 nm was as high as 2 mJ from an active volume of 20 cm3.

Anomalous temperature dependence of energy levels of electrons on helium

We report on magnetoconductivity measurements of electrons on helium exposed to resonant microwave irradiation within the temperature range associated with electron-ripplon scattering. Our findings reveal a non-monotonic temperature dependence of the intersubband frequency, with an abrupt decrease observed at temperatures below 0.3 K. We attribute this unexpected energy levels shift to the adsorption of 3He impurities near the liquid helium surface at low temperatures and such behavior is consistent with recent theoretical calculations of the surface electron energy spectra on 3He–4He mixtures.

Cavitation generated by vibrating quartz tuning fork in concentrated 3He–4He mixture

The state of the problem of cavitation in superfluid helium and the content of previous works on this topic are analyzed. The transition between turbulent flow and cavitation under oscillations of a quartz tuning fork in a normal and superfluid isotopic mixture containing 15% of 3He in the temperature range of 0.5–3 K is studied experimentally. The temperature dependences of the critical velocity for the cavitation onset and the critical transition excitation force are obtained. We compare the results of our measurements with the data obtained by other groups. The results of measurements with tuning forks in restricted and unrestricted geometries suggest that the presence of acoustic emission facilitates the conditions for the onset of cavitation and indirectly confirms the role of vortex lines. A comparison of the temperature dependences of the critical velocity of cavitation onset in pure 4He and a concentrated 3He–4He mixture did not give an unambiguous answer to the reason for the sharp increase of this velocity, at the transition to the superfluid state, and the contributions of both thermal effects and the 3He impurities to the velocity increase.

Impact of He+N2 concentration on self-modulated laser wakefield acceleration driven by pulses of a few TW

Laser wakefield electron acceleration with ionization injection has rarely been studied in the low-power, self-modulated case. We performed simulations of such regimes using a mixture of He and N2 gases and driven by laser pulses with peak powers around 1 TW. Analyses show the generation of electron bunches with an average energy of up to 70 MeV, an energy spread as low as 18%, and an emittance as good as a fraction of a mm mrad. The obtained electron beam parameters lead to several trade-offs as a function of N2 concentration, allowing for many different designs.

Determination of the apparent effective ionization coefficient in mixtures of He and O2 using steady-state Townsend discharge: effect of penning ionization and attachment

He:O2 gas mixtures are popular in many non-thermal plasma applications because of the good thermal conductivity of He and high production of reactive oxygen species. The applications utilizing reactive oxygen species, in particular, applications in biomedicine require accurate knowledge of the fundamental ionization parameters of gases such as the ionization coefficient. This study was focused on experimental determination of the reduced apparent effective ionization coefficient α ea /N in He:O2 mixtures. Experiments were conducted in the absolute pressure range of 10–800 Torr and reduced electric field E/N range of 40–1000 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with a theoretical model which was based on BOLSIG + calculation of ionization and attachment coefficients and additionally considered the ion conversion of O− to O2 −, detachment from O2 − and formation of O3 − and Penning ionization by He metastable species. The measurements agreed reasonably well with model calculations. Comparison with model suggest that He metastable species affect net ionization in He:O2 mixtures with O2 concentrations up to 10% often encountered in the applications and thus should be included in models of atmospheric pressure plasmas. The attachment of electrons became important at O2 concentrations above 10% and is therefore less important in most applications.

Collective mode resonances in superfluid 3He–4He mixtures

The experimentally observed first and second sound resonances caused by vibrations of a closed quartz tuning fork in superfluid helium mixtures are studied. Taking into account the full set of hydrodynamic modes of the system allows us to explain the unusual behavior of second sound resonances observed in experiments due to the redistribution of energy between the dissipative mode and the second sound mode.

2D-imaging of absolute OH and H2O2 profiles in a He–H2O nanosecond pulsed dielectric barrier discharge by photo-fragmentation laser-induced fluorescence

Pulsed dielectric barrier discharges (DBD) in He–H2O and He–H2O–O2 mixtures are studied in near atmospheric conditions using temporally and spatially resolved quantitative 2D imaging of the hydroxyl radical (OH) and hydrogen peroxide (H2O2). The primary goal was to detect and quantify the production of these strongly oxidative species in water-laden helium discharges in a DBD jet configuration, which is of interest for biomedical applications such as disinfection of surfaces and treatment of biological samples. Hydroxyl profiles are obtained by laser-induced fluorescence (LIF) measurements using 282 nm laser excitation. Hydrogen peroxide profiles are measured by photo-fragmentation LIF (PF-LIF), which involves photo-dissociating H2O2 into OH with a 212.8 nm laser sheet and detecting the OH fragments by LIF. The H2O2 profiles are calibrated by measuring PF-LIF profiles in a reference mixture of He seeded with a known amount of H2O2. OH profiles are calibrated by measuring OH-radical decay times and comparing these with predictions from a chemical kinetics model. Two different burst discharge modes with five and ten pulses per burst are studied, both with a burst repetition rate of 50 Hz. In both cases, dynamics of OH and H2O2 distributions in the afterglow of the discharge are investigated. Gas temperatures determined from the OH-LIF spectra indicate that gas heating due to the plasma is insignificant. The addition of 5% O2 in the He admixture decreases the OH densities and increases the H2O2 densities. The increased coupled energy in the ten-pulse discharge increases OH and H2O2 mole fractions, except for the H2O2 in the He–H2O–O2 mixture which is relatively insensitive to the additional pulses.

A [formula omitted] drift velocity monitoring chamber for the MEG II experiment

The MEG-II experiment searches for the lepton-flavor-violating decay: μ⟶e+γ. The reconstruction of the positron trajectory uses a drift chamber operated with a mixture of He and iC4H10 gas. It is crucial to provide a stable performance of the detector in terms of its electron transport parameters, avalanche multiplication, composition and purity of the gas mixture. In order to have a continuous monitoring of the quality of the gas injected, we plan to install a small drift chamber, with a simple geometry that allows to measure very precisely the electron drift velocity in a prompt way. The chamber is a small box with cathode walls, that determine a highly uniform electric field inside two adjacent drift cells. Along the axis separating the two drift cells, four staggered sense wires alternated with five guard wires collect the drifting electrons. The trigger is provided by two 90Sr radioactive sources placed on top of a two thin scintillator tiles telescope. The whole system is designed to give a response in few minutes about drift velocity variations at the 10−3 level. In this paper the development of the drift chamber is presented, with a particular focus on the details of its construction.

Equilibrium shapes of two- and three-dimensional two-phase rotating fluid drops with surface tension: Effects of inner drop displacement

The shapes of rotating fluid drops held together by surface tension are an important field of study in fluid mechanics. Recently, experiments with micrometer-scale droplets of liquid helium have been undertaken and it has proven useful to compare the shapes of the resultant superfluid droplets with classical analogs. If the helium is a mixture of He3 and He4, two phases are present. In a recent paper, the shapes of rotating two-phase fluid droplets were calculated where the inner drop was constrained to stay at the drop center. The outer shapes and dimensionless rotation rate–angular momentum relationships were shown to be similar to single-phase drops, providing that the density and surface tension scales were chosen appropriately. In the current paper, I investigate models in which the inner drop can displace from the center. In order to simplify the analyses, two-dimensional drops are first investigated. I show that the inner drop is unstable in the center position if its density is greater than the outer density and that the inner drop will move toward the outer boundary of the drop in these cases. When the inner drop has a higher density than the outer drop, the moment of inertia of displaced inner drops is increased relative to centered drops, and hence, the kinetic energy is decreased. Shapes of two- and three-dimensional drops, rotation rate–angular momentum, and kinetic and surface energy relationships are investigated for off-axis inner drops with parameters relevant to recent liquid He experiments.

Water Saturated with Pressurized CO2 as a Tool to Create Various 3D Morphologies of Composites Based on Chitosan and Copper Nanoparticles.

Methods for creating various 3D morphologies of composites based on chitosan and copper nanoparticles stabilized by it in carbonic acid solutions formed under high pressure of saturating CO2 were developed. This work includes a comprehensive analysis of the regularities of copper nanoparticles stabilization and reduction with chitosan, studied by IR and UV-vis spectroscopies, XPS, TEM and rheology. Chitosan can partially reduce Cu2+ ions in aqueous solutions to small-sized, spherical copper nanoparticles with a low degree of polydispersity; the process is accompanied by the formation of an elastic polymer hydrogel. The resulting composites demonstrate antimicrobial activity against both fungi and bacteria. Exposing the hydrogels to the mixture of He or H2 gases and CO2 fluid under high pressure makes it possible to increase the porosity of hydrogels significantly, as well as decrease their pore size. Composite capsules show sufficient resistance to various conditions and reusable catalytic activity in the reduction of nitrobenzene to aniline reaction. The relative simplicity of the proposed method and at the same time its profound advantages (such as environmental friendliness, extra purity) indicate an interesting role of this study for various applications of materials based on chitosan and metals.

Single Step Metal Nanoparticle Fabrication Using Atmospheric Pressure Plasma Jets

The interaction of atmospheric pressure plasma discharges with liquid or vapour phases is a hot-topic in plasma science and technology. Synthesis and processing of nanomaterials using atmospheric pressure plasma jets attracts more attention because of its simplicity and cost effectiveness. The plasma containing reactive electrons and active chemical species activates physical processes and reduction reaction of metal salts which leads to the formation of metal nanoparticles. Among the unique features of atmospheric pressure plasmas, the chemical non-equilibrium environment produces highly reactive radicals and ions from the precursors as well as inside the plasma. Thus the energy transfer could be initiated with high energy electrons and excited species from plasma and could be achieved by the reactions with reactive species of the precursors. Plasma compliments the production of nanomaterials in vapour phase or from aerosols and in solutions of the precursors. The interface between plasmas and vapors can be employed for rapid, simultaneous reduction and deposition of metal nanoparticles from metal salts, for instance gold nanoparticles from chloroauric acid (HAuCl4).We have employed an atmospheric pressure plasma jet setup operating with a mixture of He and Ar gases to produce gold nanocrystals onto a silicon wafer substrate. In this study, it reveals an easy and reliable synthesis mechanism of gold nanoparticles from chloroauric acid using atmospheric pressure plasma jet working with a high voltage source. A solution of the precursor in water acts as the feed solution for the process which is introduced to plasma in the form of microdroplets and metal nanoparticles were formed inside the plasma from the vapours containing the precursor molecules. Since the plasma-liquid/vapour chemistry allows the lead of accelerated reactions and instantly reduce the metal ions to metal atoms skipping the intermediate steps in the reduction process. The nanoparticles were collected on to a Si wafer substrate downstream of the plasma jet and characterized via scanning electron microscopy, Raman spectroscopy, transition electron microscopy etc. The polygonal nanoparticles sized 40-100 nm were obtained and they do not tend to agglomerate or fuse onto the substrate. Due to the low volatility of the precursor solution and the presence of comparatively larger microdroplets inside the plasma the nanoparticles tend to deposit in a pattern like galaxies on the silicon wafer substrate. These results would lead to the development of low cost and mobile, user-friendly atmospheric pressure plasma devices for the synthesis of nanoparticles without any toxic chemicals for the reduction of metal salt.The challenge in this process is in creating a vapour-plasma interface directly. This problem has been solved by incorporating a vaporizer directly to plasma. The vaporizer would introduce a new phase which would be a combination of gaseous plasma and plasma-liquid interface. To ease the transportation and diffusion of precursor molecules at the interface an inert gas has been introduced to the vaporizer as a carrier. At the interface, high energy electrons are introduced to the vapors containing the precursor metal ions and these wet electrons play the key role as initiators for the reduction process inside the plasma. Nanoparticles are formed inside the plasma by simple reduction mechanism carried out by short-lived reducing species formed at the interface. From the qualitative analysis carried our during the process implies the formation of short-lived reducing agents like hydrogen peroxide (H2O2) which is known as a reducing agent for chloroaurate ions in water medium. The size and shape of the nanoparticles are controlled by the residence time of the particles inside the plasma and the population density of the metal ions. Whereas the purity in turn the reduction rate of metal ions are dependent upon the feed gas flow as well as the applied voltage, i.e. plasma power.Concisely, atmospheric pressure plasma jets are outstanding choice for the synthesis of gold nanoparticles from chloroauric acid without any external reducing agents. The synthesized gold nanoparticles are promising for different applications because of its geometry and shape. Because of its polygonal geometries the particles are plasmonic active surfaces, the functional for highly specific sensing applications and nanoelectronics devices. However, the low-temperature plasma-vapour interphases containing droplets, the evaporation may add new complexities such as quantitative analysis of non-equilibrium chemistry to plasma chemistry which is yet to be understood and developed.

Complex ophthalmic neurostimulation in the rehabilitation of patients with glaucomatous optic neuropathy

Glaucomatous optic neuropathy differs significantly from other known ophthalmic neuropathies due to the gradual but steady progression, irreversible course, and resistance to treatment. Despite the fact that in recent decades, retinoprotective therapy and various physiotherapeutic factors have been widely used in the treatment of ophthalmic diseases and, in particular, this pathology [1–17], it has not been possible to reduce the incidence rate so far. In this regard, there is an urgent need for further development of comprehensive rehabilitation programs to prevent the progression of the disease. Material and research methods. The study included 78 patients (102 eyes): the main group included 58 eyes with stage 1 primary open-angle glaucoma (POAG1) of 42 patients aged 56±3.1 years (16 men, 26 women), who underwent a course of complex ophthalmic neurostimulation including transcranial magnetic stimulation with a magnetic field induction of 43 mT and a pulsating frequency of 100 Hz, endonasal electrophoresis with Semax, heliox inhalation of a heated mixture of He+O2 (21), and acupuncture. There were 10 procedures of each in a combined schedule. The comparison group included 36 patients (44 eyes) with POAG1 (14 men, 22 women) aged 53±3.2 years, who underwent a course of complex ophthalmic neurostimulation including transcranial magnetic stimulation with a magnetic field induction of 43 mT and a pulsating frequency of 100 Hz, and endonasal electrophoresis with Semax. The control group included 47 eyes of 38 patients aged 50±3.9 years (18 men, 23 women), who did not undergo physiotherapy. Results. The most pronounced results in POAG1 were obtained under the influence of an extended complex of ophthalmic neurostimulation including transcranial magnetic stimulation, endonasal electrophoresis with Semax, heliox therapy, and acupuncture, which was confirmed by a significant decrease in the number of relative scotomas, a decrease in electrical perceptual threshold, an increase in P50 amplitude in PERG, and an increase in the GCC layer that persisted up to 48 weeks in most cases. Somewhat less significant results were obtained in the comparison group, with the greatest therapeutic effect for most of the studied parameters observed in terms of up to 24 weeks, while in patients who received a vitamin therapy complex, there was noted only a positive trend, the duration of which was no more than 12 weeks, followed by deterioration. Conclusion: More pronounced therapeutic results obtained in the main group are explained by the formation of the trophostimulating effect of magneto-electrotherapy, the neuroprotective effect of the drug, as well as the pronounced neurotrophic effects of heliox therapy and acupuncture.

Non-chromatographic Speciation Analysis of Tellurium by HG-ICP-MS/MS at Sub ng L-1 Concentration in Natural Waters Using TiIII as a Pre-Reducing Agent.

An automated and high-throughput (36 h-1) method for extremely sensitive determination of the two main tellurium species in the environment, namely, tellurite (TeIV) and tellurate (TeVI), was developed. Flow injection hydride generation was interfaced for the first time with inductively coupled plasma triple quadrupole mass spectrometry (ICP-MS/MS) detection to assure interference-free tellurium analysis. ICP-MS/MS conditions were studied in detail. Using a mixture of He + O2 gases in the reaction cell, the background signals significantly dropped and Xe isobaric interference was eliminated, allowing measurement with the most abundant Te isotopes, that is, 128Te and 130Te, and offering a huge increase in sensitivity. Volatile H2Te was selectively generated by a HCl/NaBH4 reaction from TeIV or from both TeIV and TeVI (TeIV+VI) after pre-reduction of TeVI by a TiCl3 solution. The optimum conditions for TiCl3 as a pre-reductant and the pre-reduction kinetics were also investigated. Different reduction rates were found depending on the sample stabilization media (HCl, HNO3, or EDTA). The same sensitivity was found for TeIV and TeVI, measured after pre-reduction, and no significant matrix effect was observed in both fresh and seawaters. Therefore, external calibration was used for quantification in real samples. Under optimal conditions, this method reached an unprecedented limit of detection of 0.07 ng L-1 for both TeIV and TeIV+VI and an intra-day repeatability of 5.2% at the 5 ng L-1 level. The methodology was successfully applied to the speciation analyses in commercially available certified reference materials of river water and seawater, and in bottled water and lake water samples.

Viscosity of concentrated superfluid mixtures 3He−4He when vibrating a quartz tuning fork

The possibility has been investigated for measuring the viscosity of concentrated superfluid mixtures of 3He in 4He in the temperature range 0.4−2.2 K using commercial quartz tuning forks with a resonance frequency of ≈ 32 kHz. It was found that the temperature dependence of the viscosity coefficient in a mixture with a concentration of 5% of 3He in 4He is in good qualitative agreement with the data obtained using other experimental techniques in the entire temperature range of the research. The same dependence of a mixture with 3He concentration of 15% agrees with the previously obtained data only at temperature T > 1.4 K, and at lower temperatures a difference appears that grows with decreasing temperature. The experimental temperature dependences of the viscosity coefficient obtained by different methods are compared with those calculated within the framework of the kinetic theory for the quasiparticles in superfluid 3He−4He solutions, developed by Landau, Khalatnikov, and Zharkov for the temperature range T > 0.6 K and by Baym, Saam, and Ebner for lower temperature.

Dilution Microcryostat–Insert for Microwave Spectroscopy and Magnetic Resonance

An autonomous dilution microrefrigerator manufactured as an insert into a helium cryostat with a superconducting magnet is described. In this refrigerator, the 3He circulation in the circuit filled with a 3He–4He mixture (mixer–heat exchanger–still–condenser–heat exchanger–mixer) is achieved due to the condensation of mixture vapors on the walls of the condenser, which is cooled by the 3He bath pumped out by a sorption pump, as well as entry of the condensate into the mixer under the action of gravity. An 8-mm-range resonator that contains a sample is connected to the mixer via a heat conductor; the sample is located at the center of a superconducting solenoid with a field of up to 80 kOe. Radiation passes from the generator through a waveguide to the resonator, and the signal that passed through the resonator arrives at the detector. The generator and detector are at room temperature. The device is designed for microwave spectroscopy of magnetic materials at temperatures in the range of ~0.09–3 K. The time within which the temperature is maintained at a level of ~0.1 K is 4–6 h. The results of a test experiment on the antiferromagnetic resonance in a MnCO3 single crystal are presented.