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A new path integral representation of the quantum density of states (DOS) and distribution functions of strongly correlated fermions are derived in the Wigner formulation of quantum mechanics. A new path integral Monte Carlo approach to calculate DOS and thermodynamic functions is suggested. Using $ {}^{3}\hbox {He} $ 3 He as an interesting example, we calculate the DOS, internal energy distribution (IED), momentum distribution functions (MDFs), spin-resolved radial distribution functions at different densities and temperatures. The physical meaning and parameters of exchange-correlation holes, the quantum oscillations of IEDs and DOS as well as the high-momentum asymptotics ('quantum tails') of MDFs have been considered and explained. [ABSTRACT FROM AUTHOR]

Recycling of tritiated wastewater provides tritium products of high practical and commercial value. The recycling process includes three stages: (1) conditioning (preliminary enriching) of raw tritiated water by means of reverse osmosis; (2) concentrating the tritium oxide by means of salt rectification of the tritiated water; (3) obtaining tritiated ice. The paper presents the technological conditions for each stage with special attention paid to the opportunity of producing helium-3 as the final product of tritiated wastewater recycling. [ABSTRACT FROM AUTHOR]

The symmetry-breaking first-order phase transition between superfluid phases 3 He-A and 3 He-B can be triggered extrinsically by ionising radiation or heterogeneous nucleation arising from the details of the sample cell construction. However, the role of potential homogeneous intrinsic nucleation mechanisms remains elusive. Discovering and resolving the intrinsic processes may have cosmological consequences, since an analogous first-order phase transition, and the production of gravitational waves, has been predicted for the very early stages of the expanding Universe in many extensions of the Standard Model of particle physics. Here we introduce a new approach for probing the phase transition in superfluid 3 He. The setup consists of a novel stepped-height nanofluidic sample container with close to atomically smooth walls. The 3 He is confined in five tiny nanofabricated volumes and assayed non-invasively by NMR. Tuning of the state of 3 He by confinement is used to isolate each of these five volumes so that the phase transitions in them can occur independently and free from any obvious sources of heterogeneous nucleation. The small volumes also ensure that the transitions triggered by ionising radiation are strongly suppressed. Here we present the preliminary measurements using this setup, showing both strong supercooling of 3 He-A and superheating of 3 He-B, with stochastic processes dominating the phase transitions between the two. The objective is to study the nucleation as a function of temperature and pressure over the full phase diagram, to both better test the proposed extrinsic mechanisms and seek potential parallel intrinsic mechanisms. [ABSTRACT FROM AUTHOR]

Tritium resulting from separation processes is being stored in metal hydrides. In time, because of radioactive decay, tritium converts into 3He, which accumulates in the storage vessel. The recovery of 3He is a topic of high interest because of its wide range of applications in health care, security, and advanced research. Currently, at ICSI Râmnicu Vâlcea, a method is under development based on gas chromatography, Pd/Ag membrane permeation, and cryogenic distillation for 3He separation and enrichment having as sources both the cover gas of nuclear reactors and tritium storage containers. This paper reports the investigation of using Pd/Ag membranes for helium separation from hydrogen isotopes by experimental determination of the operating performance of the membrane in view of process integration. Tests have been performed at different temperatures in the domain of 100°C to 350°C for different hydrogen partial pressures in the upstream side of the membrane in the domain of 150 to 300 kPa, while the downstream part was continuously purged with a preliminary vacuum pump. The results for the membrane parameters are in good agreement with previous literature reports and will be utilized for the dimensioning and establishing of operating parameters of the membrane used for intermediate separation of helium isotopes from hydrogen. [ABSTRACT FROM AUTHOR]

Field Reversed Configuration (FRC) plasmas are plasma devices that have demonstrated that through magnetic compression they can be heated to thermonuclear fusion conditions in the parameter space of an energy-producing generator Kirtley et al. (IEEE Symposium on Fusion Engineering, 2021). Of particular interest, FRCs are high-beta, in that the plasma particle kinetic energy is in balance with an externally applied magnetic field at all stages of operation. The following work will show that a cylindrical approximation for the energy and particle distribution within an FRC can, within 11%, match the fusion performance results of both full Magnetohydrodynamic (MHD) simulations as well as all robust, modern theoretical spatial and energy distribution models. Further, by using the simplified cylindrical model, detailed fusion reaction, radiation, and energy transport equations are now numerically-tractable and can be modelled over a wide parameter space. In the second section of this work, a detailed numerical model will be presented with the key theoretical performance of the compression of high-beta fusion plasmas in both deuterium–tritium (D–T) and deuterium–helium-3 (D–He-3) fuels. As will be shown, a high-beta D–He-3 plasma outperforms a low-beta D–T fuel and can theoretically yield a net-positive fusion generator. [ABSTRACT FROM AUTHOR]

At the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, work is underway to create gas-filled neutron detectors. To prepare the working mixture of gases, it is necessary to use pure 3He, which is obtained by freezing impurities. A 3He refrigerator is created for this purpose. The refrigerator can also be used to obtain low temperatures in a physics experiment. In this work, the operating modes of the refrigerator are studied. In the continuous mode of 3He circulation, a temperature of 0.78 K is obtained. When 3He vapor is pumped out by an external pump in a single cooling mode, a temperature of 0.52 K is reached. We also study the relaxation modes in which, with pre-condensed 3He, the volume of the container plays the role of a pump. A mode is presented in which the temperature of the evaporator relaxes from 1 to 1.5 K within 11 days. [ABSTRACT FROM AUTHOR]

The study examines the influence of fission neutrons coming from the blanket of a thermonuclear installation into plasma which can enhance fusion reactions, including the reproduction of tritium through the 3He(n,p)T reaction. [ABSTRACT FROM AUTHOR]

Copyright of Space Education & Strategic Applications is the property of Policy Studies Organization and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the p -wave spin-triplet pairing model of superfluid Helium-3, at each point x of the region Ω occupied by the system, the order parameter field is described by a 3 × 3 complex matrix A encoding the orientation of the spin and orbital angular momentum of the Cooper pairs of Helium-3 atoms. The transition of liquid Helium-3 to a superfluid state is associated with a spontaneous breaking of the overall symmetry group G = S O (3) × S O (3) × U (1) of the system. In the Ginzburg–Landau regime (i.e., in regions near to the critical phase-transition temperature), the free-energy density f of superfluid Helium-3 is expanded into powers of the components A μ j of A and A μ j , k of its gradient ∇ A , and can be decomposed in the sum f (A , ∇ A) = f B (A) + f grad (A , ∇ A) of the bulk part, f B , and the gradient part, f grad . The free-energy density f must be invariant under the action of G defined by A ↦ A ′ = exp (i ϕ) R 1 A R 2 T , where ϕ is a phase, and R 1 , R 2 are elements of S O (3) , that is, it must be invariant against gauge transformations and against rotations in spin space and ordinary (orbital) space, separately. We address the question of G -invariance for a general free-energy density in the Ginzburg–Landau energy functional and determine all linearly independent quartic terms of the form A A ∗ ∇ A (∇ A) ∗ in the expansion of the gradient free-energy density. It is known that the superfluid phases of Helium-3 near the critical temperature correspond to the minima of the bulk free energy and that the absolute minimum corresponds to a stable equilibrium phase. In zero magnetic field, there are two distinct superfluid phases, A and B, which exhibit an absolute minimum of the bulk free energy in different regions of the phase diagram. Explicit expressions for the generalized gradient energy densities are provided for both the A and B phases. Finally, a unified approach to A and B phases is proposed, which involves an auxiliary control parameter. In this framework, the extremal properties of A and B phases are recovered and a transition between the two phases is observed in dependence of pressure. [ABSTRACT FROM AUTHOR]

A quantum path integral Monte Carlo approach [J. Phys. A 55, 035001 (2021)] for strongly correlated degenerate fermions has been modified to solve the 'fermionic sign problem'. The exchange interaction of fermions was presented in the form of a positive semidefinite Gram determinant which significantly simplified the calculations. The verification of this approach has been carried out by comparison of the calculated equation of state with experimental data for quantum and degenerate unpolarised 3 He . The obtained results agree with experimental data in a wide range of reduced inverse density 0.4 ≤ v ∗ ≤ 7.5 and temperature 1 K ≤ T ≤ 13 K . The range includes the gaseous and liquid states as well as the regions of the respective phase transition and the critical point. For the first time spin-resolved pair distribution functions have been calculated to analyse the spatial arrangement of helium atoms. The calculated internal energy has been presented for the gaseous region of quantum 3 He . The simulations have been carried out for the Lennard–Jones (LJ) potential with parameters σ = 2.71 Å and ϵ = 6.68 K. [ABSTRACT FROM AUTHOR]

The article considers the current problem of helium-3 supply constraints for industry and science. The projected 3He shortage is approximately 55000 liters (at 1 atm and 20°С) in the world production market. Tritium is the only industrial 3He source. Alternative sources of 3He are discussed in this paper. Between 25 and 50% of the 3Не shortage could be addressed with natural gas extraction. To obtain high purity 3He gas, low-temperature methods of separation (superfluid filtration, rectification and adsorption) are promising. The 3He lunar mining operation could cover the entire worldwide shortage, but this is not a perspective over the next fifteen-twenty years. The controlled thermonuclear fusion is both an energy source and a new 3He production alternative source. Between 10 and 25% of the 3He shortage could be covered with this technology. The high molar concentration of 3He in the obtained mixtures will make it possible to extract the rare isotope by the method of low-temperature adsorption with subsequent enrichment by the method of low-temperature rectification. [ABSTRACT FROM AUTHOR]

Volatiles from the solar nebula are known to be present in Earth's deep mantle. The core also may contain solar nebula‐derived volatiles, but in unknown amounts. Here we use calculations of volatile ingassing and degassing to estimate the abundance of primordial 3He now in the core and track the rate of 3He exchange between the core and mantle through Earth history. We apply an ingassing model that includes a silicate magma ocean and an iron‐rich proto‐core coupled to a nebular atmosphere of solar composition to calculate the amounts of 3He acquired by the mantle and core during accretion and core formation. Using experimentally determined partitioning between core‐forming metals and silicate magma, we find that dissolution from the nebular atmosphere deposits one or more petagrams of 3He into the proto‐core. Following accretion, 3He exchange depends on the convective history of the coupled core‐mantle system. We combine determinations of the present‐day surface 3He flux with estimates of the present‐day mantle 3He abundance, mantle and core heat fluxes, and our ingassed 3He abundances in a convective degassing model. According to this model, the mantle 3He abundance is evolving toward a statistical steady state, in which surface losses are compensated by enrichments from the core. Plain Language Summary: Each year, about 2 kg of the rare gas helium‐3 escapes from Earth's interior, mostly along the mid‐ocean ridge system. Helium‐3 is primordial, created shortly after the Big Bang and acquired from the solar nebula as the Earth formed. Geochemical evidence indicates the Earth has deep reservoirs of helium‐3, but their locations and abundances remain uncertain. Our models of volatile exchange during Earth's formation and evolution implicate the metallic core as a leaky reservoir that supplies the rest of the Earth with helium‐3. Our results also suggest that other volatiles may be leaking from the core into the mantle. Key Points: The mantle and core acquired petagrams of helium‐3 from the solar nebulaThe core is a major helium‐3 reservoir in the EarthHelium‐3 leaks from the core to the mantle [ABSTRACT FROM AUTHOR]

Copyright of Geominas is the property of FUNDA-GEOMINAS. (Fundacion de Egresados d Amigos de la Escuela de Ingenieria Geologica y de Minas) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The second and third density virial coefficients, B and C, of helium-3 (3He) are determined in the temperature range from 3.3 K to 13 K based on the analysis of experimental thermophysical data. The empirically fitted equations of B and C are obtained, which enable us to calculate the second and third acoustic virial coefficients, βa and RTγa, of 3He in the same temperature range. This study provides the first experiment-based values of βa and RTγa from 3.75 K to 13 K. The obtained density and acoustic virial coefficients of 3He are compared with previous experimental and theoretical studies. [ABSTRACT FROM AUTHOR]

We make use of the ionisation energy theory, Ramachandran interaction theory and the energy-level spacing renormalisation group technique to extend the Drude Hamiltonian to derive the Ramachandran pairing mechanism. This particular mechanism is exploited to explain the notorious discontinuous jumps in the specific heat data at critical points in both He-4 and He-3 superfluids. The well-known spin states (due to Balian–Werthamer and Anderson–Brinkman–Morel theories) and the Leggett's spontaneously broken spin-orbit symmetry are shown to enhance Ramachandran attraction between two He-3 atoms without the need to invoke the spin-induced pairing or the phonon-mediated Cooper pairing mechanism in superconductors. In addition, we shall show physically that the spin-exchange mechanism can neither cause pairing between electrons nor between He-3 atoms. [ABSTRACT FROM AUTHOR]

The iron (Fe) supply to phytoplankton communities in the Southern Ocean surface exerts a strong control on oceanic carbon storage and global climate. Hydrothermal vents are one potential Fe source to this region, but it is not known whether hydrothermal Fe persists in seawater long enough to reach the surface before it is removed by particle scavenging. A new study (Jenkins, 2020, https://doi.org/10.1029/2020GL087266) fills an important gap in this puzzle: a helium‐3 mass balance model is used to show that it takes ~100 yr for deep hydrothermally influenced waters to upwell to the surface around Antarctica. However, estimates of Fe scavenging time scales range from tens to hundreds of years and must be more narrowly constrained to fully resolve the role of hydrothermal Fe in the ocean's biological pump. Plain Language Summary: Deep‐sea volcanoes (known as hydrothermal vents) release a variety of elements into seawater, including iron. If this iron reaches the ocean surface, it can fuel photosynthesis and carbon drawdown by marine algae, especially in the remote Southern Ocean where algal communities are particularly starved of iron. New work (Jenkins, 2020, https://doi.org/10.1029/2020GL087266) uses helium‐3 (also released at hydrothermal vents) as a "gauge" to estimate that it takes approximately 100 yr for deep waters to emerge at the surface in the Southern Ocean. However, iron is also continually removed from seawater, and the potential for vent‐sourced iron to reach the surface rests on whether this loss occurs on time scales longer or shorter than 100 yr, which remains unknown. Key Points: Hydrothermal iron may stimulate phytoplankton growth in the Southern Ocean if it reaches the surface before scavenging onto particlesA new helium‐3 mass balance model shows that hydrothermally influenced deep Southern Ocean water upwells on a time scale of ~100 yrCurrent estimates of iron scavenging time scales span from much lower to much higher than 100 yr [ABSTRACT FROM AUTHOR]

We studied the thermal conductivity of superfluid 3 He in a 2.5-mm effective diameter and 0.15-m-long channel connecting the two volumes of our experimental assembly. The main volume contained pure solid 4 He, pure liquid 3 He and saturated liquid 3 He– 4 He mixture at varying proportions, while the separate heat-exchanger volume housed sinter and was filled by liquid 3 He. The system was cooled externally by a copper nuclear demagnetization stage, and, as an option, internally by the adiabatic melting of solid 4 He in the main volume. The counterflow effect of superfluid just below the transition temperature T c resulted in the highest observed conductivity about five times larger than that of the normal fluid at the T c . Once the hydrodynamic contribution had practically vanished below 0.5 T c , we first observed almost constant conductivity nearly equal to the normal fluid value at the T c . Finally, below about 0.3 T c , the conductivity rapidly falls off toward lower temperatures. [ABSTRACT FROM AUTHOR]

Background: Alveolar development and lung parenchymal simplification are not well characterized in vivo in neonatal patients with respiratory morbidities, such as bronchopulmonary dysplasia (BPD). Hyperpolarized (HP) gas diffusion magnetic resonance imaging (MRI) is a sensitive, safe, nonionizing, and noninvasive biomarker for measuring airspace size in vivo but has not yet been implemented in young infants. Objective: This work quantified alveolar airspace size via HP gas diffusion MRI in healthy and diseased explanted infant lung specimens, with comparison to histological morphometry. Methods: Lung specimens from 8 infants were obtained: 7 healthy left upper lobes (0–16 months, post-autopsy) and 1 left lung with filamin-A mutation, closely representing BPD lung disease (11 months, post-transplantation). Specimens were imaged using HP 3He diffusion MRI to generate apparent diffusion coefficients (ADCs) as biomarkers of alveolar airspace size, with comparison to mean linear intercept (Lm) via quantitative histology. Results: Mean ADC and Lm were significantly increased throughout the diseased specimen (ADC = 0.26 ± 0.06 cm2/s, Lm = 587 ± 212 µm) compared with healthy specimens (ADC = 0.14 ± 0.03 cm2/s, Lm = 133 ± 37 µm; p < 1 × 10−7); increased values reflect enlarged airspaces. Mean ADCs in healthy specimens were significantly correlated to Lm (r = 0.69, p = 0.041). Conclusions: HP gas diffusion MRI is sensitive to healthy and diseased regional alveolar airspace size in infant lungs, with good comparison to quantitative histology in ex vivo specimens. This work demonstrates the translational potential of gas MRI techniques for in vivo assessment of normal and abnormal alveolar development in neonates with pulmonary disease. [ABSTRACT FROM AUTHOR]

We studied a novel cooling method, in which 3 He and 4 He are mixed at the 4 He crystallization pressure at temperatures below 0.5 mK . We describe the experimental setup in detail and present an analysis of its performance under varying isotope contents, temperatures, and operational modes. Further, we developed a computational model of the system, which was required to determine the lowest temperatures obtained, since our mechanical oscillator thermometers already became insensitive at the low end of the temperature range, extending down to 90 ± 20 μ K ≈ T c 29 ± 5 ( T c of pure 3 He ). We did not observe any indication of superfluidity of the 3 He component in the isotope mixture. The performance of the setup was limited by the background heat leak of the order of 30 pW at low melting rates, and by the heat leak caused by the flow of 4 He in the superleak line at high melting rates up to 500 μ mol / s . The optimal mixing rate between 3 He and 4 He , with the heat leak taken into account, was found to be about 100.. 150 μ mol / s . We suggest improvements to the experimental design to reduce the ultimate achievable temperature further. [ABSTRACT FROM AUTHOR]

The 3He-based neutron detectors are no longer the default solution for neutron scattering applications. Both the inability of fulfilling the requirements in performance, needed for the new instruments, and the shortage of 3He, drove a series of research programs aiming to find new technologies for neutron detection. The characteristics of the new detector technologies have been extensively tested to prove their effectiveness with respect to the state-of-the-art technology.Among these, the background rejection capability is crucial to determine. The signal-to-background ratio is strongly related to the performance figure-of-merit for most instruments. These are designed to exploit the high flux expected from the new high intensity neutron sources. Therefore, an inadequate background rejection could significantly affect the measurements, leading to detector saturation and misleading events. This is of particular importance for the kind of techniques in which the signals are rather weak.For the first time, the sensitivity of 3He detectors to fast neutrons, up to En=10 MeV, has been estimated. Two independent measurements are presented: a direct calculation based on a subtraction method used to disentangle the thermal and the fast neutron contribution, while a further evidence is calculated indirectly through a comparison with the recently published data from a 10B-based detector. Both investigations give a characterization on the order of magnitude for the sensitivity. A set of simulations is presented as well in order to support and to validate the results of the measurements. A sensitivity of 4·10−3 is observed from the data. This is two orders of magnitude higher than that previously observed in 10B-based detectors. [ABSTRACT FROM AUTHOR]

Constraining the age of young lavas, which generally fall outside the effective range of traditional geochronology methods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies. We present an in situ cosmogenic 3He and 36Cl surface-exposure chronology, alongside new minimum-limiting 14C ages, documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four 3He-dated lavas on the Nevado Coropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentially active; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East of Coropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one of Peru's most active volcanoes. Two 3He measurements confirm the Holocene age of these deposits and expand the chronology for one of the youngest major lava fields in Peru. 36Cl surface-exposure ages from the Purupurini dome cluster and Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal 14C ages from a lava-dammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. These new data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface-exposure methods for such applications. [ABSTRACT FROM AUTHOR]

In pure superfluid 3He–B at ultra-low temperatures, the quartz tuning fork oscillator response is expected to saturate when the dissipation caused by the superfluid medium becomes substantially smaller than the internal dissipation of the oscillator. However, even with a small amount of 4He covering the surfaces, we have observed saturation already at significantly higher temperatures than anticipated, where we have other indicators to prove that the 3He liquid is still cooling. We found that this anomalous behavior has a rather strong pressure dependence, and it practically disappears above the crystallization pressure of 4He. We also observed a maximum in the fork resonance frequency at temperatures where the transition in quasiparticle flow from the hydrodynamic to the ballistic regime is expected. We suggest that such anomalous features derive from the superfluid 4He film on the oscillator surface. [ABSTRACT FROM AUTHOR]

Background: To support translational lung MRI research with hyperpolarized 129 Xe gas, comprehensive evaluation of derived quantitative lung function measures against established measures from 3 He MRI is required. Few comparative studies have been performed to date, only at 3T, and multisession repeatability of 129 Xe functional metrics have not been reported.Purpose/hypothesis: To compare hyperpolarized 129 Xe and 3 He MRI-derived quantitative metrics of lung ventilation and microstructure, and their repeatability, at 1.5T.Study Type: Retrospective.Population: Fourteen healthy nonsmokers (HN), five exsmokers (ES), five patients with chronic obstructive pulmonary disease (COPD), and 16 patients with nonsmall-cell lung cancer (NSCLC).Field Strength/sequence: 1.5T. NSCLC, COPD patients and selected HN subjects underwent 3D balanced steady-state free-precession lung ventilation MRI using both 3 He and 129 Xe. Selected HN, all ES, and COPD patients underwent 2D multislice spoiled gradient-echo diffusion-weighted lung MRI using both hyperpolarized gas nuclei.Assessment: Ventilated volume percentages (VV%) and mean apparent diffusion coefficients (ADC) were derived from imaging. COPD patients performed the whole MR protocol in four separate scan sessions to assess repeatability. Same-day pulmonary function tests were performed.Statistical Tests: Intermetric correlations: Spearman's coefficient. Intergroup/internuclei differences: analysis of variance / Wilcoxon's signed rank. Repeatability: coefficient of variation (CV), intraclass correlation (ICC) coefficient.Results: A significant positive correlation between 3 He and 129 Xe VV% was observed (r = 0.860, P < 0.001). VV% was larger for 3 He than 129 Xe (P = 0.001); average bias, 8.79%. A strong correlation between mean 3 He and 129 Xe ADC was obtained (r = 0.922, P < 0.001). MR parameters exhibited good correlations with pulmonary function tests. In COPD patients, mean CV of 3 He and 129 Xe VV% was 4.08% and 13.01%, respectively, with ICC coefficients of 0.541 (P = 0.061) and 0.458 (P = 0.095). Mean 3 He and 129 Xe ADC values were highly repeatable (mean CV: 2.98%, 2.77%, respectively; ICC: 0.995, P < 0.001; 0.936, P < 0.001). DATA CONCLUSION: 129 Xe lung MRI provides near-equivalent information to 3 He for quantitative lung ventilation and microstructural MRI at 1.5T.Level Of Evidence: 3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2018. [ABSTRACT FROM AUTHOR]

A previous paper [M. F. Atiyah and N. S. Manton, ] modeled atoms and their isotopes by complex algebraic surfaces with the projective plane modeling Hydrogen. In this paper, models of the stable isotopes Helium-4 and Helium-3 are constructed. [ABSTRACT FROM AUTHOR]

An apparatus and method for isotopic analysis of He/He for controlling the extraction of He from natural He were designed using a commercial industrial mass spectrometer. A modernized sample-injection system allowed the sample volume of rare and expensive gases for quantitative and isotopic analyses to be reduced by 3-5 orders of magnitude. The metrological characteristics of the developed analytical method including sampling and injection into the mass spectrometer were evaluated using model analyses of individual isotopes of Ar, Ne, and He. [ABSTRACT FROM AUTHOR]

Purpose: ³He ions may hold great potential for clinical therapy because of both their physical and biological properties. In this study, the authors investigated the physical properties, i.e., the depth-dose curves from primary and secondary particles, and the energy distributions of helium (³He) ions. A relative biological effectiveness (RBE) model was applied to assess the biological effectiveness on survival of multiple cell lines. Methods: In light of the lack of experimental measurements and cross sections, the authors used Monte Carlo methods to study the energy deposition of ³He ions. The transport of ³He ions in water was simulated by using three Monte Carlo codes--FLUKA, GEANT4, and MCNPX--for incident beams with Gaussian energy distributions with average energies of 527 and 699 MeV and a full width at half maximum of 3.3 MeV in both cases. The RBE of each was evaluated by using the repair-misrepair-fixation model. In all of the simulations with each of the three Monte Carlo codes, the same geometry and primary beam parameters were used. Results: Energy deposition as a function of depth and energy spectra with high resolution was calculated on the central axis of the beam. Secondary proton dose from the primary ³He beams was predicted quite differently by the three Monte Carlo systems. The predictions differed by as much as a factor of 2. Microdosimetric parameters such as dose mean lineal energy (yD), frequency mean lineal energy (yF), and frequency mean specific energy (zF) were used to characterize the radiation beam quality at four depths of the Bragg curve. Calculated RBE values were close to 1 at the entrance, reached on average 1.8 and 1.6 for prostate and head and neck cancer cell lines at the Bragg peak for both energies, but showed some variations between the different Monte Carlo codes. Conclusions: Although the Monte Carlo codes provided different results in energy deposition and especially in secondary particle production (most of the differences between the three codes were observed close to the Bragg peak, where the energy spectrum broadens), the results in terms of RBE were generally similar. [ABSTRACT FROM AUTHOR]

In this paper, the existence of a global attractor for the He-He system is investigated. By using an iteration procedure, combining with the classical existence theorem of global attractors, we prove that this system possesses a global attractor, which attracts any bounded set of $H_{\alpha}$ in $H_{\alpha}$-norm. [ABSTRACT FROM AUTHOR]

$$^{3}$$ He interpolating constant-volume gas thermometer scales are compared using different virial coefficients and gas densities for a temperature range of 3 K to the triple point of Ne (24.5561 K). The differences between the International Temperature Scale of 1990 (ITS-90) and the interpolation scale, which follows the definition of the ITS-90 but uses the second and third virial coefficients of the recent ab initio calculations, have maxima of about 0.08 mK and 0.13 mK for gas densities of $$168\,\hbox {mol}{\cdot }\hbox {m}^{-3}$$ and $$278\,\hbox {mol}{\cdot }\hbox {m}^{-3}$$ , respectively. The differences between the ITS-90 and the interpolation scale using only the ab initio second virial coefficient have maxima of about 0.08 mK and 0.14 mK for the same respective sequence of gas densities. The ITS-90 temperatures obtained in eight runs with gas densities from $$127\,\hbox {mol}{\cdot } \hbox {m}^{-3}$$ to $$278\,\hbox {mol}{\cdot }\hbox {m}^{-3}$$ agree with a polynomial of the resistance of a rhodium-iron resistance thermometer within 0.2 mK. To calculate the temperature profile along the pressure-sensing tube connecting the low temperature part of the constant-volume gas thermometer to room temperature, a calculation model is proposed that takes into account not only the thermal conductivity of the tube wall but also the radiative heat transfer between the tube and the vacuum jacket enclosing it. The calculation results of this model approximate the measured profile better than the conventional calculations that neglect the radiative heat transfer. [ABSTRACT FROM AUTHOR]

In this paper, the existence of a global attractor for the ³He-4He system is investigated. By using an iteration procedure, combining with the classical existence theorem of global attractors, we prove that this system possesses a global attractor, which attracts any bounded set of Hα in Hα-norm. [ABSTRACT FROM AUTHOR]

Purpose: Radiation induced lung injury (RILI) is a common side effect for patients undergoing thoracic radiation therapy (RT). RILI can lead to temporary or permanent loss of lung function and in extreme cases, death. Combining functional lung imaging information with conventional radiation treatment plans may lead to more desirable treatment plans that reduce lung toxicity and improve the quality of life for lung cancer survivors. Magnetic Resonance Imaging of the lung following inhalation of hyperpolarized 129Xe may provide a useful nonionizing approach for probing changes in lung function and structure associated with RILI before, during, or after RT (early and late time-points). Methods: In this study, dynamic 129Xe MR spectroscopy was used to measure whole-lung gas transfer time constants for lung tissue and red blood cells (RBC), respectively (TTr_tissue and TTr_RBC) in groups of rats at two weeks and six weeks following 14 Gy whole-lung exposure to radiation from a 60Co source. A separate group of six healthy age-matched rats served as a control group. Results: TTr_tissue values at two weeks post-irradiation (51.6 ± 6.8 ms) were found to be significantly elevated (p < 0.05) with respect to the healthy control group (37.2 ± 4.8 ms). TTr_RBC did not show any significant changes between groups. TTr_tissue was strongly correlated with TTr_RBC in the control group (r = 0.9601 p < 0.05) and uncorrelated in the irradiated groups. Measurements of arterial partial pressure of oxygen obtained by arterial blood sampling were found to be significantly decreased (p < 0.05) in the two-week group (54.2 ± 12.3 mmHg) compared to those from a representative control group (85.0 ± 10.0 mmHg). Histology of a separate group of similarly irradiated animals confirmed the presence of inflammation due to radiation exposure with alveolar wall thicknesses that were significantly different (p < 0.05). At six weeks post-irradiation, TTr_tissue returned to values (35.6 ± 9.6 ms) that were not significantly different from baseline. Conclusions: Whole-lung tissue transfer time constants for 129Xe (TTr_tissue) can be used to detect the early phase of RILI in a rat model involving 14 Gy thoracic 60Co exposure as early as two weeks post-irradiation. This knowledge combined with more sophisticated models of gas exchange and imaging techniques, may allow functional lung avoidance radiation therapy planning to be achievable, providing more beneficial treatment plans and improved quality of life for recovering lung cancer patients. [ABSTRACT FROM AUTHOR]

Nuclear fusion of helium-3 (3He) can be used to generate electrical power with little or no radioactive waste and no carbon emissions. Some forty-four tons of this fuel could meet the electricity needs of the United States for a year. Although rare on Earth, an estimated one million tons of 3He has collected on the surface of the moon. While it would cost approximately US$17 billion to develop a mine producing one ton of 3He per year, such an operation is commercially viable over the medium term given the estimated value of that ton of fuel: US$3.7 billion. This article outlines the technical and economic issues related to 3He and its extraction, and it presents a novel approach to estimating the worth of the fuel. The potential of 3He as a future energy source is set in the context of global energy forecasts and international efforts to investigate lunar 3He resources—including a recent Chinese mission. [ABSTRACT FROM AUTHOR]

Purpose MRI using hyperpolarized noble gases, 3He and 129Xe, provides noninvasive assessments of lung structure and function. Previous work demonstrated that absolute ventilated lung volumes (aVLV) measured in rats using hyperpolarized 3He agree well with micro-CT. Methods In this work, aVLV measurements were performed in rats using hyperpolarized 129Xe MRI and compared with hyperpolarized 3He measurements of aVLV under matched ventilation conditions. Whole-lung compliance was also determined. Partial volume, apparent diffusion coefficient, and effective transverse relaxation time corrections were applied during postprocessing to reduce bias between methods. Results Mean apparent diffusion coefficient of the trachea was 0.83 ± 0.09 cm2/s and 0.067 ± 0.011 cm2/s for 3He and 129Xe, respectively. Mean apparent diffusion coefficient of parenchyma was 0.21 ± 0.07 cm2/s and 0.027 ± 0.008 cm2/s for 3He and 129Xe, respectively. Mean transverse relaxation time values were 1.57 ± 0.25 ms and 2.80 ± 0.25 ms for 3He and 129Xe, respectively, in a model trachea and 3.18 ± 1.00 ms and 4.88 ± 0.60 ms for 3He and 129Xe, respectively, for lung parenchyma. Mean aVLV values were 7.07 ± 0.67 mL and 6.99 ± 1.00 mL at 14 cmH2O and 4.88 ± 0.71 mL and 5.36 ± 0.76 mL at 10 cmH2O obtained with 3He and 129Xe, respectively, demonstrating good agreement between 129Xe and 3He. Conclusions 129Xe offers an important alternative to 3He for hyperpolarized gas MRI of aVLV in rats. Magn Reson Med 71:1130-1136, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

A novel 2π detector geometry for small-angle neutron scattering (SANS) applications is presented and its theoretical performance evaluated. Such a novel geometry is ideally suited for a SANS instrument at the European Spallation Source (ESS). Motivated by the low availability and high price of 3He, the new concept utilizes gaseous detectors with 10B as the neutron converter. The shape of the detector is inspired by an optimization process based on the properties of the conversion material. Advantages over the detector geometry traditionally used on SANS instruments are discussed. The angular and time resolutions of the proposed detector concept are shown to satisfy the requirements of the particular SANS instrument. [ABSTRACT FROM AUTHOR]

Alternatives to helium-3 are being actively pursued due to the shortage and rising costs of helium-3. For safeguards applications, there are a number of ongoing investigations to find alternatives that provide the same capability in a cost-effective manner. One of the greatest challenges is to find a comparable alternative for multiplicity counters, since they require high efficiency and short collection or die-away times. Work has been progressing on investigating three commercially available alternatives for high efficiency multiplicity counters: boron trifluoride (BF3) filled proportional tubes, boron-lined proportional tubes, and lithium fluoride with zinc sulfide coated light guides. The baseline multiplicity counter used for the investigation is the Epithermal Neutron Multiplicity Counter with 121 helium-3 filled tubes at 10 atmosphere pressure, which is a significant capability to match. The primary tool for the investigation has been modeling and simulation using the Monte Carlo N-Particle eXtended (MCNPX) radiation transport program, with experiments to validate the models. To directly calculate the coincidence rates in boron-lined (and possibly other) detectors, the MCNPX code has been enhanced to allow the existing coincidence tally to be used with energy deposition rather than neutron capture reactions. This allows boron-lined detectors to be modeled more accurately. Variations of tube number and diameter along with variations in the amount of inter-tube moderator have been conducted for the BF3 and boron-lined cases. Tube pressure was investigated for BF3, up to two atmospheres, as well as optimal boron thickness in the boron-lined tubes. The lithium fluoride was modeled as sheets of material with light guides in between, and the number and thickness of the sheets investigated. The amount of light guide, which in this case doubles as a moderator, was also optimized. The results of these modeling and simulation optimization investigations are described and results presented. [ABSTRACT FROM PUBLISHER]

By permitting direct visualization of the airspaces of the lung, magnetic resonance imaging (MRI) using hyperpolarized gases provides unique strategies for evaluating pulmonary structure and function. Although the vast majority of research in humans has been performed using hyperpolarized 3He, recent contraction in the supply of 3He and consequent increases in price have turned attention to the alternative agent, hyperpolarized 129Xe. Compared to 3He, 129Xe yields reduced signal due to its smaller magnetic moment. Nonetheless, taking advantage of advances in gas-polarization technology, recent studies in humans using techniques for measuring ventilation, diffusion, and partial pressure of oxygen have demonstrated results for hyperpolarized 129Xe comparable to those previously demonstrated using hyperpolarized 3He. In addition, xenon has the advantage of readily dissolving in lung tissue and blood following inhalation, which makes hyperpolarized 129Xe particularly attractive for exploring certain characteristics of lung function, such as gas exchange and uptake, which cannot be accessed using 3He. Preliminary results from methods for imaging 129Xe dissolved in the human lung suggest that these approaches will provide new opportunities for quantifying relationships among gas delivery, exchange, and transport, and thus show substantial potential to broaden our understanding of lung disease. Finally, recent changes in the commercial landscape of the hyperpolarized-gas field now make it possible for this innovative technology to move beyond the research laboratory. J. Magn. Reson. Imaging 2013;37:313-331. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2 μ l to 3 l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the 3He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20–40 ml allows us to determine solubility temperatures by an uncertainty better than 0.5 °C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1 °C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT Background and objective: Spirometry is insensitive to small airway abnormalities in asthma. Our objective was to evaluate regional lung structure and function using hyperpolarized 3He magnetic resonance imaging (MRI) before, during and after a methacholine challenge (MCh). Methods: Twenty-five asthmatics (mean age = 34 ± 11 years) and eight healthy volunteers (HV) (mean age = 33 ± 11 years) underwent spirometry, plethysmography and hyperpolarized 3He MRI prior to a MCh. MRI was repeated following the MCh and again 25 min after salbutamol administration. 3He MRI gas distribution was quantified using semiautomated segmentation of the ventilation defect percent (VDP). Tissue microstructure was measured using the 3He apparent diffusion coefficient (ADC). Analysis of variance with repeated measures was used to evaluate changes at each time point as well as to determine interactions between regions of interest (ROI) and subject group. Pearson's correlations were performed to evaluate associations between 3He MRI measurements and established clinical measures. Results: In asthmatics, but not HV, whole-lung ADC was increased post-MCh ( P < 0.01). In asthmatics only, ADC was increased post-MCh in posterior ROI ( P < 0.01) and all ROI in the superior-inferior direction ( P < 0.01). VDP was increased in posterior and inferior ROI ( P < 0.001). There was a correlation between VDP and specific airway resistance ( r = 0.74, P < 0.0001), dyspnoea score ( r = 0.66, P < 0.01) and fractional exhaled nitric oxide ( r = 0.45, P < 0.05). Conclusions: We evaluated the regional pulmonary response to methacholine and salbutamol using 3He MRI and showed heterogeneous VDP and ADC consistent with bronchoconstriction and gas trapping, respectively, post-MCh. These regional alterations resolved post-salbutamol. [ABSTRACT FROM AUTHOR]

The Memphis aquifer in southwestern Tennessee is a confined to semi-confined unconsolidated sand aquifer and is the primary municipal water source for the Memphis metropolitan area. Leakage of modern water from shallow unconfined aquifers through the upper Claiborne confining unit locally degrades water quality in the Memphis aquifer and makes the aquifer more vulnerable to contamination. Major solute chemistry, tritium, and H/He data were used to investigate the source and mixing proportions of modern water in the Memphis aquifer in the Davis well field, Memphis, Tennessee. Water quality in several production wells in the Davis well field has declined over the past 30 years, mainly through increased total dissolved solids, iron, alkalinity, and hardness. Trends in chemical data, tritium, and other hydrogeologic data support a source for the leakage from the Mississippi River Valley Alluvial aquifer. Mixing proportions of alluvial water in production well water obtained by inverse chemical modeling with PHREEQCi range from 7 to 45%. For two of the production wells, MLGW 414 and 432, H/He data yield mixing ratios similar to those obtained from PHREEQCi in three of four cases; the dissimilar ratio is likely due to a poor solution from the PHREEQCi inverse modeling. Modeling of the age distribution obtained from MLGW 414 and 432 using an exponential-piston flow model (EPM) with an inverse solution computer code yielded mixed results. The EPM solution obtained for MLGW 414 converged with difficulty only for a 5-year transit time in the shallow aquifer and is consistent with a source from the Mississippi River Valley Alluvial aquifer; however, the modeled age of the water is greater than that observed. In comparison, the EPM solution for MLGW 432 converged for the 5- and 7-year transit periods in the shallow aquifer and yielded model ages consistent with observed H/He ages; however, the extent of the maximum radii for infiltration source is not consistent with a Mississippi River Valley Alluvial aquifer source. Other potential sources for leakage to MLGW 432 include water from the Fluvial-terrace aquifer migrating along a fault east of the well field or infiltration of water from a lake south of the well field. [ABSTRACT FROM AUTHOR]

A new set of global phenomenological optical model potential parameters has been obtained for helium-3 projectile, by simultaneously fitting the experimental data of helium-3 total reaction cross sections and elastic scattering angular distributions in the mass range of target nuclei 20⩽ A⩽209 at incident energies below 250 MeV. A comparison has been made between the extracted helium-3 global optical model potential parameters and the existing ones. The calculated results of total reaction cross sections and elastic scattering angular distributions are also compared with experimental data with their satisfactory agreement. [ABSTRACT FROM AUTHOR]

We present results of low-temperature experiments on dilute mixtures of He in He and on pure He, obtained by means of two kinds of mechanical oscillators immersed in the liquid sample: vibrating wires and quartz tuning forks. The helium sample was cooled either by adiabatic demagnetization of an immersed copper nuclear stage or by adiabatic melting of He in superfluid He. The measured effect of the surrounding fluid on the mechanical resonance of the oscillators is compared with existing theories. We also discuss resonances of second sound and the state of supersaturation, both observed by a tuning fork in helium mixtures. [ABSTRACT FROM AUTHOR]

Constant-volume gas thermometer (CVGT) measurements are conducted using He of three different densities as the working gas to obtain the thermodynamic temperature T and the second virial coefficient of He, B, at temperatures down to 3 K, using the triple point of Ne as a reference temperature. Densities of 127 mol · m and 278 mol · m are used in addition to the density of 168 mol · m used in the measurement reported previously, where T was obtained using the virial coefficient adopted by the International Temperature Scale of 1990 (ITS-90), B. T is obtained by two methods, by the single- and multi-isotherm fitting of B to the three densities and by the method used in the previous work using one of the three densities and B. B obtained from the isotherm fitting agrees with B within the uncertainty of the data used to derive B. Moreover, B obtained from a multi-isotherm fit agrees with that of recent theoretical ab initio calculations within 0.05 cm · mol at 5 K and above, and within 0.3 cm · mol down to 3 K. The values of T obtained from the multi-isotherm fits assuming different forms for the temperature dependence of B agree with each other within 0.1 mK. T obtained from the multi-isotherm fitting agrees with that obtained from the method in the previous report within 0.22 mK. The tendency of the difference between T and the ITS-90 temperature reported in the previous work is confirmed in the present work. [ABSTRACT FROM AUTHOR]

The tritium quantity stored in a steel pressure vessel decreases with time because of helium-3 decay and permeation of tritium into the steel wall of the pressure vessel. Meanwhile, the tritium quantity permeating into the steel wall also decreases with time due to helium-3 decay and diffusion in and out of the wall of tritium. Tritium and helium-3 in the steel wall will cause hydrogen and helium embrittlement of the wall material, respectively, and thereby change the carrying capacity of the vessel. Taking contemporarily both decay and permeation of tritium within the vessel and decay and diffusion of tritium having permeated into the wall into consideration, the governing equations of tritium and helium-3 contents in the wall were established and solved, and relevant formulas were deduced. Through analytical calculations, curves of tritium and helium-3 contents versus radius and time were theoretically plotted, the contents spatio-temporal distributions laws were obtained, and a law about helium-3 contents distribution in steel wall of a spherical pressure vessel was discovered which was called the law of double helium-3 content. [ABSTRACT FROM AUTHOR]

In recent years, there have been impressive advances in the technology of cameras using charged coupled devices (CCD's) and electron multiplying charged coupled devices (EMCCD's) that make possible a number of applications for the detection of ionizing radiation. The new cameras have quantum efficiencies exceeding 90%, effective noise levels less than one electron per pixel, and can be made to detect light ranging from the ultraviolet to the infrared. When combined with photomultiplier tubes (PMT's), and when used with Time-Projection-Chambers (TPC's) that contain narrow gap mesh charge amplification stages and scintillating gas compositions, these cameras can be used to provide three-dimensional images of particle tracks. There are many applications for such devices, including direction sensitive searches for dark matter, measurements of thermal and fast neutrons, and searches for double-beta-decay. I will describe the operation of optical TPC's and their various applications in this review article. [ABSTRACT FROM AUTHOR]

3H-3He measurements constitute a well-established method for the determination of the residence time of young groundwater. However, this method has rarely been applied to karstified aquifers and in particular to drip water in caves, despite the importance of the information which may be obtained. Besides the determination of transfer times of climate signals from the atmosphere through the epikarst to speleothems as climate archives, 3H-3He together with Ne, Ar, Kr, Xe data may also help to give new insights into the local hydrogeology, e.g. the possible existence of a perched aquifer above a cave. In order to check the applicability of 3H-3He dating to cave drips, we collected drip water samples from three adjacent caves in northwestern Germany during several campaigns. The noble gas data were evaluated by inverse modelling to obtain recharge temperature and excess air, supporting the calculation of the tritiogenic 3He and hence the 3H-3He age. Although atmospheric noble gases were often found to be close to equilibrium with the cave atmosphere, several drip water samples yielded an elevated 3He/4He ratio, providing evidence for the accumulation of 3He from the decay of 3H. No significant contribution of radiogenic 4He was found, corresponding to the low residence times mostly in the range of one to three years. Despite complications during sampling, conditions of a perched aquifer could be confirmed by replicate samples at one drip site. Here, the excess air indicator ΔNe was about 10 %, comparable to typical values found in aquifers in mid-latitudes. The mean 3H-3He age of 2.1 years at this site presumably refers to the residence time in the perched aquifer and is lower than the entire transit time of 3.4 years estimated from the tritium data. [ABSTRACT FROM AUTHOR]

In the framework of the investigation of enrichment processes of nitrate in groundwater of the Kalahari of Botswana near Serowe, recharge processes were investigated. The thick unsaturated zone extending to up to 100 m of mostly unconsolidated sediments and very low recharge rates pose a serious challenge to study solute transport related to infiltration and recharge processes, as this extends past the conventional depths of soil scientific investigations and is difficult to describe using evidence from the groundwater due to the limitations imposed by available tracers. To determine the link between nitrate in the vadose zone and in the uppermost groundwater, sediment from the vadose zone was sampled up to a depth of 15-20 m (in one case also to 65 m) on several sites with natural vegetation in the research area. Among other parameters, sediment and water were analysed to determine chloride and nitrate concentration depth profiles. Using the chloride mass balance method, an estimation of groundwater infiltration rates produced values of 0.2-4 mm a-1. The uncertainty of these values is, however, high. Because of the extreme thickness of the vadose zone, the travel time in the unsaturated zone might reach extreme values of up to 500 years and more. For investigations using groundwater, we applied the chlorofluorocarbons CFC-113, CFC-12, sulphur hexafluoride (SF6) and tritium to identify potential recharge, and found indications for some advective transport of the CFCs and SF6, which we accounted for as constituting potential active localised recharge. In our contribution, we show the potential and limitations of the applied methods to determine groundwater recharge and coupled solute transport in semi-arid settings, and compare travel time ranges derived from soil science and groundwater investigations. [ABSTRACT FROM AUTHOR]