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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]

The differential cross-section for the 3He+3H nuclear reaction was measured in a thin tritiated PdTi film that was deposited on a Si wafer. The sample was loaded with 3H2 gas at a temperature of 300 °C and at a pressure of 1.8 bar. The total activity of the sample, measured by the liquid scintillation technique, was found to be 395 MBq. Two peaks were observed in the spectrum of the thick Si detector, corresponding to the 3H(3He,d)4He and 3H(3He,p)5He reaction channels. The differential cross-section was determined for the energy range of the 3He beam from 0.6 to 3.4 MeV, at three scattering angles of 125, 135 and 155°. The differential cross-section for the first channel remained almost constant within the measured energy range, while the cross-section for the second channel increased with energy. In both cases, the cross-sections reached their maximum value at the lowest scattering angle measured. The differential cross-sections were verified using a thick solid tritiated tungsten target. For assessing the tritium depth profile, only the reaction channel 3H(3He,d)4He can be utilized.

A common technique for determining the mass accumulation rates of marine sediments is through measurements of constant flux proxies. These proxies, like unsupported 230Th and extraterrestrial 3He, are buried at a known rate at the seafloor, and thus their concentration in sediments is inversely proportional to the vertical mass accumulation rate of ambient sediments. These two proxies have varied assumptions regarding their behavior that have been difficult to test, particularly in regions of very low sedimentation. We present new measurements of helium and thorium isotopes in coretop sediments from the South Pacific Gyre. Our main finding is that 230Th- and 3He-derived mass accumulation rates of these sediments differ by a factor of 2–10, with 230Th-based mass accumulation rates systematically higher than those derived from 3He. While the final cause of the discrepancy is difficult to elucidate, we suggest that up to a factor of 2 worth of the sedimentary 230Th deficit can be explained by lateral transport of 230Th, while the remainder must be explained by other processes, such as ancient coretops undercorrected for post-depositional 230Th decay. Regardless of the mechanism, our findings have critical implications for the application of constant flux proxies in the South Pacific Gyre, with one example being the calibration of dust deposition models in this region. Ultimately, additional testing is required to determine the accuracy of the 3He and 230Th techniques for estimating sediment accumulation rates in regions of the open ocean with extremely low sedimentation rates. [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]

The Moon-based ground penetrating radar (GPR) carried by the Yutu rover performed in-situ radar measurements to explore extraterrestrial objects, which provides an unprecedented opportunity to study the shallow subsurface structure of the Moon and its internal resources. Exploiting lunar resources might be one of the solutions to the Earth's energy shortage in the future. In this article, first, the thickness distribution of the lunar regolith at the Chang'E-3 landing site is derived using the high-frequency Yutu radar observation data. Second, the surface concentration of helium-3 is determined based on the surface TiO$_{2}$ content of the lunar regolith. Finally, the reservoir of helium-3 resources in the lunar regolith is estimated. Our result suggests that the helium-3 reservoir along the Yutu rover traveling route from the navigation points N105 to N208 ($\sim$445 m$^{2}$) is $\sim$37–51 g, and its helium-3 content per unit area is $\sim$0.083–0.114 g/m${^{2}}$, which is at least five times higher than that of the global average. Currently, the nuclear fusion experiment is facing a severe shortage of tritium fuel. We discuss the possibility of replacing it with lunar helium-3 as the fuel for nuclear fusion. Meanwhile, we also suggest that the Chang'E-3 landing area can be a potential site selection for the exploitation of the lunar helium-3 in the future. Our results will provide a valuable reference to evaluate the economics and feasibility of mining in-situ helium-3 resources on the Moon.

Since a fusion reactor using the Deuterium-Tritium fuel cycle cannot be a source of clean energy because of the deleterious effects of energetic neutrons carrying 80% of the energy output, and it is very doubtful that it will be able to achieve Tritium self-sufficiency because of an extremely problematic and still unproven breeding procedure, this paper proposes a new reactor scheme capable of confining hot and dense plasmas using the Deuterium – Helium-3 fuel cycle. Such a reactor must be considered a source of clean energy because of its very low level of neutrons production, and its fuel is available in large quantity since we can get the needed Deuterium from seawater and likewise Helium-3 from the moon, as it was found from the samples of lunar soil brought back by the astronauts of the Apollo Mission. The proposed reactor consists of two 100 m long cylindrical plasmas, connected by semicircular sections to form a racetrack configuration. It should be capable of producing from 16 to 20 GW of fusion power when operating with an electron density of 3 × 1020 m−3, a magnetic field of 10 T and average temperatures from 40 to 45 keV. Out of this power, up to 10 GW will be used for replacing the loss of electron energy from bremsstrahlung radiation, with a consequent reduction in the reactor power output. However, such a loss could be mitigated by a partial recovery of the energy plasma radiation.

The Direct Fusion Drive (DFD) and its terrestrial counterpart, the Princeton Field Reversed Configuration (PFRC) reactor, have seen significant developments in the past decade. Various groups conducted detailed research on the required specifications of the engine and associated technology for power delivery to onboard avionics and payloads. Multiple studies have also addressed the thrust generation mechanism using empirical specific power scaling relations and plasma flow simulations. Recent studies have designed spacecraft for missions to Earth's second Lagrange point, Mars, transneptunian bodies like Pluto, and the neighboring star systems Alpha Centauri A and B. However, significant work is needed to design the engine components in detail using scientific scaling relations and ab inito calculations to develop the physical systems for prototyping and testing. After critically analyzing the reference design of the DFD and the underlying fusion reactor, this paper addresses the technological gaps and suggests avenues to improve specifications toward targets outlined in previous studies while considering costs. Further, the authors present a prototype engine and magnetohydrodynamic power conversion system design to study the engineering hurdles relevant to the practical implementation of the DFD. • Review of the current FRC fusion reactors and the Direct Fusion Drive (DFD) • DFD with High-Temperature Superconducting tape in a liquid helium cryostat • Magnetohydrodynamic (MHD) power generation cycle to overcome current design issues • Novel "Plasma Processor" concept to generate electrical power • Design exercise for a new, cost-aware 50 kW DFD [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]

In the present work experimentally determined differential cross sections of the reactions 10B(3He, p 1,3)12C, 11B(3He, p 0,1,2,3)13C and 11B(3He, d 0)12C are reported. The measurements cover the 2–3 MeV energy range, for 5 detection angles of θ = 137°, 141°, 146°, 152°, 158°. A novel experimental setup was designed for this purpose and installed at the Dual Microprobe end-station of the Ruđer Bošković Institute (RBI) in Zagreb, Croatia. It involves an annular strip charged particle silicon detector with a large solid angle, enabling a relatively fast acquisition process without significant increase in the angular uncertainty. The obtained cross sections were benchmarked with a thick amorphous boron target in a different experimental setup at RBI, as well as at the scattering chamber setup of the RUBION accelerator facility in Bochum, Germany. • Novel setup for Nuclear reaction cross section measurements designed and constructed • Nuclear reaction cross sections of 10B(3He, p 1,3)12C, 11B(3He, p 0,1,2,3)13C and 11B(3He, d 0)12C measured and evaluated • The presented setup is incorporated in the ion microprobe chamber for ion beam analysis of fusion related materials [ABSTRACT FROM AUTHOR]

We derive the semiclassical evolution equations for a system consisting of helium-3 atoms in the $2^3S$ metastable state interacting with a light field far-detuned from the $2^3S-2^3P$ transition, in the presence of metastability exchange collisions with ground state helium atoms and a static magnetic field. For two configurations, each corresponding to a particular choice of atom–light detuning in which the contribution of either the metastable level $F = 1/2$ or $F = 3/2$ is dominant, we derive a simple model of three coupled collective spins from which we can analytically extract an effective coupling constant between the collective nuclear spin and light. In these two configurations, we compare the predictions of our simplified model with the full model.

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]

Space is becoming the next frontier for human conflict and competition. The United States, the People's Republic of China (PRC), and the Russian Federation (RF) have all invested deeply in a modern space race to gain or maintain strategic superiority, with plans for lunar bases, celestial resource exploitation, and the colonization of Mars. With technological advancements and a weak regulatory framework governing space operations, the development of spacebased and counterspace military assets, advanced space weaponry, space transportation and space resource exploitation operations are an inherent part of mankind's future. This article assumes the inevitability of space exploration--including celestial body resource exploitation, weapon research and developments, and the human colonization of Mars--to show the importance of American leadership of human expansion into space. Power in space will be drawn from technological developments, including new types of weaponry and energy production. The author explores the technologies available in today's space race environment, including potential future energy resources available in space, weapon systems designed for space and counterspace warfare, the legal implications of each, and some potential consequences of different nations gaining the upper hand in the heavens. [ABSTRACT FROM AUTHOR]

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]

The HENRI system was developed to narrow the pulse width of TREAT from 89 ms to below 60 ms with the goal of improving the test reactor's ability to simulate RIAs in LWRs by rapidly injecting helium-3, a strong neutron poison, into the core. A coupled model using the CFD code STAR-CCM+ and the reactor physics code Serpent 2, called CONSTELATION, was developed to investigate the physics of the helium-3 injection into TREAT. This study proposes an experimental methodology to quantify the accuracy of the coupled transient CFD-reactor physics model CONSTELATION. Physics were identified that are captured only in the coupled model. Experiments were then designed to measure the identified physics and the OSTR was selected to carry out the testing campaign. Modeling the experiments with the coupled model produced results that provide multiple phenomena that can be measured experimentally. Thus, the model can be compared to future experimental data and the accuracy can be quantified. • Reactor feedback during helium-3 injection causes measurable deviation in pressure evolution. • Smaller experiment in a different reactor captures characteristic shock waves and oscillation. • Helium-3 injection into reactor leads to helium flow stagnation and reversal. [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]

Dedicated fast ion D-D and D-3He fusion experiments were performed on JET with carbon wall (2008) and ITER-like wall (2014) for testing the upgraded neutron and energetic ion diagnostics of fusion products. Energy spectrum of D-D neutrons was the focus of the studies in pure deuterium plasmas. A significant broadening of the energy spectrum of neutrons born in D-D fast fusion was observed, and dependence of the maximum D and D-D neutron energies on plasma density was established. Diagnostics of charged products of aneutronic D-3He fusion reactions, 3.7 MeV alpha-particles similar to those in D-T fusion, and 14.6 MeV protons, were the focus of the studies in D-3He plasmas. Measurements of 16.4 MeV gamma-rays born in the weak secondary branch of D(3He, γ)5Li reaction were used for assessing D-3He fusion power. For achieving high yield of D-D and D-3He reactions at relatively low levels of input heating power, an acceleration of D beam up to the MeV energy range was used employing 3rd harmonic () ICRH technique. These results were compared to the techniques of D beam injection into D-3He mixture, and 3He-minority ICRH in D plasmas.

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]

Abstract 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.

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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]

Abstract 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 E n =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.

This paper reports the full range Joule-Thomson inversion curve of helium-3 (3He) constructed by a virial-type equation of state of this quantum fluid. In order to evaluate the equation of state, the virial coefficients of 3He calculated from the result of the analysis of this study are compared with previous studies. The inversion curve is confirmed to agree with the empirical inversion points reported previously. The peak temperature and the peak pressure of the inversion curve are respectively determined to be 19.6 K and 2.588 MPa. The minimum and the maximum inversion temperatures at zero pressure are estimated to be 2.8 K and 48.5 K, respectively. The reduced inversion curve of 3He is also obtained with the critical parameters and it is compared with other reduced inversion curves of quantum and non-quantum fluids. The discrepancy of the reduced inversion curve of 3He from the general reduced inversion curves is explained by means of the thermal de Broglie wavelength, similar to other quantum fluids. [ABSTRACT FROM AUTHOR]

We propose to take advantage of the very weak coupling of the ground-state helium-3 nuclear spin to its environment to produce very long-lived macroscopic quantumstates, here nuclear spin squeezed states, in a gas cell at roomtemperature. To performa quantumnon-demolitionmeasurement of a transverse component of the previously polarized collective nuclear spin, a discharge is temporarily switched on in the gas, which populates helium-3 metastable state. The collective spin corresponding to the F Æ 1/2 metastable level then hybridizes slightly with the one in the ground state by metastability exchange collisions. To access the nuclear spin fluctuations, one continuously measures the light field leaking out of an optical cavity, where it has interacted dispersively with the metastable state collective spin. In a model of three coupled collective spins (nuclear, metastable and Stokes for light) in the Primakoff approximation, and for two measurement schemes, we calculate the moments of the collective nuclear spin squeezed component Iz conditioned on the optical signal averaged over the observation time t. In the photon counting scheme, we find that the squeezed observable is I 2 z rather than Iz. In the homodyne detection scheme, we analytically solve the stochastic equation for the state of the system conditioned to the measurement; the conditional expectation value of Iz depends linearly on the signal and the conditional variance of Iz does not depend on it. The conditional variance decreases as (¡sqt)¡1, where the squeezing rate ¡sq, which we calculate explicitly, depends linearly on the light intensity in the cavity at weak atom-field coupling and saturates at strong coupling to the ground state metastability exchange effective rate, proportional to the metastable atom density. Finally, we take into account the de-excitation of metastable atoms at the walls, which induces nuclear spin decoherence with an effective rate °®. It imposes a limit / (°®/¡sq)1/2 on the conditional variance reached in a time / (°®¡sq)¡1/2. A multilingual version is available on the open archive HAL at https://hal.archives-ouvertes.fr/hal-03083577. [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]

• Near-ridge sedimentary 230ThXS deposition rates constrained using 3HeET. • Surplus 230ThXS deposition rates occur in close proximity to vent sites. • Diffusive seawater 230Th transport drives deficit 230ThXS deposition off-axis. • Spatial extent of hydrothermal influence on 230ThXS varies by ridge and over time. • 230ThXS deposition approaches seawater production rate within ∼10 km of most ridges. Mid-ocean ridges are valuable archives of sedimentary flux records used to investigate atmospheric, oceanographic, and solid Earth responses to climate variability. Constant flux proxies, such as extraterrestrial helium-3 (3He ET) and excess thorium-230 (230Th XS), constrain vertical mass accumulation rates independent of the biases associated with lateral sediment transport and age model resolution. However, thorium scavenging by hydrothermal particles can perturb local 230Th XS deposition and complicate its application as a constant flux proxy in near-ridge environments. We characterize the footprint of hydrothermal scavenging on sedimentary 230Th XS using coupled 3He ET -230Th XS analyses in cores from the Mid-Atlantic Ridge and the Juan de Fuca Ridge. Samples deposited >10 km from the Juan de Fuca Ridge indicate reliable off-axis behavior of both constant flux proxies. In contrast, samples deposited <10 km from the Juan de Fuca Ridge axis and within the axial valley of the Mid-Atlantic Ridge suggest 50–80% deficits in sedimentary 230Th XS relative to its production rate. These deficits contrast with sedimentary 230Th XS surpluses recently observed on the East Pacific Rise. The spatial footprint of hydrothermal scavenging varies globally and temporally, likely as a function of the intensity of local hydrothermal activity. The combined ridge data suggest that near-vent sediments (typically within ∼5 km, but variable by ridge) receive relatively high 230Th XS deposition rates as a direct result of hydrothermal particle scavenging, while more distal sediments receive relatively low 230Th XS deposition rates due to diffusive loss of overlying seawater 230Th XS towards the vent. Aside from the East Pacific Rise, far-field sediments are likely to exhibit typical 230Th XS deposition rates at distances greater than ∼10 km of the ridge axis. However, 230Th XS systematics within the axial valleys of slow-spreading ridges may be complicated by other factors. Combined 3He ET -230Th XS studies at multiple ridges are needed to further characterize the nature of hydrothermal scavenging and to evaluate the potential of sedimentary 230Th XS anomalies to record large-scale variability in past hydrothermal activity. [ABSTRACT FROM AUTHOR]