Search

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]

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]

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]

Abstract: 3He is among the most commonly measured terrestrial cosmogenic nuclides, but an incomplete understanding of the 3He production rate has limited robust interpretation of cosmogenic 3He concentrations. We use new measurements of cosmogenic 3He in olivine from a well-dated lava flow at Tabernacle Hill, Utah, USA, to calibrate the local 3He production rate. The new 3He measurements (n = 8) show excellent internal consistency and yield a sea level high latitude (SLHL) production rate of 123 ± 4 at g−1 yr−1 following the / scaling model [Lal, D., 1991. Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters, 104, 424–439.; . Air pressure and cosmogenic isotope production. Journal of Geophysical Research, 105, 23753–23759.]. We incorporate the new measurements from Tabernacle Hill in a compilation of all published production rate determinations, characterizing the mean global SLHL production rates (e.g. 120 ± 9.4 at g−1 yr−1 with /Stone (2000)). The internal consistency of the global 3He production rate dataset is as good as the other commonly used cosmogenic nuclides. Additionally, 3He production rates in olivine and pyroxene agree within experimental error. The 3He production rates are implemented in an age and erosion rate calculator, forming a new module of the CRONUS-Earth web-based calculator, a simple platform for cosmogenic nuclide data interpretation [Balco, G., Stone, J., Lifton, N.A., and Dunai, T.J., 2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements. Quaternary Geochronology, 3, 174–195.]. The 3He calculator is available online at http://www.cronuscalculators.nmt.edu/. [Copyright &y& Elsevier]

On the basis of the equation of state and the phase equilibrium equations of helium-3 (3He), a computer program for calculating the thermodynamic properties of 3He has been created. With this program, many iso-property tables were prepared for generating p– h and T– s diagrams of 3He over the range of temperature from 0.2 K to 300 K and pressures up to 300 MPa. Compared with the previous diagrams plotted with interpolated experimental data sets, the new ones are more thermodynamically consistent and cover a broader temperature and pressure range. The estimated overall random errors of the diagrams are within 2 %. [ABSTRACT FROM AUTHOR]

There is ongoing controversy as to the dynamical significance of geothermal heat flow in shaping the abyssal circulation. In this paper, we gauge the impact of geothermal heating and vertical mixing parameterizations in the general circulation model OPA. The experiments are evaluated by comparing simulated mantle 3He with observations collected during the GEOSECS and WOCE programs. This tracer is particularly adapted to the validation of our numerical simulations because its injection into the ocean interior is tightly linked to geothermal processes. In agreement with previous studies, the model circulation is found very sensitive to the parameterization of the vertical mixing. The meridional overturning circulation (MOC) is globally intensified when moving from a constant mixing to a version with enhanced mixing near the ocean bottom, with the most drastic variation observed for AABW (+ 50%). Adding the geothermal heat flux mainly affects AABW circulation in the model, enhancing it all the more as the meridional circulation is slow (low vertical mixing), but proportionally less so when it is more vigorous (enhanced vertical mixing). This can be understood from the requirement of the abyssal ocean to maintain heat balance. The evaluation with mantle 3He simulations reveals that the version with low vertical mixing, with its sluggish circulation, produces unrealistically high a 3He isotopic composition. However, with a vertical mixing that is enhanced at depth, the 3He distribution falls within an acceptable range of values in the deep ocean. Finally, adding the geothermal heating to this enhanced mixing case provides a substantial improvement of the simulation of AABW in all basins but the Indian Ocean. 3He isotopic composition is then in good agreement with the observations. Taken jointly with observational estimates of the MOC intensity, these independent isotopic constraints suggest that both geothermal heating and enhanced diapycnal mixing at depth are key ingredients in the realistic simulation of abyssal circulation. [ABSTRACT FROM AUTHOR]

Abstract: The design, setup and performance of a mass spectrometric system for the analysis of low to very low-level tritium in environmental samples are described. The tritium concentration is measured indirectly by the 3He ingrowth from radioactive decay after complete initial degassing of the sample. The analytical system is fully computer-controlled and consists in a commercial helium isotope mass spectrometer coupled with a high vacuum inlet system. A detection limit of 0.15Bq/kg is routinely obtainable for sample sizes of 20g of water equivalent and an accumulation time of three months. Larger samples (and/or longer accumulation time) can be used to obtain lower detection limits. In addition to the benefit of a lower detection limit, another advantage of this non-destructive method lies in the simplicity of the analytical procedure which strongly limits the risk of contamination. An inter-comparison was successfully performed with the conventional beta counting technique on lyophilized grass samples, in a range of tritium concentrations of environmental interest. It shows that the 3He mass spectrometry method yields results that are fully consistent with the conventional liquid scintillation technique over a wide range of tritium concentrations. [Copyright &y& Elsevier]

A Stirling-type pulse tube cryocooler (PTC) with precooling was designed and manufactured to investigate its performance at 4 K. Numerical simulation was carried out based on the well-known regenerator model REGEN with an emphasis on the performance of a 4 K stage regenerator of the Stirling-type PTC as influenced by the warm end temperature, pressure ratio, frequency and average pressure with helium-4 and helium-3 as the working fluid respectively. This study demonstrates that the use of a cold inertance tube can significantly improve the efficiency of a 4 K Stirling-type PTC. A preliminary experimental investigation was carried out with helium-4 as the working fluid and a refrigeration temperature of 4.23 K was achieved. The experimental results show that the operating frequency has a significant influence on the performance of the Stirling-type PTC and a relatively low average pressure is favorable for decreasing the loss associated with the real gas effects of a 4 K Stirling-type PTC. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to assess the properties of a model system for hyperpolarized He-3 (HHe) diffusion MR imaging created from the lungs of New Zealand white rabbits by drying the lungs while inflated at constant pressure. The dried lungs were prepared by sacrificing the animal, harvesting the lungs en bloc and dehydrating the lungs for several days using dry compressed air. In four rabbits, the apparent diffusion coefficient (ADC) of HHe gas was measured in vivo and, within 1 week, in vitro in the dried lungs. To assess long-term repeatability, in vitro ADC values were measured again 3 months later. Dried lungs from four additional rabbits were imaged twice on the same day to assess the short-term repeatability of ADC measurements, and tissue samples from these lungs were then removed for histology. In vivo and in vitro ADC maps showed similar features and similar distributions of ADC values; mean in vivo and in vitro ADC values differed by less than 12%. The in vitro mean ADC values were highly reproducible, with no more than 5% difference between measurements for the short-term repeatability and less than 17% difference between measurements for the long-term repeatability. Histological samples from the dried lungs demonstrated that the lung structure remained intact. These results suggest that the dried lungs are a useful and inexpensive alternative to human or in vivo animal studies for HHe diffusion MR sequence development, testing and optimization. [Copyright &y& Elsevier]

We describe the mass spectrometric facility for measuring helium isotopes, neon, and tritium that has been operative at this institute since 1989, and also the sampling and sample preparation steps that precede the mass spectrometric analysis. For water samples in a near-equilibrium with atmospheric air, the facility achieves precision for 3He/4He ratios of±0.4% or better, and±0.8 % or better for helium and neon concentrations. Tritium precision is typically±3 % and the detection limit 10 mTU (≈ 1.2·10-3 Bq/kg of pure water). Sample throughputs can reach some thousands per year. These achievements are enabled, among other features, by automation of the measurement procedure and by elaborate calibration, assisted by continual development in detail. To date, we have measured more than 15,000 samples for tritium and 23,000 for helium isotopes and neon, mostly in the context of oceanographic and hydrologic work. Some results of such work are outlined. Even when atmospheric tritium concentrations have become rather uniform, tritium provides water ages if 3He data are taken concurrently. The technique can resolve tritium concentrations in waters of the pre-nuclear era. [ABSTRACT FROM AUTHOR]

The developments of helium-3 nuclear magnetic resonance (NMR) technique to assess porous media properties such as porosity and pore size distribution (PSD) are reported. The method is suitable for use to characterize unconventional extra-heavy oil reservoirs, has a potential in application to tight shales and other unconventional formations, and has several advantages over conventional water NMR. It is based on 3He nuclear magnetic relaxation measurements for different pore loadings and inverse Laplace transform of the data. The relation between different pore types as well as their mean radii are found within the models of spherical, cylindrical and planar pores. The method was applied to study porosity and PSD of rock samples acquired at the North belt of crude oil, Republic of Cuba, the unconventional formation known for its complexity. The obtained pore sizes and porosities are in a good agreement with conventional methods which validates the proposed 3He NMR approach for porous media studies. Advantages of the 3He liquid and gas as probes are discussed. • Characterization of pore structure with the smallest probing atoms — helium-3. • Advantages over conventional water nuclear magnetic resonance technique. • No need to separate the signal from sample and probe molecules. • Access to hidden pores and pores with weak connectivity. • Porosity and pore size distributions of unconventional and clay-rich oil formations. [ABSTRACT FROM AUTHOR]

Abstract: Accurate determination of cosmogenic 3He concentrations in olivine and pyroxene phenocrysts requires knowledge of the amount of magmatic 3He also in the sample. The magmatic 3He component is commonly estimated by measuring the magmatic 3He/4He ratio and assuming that all 4He is magmatic. However, this approach yields incorrect results if 4He produced by U and Th decay is also present. Here we propose several strategies to account for the presence of radiogenic 4He. The optimal approach depends on whether the helium closure age (T c) is similar to the exposure age (T e) of the analyzed phenocrysts. (i) When T c = T e, which applies to uneroded lava flows, the ratio of cosmogenic 3He to radiogenic 4He is constant and the correction for radiogenic helium is independent of time. We provide a simple expression for a correction factor (R) that can be applied in this case. (ii) In the more common case that T c > T e, it is necessary to obtain an independent constraint on the closure age to estimate the radiogenic correction. In either case a quantitative estimate of the radiogenic 4He production rate is required. Because of the long stopping distance of α-particles, this production rate depends on the U and Th concentrations of both phenocryst and host, and also on phenocryst grain size. To illustrate the magnitude and uncertainty of the necessary corrections, we compiled U and Th measurements on phenocrysts and whole rock samples of basalts and andesites, supplemented by new measurements on Hawaiian basalts and Altiplano andesites. Our data and models suggest that some published cosmogenic 3He production rate determinations may have underestimated the true production rate by up to 5% because the presence of radiogenic 4He was not recognized. Similarly, a recent study presenting cosmogenic 3He derived erosion rates in >4 Ma Hawaiian olivines probably overestimates true erosion rates by an order of magnitude or more. [Copyright &y& Elsevier]

Abstract: This article presents a phenomenological dynamic phase transition theory–modeling and analysis–for liquid helium-3. We derived two new models, for liquid helium-3 with or without applied field, by introducing three wave functions and using a unified dynamical Ginzburg–Landau model. The analysis of these new models leads to predictions of existence of (1) a metastable region, (2) a new phase C in a narrow region, and (3) switch points of transition types on the coexistence curves near two triple points. It is hoped that these predictions will be useful for designing better physical experiments and lead to better understanding of the physical mechanism of superfluidity. [Copyright &y& Elsevier]

Abstract: This study evaluates an alternative isochron method designed to improve the precision and the accuracy of the measurement of cosmogenic 3He (3Hec) and the calibration of 3Hec production rates in lava flows. While the accuracy of the standard two-steps routine ((i) crushing, (ii) melting) may be affected by possible crushing-induced release of matrix-sited 3Hec, this new isochron technique does not involve the preliminary crushing step. Such advance is thus potentially able to improve the accuracy of 3Hec determination. Moreover this method has the advantage to yield cosmogenic 3He concentrations using only one type of extraction technique. Cosmogenic 3He isochrons can be built successfully measuring the 3He and 4He concentrations of several phenocrysts replicates fused in vacuo, provided that these aliquots have identical magmatic 3He/4He ratios, identical 3Hec concentrations and variable magmatic helium contents. When plotted in the 3He/4He vs 1/4He space, such a suite of data define a straight line whose intercept yield the magmatic (3He/4He)mag ratio, and whose slope is the cosmogenic 3He concentration. The frequent addition of radiogenic 4He (4He⁎) may be easily accounted taking advantage of a property that is characteristic of non-eroded lava flows: the 3Hec/4He⁎ ratio is not time-dependent. This radiogenic correction of the isochron slope involves the R-factor, whose calculation requires that the U and Th abundances in the phenocrysts and the host lava be known, as well as the diameter and the shape of the analyzed minerals. This correction also requires that all the analyzed aliquots have identical radiogenic 4He concentration. The isochron method was tested on surface samples of three Quaternary basalt flows from Mount Etna and Mauna Loa (aged of 6±1, 8.2±0.1 and 41±3 ka). The obtained data set yielded statistically robust isochrons and cosmogenic 3He concentrations that are not significantly different from those obtained with the standard method. Importantly, for samples with high magmatic/cosmogenic 3He ratio, the isochron technique offers both better accuracy and precision than the standard two-steps method. This alternative technique should thus open new perspectives for the particularly important task of 3Hec production rate calibrations from lava flow surfaces. [Copyright &y& Elsevier]

Abstract: Despite the importance of the tobacco smoke particulate matter in the lungs to the etiology of pulmonary disease in cigarette smokers, little is currently known about the spatial distribution of particle deposition or the persistence of the resulting deposits in humans, and no satisfactory technique currently exists to directly observe tobacco smoke condensate in airways. In this proof-of-principle work, hyperpolarized (hp) 83Kr MRI and NMR spectroscopy are introduced as probes for tobacco smoke deposition in porous media. A reduction in the hp-83Kr longitudinal (T 1) relaxation of up to 95% under near-ambient humidity, pressure and temperature conditions was observed when the krypton gas was brought into contact with surfaces that had been exposed to cigarette smoke. This smoke-induced acceleration of the 83Kr self-relaxation was observed for model glass surfaces that, in some experiments, were coated with bovine lung surfactant extract. However, a similar effect was not observed with hp-129Xe indicating that the 83Kr sensitivity to smoke deposition was not caused by paramagnetic species but rather by quadrupolar relaxation due to high adsorption affinity for the smoke deposits. The 83Kr T 1 differences between smoke-treated and untreated surfaces were sufficient to produce a strong contrast in variable flip angle FLASH hp-83Kr MRI, suggesting that hp-83Kr may be a promising contrast agent for in vivo pulmonary MRI. [Copyright &y& Elsevier]

Abstract: A new semi-empirical formula for the evaluation of (n,3He) reaction cross-sections at the energy of 14.6 and 20MeV is presented. Formula was derived using the analytical expression for the evaluation of the 3He spectrum within the frame of pre-equilibrium exciton model. The systematics obtained is compared with the empirical formula for the (n,3He) reaction cross-section. [Copyright &y& Elsevier]

Abstract: The presence and diagnosis of radiation damping could have major implications in NMR experiments with hyperpolarised gases, where accurate knowledge of the flip angle is imperative. In this work radiation damping was observed and investigated in a low-pass birdcage resonator (Q =250) with samples of hyperpolarised 3He at 1.5T. With an initially highly polarised (P =38%) sample of 3He in a spherical cell, the observed FID had a distorted line shape with a spectral line width that was three times that of the same sample in a virtually depolarised state (1Hz line width for P <1%). Moreover a linear relation between the sample’s magnetisation (M 0) and the line width of the spectrum was observed which is indicative of radiation damping. With highly polarised samples, significant radiation damping was observed and the effect was a lower than expected rate of depletion of M 0 in RF flip angle calibration experiments, which led to significant underestimate of the RF flip angle. To our knowledge this is the first report of radiation damping in a birdcage resonator with samples hyperpolarised or otherwise. Experimental observation of radiation damping could be used as means of measuring coil efficiency as an alternative to the geometrical filling factor (η) the definition of which is open to question for a birdcage resonator. Estimates of the birdcage filling factor from the measured damping time constants (η RD =0.4%) are compared to those derived from electromagnetic energy ratios (η E =1.6%) and metallic sphere frequency shift methods (η fs =1.4%). These figures are much lower than the simple volume geometrical upper limit of η v =3.7% derived from the ratio of cell volume to total coil volume (shield included). The physical explanation for this shortfall is that the bulk of the magnetic energy stored in the birdcage is spatially distributed predominantly between the rungs and the shield, and not in the coil centre where the sample is placed and where the field has its highest spatial homogeneity. [Copyright &y& Elsevier]

An equation of state for normal liquid 3He has been constructed in the form of Helmholtz free energy as a function of independent parameters—temperature, and density. The equation was fitted simultaneously to the collected experimental p-ρ- T, specific heat, sound velocity, isobaric expansion coefficient and isothermal compressibility coefficient from the world’s literature to accuracies comparable with reasonable experimental errors in the measured quantities. Extensive comparisons between the equation of state and experimental data have been made by a set of deviation plots. The state equation is valid in the region for temperatures from 0.1 K to T c = 3.3157 K, and for pressures from vapor pressures to melting pressures. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: MR imaging of the restricted diffusion of laser-polarized 3He gas provides unique insights into the changes in lung microstructure in emphysema.Results: We discuss measurements of ventilation (spin density), mean diffusivity, and the anisotropy of diffusion, which yields the mean acinar airway radius. In addition, the use of spatially modulated longitudinal magnetization allows diffusion to be measured over longer distances and times, with sensitivity to collateral ventilation paths. Early results are also presented for spin density and diffusivity maps made with a perfluorinated inert gas, C3F8.Methods: Techniques for purging and imaging excised lungs are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Based on the collected experimental and smoothed p–ρ–T data, isochoric and isobaric specific heat capacity data, etc., p–H and T–S diagrams of 3He are plotted in the range of temperatures from 0.2K to 20K and pressures from 0.0001MPa to 20MPa, with data calculated numerically instead of using an equation of state. [Copyright &y& Elsevier]

A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized ³He MRI to detect the build-up of the signal intensity after increasing numbers of ³He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume ∼2 mm³). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of -0.11 ± 0.03 cm-1. In prone posture, the distribution of ventilation was more uniform, with a significantly (P < 0.001) smaller gradient of the ventilation index of -0.01 ± 0.02 cm-1. It is concluded that the ³He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal. [ABSTRACT FROM AUTHOR]

Abstract: The potentialities of MIMAC-He3, a MIcro-tpc MAtrix of Chambers of Helium-3, for supersymmetric dark matter search are discussed within the framework of effective MSSM models without gaugino mass unification at the GUT scale. A phenomenological study has been done to investigate the sensitivity of the MIMAC-He3 detector to neutralinos () via spin-dependent interaction with 3He as well as its complementarity to direct and indirect detection experiments. Comparison with other direct dark matter searches will be presented in a WIMP model-independent framework. [Copyright &y& Elsevier]

We present NMR spectra of liquid 3He, confined to a cylindrical cell, in the temperature range from 2.3 to 1000 mK for a static field of 11.33 tesla and range of applied field gradients. The spectra are generated by taking the Fourier transform of the free induction decay (FID) following NMR tipping pulses. For small tipping angles, the spectra exhibit sharp lines which correspond to long-lived modes with decay times greater than 100 ms. The cause of these magneto-dynamic modes is oscillation of the transverse magnetisation in the applied magnetic field and the demagnetising field. The frequencies of the modes for a given field gradient are independent of temperature, but their damping depends on the effective spin diffusion coefficient which is determined by the Leggett-Rice effect. We also investigate how the spectrum changes with the magnetisation. We are able to simulate the spectra using a model that includes the demagnetising field. The predicted spectral-line frequencies are in reasonable agreement with experiment when there is an applied field gradient. The damping of the modes is due to diffusion, but because of the finite size of the matrices used in the calculation, we have found it necessary to increase the effective diffusion coefficient in the model above the experimental value in order to obtain a spectrum which resembles the experimental one. [ABSTRACT FROM AUTHOR]

We compare simulations of the injection of mantle helium-3 into the deep ocean from six global coarse resolution models which participated in the Ocean Carbon Model Intercomparison Project (OCMIP). We also discuss the results of a study carried out with one of the models, which examines the effect of the subgrid-scale mixing parameterization. These sensitivity tests provide useful information to interpret the differences among the OCMIP models and between model simulations and the data.We find that the OCMIP models, which parameterize subgrid-scale mixing using an eddy-induced velocity, tend to underestimate the ventilation of the deep ocean, based on diagnostics with δ3He. In these models, this parameterization is implemented with a constant thickness diffusivity coefficient. In future simulations, we recommend using such a parameterization with spatially and temporally varying coefficients in order to moderate its effect on stratification.The performance of the models with regard to the formation of AABW confirms the conclusion from a previous evaluation with CFC-11. Models coupled with a sea-ice model produce a substantial bottom water formation in the Southern Ocean that tends to overestimate AABW ventilation, while models that are not coupled with a sea-ice model systematically underestimate the formation of AABW.We also analyze specific features of the deep 3He distribution (3He plumes) that are particularly well depicted in the data and which put severe constraints on the deep circulation. We show that all the models fail to reproduce a correct propagation of these plumes in the deep ocean. The resolution of the models may be too coarse to reproduce the strong and narrow currents in the deep ocean, and the models do not incorporate the geothermal heating that may also contribute to the generation of these currents. We also use the context of OCMIP-2 to explore the potential of mantle helium-3 as a tool to compare and evaluate modeled deep-ocean circulations. Although the source function of mantle helium is known with a rather large uncertainty, we find that the parameterization used for the injection of mantle helium-3 is sufficient to generate realistic results, even in the Atlantic Ocean where a previous pioneering study [J. Geophys. Res. 100 (1995) 3829] claimed this parameterization generates inadequate results. These results are supported by a multi-tracer evaluation performed by considering the simulated distributions of both helium-3 and natural 14C, and comparing the simulated tracer fields with available data. [Copyright &y& Elsevier]

The neutron-detection characteristics of a cryogenic neutron detector comprising an InSb semiconductor detector and a helium-3 gas converter were evaluated at a gas pressure up to 12.4 atm at 4.2 K. The detector successfully detected stable neutrons under these conditions, where the density of the helium-3 gas is a few-hundred times higher than that at room temperature. It was found that the neutron detection efficiency was correlated with the gas pressure—even in a backward-detection configuration—in low-temperature, high-pressure helium-3. [Copyright &y& Elsevier]

Rock varnish is a manganiferous dark coating ubiquitous in desert landscapes. To test the validity of varnish microstratigraphy as a chronometric indicator, varnish samples were collected from radiometrically dated and undated late Quaternary lava flows in Amboy, Cima, and Pisgah volcanic fields (AVF, CVF, PVF) in the Mojave Desert of California, western United States. Varnish microstratigraphies show a replicable layering sequence that appears to record regional climate changes that likely correspond in time to the Younger Dryas and Heinrich events in the North Atlantic region. Microstratigraphic patterns on these volcanic fields match patterns found in varnishes from other western US sites with available radiometric age constraints. Based on this regional chronology, varnishes from the A flow, H flow, and a stone pavement surface in the Cima volcanic field were estimated to be 16.5–24, 74–85, and 74–85 ka, respectively; these ages are consistent with previously published cosmogenic 3He ages of 18–20, 72–74, and 80–85 ka for these geomorphic surfaces. Varnishes from the I flow at Cima yielded a puzzling age estimate of 39 ka, which is consistent with an older 3He age of 37±6 ka reported for the I flow, but inconsistent with a younger 3He age of 31±7 ka and a cosmogenic 36Cl age of 27±1.3 ka for the same flow. Reinterpretation of the original varnish age data, with knowledge of then available field mapping results of the I flow, suggests that the I cone is polycyclic and different flow units were probably unintentionally sampled in the field. The revised varnish ages of 30 and 39 ka for the I flow thus may be in good agreement with their corresponding 3He and 36Cl ages. In a blind test of the method, varnishes from the Phase 1 flow at Pisgah, an unnamed flow (called here the I′ flow) at Cima, and the Amboy flow were estimated to be 24–30, 46–60, and 74–85 ka, respectively; these ages agree well with 36Cl ages of 22.5±1.3, 46±2, and 79±5 ka reported for the same flows by Phillips [Geomorphology (2002).]. These test results provide convincing evidence that varnish microstratigraphy, once radiometrically calibrated, can be used as a valid dating tool to estimate surface exposure ages of desert landforms in the western US drylands. [Copyright &y& Elsevier]

The properties of superfluid 3He in the regime of negligible normal fluid density is both of fundamental interest and yet very simple. The behaviour is dominated by the properties of the condensate, and several phenomena, otherwise masked by the normal fluid, become observable. We discuss the techniques needed to cool the superfluid to T≪0.1 Tc. We discuss some examples of the unique low temperature behaviour; quasi-persistent spin precession, possible orbital precession, imaging turbulence, nucleation and the phase diagram in aerogel. [Copyright &y& Elsevier]