Loss Of He Research Articles

Lactobacillus johnsoniiLa1 AttenuatesHelicobacter pylori-Associated Gastritis and Reduces Levels of Proinflammatory Chemokines in C57BL/6 Mice

In clinical settings, Lactobacillus johnsonii La1 administration has been reported to have a favorable effect on Helicobacter pylori-associated gastritis, although the mechanism remains unclear. We administered, continuously through the water supply, live La1 to H. pylori-infected C57BL/6 mice and followed colonization, the development of H. pylori-associated gastritis in the lamina propria, and the levels of proinflammatory chemokines macrophage inflammatory protein 2 (MIP-2) and keratinocyte-derived cytokine (KC) in the serum and gastric tissue over a period of 3 months. We documented a significant attenuation in both lymphocytic (P=0.038) and neutrophilic (P=0.003) inflammatory infiltration in the lamina propria as well as in the circulating levels of anti-H. pylori immunoglobulin G antibodies (P=0.003), although we did not observe a suppressive effect of La1 on H. pylori colonizing numbers. Other lactobacilli, such as L. amylovorus DCE 471 and L. acidophilus IBB 801, did not attenuate H. pylori-associated gastritis to the same extent. MIP-2 serum levels were distinctly reduced during the early stages of H. pylori infection in the La1-treated animals, as were gastric mucosal levels of MIP-2 and KC. Finally, we also observed a significant reduction (P=0.046) in H. pylori-induced interleukin-8 secretion by human adenocarcinoma AGS cells in vitro in the presence of neutralized (pH 6.8) La1 spent culture supernatants, without concomitant loss of H. pylori viability. These observations suggest that during the early infection stages, administration of La1 can attenuate H. pylori-induced gastritis in vivo, possibly by reducing proinflammatory chemotactic signals responsible for the recruitment of lymphocytes and neutrophils in the lamina propria.

Studies of electronic stopping powers using time of flight spectrometry

Electronic stopping powers have been determined by measuring the energy loss of He, O and Al particles using a time of flight (ToF) elastic recoil detection analysis set-up. In transmission geometry, the energy loss of particles in self-supporting foils of C and SiC is measured over a continuous energy range using the ToF spectrometer. By calibrating the Si detector for each channel over the measured energy region based on ToF spectrometry, the current approach eliminates much of the error associated with pulse height defects in Si detectors, and measurement uncertainties of less than 4% are achieved.

NRA and ERDA investigation of helium retention in SiC as a function of irradiation and annealing

Silicon carbide has been proposed for coating applications in advanced reactor designs, so studies of its behavior in the presence of ion irradiation and fission products are of interest. We investigated the retention of He in single crystal 6H SiC as a function of irradiation fluence and annealing temperature using both nuclear reaction analysis (NRA) and time-of-flight elastic recoil detection analysis (ToF ERDA). Ions of 3He + were implanted at 40 keV in SiC to a depth of ∼200 nm at room temperature. NRA was performed using 1.0 MeV D + and the 3He(D,α) 1H reaction. No change in the He profile was seen for irradiation fluence up to 6.8 × 10 17 D +/cm 2 at room temperature. Isochronal annealing of the SiC between 300 and 1200 K also showed no significant helium loss. Subsequently, a sample was irradiated with D + at 900 K and again at 1100 K. No loss of 3He associated with irradiation was seen for a fluence up to 5 × 10 17 D +/cm 2. Annealing the sample above 1200 K resulted in thermally activated loss of He. ToF ERDA measurements were performed using 44 MeV 127I 10+ for both irradiation and analysis. Depth profiles of the He distribution showed no significant change under I bombardment with an ion fluence up to ∼10 14/cm 2 at room temperature. NRA was performed on the implanted sample subjected to ERDA. The 3He profiles for regions subjected to I irradiation were similar in shape to those with no I irradiation.

Energy loss of He, Li and B isotopes with MeV energies in Au

The objective of this study was to experimentally investigate the stopping power and energy straggling of helium, lithium and boron isotopes with MeV energies in Au. A 9SDH-2 tandem accelerator was employed to perform ion bombardment experiments. The detection measurements were carried out using partially-coated silicon detectors. Furthermore, both the Monte-Carlo simulations and experimental results yielded by other findings were also conducted in this study in order to make comparisons. The uncertainty in this experiment was estimated to be less than 1%. The results indicated that our experimental results were in good agreements with both the theoretical and previous experimental results.

Age and temperature of shock metamorphism of Martian meteorite Los Angeles from (U-Th)/He thermochronometry

Mineralogic features attributed to impact-induced shock metamorphism are commonly observed in meteorites and terrestrial impact craters. Partly because the duration of shock metamorphism is very short, constraining the timing and temperature of shock events has been problematic. We measured (U-Th)/He ages of single grains of merrillite and chlorapatite from the Martian meteorite Los Angeles (LA). Merrillite and chlorapatite ages cluster at 3.28 6 0.15 Ma (2s) and 2.18 6 0.19 (2s) Ma, respectively. The mean age of the merrillites, which are larger than chlorapatites, is indistinguishable from cosmic-ray exposure ages (3.1 6 0.2 Ma), suggesting that impact-induced shock metamorphism was coeval with ejection of the LA precursor from Mars. To constrain the initial temperature of shock metamorphism in the LA precursor body, we modeled diffusive loss of He from merrillite as a function of diffusion domain size, LA precursor body size, and ablation depth. From these calculations, we suggest that the metamorphic temperature of the shock event was higher than 450 8C. These results support the idea that shock pressures of the Martian meteorite Shergotty were higher than 45 GPa, as inferred from the presence of post-stishovite SiO2 polymorphs. Single-grain (U-Th)/He dating of phosphates may provide unique constraints on the timing and pressure-temperature dynamics of shock metamorphism in a wide variety of extraterrestrial materials.

U–Th/He age of phenocrystic garnet from the 79 AD eruption of Mt. Vesuvius

The U–Th/He system can potentially be used for dating volcanic rocks with ages as young as a few thousand years and as old as several million years, thus providing a valuable supplement to radiocarbon and K–Ar dating. Garnet phenocrysts from the 79 AD eruption of Mt. Vesuvius were dated to evaluate the accuracy with which the necessary measurements and corrections can be made. The determined age, corrected for diffusive loss of He, alpha ejection, and initial U-series disequilibrium, is 1885±188 yr which compares well with the known age of 1923 yr. U and Th concentrations were measured by isotope dilution on different aliquots than were used for He concentration measurements. Step-wise degassing yielded an Arrhenius relationship for He diffusion in garnet with an activation energy of 91.31±5.76 kJ/mol and ln D 0/ a 2=−2.00±0.56. The uniformity of U and Th concentrations in garnet was checked by ion microprobe analysis. The 234U/ 238U and 230Th/ 238U activity ratios were measured by MC-ICPMS. The results suggest that with proper analysis and corrections, the U–Th/He method can be used to date young volcanic minerals with useful precision and accuracy, and may therefore be valuable for dating volcanic rocks that have low K or are otherwise difficult to date accurately with Ar–Ar or radiocarbon.

Two-center electron-electron correlation within the independent event model

The Independent Event Model (IEVM) is used to analyze collision processes for systems with three and four electrons, in situations where up to three active electrons are involved and dynamical correlation effects play a major role. The model is applied to single electron loss and loss-ionization processes. All the possible ionization mechanisms for both collision partners in each exit channel are considered, including antiscreening, which, in the IEVM, can be taken into account in a consistent way along all the other ones, keeping unitarity. As a casestudy, the IEVM is applied to the analysis of the single loss of He+, Li+, and Li2+ ions by He atoms with the simultaneous single and double ionization of the target. We present plots of the cross sections of single electron loss accompanied or not by the ionization of the target as functions of the projectile energy. The calculations describe well the experimental energy dependence and the high-velocity absolute values for the cross sections.

Helium in solubility equilibrium with quartz and porefluids in rocks: A new approach in hydrology

Quartz crystals in sandstones at depths of 1200 m–1400 m below the surface appear to reach a solubility equilibrium with the 4He‐concentration in the surrounding pore‐ or groundwater after some time. A rather high 4He‐concentration of 4.5 · 10−3 cc STP 4He/cm3 of water measured in a groundwater sample would for instance maintain a He pressure of 0.47 atm in a related volume. This value is equal within analytical error to the pressure deduced from the measured helium content of the quartz and its internal helium‐accessible volume. To determine this volume, quartz crystals of 0.1 to 1 mm were separated from sandstones and exposed to a helium gas pressure of 32 atm at a temperature of 290°C for up to 2 months. By crushing, melting or isothermal heating the helium was then extracted from the helium saturated samples. A volume on the order of 0.1% of the crystal volume is only accessible to helium atoms but not to argon atoms or water molecules. By monitoring the diffusive loss of He from the crystals at 350°C an effective diffusion constant on the order of 10−9 cm2/s is estimated. Extrapolation to the temperature of 70°C in the sediments at a depth of 1400 m gives a typical time of about 100 000 years to reach equilibrium between helium in porewaters and the internal He‐accessible volume of quartz crystals. In a geologic situation with stagnant pore‐ or groundwaters in sediments it therefore appears to be possible with this new method to deduce a 4He depth profile for porewaters in impermeable rocks based on their mineral record.

Accurate RBS measurement of ion implant doses in silicon

AbstractWe demonstrate very accurate ion implant dose measurements using Rutherford backscattering spectrometry (RBS) traceable to a certified reference material from IRMM, Geel and the Bundesanstalt für Materialforschung (BAM), Berlin. The measurements have an absolute accuracy of better than 1.4% and a precision of better than 1.25%. The certified standard sample is compared directly with recent absolute determinations of the energy loss of He in Si, and also with a sample calibrated against the Harwell Bi standard. We determine the dose in a series of three In implants and six As implants of various doses and energies. Some of the samples were amorphized to eliminate channelling effects. A double detector geometry was used, giving pairs of spectra with a common incident charge but where the solid angle and the electronic gain were determined for each detector channel independently. The statistical uncertainty is reduced to <1%. The non‐linear pile‐up background is determined carefully. The errors are determined critically. The experiments were carried out at different dates and different places, so time and space reproducibility of the results is confirmed. The IBA DataFurnace is used for analysis of the certified standard reference material and compared with a transparent manual data reduction method: the use of this code for routine data analysis at the highest accuracy is validated. Copyright © 2002 John Wiley & Sons, Ltd.

Channeling energy loss of He 2+ in Si by transmission and back-scattering measurements: Experiments and computer modeling

Path-dependent electronic stopping of 3.35 MeV He 2+ ions in Si, is investigated by Rutherford back-scattering channeling in Si/SiO 2 wafers and transmission energy loss measurements in thin (1 1 0) membranes. A model which makes use of the 3-D Si electron density to calculate the stopping due to valence electrons, and the program convolution approximation for swift particles (CASP) to calculate the stopping due to core electrons, has been introduced into a Monte Carlo code for the simulation of channeling. The only adjustment allowed is the normalization to the empirical random stopping. An agreement of simulations and experiments within ±10–15% is obtained if both valence and core electron stopping components are scaled in the normalization procedure. To perform a significant comparison with the results obtained by a full atomic (CASP) model, we have also used a different normalization scheme, keeping the core component fixed and scaling only the valence electron contribution. In this case the results of the solid model, although slightly less accurate, become very similar to those obtained with the free-atom model.

The Lohawat howardite: Mineralogy, chemistry and cosmogenic effects

Abstract— The Lohawat meteorite is a texturally heterogeneous breccia having a variety of mineral and lithic fragments. Among mineral fragments, pyroxenes show a wide range of composition (Wo0.011–0.17En0.37–0.78Fs0.21–0.60) whereas plagioclase is anorthitic (An0.92Ab0.07Or0.007). Abundant rounded “chondrule‐like” objects ranging in size up to ∼7 mm, some with concentric layering, have been observed. Petrographic features, trace element composition and rare earth element patterns show the presence of eucritic and diogenitic components confirming that it is a typical howardite. Cosmogenic tracks, rare gases (He, Ne, and Ar) and radionuclides (22Na and 26Al) were measured. Track density in olivine and plagioclase varies between 0.7 to 6 times 106/cm2. 38Ar exposure age is estimated to be ∼110 Ma, being the highest among howardites. The track production rates correspond to ablation of 9 to 15 cm, implying a radius for its preatmospheric size of ∼27 cm. 22Na/26Al ∼ 1, as expected from the production models and solar modulation of galactic cosmic‐ray fluxes before its fall, suggesting that the meteoroid did not undergo any fragmentation during the past ∼2 Ma in interplanetary space. The radiogenic age based on K‐Ar method is 4.3 Ga while the U‐Th‐4He age is 3.3 Ga indicating partial loss of He.

Influence of crystal size on apatite (U–Th)/He thermochronology: an example from the Bighorn Mountains, Wyoming

Near-surface tectonic and geomorphic processes involve cooling of rocks through low temperatures (50–200°C). Because rates of helium diffusion in apatite, titanite, and zircon are sensitive to temperature variations in this range, uranium–thorium/helium thermochronometry ((U–Th)/He dating) is well-suited to establishing the timing and rates of these processes in the geologic record. However, because fractional loss of He is controlled by crystal size such that larger crystals retain a larger fraction of radiogenic He, (U–Th)/He ages must vary not only with thermal history but also with crystal size. Here we present crystal size-correlated He ages from co-existing apatites from the Bighorn Mountains, Wyoming that range from 100 to 350 Ma. These correlations are a sensitive indicator of the rock’s thermal history in a temperature range below the system’s nominal closure temperature ( T c∼70°C for apatite), and are consistent with a thermal history involving residence in the upper 2–3 km of crust since the Precambrian, with maximum temperatures of 65–80°C just prior to Laramide orogenic exhumation. The influence of crystal size on He ages will be most apparent in rocks where temperatures have been in the range of partial He retention for long periods of time (∼30–70°C for >10 7 years). In such cases, accurate interpretation of (U–Th)/He ages must incorporate the effect of crystal size, and this method may provide insights to thermal histories of rocks in previously inaccessible low-temperature ranges.

A helium, argon, and nitrogen record of the upper continental crust (KTB drill holes, Oberpfalz, Germany): implications for crustal degassing

An extensive set of bulk rock samples and mineral separates from the German Deep Drilling Project (KTB) has been analyzed for nitrogen, helium, and argon concentrations. The samples comprise metabasites, paragneisses, and hornblende–gneisses from a 7-km section in the crystalline basement metamorphosed during the Variscan orogeny. The data indicate a dependence of the N and Ar concentrations on the mica content of the rocks. The He–N 2–Ar composition of fluid inclusions in quartz from felsic veins suggests that the fluids are old basement brines with large proportions of radiogenic He and Ar. There is no systematic down-hole variation in N and Ar concentrations, but He concentrations appear to increase with depth. Calculated degassing rates suggest near complete degassing of He from the gneisses, but some He retention in the metabasites. Nonetheless, overall degassing fluxes of He (1.2–4.0×10 10 atoms m −2 s −1) are not in conflict with estimates of the He flux in continental crust based on the steady-state degassing model. In contrast, our estimates indicate that Ar fluxes are significantly lower than predicted by a steady-state degassing model which is thus probably inappropriate to describe Ar fluxes correctly. The down-hole trend of increasing He concentration is interpreted as a degassing profile. A model of simultaneous radiogenic ingrowth and diffusive loss of He has been applied to determine the bulk transport coefficient of He in crystalline basement, which was found to be between 10 −10 and 10 −7 m 2 s −1. This is much higher than reasonable diffusion rates, suggesting that episodes of enhanced degassing, probably related to hydrothermal or tectonic activities, played an important role in the degassing history of the crust. The relationship between the transport of heat and He in the crust in the KTB area is examined. Under the assumption that the ratio of heat flow and He flux from the mantle is the same as in ocean basins, the He isotopic composition of the basement fluids in the KTB boreholes is consistent with the inferred reduced heat flow at the KTB site. On a global scale, however, heat flow and flux of mantle He are probably not correlated.

Multiple fluid pulses in a Samoan harzburgite

Noble gases trapped in fluid inclusions in residual mantle xenoliths from Samoa have a wide range in 4He/ 40Ar * which anti-correlates with enrichments in non-atmospheric Ar, Ne and Xe isotopes and with the concentration of 40Ar * trapped in the mineral. These correlations cannot be due to post-eruption loss of He from the inclusions, but are likely due to mixing of a He-depleted mantle fluid and an unfractionated, plume-derived, fluid that has entrained significant atmospheric noble gases. Mixing of the two fluids occurred within the mantle or at the base of the Samoan lithosphere. Helium loss at depth is implied.

Open system behavior of helium in case of the HIMU source area

Lower ³He/4He than that of mid‐ocean ridge basalts (MORBs) observed in HIMU‐ocean island basalts (OIBs) has been considered to be the evidence that the HIMU source is related to recycled materials. However, typical ³He/4He value of Polynesian HIMU‐OIBs (∼6.8 RA) is too high to be explained by addition of in situ radiogenic 4He in the recycled oceanic crust. Mixing of the upper mantle material with the recycled oceanic crust cannot explain ³He/4He of HIMU‐OIBs as revealed from mixing calculation in the He‐Pb isotope system. As another possibility, if we assume that large mobility of helium affects ³He/4He of recycled materials, the model calculation indicates that the balance between radiogenic 4He production in the recycled oceanic crust and diffusive loss of 4He to the surrounding mantle accounts for ³He/4He of HIMU. The model suggests the thickness of HIMU source body to be in the order of 1 km.

Noble gases in twenty‐one Saharan LL‐chondrites: Exposure ages and possible pairings

Abstract— Nineteen LL‐chondrites and two L/LL‐chondrites (Adrar 003 and Tanezrouft 010) from the Saharan desert of Algeria and Libya have been analysed for their He, Ne and Ar composition as well as for their abundance of 84Kr and 132Xe. Calculated 21Ne cosmic‐ray exposure ages vary between 2 and 35 Ma. The age distribution is consistent with that of modern LL‐chondrite falls except that no dominant peaks can be observed, especially not the one related to a 15 Ma collisional event. However, the lack of young exposure ages of <8 Ma is obvious. This is a characteristic feature of LL‐chondrites. Only one of the 21 LL‐chondrites, namely Acfer 066, contains solar gases and is thus considered a regolith breccia. Three specimens reveal considerable loss of 3He, probably due to periods of elevated temperatures in orbits with small perihelion distances. Furthermore, severe loss of 4He and 40Ar is found in two samples. Considering possible pairings, we suggest 14 individual falls basically on the basis of the noble gas data, the petrographic sub‐classification and by taking the find location into consideration. However, there are constraints on confirming pairings solely on the basis of our studies. Thus, we can only exclude individual samples with a unique noble gas fingerprint from paired specimens.

Electron-electron interaction in the electron loss of He + on H 2 and He

The simultaneous ionization of the projectile and the target is studied in He + +{H 2,He} collisions. The energy dependence of the cross section for this process is analyzed through experimental results obtained by coincidence measurements and theoretical calculations considering the antiscreening and two-center double-ionization mechanisms. The excellent agreement obtained between theory and experiment allows one to obtain a good understanding of the dynamics of this projectile loss mechanism.

Separation of the screening and antiscreening effects in the electron loss of He+ on H2 and He.

The screening and antiscreening contributions to electron loss are separated experimentally through the measurement of the recoil ions and the emergent charge states in the collisions ${\mathrm{He}}^{+}$+(${\mathrm{H}}_{2}$,He) \ensuremath{\rightarrow}${\mathrm{He}}^{2+}$+(${\mathrm{H}}_{2}^{+}$,${\mathrm{He}}^{+}$). The experimental data are in excellent agreement with calculations which include second-order contributions for the simultaneous ionization of the projectile and the target.

Fuel management effects on inherent safety of modular high temperature reactor.

Analysis was performed on the effects of fuel loading schemes and fuel materials on the inherent (passive) safety characteristic of the modular pebble-bed type high-temperature reactor against depressurization accident involving loss of He forced circulation Two extreme fuel loading schemes, the infinite-velocity multipass and Once-Through-Then-Out (OTTO), were evaluated for both U and Th fuel cycles. The results of the analysis show that the maximum core temperatures attained following the accident were much lower for the infinite-velocity multipass scheme than for the OTTO scheme. For both schemes, the Th cycle showed slightly higher maximum peak temperatures, compared to U cycle.

Diffusion and trapping of ion-implanted helium in nickel

Helium concentration versus depth profiles have been measured and analyzed for 200 keV He implanted into nickel at temperatures between 300 and 1064 K. Below 973 K, the profiles do not exhibit appreciable temperature dependence and are similar to theoretical range distributions. Above 973 K the range peak begins to exhibit broadening with some loss of He. The changes in the peak shape could be accounted for the assuming that the He and its ion-beam generated vacancies migrate simultaneously and become trapped with each other. A helium-vacancy binding enthalpy of 3.2 eV and an effective helium migration energy of approximately 2.6 eV was found to be consistent with the data when analyzed by a limited system of diffusion equations.