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We have analysed the petrography, major element abundances and bulk Al-Mg isotope systematics of 19 ferromagnesian chondrules from the CV3 chondrites Allende, Mokoia, and Vigarano, together with an Al-rich chondrule and refractory olivine from Mokoia. Co-variations of Al/Mg with Na/Mg and Ti/Mg in our bulk chondrules suggest their compositions are dominantly controlled by reworking of different proportions of chondrule components (e.g. mafic minerals and mesostatis); their precursors are thus fragments from prior generations of chondrules. Our samples show a range in fractionation corrected 26 Mg/ 24 Mg (Δ′ 26 Mg) ∼ 60 ppm, relative to precisions <±5 ppm (2se) and these values broadly covary with 27 Al/ 24 Mg. The data can be used to calculate model initial 26 Al/ 27 Al, or ( 26 Al/ 27 Al) 0 , of the chondrule precursors. Our resolvably radiogenic chondrules yield model ( 26 Al/ 27 Al) 0  ∼ 1–2 × 10 −5 , equivalent to model “ages” of precursor formation ≦1 Ma post CAI. However, many of our chondrules show near solar Δ′ 26 Mg and no variability despite a range in 27 Al/ 24 Mg. This suggests their derivation either from younger precursor chondrules or open system behaviour once 26 Al was effectively extinct (( 26 Al/ 27 Al) 0  < 0.8 × 10 −5 , given the resolution here). Evidence for the latter explanation is provided by marked rims of orthopyroxene replacing olivine, indicating reaction of chondrules with a surrounding silicate vapour. Concurrent isotopic exchange of Mg with a near chondritic vapour during late reworking could explain their isotopic systematics. One ferromagnesian object is dominated by a high Mg# olivine with elevated Ti and Ca abundances. This refractory olivine has a markedly negative Δ′ 26 Mg = −16 ± 3 ppm (2se), reflecting its early removal (model age of <0.5 Ma post CAI), from a reservoir with evolving Δ′ 26 Mg. If representative of the chondrule forming region, this grain defines a minimum interval of radiogenic ingrowth for CV chondrites commensurate with ( 26 Al/ 27 Al) 0  > 3.4 ± 0.6 × 10 −5 . Overall, our samples record a sequence of events from the formation of ferromagnesian objects within 0.5 Ma of CAI to re-equilibration of chondrules and silicate vapour >2 Ma post CAI, assuming an initially homogeneous 26 Al/ 27 Al. Metamorphism on the asteroid parent body may have played a subsequent role in affecting Mg isotope composition, but we argue this had a minor influence on the observations here. [ABSTRACT FROM AUTHOR]

Renazzo-type carbonaceous (CR) chondrites are distinct from most other chondrites in having younger chondrule 26 Al- 26 Mg ages, but the significance of these ages and whether they reflect true formation times or spatial variations of the 26 Al/ 27 Al ratio within the solar protoplanetary disk are a matter of debate. To address these issues and to determine the timescales of metal-silicate fractionation and chondrule formation in CR chondrites, we applied the short-lived 182 Hf- 182 W chronometer to metal, silicate, and chondrule separates from four CR chondrites. We also obtained Mo isotope data for the same samples to assess potential genetic links among the components of CR chondrites, and between these components and bulk chondrites. All investigated samples plot on a single Hf-W isochron and constrain the time of metal-silicate fractionation in CR chondrites to 3.6 ± 0.6 million years (Ma) after the formation of Ca-Al-rich inclusions (CAIs). This age is indistinguishable from a ∼3.7 Ma Al-Mg age for CR chondrules, suggesting not only that metal-silicate fractionation and chondrule formation were coeval, but also that these two processes were linked to each other. The good agreement of the Hf-W and Al-Mg ages, combined with concordant Hf-W and Al-Mg ages for angrites and CV chondrules, provides strong evidence for a disk-wide, homogeneous distribution of 26 Al in the early solar system. As such, the young Al-Mg ages for CR chondrules do not reflect spatial 26 Al/ 27 Al heterogeneities but indicate that CR chondrules formed ∼1–2 Ma later than chondrules from most other chondrite groups. Metal and silicate in CR chondrites exhibit distinct nucleosynthetic Mo and W isotope anomalies, which are caused by the heterogeneous distribution of the same presolar s -process carrier. These data suggest that the major components of CR chondrites are genetically linked and therefore formed from a single reservoir of nebular dust, most likely by localized melting events within the solar protoplanetary disk. Taken together, the chemical, isotopic, and chronological data for components of CR chondrites imply a close temporal link between chondrule formation and chondrite accretion, indicating that the CR chondrite parent body is one of the youngest meteorite parent bodies. The relatively late accretion of the CR parent body is consistent with its isotopic composition (for instance the elevated 15 N/ 14 N) that suggests a formation at a larger heliocentric distance, probably beyond the orbit of Jupiter. As such, the accretion age of the CR chondrite parent body of ∼3.6 Ma after CAI formation provides the earliest possible time at which Jupiter's growth could have led to scattering of carbonaceous meteorite parent bodies from beyond its orbit into the inner solar system. [ABSTRACT FROM AUTHOR]

The rates and chronologies of valley incision are closely modulated by the tectonic uplift of active mountain ranges and were controlled by repeated climate changes during the Quaternary. The continental collision between the Iberian and Eurasian plates induced a double-vergence orogen, the Pyrenees, which has been considered a mature mountain range despite significant seismicity and evidence of neotectonics. Nevertheless, recent studies indicated that the range may have never reached a steady state. One option for resolving this controversy is to quantify the incision rates since the Miocene by reconstructing the vertical movement of geometric markers such as fluvial terraces. However, the few available ages for the Pyrenean terrace systems do not exceed the Middle Pleistocene. Thus, we study alluvium-filled horizontal epiphreatic passages in limestone karstic networks to increase the span of this dataset. Such landforms are used as substitutes of fluvial terraces because they represent former valley floors. These features record the transient position of former local base levels during the process of valley deepening. The Têt river valley (southern Pyrenees) is studied near the Villefranche-de-Conflent limestone gorge, where 8 cave levels have been recognized over a vertical height of 600 m. In this setting, already published 26 Al/ 10 Be cosmogenic burial data were limited to the last ∼5 Ma. This work extends this initial dataset through the acquisition of cosmogenic 10 Be/ 21 Ne data, which should enable us to reconstruct a more complete valley incision chronology. We also revise the 26 Al/ 10 Be record for the lowest portion of the valley. The obtained quantitative results are surprising relative to certain geological evidence, and the limitations of such an approach in the investigated geodynamic context are discussed. In particular, sampling within a detrital deposit (the Escaro Formation) and in the riverbeds suggests that the 26 Al/ 10 Be ratios that are associated with the lower cave levels could have been inherited by pre-burial episodes. Similarly, pre-burial catchment denudation rates that do not exceed hundreds of cm/ka are probably tainted by the same amalgamation processes. [ABSTRACT FROM AUTHOR]

The Centre for Accelerator Science at ANSTO operates four tandem accelerator systems for Accelerator Mass Spectrometry (AMS) and Ion Beam Analysis (IBA). The latest addition to the fleet is SIRIUS, a 6 MV combined IBA and AMS system. Following initial ion beam testing, conditioning and debugging software and hardware, SIRIUS is now commissioned. Details of the instrument design and performance data for 10 Be, 26 Al and 36 Cl are presented. [ABSTRACT FROM AUTHOR]

For accelerator mass spectrometry (AMS) measurements of 26 Al the use of AlO − ions holds considerable promise given their ionization yield which is about an order of magnitude higher compared to the commonly used Al − ions. However, the strong isobaric interference introduced by 26 MgO − ions must be reduced before the identification in a gas ionization chamber (GIC). At the ETH Zurich 6 MV EN-TANDEM accelerator the foil degrader method as well as the gas-filled magnet (GFM) method were systematically investigated with respect to suppression of 26 Mg and acceptance of 26 Al. Additionally a new, large-acceptance GIC was designed to capture as large a fraction of the broad beams as possible. The GFM method achieves a 26 Mg suppression factor of 10 3 and an acceptance of 26 Al of > 50 % and therefore provides a significant advantage over the degrader foil method ( s Foil ( 26 Mg ) ≈ 3 · 10 2 , τ Foil ( 26 Al ) ≈ 30 % ). In combination with the 26 Mg separation of 10 4 in the GIC it is now possible to measure samples with a Mg content in the ppm range down to 26 Al/ 27 Al ≈ 10 - 14 with an overall efficiency that is approximately 5 × improved with respect to the previous TANDEM setup. [ABSTRACT FROM AUTHOR]

Calcium-aluminum-rich inclusions with isotopic mass fractionation effects and unidentified nuclear isotopic anomalies (FUN CAIs) have been studied for more than 40 years, but their origins remain enigmatic. Here we report in situ high precision measurements of aluminum-magnesium isotope systematics of FUN CAIs by secondary ion mass spectrometry (SIMS). Individual minerals were analyzed in six FUN CAIs from the oxidized CV3 carbonaceous chondrites Axtell (compact Type A CAI Axtell 2271 ) and Allende (Type B CAIs C1 and EK1-4-1 , and forsterite-bearing Type B CAIs BG82DH8 , CG-14 , and TE ). Most of these CAIs show evidence for excess 26 Mg due to the decay of 26 Al. The inferred initial 26 Al/ 27 Al ratios [( 26 Al/ 27 Al) 0 ] and the initial magnesium isotopic compositions (δ 26 Mg 0 ) calculated using an exponential law with an exponent β of 0.5128 are (3.1 ± 1.6) × 10 −6 and 0.60 ± 0.10‰ ( Axtell 2271 ), (3.7 ± 1.5) × 10 −6 and −0.20 ± 0.05‰ ( BG82DH8 ), (2.2 ± 1.1) × 10 −6 and −0.18 ± 0.05‰ ( C1 ), (2.3 ± 2.4) × 10 −5 and −2.23 ± 0.37‰ ( EK1-4-1 ), (1.5 ± 1.1) × 10 −5 and −0.42 ± 0.08‰ ( CG-14 ), and (5.3 ± 0.9) × 10 −5 and −0.05 ± 0.08‰ ( TE ) with 2 σ uncertainties. We infer that FUN CAIs recorded heterogeneities of magnesium isotopes and 26 Al in the CAI-forming region(s). Comparison of 26 Al- 26 Mg systematics, stable isotope (oxygen, magnesium, calcium, and titanium) and trace element studies of FUN and non-FUN igneous CAIs indicates that there is a continuum among these CAI types. Based on these observations and evaporation experiments on CAI-like melts, we propose a generic scenario for the origin of igneous (FUN and non-FUN) CAIs: ( i ) condensation of isotopically normal solids in an 16 O-rich gas of approximately solar composition; ( ii ) formation of CAI precursors by aggregation of these solids together with variable abundances of isotopically anomalous grains—possible carriers of unidentified nuclear (UN) effects; and ( iii ) melt evaporation of these precursors accompanied by crystallization under different temperatures and gas pressures, leading to the observed variations in mass-dependent isotopic fractionation (F) effects. [ABSTRACT FROM AUTHOR]

In order to further elucidate possible temporal relationships between different varieties of calcium-, aluminum-rich inclusions (CAIs), we measured the aluminum–magnesium isotopic systematics of seven examples of the rare type known as forsterite-bearing Type B (FoB) inclusions from four different CV3 carbonaceous chondrites: Allende, Efremovka, NWA 3118, and Vigarano. The primary phases (forsterite, Al–Ti-rich diopside, spinel, melilite, and anorthite) in each inclusion were analyzed in situ using high-precision secondary ion mass-spectrometry (SIMS). In all cases, minerals with low Al/Mg ratios (all except anorthite) yield well-defined internal Al–Mg isochrons, with a range of initial 26 Al/ 27 Al ratios [( 26 Al/ 27 Al) 0 ] ranging from (5.30 ± 0.22) × 10 −5 down to (4.17 ± 0.43) × 10 −5 . Anorthite in all cases is significantly disturbed relative to the isochrons defined by the other phases in the same CAIs, and in several cases contains no resolved excesses of radiogenic 26 Mg (δ 26 Mg ∗ ) even at 27 Al/ 24 Mg ratios greater than 1000. The fact that some FoBs preserve ( 26 Al/ 27 Al) 0 of ∼5.2 × 10 −5 , close to the canonical value of (5.23 ± 0.13) × 10 −5 inferred from bulk magnesium-isotope measurements of CV CAIs ( B. Jacobsen et al., 2008 ), demonstrates that FoBs began forming very early, contemporaneous with other more-refractory CAIs. The range of ( 26 Al/ 27 Al) 0 values further shows that FoBs continued to be reprocessed over ∼200,000 years of nebular history, consistent with results obtained for other types of igneous CAIs in CV chondrites. The absence of any correlation between of CAI + FoB formation or reprocessing times with bulk composition or CAI type means that there is no temporal evolutionary sequence between the diverse CAI types. The initial δ 26 Mg ∗ value in the most primitive FoB (SJ101) is significantly lower than the canonical solar system value of −0.040 ± 0.029‰. [ABSTRACT FROM AUTHOR]

Detailed petrologic, geochemical and isotopic analyses of a new FUN CAI from the Allende CV3 meteorite (designated CMS-1) indicate that it formed by extensive melting and evaporation of primitive precursor material(s). The precursor material(s) condensed in a 16 O-rich region (δ 17 O and δ 18 O ∼ −49‰) of the inner solar nebula dominated by gas of solar composition at total pressures of ∼10 −3 –10 −6 bar. Subsequent melting of the precursor material(s) was accompanied by evaporative loss of magnesium, silicon and oxygen resulting in large mass-dependent isotope fractionations in these elements (δ 25 Mg = 30.71–39.26‰, δ 29 Si = 14.98–16.65‰, and δ 18 O = −41.57 to −15.50‰). This evaporative loss resulted in a bulk composition similar to that of compact Type A and Type B CAIs, but very distinct from the composition of the original precursor condensate(s). Kinetic fractionation factors and the measured mass-dependent fractionation of silicon and magnesium in CMS-1 suggest that ∼80% of the silicon and ∼85% of the magnesium were lost from its precursor material(s) through evaporative processes. These results suggest that the precursor material(s) of normal and FUN CAIs condensed in similar environments, but subsequently evolved under vastly different conditions such as total gas pressure. The chemical and isotopic differences between normal and FUN CAIs could be explained by sorting of early solar system materials into distinct physical and chemical regimes, in conjunction with discrete heating events, within the protoplanetary disk. [ABSTRACT FROM AUTHOR]

We report on the mineralogy, petrography, and in situ measured oxygen- and magnesium-isotope compositions of eight porphyritic chondrules (seven FeO-poor and one FeO-rich) from the Renazzo-like carbonaceous (CR) chondrites Graves Nunataks 95229, Grosvenor Mountains 03116, Pecora Escarpment 91082, and Queen Alexandra Range 99177, which experienced minor aqueous alteration and very mild thermal metamorphism. We find no evidence that these processes modified the oxygen- or Al–Mg isotope systematics of chondrules in these meteorites. Olivine, low-Ca pyroxene, and plagioclase within an individual chondrule have similar O-isotope compositions, suggesting crystallization from isotopically uniform melts. The only exceptions are relict grains in two of the chondrules; these grains are 16 O-enriched relative to phenocrysts of the host chondrules. Only the FeO-rich chondrule shows a resolvable excesses of 26 Mg, corresponding to an inferred initial 26 Al/ 27 Al ratio [( 26 Al/ 27 Al) 0 ] of (2.5 ± 1.6) × 10 −6 (±2SE). Combining these results with the previously reported Al–Mg isotope systematics of CR chondrules (Nagashima et al., 2014, Geochem. J . 48 , 561), 7 of 22 chondrules (32%) measured show resolvable excesses of 26 Mg; the presence of excess 26 Mg does not correlate with the FeO content of chondrule silicates. In contrast, virtually all chondrules in weakly metamorphosed (petrologic type 3.0–3.1) unequilibrated ordinary chondrites (UOCs), Ornans-like carbonaceous (CO) chondrites, and the ungrouped carbonaceous chondrite Acfer 094 show resolvable excesses of 26 Mg. The inferred ( 26 Al/ 27 Al) 0 in CR chondrules with resolvable excesses of 26 Mg range from (1.0 ± 0.4) × 10 −6 to (6.3 ± 0.9) × 10 −6 , which is typically lower than ( 26 Al/ 27 Al) 0 in the majority of chondrules from UOCs, COs, and Acfer 094. Based on the inferred ( 26 Al/ 27 Al) 0 , three populations of CR chondrules are recognized; the population characterized by low ( 26 Al/ 27 Al) 0 (<3 × 10 −6 ) is dominant. There are no noticeable trends with major and minor element or O-isotope compositions between these populations. The weighted mean ( 26 Al/ 27 Al) 0 of 22 CR chondrules measured is (1.8 ± 0.3) × 10 −6 . An apparent agreement between the 26 Al– 26 Mg ages (using weighted mean value) and the revised (using 238 U/ 235 U ratio for bulk CR chondrites of 137.7789 ± 0.0085) 207 Pb– 206 Pb age of a set of chondrules from CR chondrites (Amelin et al., 2002, Science 297 , 1678) is consistent with the initial 26 Al/ 27 Al ratio in the CR chondrite chondrule-forming region at the canonical level (∼5.2 × 10 −5 ), allowing the use of 26 Al– 26 Mg systematics as a chronometer for CR chondrules. To prove chronological significance of 26 Al for CR chondrules, measurements of Al–Mg and U–Pb isotope systematics on individual chondrules are required. The presence of several generations among CR chondrules indicates some chondrules that accreted into the CR chondrite parent asteroid avoided melting by later chondrule-forming events, suggesting chondrule-forming processes may have occurred on relatively limited spatial scales. Accretion of the CR chondrite parent body occurred at > 4.0 - 0.3 + 0.5 Ma after the formation of CAIs with the canonical 26 Al/ 27 Al ratio, although rapid accretion after formation of the major population of CR chondrules is not required by our data. [ABSTRACT FROM AUTHOR]

The denudation rates of granitic regolith are essential to our understanding of the geomorphic changes and landscape evolution of a region and for soil resource management. We present denudation rates derived from four regolith profiles along a granitic slope in Longnan, southeastern China, using depth profiles of in-situ produced cosmogenic 10 Be and 26 Al. The concentration ranges of 10 Be, 26 Al, and 26 Al/ 10 Be ratio were 2.98 × 10 4 –1.72 × 10 5 atoms/g, 2.18 × 10 5 –1.12 × 10 6 atoms/g, and 6.07–7.50, respectively. Analysis of the results shows that the surface-lowering rates are 19 ± 3, 41 ± 4, 47 ± 4, 22 ± 3 m/Ma for the four profiles from the foot of the hill to the top along the hillslope. The mean denudation rate for the four profiles is ∼30 m/Ma. This rate is lower than that derived by other methods in nearby areas and also lower than the mean global denudation rate in basins deduced from 10 Be levels in river sediment; this suggests an unevenness of the erosion process on a basin scale. The denudation rate at the ridge is twice that estimated for the summit and the foothill, indicating that the hillslope has not reached its steady state. Thus, the slopes below the ridge may become smoother and the ridge sharper in the long-term landscape evolution. The difference in topography may account for the variance among the profiles. In addition, bioturbation may have contributed to the lower concentration in the surface layer at the foot of the hill, producing a higher denudation rate than the average for the basin. The concentration of insoluble element Zr in the soil surface layer and fresh bedrock suggests that chemical weathering accounts for about one third of the denudation rate. [ABSTRACT FROM AUTHOR]

Inter University Accelerator Centre (IUAC), a national facility of government of India, is having a 15UD Pelletron accelerator for multidisciplinary ion beam based research programs. Recently, a new accelerator mass spectrometry (AMS) facility has been developed after incorporating many changes in the existing 15UD Pelletron accelerator. A clean chemistry laboratory for 10 Be and 26 Al with all the modern facilities has also been developed for the chemical processing of samples. 10 Be measurements on sediment samples, inter laboratory comparison results and 26 Al measurements on standard samples are presented in this paper. In addition to the 10 Be and 26 Al AMS facilities, a new 14 C AMS facility based on a dedicated 500 kV tandem ion accelerator with two cesium sputter ion sources, is also being setup at IUAC. [ABSTRACT FROM AUTHOR]

A new 1 MV NEC pelletron AMS system at ANSTO is presented. The spectrometer comprises large radius magnets for actinide measurements. A novel feature of the system is fast switching between isotopes both at low and high energy sections allowing measurements of up to 8 isotopes within a single sequence. Technical details and layout of the spectrometer is presented. Performance data for 14 C, 10 Be, 26 Al and actinides demonstrate the system is ready for routine AMS measurements. [ABSTRACT FROM AUTHOR]

Proof-of-principle 26 Al-AMS analysis is achieved with a single-stage accelerator mass spectrometer (SSAMS) utilising very low ion energy. The SSAMS operates by discriminating against atomic isobar interference in a negative ion source and suppressing molecules with thick gas stripper. Resulting 1+ ions counting is with a surface barrier detector. The NEC designed SSAMS for 14 C analysis is a popular model accelerator mass spectrometer and the developed further capability might be a significant addition to established 26 Al-AMS capacity. Measurements at these energies should also be sufficient for alternative 26 Al positive-ion mass spectrometry (PIMS). [ABSTRACT FROM AUTHOR]

We present results and discuss the use of aluminum nitride as a promising source material for Accelerator Mass Spectrometry (AMS) and Radioactive Ion Beams (RIBs) science applications of 26 Al isotopes. The measurement of 26 Al in geological samples by AMS is typically conducted on Al 2 O 3 targets. However, Al 2 O 3 is not an ideal source material because it does not form a prolific beam of Al − required for measuring low-levels of 26 Al. Multiple samples of aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), mixed Al 2 O 3 –AlN as well as aluminum fluoride (AlF 3 ) were tested and compared using the ion source test facility and the stable ion beam (SIB) injector platform at the 25-MV tandem electrostatic accelerator at Oak Ridge National Laboratory. Negative ion currents of atomic and molecular aluminum were examined for each source material. It was found that pure AlN targets produced substantially higher beam currents than the other materials and that there was some dependence on the exposure of AlN to air. The applicability of using AlN as a source material for geological samples was explored by preparing quartz samples as Al 2 O 3 and converting them to AlN using a carbothermal reduction technique, which involved reducing the Al 2 O 3 with graphite powder at 1600 °C within a nitrogen atmosphere. The quartz material was successfully converted to AlN. Thus far, AlN proves to be a promising source material and could lead towards increasing the sensitivity of low-level 26 Al AMS measurements. The potential of using AlN as a source material for nuclear physics is also very promising by placing 26 AlN directly into a source to produce more intense radioactive beams of 26 Al. [ABSTRACT FROM AUTHOR]

The Centre for Dating and Diagnostics (CEDAD) at the University of Salento was established in 2001 and became fully operational for routine 14 C radiocarbon dating in 2003. The facility has been continuously upgraded over the years with the installation of different beam lines for high energy ion implantation, IBA analyses both in vacuum and in air and nuclear microprobe. In 2011 a second AMS beamline was installed consisting of a dedicated high energy mass spectrometer for the AMS analysis of rare nuclides such as 10 Be, 26 Al, 129 I and actinides. First tests on 10 Be allowed to optimize the operating parameters resulting in the proper separation of 10 Be from the interfering isobar 10 B. In this paper we present the further tests and optimizations which resulted in an enhancement of the overall transmission efficiency, the reduction of the background (in the 10 −15 range) and in the possibility to obtain precision levels in routine 10 Be/ 9 Be measurements of the order of 0.5%. Furthermore the first results obtained for the analysis of 26 Al and 129 I are also presented. [ABSTRACT FROM AUTHOR]

A detailed description is given of the 0.5 MV tandem accelerator mass spectrometry (AMS) system for 10 Be, 14 C, 26 Al, installed in early 2010 at GNS Science, New Zealand. Its design follows that of previously commissioned Compact 14 C-only AMS (CAMS) systems based on the Pelletron tandem accelerator. The only basic departure from that design is an extension of the rare-isotope achromat with a 45° magnet and a two-anode gas-ionisation detector, to provide additional filtering for 10 Be. Realised performance of the three AMS modes is discussed in terms of acceptance-test scores, 14 C Poisson and non-Poisson errors, and 10 Be detection limit and sensitivity. Operational details and hardware improvements, such as 10 Be beam transport and particle detector setup, are highlighted. Statistics of repeat measurements of all graphitised 14 C calibration cathodes since start-up show that 91% of their total uncertainty values are less than 0.3%, indicating that the rare-isotope beamline extension has not affected precision of 14 C measurement. For 10 Be, the limit of detection in terms of the isotopic abundance ratio 10 Be/ 9 Be is 6 × 10 −15 at at −1 and the total efficiency of counting atoms in the sample cathode is 1/8500 (0.012%). [ABSTRACT FROM AUTHOR]

The JAEA-AMS-TONO (Japan Atomic Energy Agency’s Accelerator Mass Spectrometer established at the Tono Geoscience Center) facility has been used for the dating of geological samples. The AMS system is versatile, based on a 5 MV tandem Pelletron-type accelerator. Since its establishment in 1997, the AMS system has been used for measurement of carbon-14 ( 14 C) mainly for 14 C dating studies in neotectonics and hydrogeology, in support of JAEA’s research on geosphere stability applicable to the long-term isolation of high-level radioactive waste. Results of the measurement of 14 C in soils and plants has been applied to the dating of fault activity and volcanism. Development of beryllium-10 ( 10 Be) and aluminum-26 ( 26 Al) AMS systems are now underway to enhance the capability of the multi-nuclide AMS in studies of dating by cosmogenic nuclides. The 10 Be-AMS system has already been used for routine measurements in applied studies and improvements of the measurement technique have been made. Now we plan to fine tune the system and perform test measurements to develop the 26 Al-AMS system. [ABSTRACT FROM AUTHOR]

The use of helium as stripper gas improved the measurement efficiency of compact AMS systems for many radionuclides significantly because of a higher mean charge state and reduced scattering losses compared with other conventional gases. Recent tests at the ETH 500 kV AMS facility (Tandy) with aluminum have demonstrated that a transmission of more than 50% is achievable in the charge state 2+ at terminal voltages between 300 and 500 kV. On the other hand the m/q interference of 13 C 1+ entering the detector at very high intensity has to be suppressed. Based on first positive results with a very simple absorber cell a more elaborate absorber detector configuration was designed and built in order to eliminate the carbon interference. The suppression of carbon with the new detector–absorber design has been studied extensively at 300 kV (950 keV) and 500 kV (1550 keV) and the results are compared with simulated data. With the new configuration an overall transmission for 26 Al of more than 42% at 500 kV and about 30% at 300 kV terminal voltage is achieved, while 26 Al/ 27 Al blank ratios of aluminum targets in the range of 5–14·10 −15 are measured. [ABSTRACT FROM AUTHOR]

AMS research started more than 15 years ago at our National Institute for Physics and Nuclear Engineering (IFIN-HH), Bucharest. A first facility was constructed based on our multipurpose 9 MV tandem accelerator and was upgraded several times. In May 2012 a new Cockcroft Walton type 1 MV HVEE tandetron AMS system, was commissioned. Two chemistry laboratories were constructed and are routinely performing the target preparation for carbon dating and for other isotope applications such as for geology, environment physics, medicine and forensic physics. Performance parameters of the new system are shown. [ABSTRACT FROM AUTHOR]

Radionuclides are cosmogenically produced in meteorites before they fall to the surface of the Earth. Measurement of the radioactive decay of such nuclides provides a wealth of information on the irradiation conditions of the meteorite fragment, the intensity of cosmic rays in the inner solar system, and the magnetic activity of the Sun. We report here on the detection of 26 Al using a sophisticated spectrometer consisting of a HPGe detector and a NaI(Tl) annulus. It is shown that modern γ -ray spectrometers represent an interesting alternative to other detection techniques. Data are obtained for a fragment of the Farmville meteorite and compared to results from Geant4 simulations. In particular, we report on optimizing the detection sensitivity by using suitable coincidence gates for deposited energy and event multiplicity. We measured an 26 Al activity of 48.5±3.5 dpm/kg for the Farmville meteorite, in agreement with previously reported values for other H chondrites. [ABSTRACT FROM AUTHOR]

Ca–Al-rich inclusions (CAI) are the oldest dated objects formed in the solar system and are pivotal reference points in early solar system chronology. Knowledge of their initial 182 Hf/ 180 Hf and 182 W/ 184 W is essential, not only for obtaining precise Hf–W ages relative to the start of the solar system, but also to assess the distribution of short-lived radionuclides in the early solar nebula. However, the interpretation of Hf–W data for CAI is complicated by nucleosynthetic W isotope variations. To explore their extent and nature, and to better quantify the initial Hf and W isotope compositions of the solar system, we obtained Hf–W data for several fine- and coarse-grained CAI from three CV3 chondrites. The fine-grained CAI exhibit large and variable anomalies in ε 183 W ( ε i W equals 0.01% deviation from terrestrial values), extending to much larger anomalies than previously observed in CAI, and reflecting variable abundances of s - and r -process W isotopes. Conversely, the coarse-grained (mostly type B) inclusions show only small (if any) nucleosynthetic W isotope anomalies. The investigated CAI define a precise correlation between initial ε 182 W and ε 183 W, providing a direct empirical means to correct the ε 182 W of any CAI for nucleosynthetic isotope anomalies using their measured ε 183 W. After correction for nucleosynthetic W isotope variations, the CAI data define an initial 182 Hf/ 180 Hf of ( 1.018 ± 0.043 ) × 10 − 4 and an initial ε 182 W of − 3.49 ± 0.07 . The Hf–W formation intervals of the angrites D'Orbigny and Sahara 99555 relative to this CAI initial is 4.8 ± 0.6 Ma , in good agreement with Al–Mg ages of these two angrites. This renders a grossly heterogeneous distribution of 26 Al in the inner solar system unlikely, at least in the region were CAI and angrites formed. [ABSTRACT FROM AUTHOR]