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Oceanic archives are contemporary witnesses of Earth's recent astrophysical history by incorporating extraterrestrial radionuclides. VA13/2 - 237KD is one of the most studied ferromanganese crusts and it has been shown that the crust contains live interstellar 60Fe. Here, we have characterized a large piece of this crust with a 3D optical scan, a micro-CT scan and 3D modeling, followed by the chemical extraction of highly purified, element-specific fractions for accelerator mass spectrometry. High-accuracy cosmogenic 10Be dating of two independent drill-holes showed a time-dependent variability in growth rate across the surface of the crust. This well-characterized crust is used to search for interstellar radionuclides, such as supernova-produced 60Fe and the r-process nuclide 244Pu. Other extraterrestrial radionuclides including 26Al, 53Mn, 129I, 182Hf or 247Cm could be investigated in the future.

Typical neutron energies for the astrophysical s-process follow the Maxwell-Boltzmann distribution in the keV energy range. Neutron capture cross sections highly relevant for modelling the s-process can be experimentally determined by using the Time-of-Flight (ToF) method [1] or by the activation technique. If the reaction product is a long-lived radionuclide (t1/2 ~ yr -100 Myr), the cross section can be determined by activation with a quasi-stellar neutron distribution (typically kT = 25 keV) and a subsequent accelerator mass spectrometry (AMS) measurement of the reaction product [2]. Comparison of a number of such neutron capture cross sections shows a systematic bias, i.e. AMS data being lower than the ToF data [3, 4]. To investigate this discrepancy, we repeated experiments for two reactions that allow for highly precise AMS data: Maxwellian-averaged cross sections for the reactions 54Fe(n,γ)55Fe and 35Cl(n,γ)36Cl were investigated with dedicated activations at the Frankfurt Neutron Source (FRANZ) in Germany [5] and AMS measurements at two independent facilities. Analogously to previous activations, a quasi-stellar neutron spectrum of kT = 25 keV was produced via the 7Li(p,n) reaction, but at a different neutron-producing facility. Furthermore, to complement existing ToF and AMS data, an additional neutron activation of 54Fe and 35Cl at a proton energy of 2 MeV was performed, yielding data in the not-yet explored kT = 90 keV region. The irradiated metallic Fe foil and NaCl pellet (both of natural isotopic composition) were chemically processed and converted to AMS targets (Fe2O3 and AgCl) together with non-irradiated blanks. The subsequent AMS measurements of both radionuclides, 36Cl and 55Fe, were performed at two complementary AMS facilities, the Heavy Ion Accelerator Facility (HIAF) at the Australian National University [6] and at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany [7]. AMS allows a direct measurement of the 55Fe/54Fe and 36Cl/35Cl conversion ratios that result from the irradiation. The cross section is then deduced from the isotope ratio and the neutron fluence, which is determined using Au monitor foils. The new experiment was designed to produce highly accurate data and, owing to the two independent AMS measurements, it minimizes unrecognized sources of uncertainties in the AMS technique. The new preliminary data obtained in this work seem to confirm the previous AMS results. Consequently, the systematic discrepancy between AMS and ToF data remains unresolved. [1] Guber, K.H., et al., Phys. Rev. C 65, 058801 (2002). [2] Györky, Gy., et al., Eur. Phys. J. A 55, 41 (2019). [3] Capote, R., et al., Nucl. Data Sheets 163 (2020): 191. [4] Slavkovská, Z., et al., EPJ Web Conf. Vol. 232, p.02005, EDP Sciences, 2020. [5] Reifarth, R., et al., Publ. Astron. Soc. Aust. 26.3 (2009): 255. [6] Fifield, L.K., et al. Nucl. Instr. Meth. B: 268 (2010): 858. [7] Rugel, G., et al., Nucl. Instr. and Meth. in Phys. Res. B 370 (2016) 94.

The AMS program at ANU’s Department of Nuclear Physics is based on a 14UD tandem accelerator which runs regularly above 14 MV with stable measurement conditions. This setup provides particle energies between ~24 MeV (actinides) and >200 MeV (e.g. 53Mn, 93Zr). The facility is equipped with a dedicated SNICS ion source, provides typically 155 keV beam injection energy and is capable of a simultaneous use of both gas and foil stripper. Dedicated beamlines feature multi-anode ionisation chambers, an ENGE gas-filled magnet and a 6m TOF flight path. Further, a new fast cycling system is now being implemented (see contribution by L.K. Fifield et al.) that will replace our slow cycling method. The ANU has a strong focus in projects in environmental, safeguards and geological research with several nuclear astrophysics projects added recently as an additional major research topic. New isotopes recently introduced include 60Fe, 93Zr, 210Pb, 210mBi and 231Pa. We will give an overview of recent research activities and will summarize the performance of the different AMS setups. The potential of the ENGE setup for isobaric suppression will be exemplified for the two isotopes 60Fe and 53Mn. Measurement reproducibility and absolute detection efficiency will be compared.

The establishment of the gut microbiota immediately after birth is a dynamic process that may impact lifelong health. At this important developmental stage in early life, human milk oligosaccharides (HMOs) serve as specific substrates to shape the gut microbiota of the nursling. The well-orchestrated transition is important as an aberrant microbial composition and bacterial-derived metabolites are associated with colicky symptoms and atopic diseases in infants. Here, we study the trophic interactions between an HMO-degrader, Bifidobacterium infantis and the butyrogenic Anaerostipes caccae using carbohydrate substrates that are relevant in the early life period including lactose and total human milk carbohydrates. Mono- and co-cultures of these bacterial species were grown at pH 6.5 in anaerobic bioreactors supplemented with lactose or total human milk carbohydrates. A. caccae was not able to grow on these substrates except when grown in co-culture with B. infantis, leading to growth and concomitant butyrate production. Two levels of cross-feeding were observed, in which A. caccae utilised the liberated monosaccharides as well as lactate and acetate produced by B. infantis. This microbial cross-feeding points towards the key ecological role of bifidobacteria in providing substrates for other important species that will colonise the infant gut. The progressive shift of the gut microbiota composition that contributes to the gradual production of butyrate could be important for host-microbial crosstalk and gut maturation.

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust: 60Fe (half-life 2.6 million years, Myr), predominantly produced in massive stars and ejected in SN explosions; and 244Pu, (half-life 80.6 Myr) produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 Myr and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, implying some contribution from other sources.

More than 20 years have passed since the first attempts to find live supernova Fe-60 (t1/2 = 2.6 Myr) in a deep-sea ferromanganese crust [1]. Within these 20 years, strong evidence was presented for a global influx of supernova dust into several geological samples around 2 Myr ago. Recently, a much younger continuous influx was found in Antarctic snow and in deep-sea sediments [2-4] and an older peak around 7 Myr in deep-sea crusts [5,6]. The long-lived isotope Pu-244 (t1/2 = 80 Myr) is produced in the astrophysical r-process similarly to most of the heaviest elements. Although the production mechanism is believed to be understood, the astrophysical site is heavily disputed. Most likely scenarios involve a combination of rare supernovae and neutron star mergers. The search for Pu-244 signatures in samples with known Fe-60 signatures allows to test for either common influx patterns or a independent Pu-244 influxes disentangled from stellar Fe-60. Accordingly, this information provides a unique and direct experimental approach for identifying the production site of the heavy elements. Very recently and first reported in the AMS-14 conference, the first detection of interstellar Pu-244 was published [6]. This was only feasible by achieving the highest detection efficiencies for plutonium in AMS ever reported [7]. The achieved time resolution of 4.5 Myr integrates over the supernova influxes and is therefore not high enough to unequivocally show a correlated influx pattern of Fe-60 and Pu-244. Based on this progress, we are now aiming to measure highly time-resolved profiles of Fe-60 and Pu-244 in the largest ferromanganese crust used so far. Results on the characterisation of the crust including cosmogenic Be-10 (t1/2 = 1.4 Myr) dating and a 10 Myr profile of interstellar Fe-60 including the confirmation of the 7 Myr influx will be presented along with first data on interstellar Pu-244. [1] Knie et. al., Phys. Rev. Lett. 83 (1999). [2] Koll et al., Phys. Rev. Lett. 123 (2019). [3] Koll et al., EPJ 232 (2020). [4] Wallner et al., PNAS 117 (2020). [5] Wallner et al., Nature 532 (2016) [6] Wallner et al., Science 372 (2021) [7] Hotchkis et al., NIMB 438 (2019)

Stars are the major element factories in the universe. In 1999, live supernova Fe-60 (t1/2 =2.6 Myr) was detected in a deep-sea ferromanganese crust (1 ) indicating the accumulation of supernova dust on Earth about 2 million years ago. This was followed by several projects reinforcing the initial evidence for a global influx of supernova Fe-60. Recently, a much younger continuous influx was found in Antarctic snow and in deep-sea sediments (2 –4 ) and an older peak around 6 - 8 Myr in deep-sea crusts (5 , 6 ). In contrast to the well-known production mechanism and synthesis site of Fe-60, the long-lived plutonium isotope Pu-244 (t1/2 =80 Myr) is a pure r-process nucleus. The nucleosynthesis site for the astrophysical r-process is still debated in the astrophysics community. Potential candidates involve rare supernovae and neutron star mergers. To date no evidence was presented that would point to an exclusive r-process site and combinations of different sites are considered. Experimentally, we can search for Pu-244 signatures in samples with known Fe-60 signatures to test for either common influx patterns or independent Pu-244 influxes disentangled from stellar Fe-60. Accordingly, this information provides a unique and direct experimental approach for identifying the production site of the heavy elements. Based on the recent publication of the first detection of interstellar Pu-244 in a ferromanganese crust with a time resolution of 4.5 Myr (integrating over much shorter Fe-60 influxes) (6 ), we are now working on a highly time-resolved profile of Fe-60 and Pu-244 in the large ferromanganese crust VA13/237KD. This direct experimental input will further constrain models for r-process nucleosynthesis in the galaxy. The recently determined profile of Fe-60 clearly shows two influxes, one at 2 Myr, the other at 7 Myr, confirming and refining previous results. Preliminary data on Pu-244 and an outlook for future measurement campaigns will be given. References 1. K. Knie et al., Phys. Rev. Lett. 83, 18–21 (1999). 2. D. Koll et al., Phys. Rev. Lett. 123, 072701 (2019). 3. A. Wallner et al., Proceedings of the National Academy of Sciences 117, 21873–21879 (2020). 4. D. Koll et al., EPJ Web Conf. 232, 02001 (2020). 5. A. Wallner et al., Nature 532, 69–72 (2016). 6. A. Wallner et al., Science 372, 742–745 (2021).

Nuclides synthesized in massive stars are ejected into space via their stellar winds and in supernova explosions. The Solar System moves through the interstellar medium and collects some of these nucleosynthesis products. One such product is ⁶⁰Fe, a radionuclide with 2.6 million years half-life, that is predominantly produced in massive stars and ejected in supernova explosions. Extraterrestrial ⁶⁰Fe has been found on Earth, suggesting close-by supernova explosions ~2–3 and ~6 million years ago. Here, we report on the detection of a continuous interstellar ⁶⁰Fe-influx on Earth over the past ~33,000 years. This time period coincides with passage of our Solar System through such interstellar clouds, which have a significantly larger particle density compared to the local average interstellar medium embedding our Solar System for the past few million years. The interstellar ⁶⁰Fe was extracted from five deep-sea sediment samples and accelerator mass spectrometry was used for single atom counting. Despite the low number of 19 detected atoms, owing to a low influx, the ⁶⁰Fe-deposition rate does not indicate large variations over the 33,000 years. The measured approximately constant ⁶⁰Fe-time profile does not seem to reflect any large changes in the interstellar particle density during Earth’s passage through local interstellar clouds, that could be expected if the local cloud represented an isolated remnant of the most recent Supernova ejecta that traversed the Earth ~2–3 million years ago. The identified ⁶⁰Fe influx may signal a late echo of some million-year old supernovae with the ⁶⁰Fe-bearing dust particles still permeating the interstellar medium.

Beneficial modulation of the gut microbiota is an attractive therapeutic approach to improve the efficacy of vaccine-induced immunity. In this study, mice were supplemented with the prebiotic milk oligosaccharide 2’-fucosyllactose (2’FL) as well as a complex mixture of immune modulatory prebiotic short-chain galacto-oligosaccharides and long-chain fructo-oligosaccharides (scGOS/lcFOS) from different stages in early life. Adult mice were vaccinated with trivalent influenza vaccine (TIV) and both development of the gut microbiota and antibody-mediated vaccine responses were followed over time. Within the control group, female mice demonstrated a larger antibody response to TIV vaccination than male mice, which was accompanied by enhanced cytokine production by splenocytes and a higher percentage of plasma cells in skin draining lymph nodes. In addition, the prebiotic diet improved vaccine-specific antibody responses in male mice. Introduction of prebiotics into the diet modulated the gut microbiota composition and at the genus level several bacterial groups showed a significant interaction effect which potentially contributed to the immunological effects observed. This study provides insight in the effect of scGOS/lcFOS/2’FL in influenza vaccination antibody production.

Over the last 20 years the long-lived radionuclide ⁶⁰Fe with a half-life of 2.6 Myr was shown to be an expedient astrophysical tracer to detect freshly synthesized stardust on Earth. The unprecedented sensitivity of Accelerator Mass Spectrometry for ⁶⁰Fe at The Australian National University (ANU) and Technical University of Munich (TUM) allowed us to detect minute amounts of ⁶⁰Fe in deep-sea crusts, nodules, sediments and on the Moon [1-5]. These signals, around 2-3 Myr and 6.5-9 Myr before present, were interpreted as a signature from nearby Supernovae which synthesized and ejected ⁶⁰Fe into the local interstellar medium. Triggered by these findings, ANU and TUM independently analyzed recent surface material for ⁶⁰Fe, deep-sea sediments and for the first time Antarctic snow, respectively [6, 7]. We find in both terrestrial archives corresponding amounts of recent ⁶⁰Fe. We will present these discoveries, evaluate the origin of this recent influx and bring it into line with previously reported ancient ⁶⁰Fe findings. [1] K. Knie et. al. “Indication for supernova produced ⁶⁰Fe activity on Earth”, Phys. Rev. Lett. 83 (1999) 18. [2] K. Knie et. al. “⁶⁰Fe anomaly in a deep-sea manganese crust and implications for a nearby supernova source”, Phys. Rev. Lett. 93 (2004) 171103. [3] P. Ludwig et. al. “Time-resolved 2-million-year-old super-nova activity discovered in Earth's microfossil record”, PNAS 113 (2016) 9232. [4] A. Wallner et. al. “Recent near-Earth supernovae probed by global deposition of interstellar radioactive ⁶⁰Fe”, Nature 532 (2016) 69. [5] L. Fimiani et. al. “Interstellar ⁶⁰Fe on the surface of the Moon”, Phys. Rev. Lett. 116 (2016) 151104. [6] D. Koll et. al. “Interstellar ⁶⁰Fe in Antarctica”, Phys. Rev. Lett., submitted [7] A. Wallner et al. in preparation

The nuclide ³⁵Cl can act as a minor "neutron poison" in the stellar slow neutron capture process. Neutron activation combined with accelerator mass spectrometry (AMS) was applied to measure the (n,gamma) cross section of ³⁵Cl for neutron spectra simulating Maxwell-Boltzmann distributions of kT ~30 keV and 40 keV, respectively. The neutron activations were performed at the Karlsruhe Van de Graaff accelerator and at the superconducting linear accelerator of the Soreq Applied Research Accelerator Facility utilizing the ⁷L(p,n)⁷Be reaction. AMS measurements of the irradiated samples were performed at the 3 MV Vienna Environmental Research Accelerator, the 6 MV tandem accelerator at the Dresden AMS facility, and the 14 UD tandem accelerator of the Australian National University in Canberra. Our method is independent of previous measurements. For an energy of kT=30 keV, we report a Maxwellian averaged cross sections of 8.33(32) mb. Using this new value in stellar isotopic abundance calculations, minor changes for the abundances of ³⁵Cl, ³⁶Cl and ³⁶S are derived.

We searched for presence of 26Al (t1/2=0.7 Myr) in deep-sea sediments as a signature for extraterrestrial influx. Our data show an exponential dependence of 26Al with the sample age that is fully compatible with radioactive decay of terrigenic 26Al. The same set of samples demonstrated a clear extraterrestrial 60Fe signal between 1.7 and 3.2 Myr ago. Combining our 26Al data with the recently reported 60Fe data [1] gives a lower limit for the local interstellar 60Fe/26Al isotope ratio. Our Limit of 0.24 is higher than the observed average galactic 60Fe/26Al flux ratio of (0.15 + 0.05).It favours the higher ratios deduced from nucleosynthesis models.

Podeu consultar el III Workshop anual INSA-UB complet a: http://hdl.handle.net/2445/118993, Sessió 2. Comunicació oral núm. 2

The long-lived radionuclide 26Al (t1/2=~0.7 Myr) has been observed throughout our galaxy, reflecting ongoing nucleosynthesis over the past few million years [1]. It is produced and ejected into the interstellar medium by stellar winds and during supernova explosions. A nearby supernova may leave an imprint of 26Al in terrestrial archives, complementing the observation of supernova-produced 60Fe in deep-sea samples. The same set of sediment samples from the Indian Ocean that showed a distinct 60Fe-signature in layers of ages between 1.7 and 3.2 Myr [2] was also analyzed for 26Al. However, additional terrestrial sources producing 26Al on Earth, such as cosmogenic production in the atmosphere and in-situ production within the sediment, may obscure a supernova imprint. We used our experimental 26Al data to infer lower limits on 60Fe/26Al nucleosynthesis ratios by comparing the width and the strength of the previously measured 60Fe-signal to our 26Al data. We find that our results generally favour the higher theoretical isotopic supernova ratios and deviate from the observed galactic 60Fe/26Al flux ratio by 2-3 times of the measurement uncertainty. [1] Diehl et al., New Astron. Rev., 52, 440 (2008) [2] Wallner, Feige et al., Nature, 532, 69 (2016)

The Interstellar Medium (ISM) is continuously fed with new nucleosynthetic products. The solar system moves through the ISM and collects dust particles. Therefore, direct detection of freshly produced radionuclides on Earth, i.e. before decaying, provide insight into recent and nearby nucleosynthetic activities [1,2]. Indeed, a pioneering work at TU Munich [3,4], which applied the ultra-sensitive single atom counting technique of accelerator mass spectrometry (AMS) to an ocean crust-sample, showed an enhanced 60Fe signal possibly of extraterrestrial origin. Within an international collaboration [5-7] we have continued to search for ISM radionuclides incorporated in terrestrial archives. We have analyzed several deep-sea sediments, crusts and nodules for extraterrestrial 60Fe (t1/2=2.6 Myr), 26Al (t1/2=0.7 Myr) and 244Pu (t1/2=81 Myr) [5-8] which are complemented by independent work at TU Munich [9-11]. All the data demonstrate a clear global 60Fe influx that is interpreted as exposure of Earth to recent (≤10 Myr) supernova explosions. Furthermore, the low concentrations measured for 244Pu suggest an unexpectedly low abundance of interstellar 244Pu [5]. This finding signals a rarity of actinide r–process nucleosynthesis which is incompatible with the rate and expected yield of standard core collapse supernovae as the predominant actinide-producing sites. In this talk I will also present additional new results for 60Fe and 244Pu measured with unprecedented sensitivity. These data provide new insights into their concomitant influx and their ISM concentrations over a time period of the last 11 million years. [1] J. Ellis et al., ApJ. 470, 1227 (1996). [2] G. Korschinek et al., Radiocarbon 38, 68 (1996); abstract. [3] K. Knie et al., Phys. Rev. Lett. 83, 18 (1999). [4] K. Knie et al., Phys. Rev. Lett. 93, 171103 (2004). [5] A. Wallner et al., Nature Comm. 6, 5956 (2015). [6] J. Feige et al., EPJ Web of Conf. 63, 3003 (2013). [7] A. Wallner et al., Nature 532, 69 (2016). [8] M. Paul M. et al. Astrophys. J. Lett. 558, L133L135 (2001). [9] C. Wallner et al. New Astron. Rev. 48, 145150 (2004). [10] L. Fimiani et al., Phys. Rev. Lett. 116, 151104 (2016). [11] P. Ludwig et al., PNAS 113, 9232 (2016).

Cosmogenic nuclides in meteorites can provide information on cosmic ray exposure (CRE) histories. In space, meteoroids are irradiated by galactic cosmic ray particles, inducing the production of cosmogenic nuclides (10Be, 26Al, 36Cl, 41Ca, 53Mn, 60Fe). Meteorites are routinely measured for 10Be, 26Al, and 36Cl. However the database for 53Mn and 60Fe is scarce due to the low availability of high-MV accelerators and the debate over the half-lives of 53Mn and 60Fe. We Report new 53Mn and 60Fe data for iron meteorites measured at Canberra (53Mn, 60Fe) and Munich (60Fe). Among these radionuclides, 53Mn has the longest half-life, thus is least influenced by terrestrial ages. The advantage of 53Mn and 60Fe isotopes is that only two (Fe, Ni) and one (Fe) target element(s), respectively, dominate production, overcoming the problem of inhomogeneous S and P distribution. Our new 60Fe data almost doubles that present in the literature. We measured 53Mn in seven subsamples of the iron meteorite Twannberg. The new 53Mn and 60Fe data, with 10Be, 26Al, 36Cl, 41Ca and the noble gases, will better constrain the CRE histories of meteorites and will also serve as benchmarks to validate and improve Monte-Carlo model calculations.

Most current approaches for analyzing metagenomic data rely on comparisons to reference genomes, but the microbial diversity of many environments extends far beyond what is covered by reference databases. De novo segregation of complex metagenomic data into specific biological entities, such as particular bacterial strains or viruses, remains a largely unsolved problem. Here we present a method, based on binning co-abundant genes across a series of metagenomic samples, that enables comprehensive discovery of new microbial organisms, viruses and co-inherited genetic entities and aids assembly of microbial genomes without the need for reference sequences. We demonstrate the method on data from 396 human gut microbiome samples and identify 7,381 co-abundance gene groups (CAGs), including 741 metagenomic species (MGS). We use these to assemble 238 high-quality microbial genomes and identify affiliations between MGS and hundreds of viruses or genetic entities. Our method provides the means for comprehensive profiling of the diversity within complex metagenomic samples.

The terrestrial 2-3 Myr old 60Fe signal has been probed to be a global phenomenon [1]. Even lunar samples show an 60Fe excess pointing towards a recent injection into the solar system [2]. The most likely sources are stellar explosions within a moving group that passed the solar neighborhood, and whose surviving members are now in the Sco-Cen association [3]. We have traced the trajectories of those stars back in time and, by analyzing the uncertainties of the stellar positions, calculated the most probable explosion sites of the perished stars. By determining their masses and explosion times, we found a sequence of supernovae starting 13 Myr ago. We used analytical and numerical methods to generate the Local Superbubble, as well as its neighboring Loop I Superbubble, and link its formation to the 60Fe signature. Similar calculations with 26Al show only a marginal signal due to its shorter half-life and the broad extension of the supernova signal of ~1.5 Myr. Recent AMS measurements of 26Al contents in four deep-sea sediment cores from the Indian Ocean confirm this result. The data show an exponential decrease towards larger depths as expected from atmospherically-produced 26Al. This terrestrial concentration overwhelms a possible signature from nearby supernovae. With 60Fe data determined from the sediment samples [1] lower limits of 60Fe/26Al ratios were calculated. These are in line with gamma-line flux ratios from SPI/INTEGRAL data in the interstellar medium [4]. [1] A. Wallner et al., this conference. [2] L. Fimiani et al., in Proceedings of the Lunar and Planetary Science Conference, Texas, 2014, p. 1778. [3] B. Fuchs et al., MNRAS 373, 993 (2006). [4] W. Wang, Proceedings of the International Astronomical Union, China, 2008, p. 333.

In stellar environments neutron capture reactions produce 99% of all elements heavier than iron. In the slow neutron capture process (s-process) lighter isotopes, especially those with high abundances and large neutron capture cross sections, act as “neutron poisons” by reducing the number of available neutrons and hence, decreasing the production of the heavier nuclei. 35Cl, which is produced in advanced burning phases of stars, contributes to the poisoning effect. Accordingly, its Maxwellian-averaged cross section (MACS) is of significant astrophysical interest. A combination of activation technique and accelerator mass spectrometry (AMS) was used for the determination of the MACS of 35Cl(n,gamma)36Cl. NaCl pellets were irradiated at KIT and SARAF-LiLiT (Soreq Applied Research Accelerator Facility-Liquid-Lithium Target) with a quasi-Maxwellian neutron energy distribution of 25 keV. The neutron fluence was monitored by gold foils. AMS measurements at VERA (Vienna Environmental Research Accelerator), the DREAMS (DREsden AMS) facility and the ANU Heavy Ion Accelerator Facility quantified the 36Cl/35Cl ratio of the samples. The product of the neutron fluence and the isotopic ratio gives the spectrum-averaged cross section of the reaction. By normalizing this value to a real Maxwellian spectrum a new value for the 25 keV MACS of (9.5±0.4) mb for the reaction 35Cl(n,gamma)36Cl was obtained. This is ~16% lower than the previously determined value in Guber et al [1]. [1] K. H. Guber et al., Phys. Rev. C 65, 058801 (2002).

Massive stars, which end their lives in a supernova (SN) explosion, eject freshly produced nuclides into the surrounding interstellar medium. Among them long-lived radionuclides, that can be deposited into terrestrial archives, if such an event occurs close to the Solar System. About 100 samples of four deep-sea sediment cores originating from the Indian Ocean were analyzed for their content in the isotopes 26Al and 60Fe for the time range of 2-3 Myr. These nuclides are produced in SNe and the time range corresponds to an 60Fe enhancement observed in a deep-ocean crust sample (Knie et al., 2004). The method used for analysis is accelerator mass spectrometry (AMS), a very sensitive technique for the detection of long-lived radionuclides. A clear signal of 60Fe throughout the whole measured time period was observed. This observation is in contrast to a narrow peak if originating from a direct input from a single SN. Further, no 60Fe was detected in much older or younger sediment samples. A concurring SN-signal of 26Al is, however, hidden underneath a dominant terrestrial background from continuous atmospheric and in-situ production. The resulting limits on the ratios of 60Fe/26Al were compared to nucleosynthesis models.

Meteorite sind während ihres Fluges durch das Weltall der kosmischen Strahlung ausgesetzt. Diese induziert Kernreaktionen, deren Produkte die sog. kosmogenen Nuklide (KN) sind. Landet ein Meteorit auf der Erde, stoppt deren Produktion mehrheitlich, während die Radionuklide weiterhin zerfallen. Somit speichern stabile und radioaktive KNs Informationen über Expositionszeit und terrestrische Aufenthaltsdauer von Meteoriten. Wird eine große Zahl von Meteoriten betrachtet, können zudem Rückschlüsse auf die Konstanz der kosmischen Strahlung selbst gezogen werden [1]. An der Beschleunigermassenspektrometrie-Anlage DREAMS (DREsden Accelerator Mass Spectrometry) werden kosmogene Radionuklide wie 10Be, 26Al, 36Cl und 41Ca (t½=0.1-1.4 Ma) bestimmt [2]. Ergänzende Daten von schweren Radionukliden wie 53Mn (t½=3.7 Ma) und 60Fe (t½=2.6 Ma), welche an größeren Tandembeschleunigern in Canberra und München gemessen werden, und stabile Edelgasisotopendaten aus Mainz und Bern, ermöglichen die vollständige Rekonstruktion der Geschichte der Meteorite. Beispielhaft sind Untersuchungen des Eisenmeteoriten Gebel Kamil, der einen ~45 m großen Krater in Südägypten verursachte. Der Vergleich von KN-Konzentrationen mit Monte-Carlo-Rechnungen zeigt, dass Gebel Kamil als Körper mit einem Radius von 115-120 cm (~50-60 t) für (366 ± 18) Ma der kosmischen Strahlung ausgesetzt war [3]. Ref.: [1] Smith et al., 13th Int. Conf. on AMS. [2] Akhmadaliev et al., NIMB 294 (2013) 5. [3] Ott et al., MAPS, subm.

While meteorites travel through space, they are exposed to cosmic rays, which induce nuclear reactions producing so-called cosmogenic nuclides (CNs). If meteorites land on Earth, production stops and radioactive nuclides start to decay. Thus, CNs, stable and radioactive, are archives of the exposure and terrestrial history of individual meteorites. Moreover, when looking at a larger number of meteorites, this may also give hints about the constancy of the cosmic radiation itself [1]. Data for the lighter cosmogenic radionuclides 10Be, 26Al, 36Cl, and 41Ca (t1/2=0.1-1.4 Ma) are now attainable at the accelerator mass spectrometry facility DREAMS [2]. Accompanied by data for the heavier radionuclides 53Mn (t1/2=3.7 Ma) and 60Fe (t1/2=2.6 Ma), which are measured at the large tandems at Canberra and Munich, and stable noble gas nuclides from Mainz and Bern, complete exposure histories of extraterrestrial material can be reconstructed. One of the first meteorites investigated by this team is Gebel Kamil, an ungrouped Ni-rich iron meteorite that produced an impact crater (Ø: 45 m) in southern Egypt. Two neighboured shrapnel (S) samples and two from the only individual (I) fragment (~83 kg) have been analysed. Concentrations of all CNs – stable and radioactive – are a factor ~4 x lower in S-samples than in I-samples. Comparison with Monte-Carlo calculations of production rates indicate that Gebel Kamil was exposed as a meteoroid body of 115-120 cm radius (50-60 tons). Samples I originate from a moderate shielding of ~20 cm, whereas samples S are from a deeper position of 50-80 cm. Most reliable 36Cl-36Ar ages of I and S are (366 ± 18) Ma [3]. Chemically and analytically more challenging are the analyses of corresponding pairs of chondrule and matrix to decipher the ancient and recent exposure history from two highly primitive meteorites [4]. Chondrules may have been irradiated for millions of years as free-floating particles in the solar nebula by the cosmic rays at that time. Despite sample masses of only 1.6-1.8 mg for single chondrules, radioactive CN results for two highly primitive Renazzo-type (CR3) chondrites from Antarctica (MET00426 & QUE99177) are clearly dis-tinguishable from processing blank and can, thus, be used in combination with noble gas data. Chemically and analytically demanding for both noble gases and 36Cl are also the analyses of pairs of troilite (FeS) inclusions and metal fractions from the iron meteorite Mundrabilla. This work is struggling with mg-amounts of sulphur, where 36S is a troublesome isobar of 36Cl and also causes severe problems in noble gas spectrometry. It is aimed at improving determination of production rates for lighter nuclides such as 3,4He, 10Be, 21Ne, 26Al and 36Cl. Ackn.: L. Folco, J. Zipfel (meteorites) & accelerator crews and colleagues (support AMS). [1] Smith et al. contribution to 13th Int. Conf. on Accelerator Mass Spectrometry (AMS-13). [2] Akhmadaliev et al., Nucl. Instr. Meth. B 294, 5 (2013) & Pavetich et al., this meeting. [3] Ott et al., submitted to Meteorit. Planet. Sci. [4] Ott et al., contribution to 13th Int. Conf. on Accelerator Mass Spectrometry (AMS-13).