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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.

Zirconium-93 is a long-lived radionuclide with a half-life of (1.61 ± 0.05) × 106 yr. Production cross sections for 93Zr by neutron capture on stable 92Zr in the keV and thermal energy ranges are important input parameters for astrophysical network calculations and nuclear industry, respectively. Despite their importance, existing experimental data suffer from large uncertainties. Here, the combination of neutron activation and accelerator mass spectrometry (AMS) is presented as an alternative method to online time-of-flight measurements for the determination of these cross sections. The main challenges for AMS of 93Zr are the interference from the stable isobar 93Nb and the production of suitable reference material. At the Heavy Ion Accelerator Facility (HIAF) the first challenge is tackled with the available high particle energies and by investigating different Zr compounds and extracted molecular beams. Using ZrF5− beams extracted from ZrF4 sample material, it is shown that the Nb background can be reduced by up to two orders of magnitude relative to the extraction of ZrO− beams from ZrO2. Using the 13+ charge state and particle energies of ∼190 MeV, 93Zr/Zr background levels in the 10−12 range are regularly achieved at HIAF. The ZrF5− output from ZrF4 samples may be highly variable but can be stabilised using an intimate mixture of ZrF4 and PbF2 at a ratio of 1:10 that has been dried down from a concentrated hydrofluoric acid solution. An option to produce a well-characterised 93Zr reference material by utilising the well-known 235U-fission yield of 93Zr is discussed. Once this remaining challenge is resolved, accurate measurements of the astrophysically and technologically relevant neutron-capture cross sections of 92Zr using AMS will be possible at HIAF.

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.

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.

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

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

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.

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.

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

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

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.

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

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

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.

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.

Based on AMS analysis, it is shown that no Pu signals from the Fukushima accident could be discerned in marine sediments collected 1.5-57km away from the Fukushima Da-ichi power plant (FDNPP), which were clearly influenced by accident-derived radiocesium. The 240Pu/239Pu atom ratios (0.21-0.28) were significantly higher than terrestrial global fallout (0.182 ± 0.005), but still in agreement with pre-FDNPP accident baseline data for Pu in near coastal seawaters influenced by global fallout and long-range transport of Pu from the Pacific Proving Grounds.

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 (200

Traces of 2-3 Myr old 60Fe were recently discovered in a manganese crust and in lunar samples. We have found that this signal is extended in time and is present in globally distributed deep-sea archives. A second 6.5-8.7 Myr old signature was revealed in a manganese crust. The existence of the Local Bubble hints to a recent nearby supernova-activity starting 13 Myr ago. With analytical and numerical models generating the Local Bubble, we explain the younger 60Fe-signature and thus link the evolution of the solar neighborhood to terrestrial anomalies.

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.

Traces of 2-3 Myr old 60Fe were recently discovered in a manganese crust and in lunar samples. We have found that this signal is extended in time and is present in globally distributed deep-sea archives. A second 6.5-8.7 Myr old signature was revealed in a manganese crust. The existence of the Local Bubble hints to a recent nearby supernova-activity starting 13 Myr ago. With analytical and numerical models generating the Local Bubble, we explain the younger 60Fe-signature and thus link the evolution of the solar neighborhood to terrestrial anomalies.

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, before decaying, provides insight into recent and nearby nucleosynthesis [1,2]. Indeed, a pioneering work at Munich [3], using AMS for ocean crust-samples, showed an enhanced 60Fe signal of extraterrestrial origin. Within an international collaboration we have continued to search for ISM radionuclides trapped in deep oceanarchives. We have analyzed sediments, crusts and nodules for extraterrestrial 60Fe (t1/2=2.6 Myr), 26Al (0.7 Myr) and 244Pu (81 Myr) [4-7] complemented by independent work at Munich [8-10]. We demonstrated that multiple events happened in our galactic neighbourhood and left their fingerprint on Earth. A global 60Fe influx is evidence for exposure to recent (<10 Myr) supernova explosions. The site where the heaviest elements are made in nature is, however, still unknown. The low concentrations measured for 244Pu suggest an unexpectedly low abundance of interstellar 244Pu [5]. It signals a rarity of actinide r-process nucleosynthesis, which is incompatible with the rate and expected yield of supernovae as the predominant actinide-producing sites. We will present new results for 60Fe measured at the ANU and 244Pu at ANSTO with unprecedented sensitivity. These data provide new insights into their concomitant influx and their ISM concentrations over a time period of the last 11 Myr. [1] Korschinek et al., Radiocarbon38 68, ‘96 [2] Ellis et al., ApJ.470 1227, ‘96 [3] Knie et al., PRL83, 18 (‘99) & PRL93 171103, ‘04 [4] Wallner et al., Nature Comm.6 5956, ‘15 [5] Feige et al., EPJ63 3003, ‘13 [6] Wallner et al., Nature532 69, ‘16 [7] Paul et al. ApJL558 L133, ‘01 [8] C. Wallner et al. NAstrRev48, 145150, ‘04 [9] Fimiani et al.

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 (200

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.

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).

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.

The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t1/2 ≤ 100 Myr, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is 60Fe (t1/2=2.6 Myr) which is ejected in supernova explosions and winds from massive stars. Here we report that the 60Fe signal observed previously in deep-sea crusts, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for 60Fe deposition via accretion of interstellar dust particles. Our results, based on 60Fe atom-counting at state-of-the-art sensitivity, reveal 60Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh 60Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.

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.

The Daly River drains a large (52500 km2) and mainly undisturbed catchment in the Australian wet–dry tropics. Clearing and cropping since 2002 have raised concerns about possible increased sediment input into the river and motivated this study of its fine sediment sources. Using 239Pu as a tracer it is shown that the fine sediments originate mainly from erosion by gullying and channel change. Although the results also indicate that the surface soil contribution to the river channel sediments from sheet erosion has increased to 5-22% for the Daly River and 7-28% for the Douglas River (a tributary of the Daly River) in 2009 vs. 3-6% for the Daly River and 4-9% for the Douglas River in 2005. This excess top soil likely originates from thecleared land adjacent to the Daly River since 2005. However, channel widening largely as a result of hydrologic change is still the dominant sediment source in this catchment.

The motivation of this work is to establish a new multi-isotope plutonium standard for isotopic ratio measurements with accelerator mass spectrometry CAMS), since stocks of existing solutions are declining. To this end, certified reference materials (CRMs) of each of the individual isotopes (PU)-P-239, (240)pu, (242)pu and Pu-244 were obtained from JRC IRMM (Joint Research Center Institute for Reference Materials and Measurements). These certified reference materials (IRMM-081a, IRMM-083, IRMM-043 and IRMM-042a) were diluted with nitric acid and mixed to obtain a stock standard solution with an isotopic ratio of approximately 1.0:1.0:1.0:0.1 ((239)pu:(240)pu:(242)pu:(244)pu). From this stock solution, samples were prepared for measurement of the plutonium isotopic composition by AMS. These samples have been measured in a round-robin exercise between the AMS facilities at CologneAMS, at the ANU Canberra and ETH Zurich to verify the isotopic ratio and to demonstrate the reproducibility of the measurements. The results show good agreement both between the different AMS measurements and with the gravimetrically determined nominal ratios. (C) 2015 Elsevier B.V. All rights reserved.

In order to resolve a recent discrepancy in the half-life of ⁶⁰Fe, we performed an independent measurement with a new method that determines the ⁶⁰Fe content of a material relative to Fe55 (t1/2=2.744yr) with accelerator mass spectrometry. Our result of (2.50±0.12)×10⁶yr clearly favors the recently reported value (2.62±0.04)×10⁶yr, and rules out the older result of (1.49±0.27)×10⁶yr. The present weighted mean half-life value of (2.60±0.05)×10⁶yr substantially improves the reliability as an important chronometer for astrophysical applications in the million-year time range. This includes its use as a sensitive probe for studying recent chemical evolution of our Galaxy, the formation of the early Solar System, nucleosynthesis processes in massive stars, and as an indicator of a recent nearby supernova.

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.

Cosmogenic noble gases and radionuclides in meteorites are the only tools that provide information about the cosmic ray exposure (CRE) history of meteorites. In space, meteoroids are irradiated by galactic cosmic rays (GCR), which produces, among others, stable and radioactive cosmogenic nuclides. It has been demonstrated that periodic variations in the GCR intensity induce periodic peaks in the CRE age histograms. Therefore, searching for periodic peaks in CRE histograms enables one to obtain information about GCR fluency variations. Since expected GCR fluency variations have periodicities of a few hundred million years, one needs meteorites irradiated for at least that long. Iron meteorites, which have CRE ages ranging from a few million to a few billion years, are the best candidates. So far we measured noble gases and radionuclides in 28 iron meteorites by noble gas mass spectrometry and accelerator mass spectrometry. First CRE age histograms have been established and will be presented. Further analyses are ongoing and will improve the statistical interpretation, providing new information on the temporal variability of the GCR fluency.

Bei der Explosion massereicher Sterne werden langlebige Radionuklide erzeugt und in den Weltraum hinausgeschleudert. Relikte naher Supernovae lassen sich nicht nur im All, sondern auch auf der Erde selbst entdecken [1]. Um Supernova-Spuren in Tiefseearchiven nachzuweisen, wurden 100 Proben aus 4 Sedimenten untersucht. Die Bohrkerne stammen aus einer Tiefe von 4 200 m des Indischen Ozeans. Sie umfassen ein Altersprofil von 1,7-3,2 Millionen Jahren, in dem sich Supernova-Radionuklide abgelagert haben. Die Proben wurden chemisch aufbereitet, einzelne Elementfraktionen voneinander getrennt und analysiert. Mit der Beschleunigermassenspektrometrie (AMS), einer sehr sensitiven Methode zur Bestimmung extrem niedriger Konzentrationen langlebiger Radionuklide, wurden 10Be, 26Al, und 60Fe gemessen. Isotopenverhältnisse im Bereich von 10-9 (10Be/9Be) bis zu 10-16 (60Fe/Fe) konnten so quantifiziert werden. Die Nuklide 10Be und 26Al werden kontinuierlich in der Erdatmosphäre durch hochenergetische Kernreaktionen hauptsächlich an Stickstoff, Sauerstoff und Argon gebildet und können zur Datierung der Sedimente verwendet werden. 60Fe hat keine terrestrischen Quellen, wird jedoch kurz vor und während einer Sternexplosion produziert. Da in dem gemessenen Zeitbereich eine Erhöhung dieses Eisen-Isotops festgestellt wurde, kann davon ausgegangen werden, dass es aus dem Weltall in die Tiefseesedimente eingetragen wurde. [1] K. Knie, Phys. Rev. Lett., 2004, 93, id. 171103

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.

Cosmogenic noble gases and radionuclides in meteorites are the only tools that provide information about the cosmic ray exposure (CRE) history of meteorites. In space, meteoroids are irradiated by galactic cosmic rays (GCR), which produces, among others, stable and radioactive cosmogenic nuclides. It has been demonstrated that periodic variations in the GCR intensity induce periodic peaks in the CRE age histograms. Therefore, searching for periodic peaks in CRE histograms enables one to obtain information about GCR fluency variations. Since expected GCR fluency variations have periodicities of a few hundred million years, one needs meteorites irradiated for at least that long. Iron meteorites, which have CRE ages ranging from a few million to a few billion years, are the best candidates. So far we measured noble gases and radionuclides in 28 iron meteorites by noble gas mass spectrometry and accelerator mass spectrometry. First CRE age histograms have been established and will be presented. Further analyses are ongoing and will improve the statistical interpretation, providing new information on the temporal variability of the GCR fluency.

The motivation of this work is to establish a new multi-isotope plutonium standard for isotopic ratio measurements with accelerator mass spectrometry CAMS), since stocks of existing solutions are declining. To this end, certified reference materials (CRMs) of each of the individual isotopes (PU)-P-239, (240)pu, (242)pu and Pu-244 were obtained from JRC IRMM (Joint Research Center Institute for Reference Materials and Measurements). These certified reference materials (IRMM-081a, IRMM-083, IRMM-043 and IRMM-042a) were diluted with nitric acid and mixed to obtain a stock standard solution with an isotopic ratio of approximately 1.0:1.0:1.0:0.1 ((239)pu:(240)pu:(242)pu:(244)pu). From this stock solution, samples were prepared for measurement of the plutonium isotopic composition by AMS. These samples have been measured in a round-robin exercise between the AMS facilities at CologneAMS, at the ANU Canberra and ETH Zurich to verify the isotopic ratio and to demonstrate the reproducibility of the measurements. The results show good agreement both between the different AMS measurements and with the gravimetrically determined nominal ratios. (C) 2015 Elsevier B.V. All rights reserved.