Al Isotopes Research Articles

A Study of the Abundance of Aluminium in Massive Stars

Abstract: This study presents the results of the calculation of the mass fractions of isotopes from hydrogen to nickel during the entire core burning phases of a 25 M⊙ star. A simple stellar model was used, considering four main parameters: temperature, density, initial composition, and time, without accounting for mass loss or mixing. The mass fractions of the isotopes were calculated using the open-source package NucNet Tools and the updated reaction rates from the JINA Reaclib database. A comparison of our results with existing similar data is performed and acceptable agreement is conspicuous. Hydrodynamic conditions in massive stars favor the production of 26Al, therefore particular attention was given to the isotopes 26Al and 27Al and the ratio of their mass fractions R_Al for comparison with the literature. The averaged value of the controversial R_Al during the star's lifetime is found to be 1.68×10-4. Keywords: Elemental abundances in stars, Evolution, Stellar, Nuclear astrophysics, Hydrostatic stellar nucleosynthesis, Nucleosynthesis: stellar, Stars formation. PACS: 97.10.Tk, 87.23.-n, 97.10.Cv, 26.20.-f, 7.10.Cv, 97.10.Bt.

Study of the 20Ne(p,γ)21Na reaction at LUNA

The NeNa-MgAl cycles are involved in the synthesis of Ne, Na, Mg, and Al isotopes. The 20Ne(p,γ)21Na (Q = 2431.68 keV) reaction is the first and slowest reaction of the NeNa cycle and it controls the speed at which the entire cycle proceeds. At the state of the art, the uncertainty on the 20Ne(p,γ)21Na reaction rate affects the production of the elements in the NeNa cycle. In particular, in the temperature range from 0.1 GK to 1 GK, the rate is dominated by the 366 keV resonance corresponding to the excited state of EX = 2797.5 keV and by the direct capture component. The present study focus on the study of the 366 keV resonance and the direct capture below 400 keV. At LUNA (Laboratory for Underground Nuclear Astrophysics) the 20Ne(p,γ)21Na reaction has been measured using the intense proton beam delivered by the LUNA 400 kV accelerator and a windowless differential-pumping gas target. The products of the reaction are detected with two high-purity germanium detectors. The experimental details and preliminary results on the 366 keV resonance and on the direct capture component at very low energies will be shown, together with their possible impact on the 20Ne(p,γ)21Na reaction rate.

Ab initio calculations of mirror energy difference in sd-shell nuclei* *Supported by the National Natural Science Foundation of China (12205340, 11975282); the Gansu Natural Science Foundation (22JR5RA123); the Special Research Assistant Project of the Chinese Academy of Sciences; the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000); the Key Research Program of the Chinese Academy of Sciences (XDPB15);

Mirror energy difference is a key observable in isospin symmetry breaking, containing rich information about nuclear structure. Understanding the mechanisms underlying mirror energy difference is important in nuclear physics. In the present work, we extensively investigated mirror energy difference using ab initio valence-space in-medium similarity renormalization group approach, focusing specifically on -shell nuclei. The low-lying spectra of Al isotopes and isotones, together with their mirror nuclei, were calculated, followed by a systematic analysis of the evolution of the mirror energy difference. The results suggest that the large mirror energy difference is mainly caused by the weakly-bound effects and large average occupations of the orbit. Lastly, we compare the results of our ab initio calculations with shell model results, elucidating the relationship and coherence between these two models.

Evolution of rotating massive stars with new hydrodynamic wind models

Context. Mass loss due to radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating the stellar evolution at different metallicities, particularly in the case of massive stars with M* ≥ 25 M⊙. Aims. We extend the evolution models introduced in Paper I, where the mass-loss recipe is based on the simultaneous calculation of the wind hydrodynamics and the line acceleration, by incorporating the effects of stellar rotation. Methods. As in Paper I, we introduce a grid of self-consistent line-force parameters (k, α, δ) for a set of standard evolutionary tracks using GENEC. Based on this grid, we analysed the effects of stellar rotation, CNO abundances, and He/H ratio on the wind solutions to derive additional terms for the recipe with which we predict the self-consistent mass-loss rate, Ṁsc. With this, we generated a new set of evolutionary tracks with rotation for MZAMS = 25, 40, 70, and 120 M⊙, and for metallicities Z = 0.014 (Galactic) and 0.006 (Large Magellanic Cloud). Results. In addition to the expected correction factor due to rotation, the mass-loss rate decreases when the surface becomes more helium rich, especially in the later moments of the main-sequence phase. The self-consistent approach gives lower mass-loss rates than the standard values adopted in previous GENEC evolution models. This decrease strongly affects the tracks of the most massive models. Weaker winds allow the star to retain more mass, but also more angular momentum. As a consequence, weaker wind models rotate faster and show a less efficient mixing in their inner stellar structure at a given age. Conclusions. The self-consistent tracks predict an evolution of the rotational velocities through the main sequence that closely agrees with the range of v sin i values found by recent surveys of Galactic O-type stars. As subsequent implications, the weaker winds from self-consistent models also suggest a reduction of the contribution of the isotope 26Al to the interstellar medium due to stellar winds of massive stars during the MS phase. Moreover, the higher luminosities found for the self-consistent evolutionary models suggest that some populations of massive stars might be less massive than previously thought, as in the case of Ofpe stars at the Galactic centre. Therefore, this study opens a wide range of consequences for further research based on the evolution of massive stars.

New Constraints for Supernova Models from Presolar Silicon Carbide X Grains with Very High 26Al/27Al Ratios

We report C, N, Mg-Al, Si, and S isotope data of six 1–3 μm-sized SiC grains of Type X from the Murchison CM2 chondrite, believed to have formed in the ejecta of core-collapse supernova (CCSN) explosions. Their C, N, and Si isotopic compositions are fully compatible with previously studied X grains. Magnesium is essentially monoisotopic 26Mg which gives clear evidence for the decay of radioactive 26Al. Inferred initial 26Al/27Al ratios are between 0.6 and 0.78 which is at the upper end of previously observed ratios of X grains. Contamination with terrestrial or solar system Al apparently is low or absent, which makes the X grains from this study particularly interesting and useful for a quantitative comparison of Al isotope data with predictions from supernova models. The consistently high 26Al/27Al ratios observed here may suggest that the lower 26Al/27Al ratios of many X grains from the literature are the result of significant Al contamination and in part also of an improper quantification of 26Al. The real dispersion of 26Al/27Al ratios in X grains needs to be explored by future studies. The high observed 26Al/27Al ratios in this work provide a crucial constraint for the production of 26Al in CCSN models. We explored different CCSN models, including both “classical” and H ingestion CCSN models. It is found that the classical models cannot account for the high 26Al/27Al ratios observed here; in contrast, H ingestion models are able to reproduce the 26Al/27Al ratios along with C, N, and Si isotopic ratios reasonably well.

Evolution of massive stars with new hydrodynamic wind models

Context. Mass loss through radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating massive star evolution at different metallicities, especially in the case of very massive stars (M* ≥ 25 M⊙). Aims. Here we present evolutionary models for a set of massive stars, introducing a new prescription for the mass-loss rate obtained from hydrodynamical calculations in which the wind velocity profile, v(r), and the line-acceleration, gline, are obtained in a self-consistent way. These new prescriptions cover most of the main sequence phase of O-type stars. Methods. We made a grid of self-consistent mass-loss rates Ṁsc for a set of standard evolutionary tracks (i.e. using the old prescription for mass-loss rate) with different values for initial mass and metallicity. Based on this grid, we elaborate a statistical analysis to create a new simple formula for predicting the values of Ṁsc from the stellar parameters alone, without assuming any extra condition for the wind description. Therefore, replacing the mass-loss rates at the main sequence stage provided by the standard Vink’s formula with our new recipe, we generate a new set of evolutionary tracks for MZAMS = 25, 40, 70, and 120 M⊙ and metallicities Z = 0.014 (Galactic), Z = 0.006 (LMC), and Z = 0.002 (SMC). Results. Our new derived formula for mass-loss rate predicts a dependence Ṁ ∝ Za, where a is no longer constant but dependent on the stellar mass: ranging from a ∼ 0.53 when M* ∼ 120 M⊙, to a ∼ 1.02 when M* ∼ 25 M⊙. We find important differences between the standard tracks and our new self-consistent tracks. Models adopting the new recipe for Ṁ (which starts off at around three times weaker than the mass-loss rate from the old formulation) retain more mass during their evolution, which is expressed as larger radii and consequently more luminous tracks over the Hertzsprung-Russell diagram. These differences are more prominent for the cases of MZAMS = 70 and 120 M⊙ at solar metallicity, where we find self-consistent tracks are ∼0.1 dex brighter and retain up to 20 M⊙ more than with the classical models using the previous formulation for mass-loss rate. Later increments in the mass-loss rate for tracks when self-consistency is no longer used, attributed to the LBV stage, produce different final stellar radii and masses before the end of the H-burning stage, which are analysed case by case. Moreover, we observe remarkable differences in the evolution of the radionuclide isotope 26Al in the core and on the surface of the star. As Ṁsc is weaker than the commonly adopted values for evolutionary tracks, self-consistent tracks predict a later modification in the abundance of 26Al in the stellar winds. This new behaviour could provide useful information about the real contribution of this isotope from massive stars to the Galactic interstellar medium.

Comparison between Core-collapse Supernova Nucleosynthesis and Meteoric Stardust Grains: Investigating Magnesium, Aluminium, and Chromium

Abstract Isotope variations of nucleosynthetic origin among solar system solid samples are well documented, yet the origin of these variations is still uncertain. The observed variability of 54Cr among materials formed in different regions of the protoplanetary disk has been attributed to variable amounts of presolar, chromium-rich oxide (chromite) grains, which exist within the meteoritic stardust inventory and most likely originated from some type of supernova explosion. To investigate if core-collapse supernovae (CCSNe) could be the site of origin of these grains, we analyze yields of CCSN models of stars with initial masses 15, 20, and 25 M ⊙, and solar metallicity. We present an extensive abundance data set of the Cr, Mg, and Al isotopes as a function of enclosed mass. We find cases in which the explosive C ashes produce a composition in good agreement with the observed 54Cr/52Cr and 53Cr/52Cr ratios as well as the 50Cr/52Cr ratios. Taking into account that the signal at atomic mass 50 could also originate from 50Ti, the ashes of explosive He burning also match the observed ratios. Addition of material from the He ashes (enriched in Al and Cr relative to Mg to simulate the make-up of chromite grains) to the solar system’s composition may reproduce the observed correlation between Mg and Cr anomalies, while material from the C ashes does not present significant Mg anomalies together with Cr isotopic variations. In all cases, nonradiogenic, stable Mg isotope variations dominate over the variations expected from 26Al.

Exploring the astrophysical energy range of the 27Al[formula omitted]Mg reaction: A new recommended reaction rate

The 26Al abundance holds a special role in present-day astrophysics, since it is a probe of active nucleosynthesis in the Galaxy and a valuable constraint of Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809-keV γ-line of the daughter 26Mg and from the superabundance of 26Mg in comparison with the most abundant 24Mg isotope in meteorites. Accurate knowledge of the reaction rates involving 26Al, its stable counterpart 27Al and 24Mg is then mandatory. Moreover, these nuclei enter the MgAl cycle playing an important role in the production of Al and Mg isotopes. Recently, high-resolution stellar surveys have shown that the Mg-Al anti-correlation in red giants of globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not show correlation with Al.The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show an order of magnitude uncertainty owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84-keV resonance and to lower the upper limits on the strength of nearby resonances, with potential important impact for astrophysics. In particular, modifications in the 27Al and 24Mg abundances up to ∼30% are predicted for intermediate mass stars.

26Aluminum from Massive Binary Stars. II. Rotating Single Stars Up to Core Collapse and Their Impact on the Early Solar System

Abstract Radioactive nuclei were present in the early solar system (ESS), as inferred from analysis of meteorites. Many are produced in massive stars, either during their lives or their final explosions. In the first paper of this series (Brinkman et al. 2019), we focused on the production of 26Al in massive binaries. Here, we focus on the production of another two short-lived radioactive nuclei, 36Cl and 41Ca, and the comparison to the ESS data. We used the MESA stellar evolution code with an extended nuclear network and computed massive (10–80 M ⊙), rotating (with initial velocities of 150 and 300 km s−1) and nonrotating single stars at solar metallicity (Z = 0.014) up to the onset of core collapse. We present the wind yields for the radioactive isotopes 26Al, 36Cl, and 41Ca, and the stable isotopes 19F and 22Ne. In relation to the stable isotopes, we find that only the most massive models, ≥60 and ≥40 M ⊙ give positive 19F and 22Ne yields, respectively, depending on the initial rotation rate. In relation to the radioactive isotopes, we find that the ESS abundances of 26Al and 41Ca can be matched with by models with initial masses ≥40 M ⊙, while 36Cl is matched only by our most massive models, ≥60 M ⊙. 60Fe is not significantly produced by any wind model, as required by the observations. Therefore, massive star winds are a favored candidate for the origin of the very short-lived 26Al, 36Cl, and 41Ca in the ESS.

Surface properties for Ne, Na, Mg, Al, and Si isotopes in the coherent density fluctuation model using the relativistic mean-field densities

We have systematically studied the surface properties, such as symmetry energy, neutron pressure, and symmetry energy curvature coefficient for Ne, Na, Mg, Al, and Si nuclei from the proton to neutron drip lines. The coherent density fluctuation model (CDFM) is used to estimate these quantities taking the relativistic mean-field densities as inputs. The Brückner energy density functional is taken for the nuclear matter binding energy and local density approximation is applied for its conversion to coordinate space. The symmetry energy again decomposed to the volume and surface components within the liquid drop model formalism to the volume and surface parts separately. Before calculating the surface properties of finite nuclei, the calculated bulk properties are compared with the experimental data, whenever available. The NL3* parameter set with the Bardeen–Cooper–Schrieffer (BCS) pairing approach in an axially deformed framework is used to take care of the pairing correlation when needed. The deformed density is converted to its spherical equivalent with a two-Gaussian fitting, which is used as an input for the calculation of weight function in the CDFM approximation. With the help of the symmetry energy, the isotopes 29F, 28Ne, 29,30Na, and 31,35,36Mg are considered to be within the island of inversion (Han et al. Phys. Lett. B, 772, 529 (2017). doi:10.1016/j.physletb.2017.07.007). Although we get large symmetry energies corresponding to a few neutron numbers for this isotopic chain as expected, an irregular trend appears for all these considered nuclei. The possible reason behind this abnormal behavior of symmetry energy for these lighter mass nuclei is also included in the discussion, which gives a direction for future analysis.

Hints on the Late Miocene Evolution of the Tonale-Adamello-Brenta Region (Alps, Italy) Based on Allochtonous Sediments From Raponzolo Cave

Raponzolo is a paleo-phreatic cave explored in 2011 in the Brenta Dolomites (Trentino, Italy), at the remarkable altitude of 2,560 m a.s.l. Differently to all other caves of the area, it hosts well-cemented fine to medium sands of granitic-metamorphic composition. The composition suggests a sediment source from the Adamello and Tonale Unit, separated from the Brenta by one of the most important tectonic lineaments of the Alps (Giudicarie Line). The fine-sand sediment was sampled to determine burial time and thus a minimum age of the cave. Cosmogenic isotopes (26Al and 10Be) in quartz grains allowed to estimate a minimum burial age of 5.25 Ma based on the mean sediment transport time at the surface and infer original altitude of the catchment area. Detrital apatite fission-track (AFT) and U-Pb dating on zircons provide information on the source, both from a regional and altitude (exhumation) perspective. Two populations of detrital AFT ages center at 17 (−2.3 + 2.6) Ma and 23 (−3.3 + 3.9) Ma, whereas the main detrital zircon U-Pb age populations are younger than 40 Ma. These correspond to intrusive and metamorphic sources nowadays outcropping exclusively above 2,200–2,300 m a.s.l. in Northern Adamello and Tonale. The results point to a late Miocene erosion and infilling of the cave by allochtonous sediments, with important implications on the timing of cave speleogenesis, as well as the paleogeographical connection, tectonic evolution and uplift of different structural units of the Alps. The roundness and the well sorted size of the quartz grains suggest a fluvial or aeolian origin, possibly recycled by glacial activity related to cold events reported in high latitude areas of the world at 5.75 and 5.51 Ma. These glacial phases have never been documented before in the Alps. This information confirms that the valleys dividing these geological units were not yet deeply entrenched during the onset of the Messinian Salinity Crisis (5.6–5.5 Ma), allowing an efficient transport of sediments across major tectonic lineaments of the Alps. This study shows the potential of cave sediments to provide information not only on the age of speleogenesis but also on the paleogeography of a wide area of the Alps during the late Miocene.

The Thermal Evolution of Planetesimals During Accretion and Differentiation: Consequences for Dynamo Generation by Thermally‐Driven Convection

AbstractThe meteorite paleomagnetic record indicates that differentiated (and potentially, partially differentiated) planetesimals generated dynamo fields in the first 5–40 Myr after the formation of calcium‐aluminum‐rich inclusions (CAIs). This early period of dynamo activity has been attributed to thermal convection in the liquid cores of these planetesimals during an early period of magma ocean convection. To better understand the controls on thermal dynamo generation in planetesimals, we have developed a one dimensional model of the thermal evolution of planetesimals from accretion through to the shutdown of convection in their silicate magma oceans for a variety of accretionary scenarios. The heat source of these bodies is the short‐lived radiogenic isotope 26Al. During differentiation, 26Al partitions into the silicate portion of these bodies, causing their magma oceans to heat up and introducing stable thermal stratification to the top of their cores, which inhibits dynamo generation. In “instantaneously” accreting bodies, this effect causes a delay on the order of >10 Myr to whole core convection and dynamo generation while this stratification is eroded. However, gradual core formation in bodies that accrete over >0.1 Myr can minimize the development of this stratification, allowing dynamo generation from ∼4 Myr after CAI formation. Our model also predicts partially differentiated planetesimals with a core and mantle overlain by a chondritic crust for accretion timescales >1.2 Myr, although none of these bodies generate a thermal dynamo field. We compare our results from thousands of model runs to the meteorite paleomagnetic record to constrain the physical properties of their parent bodies.

Constraints on the neutron drip line with the newly observed Na39

The recently observed weakly-bound 39Na provides a stringent theoretical constraint on the neutron drip-line. We studied the properties of drip-line nuclei around 39Na with the Hartree-Fock-Bogoliubov method and various Skyrme interactions. We adopted the extended SkM*-ext1 parameterization which can properly describe two-neutron separation energies of oxygen and fluorine isotopes and deformations at the center of the "island of inversion". Systematic calculations of drip lines of O, F, Ne, Na, Mg, and Al isotopes have been performed. We infer that 42Mg is weakly bound and 45Al is less weakly bound. 44Mg and 47Al could be barely existed. We also demonstrated the deformed halo properties of 39Na. Our studies could be valuable for experimental explorations of drip-line nuclei in the forthcoming FRIB and other rare-isotope beam facilities .

Gamma-Ray Emission of 60Fe and 26Al Radioactivity in Our Galaxy

Abstract The isotopes 60Fe and 26Al originate from massive stars and their supernovae, reflecting ongoing nucleosynthesis in the Galaxy. We studied the gamma-ray emission from these isotopes at characteristic energies 1173, 1332, and 1809 keV with over 15 yr of SPI data, finding a line flux in 60Fe combined lines of and the Al line flux of above the background and continuum emission for the whole sky. Based on the exponential disk grid maps, we characterize the emission extent of 26Al to find scale parameters and kpc; however, the 60Fe lines are too weak to spatially constrain the emission. Based on a point-source model test across the Galactic plane, the 60Fe emission would not be consistent with a single strong point source in the Galactic center or somewhere else, providing a hint of a diffuse nature. We carried out comparisons of emission morphology maps using different candidate source tracers for both 26Al and 60Fe emissions and suggest that the 60Fe emission is more likely to be concentrated toward the Galactic plane. We determine the 60Fe/26Al γ-ray flux ratio at 18.4% ± 4.2% when using a parameterized spatial morphology model. Across the range of plausible morphologies, it appears possible that 26Al and 60Fe are distributed differently in the Galaxy. Using the best-fitting maps for each of the elements, we constrain flux ratios in the range 0.2–0.4. We discuss the implications for massive star models and their nucleosynthesis.

Characterization of the new hybrid low-energy accelerator facility in Mexico

In 2013, a new accelerator mass spectrometry (AMS) facility was inaugurated in Mexico. Since then a substantial number of precise measurements of low concentrations of radioactive isotopes (14C, 10Be, 26Al and Pu) have been made. This paper describes the extension to the isotope separator installed at the end of 2017. It takes advantage of the 1MV High Voltage Engineering Europa (HVEE) tandem accelerator with the multicathode ion source (MCIS) and the fine-tuned injection system which delivers low-energy beams into a multipurpose scattering chamber. The MCIS allows for a quick and smooth change of the ion species to be accelerated. The ability to automatically tune all the optics in the injection system produces an accelerator laboratory that can change the beam species, intensities and energies in a few seconds. The careful and detailed study of the high-energy analyzing magnet using well-known proton resonances in 12C and 28Si, allowed for a calibration of the terminal voltage and beam energy. Stable ion beams with energies as low as 300 keV and as high as 8 MeV, from H to Fe, and with intensities in the range 109-1015 particles per second, were produced as listed.

Redox conditions and manganese metallogenesis in the Cryogenian Nanhua Basin: Insight from the basal Datangpo Formation of South China

In South China, the Datangpo Formation was deposited during the Cryogenian interglacial stage between the Sturtian and Marinoan glaciations. The variations in paleoocean chemistry recorded in the Datangpo Formation are important to understand the formation of Mn ore as well as the early evolution of animals, which are not well constrained. Based on lithological observation and multi-geochemical proxies (iron speciation, Mo, U, V, Mn, Al and pyrite sulfur isotope) from drill core ZK43-6 from southeastern Chongqing, South China, the results indicate an anoxic (mostly euxinic) water condition for the lower black shales of the Datangpo Formation, which can be further divided into four intervals (I, II, III, IV). Among of them, very high Mn content and manganese metallogenesis is related to the suboxic Interval II between two euxinic depositions (Interval I and Interval III). Thus, our new findings suggest that the general euxinic condition at the basal Datangpo Formation is interrupted by a suboxic deposition (Interval II) where the manganese deposits formed. An updated model is proposed to shed light on the evolution in redox conditions of the Datangpo Formation as a function of sea-level and terrigenous input, and the genesis of “Datangpo-type” manganese in light of the temporal seawater redox conditions and microbial activity.

Time and duration of chondrule formation: Constraints from 26Al-26Mg ages of individual chondrules

Chondrules from unequilibrated ordinary and carbonaceous chondrites belong to the oldest and most primitive materials from the early solar system and record chemical and isotopic signatures relating to their formation and evolution. These signatures allow tracing protoplanetary disk processes that eventually led to the formation of planetary building blocks and rocky planets. 26Al-26Mg ages based on mineral-mesostasis isochrons of 31 porphyritic ferromagnesian chondrules, that belong mainly to type-II, constrain the time of chondrule melting prior to incorporation into the respective chondrite parent bodies. For this study chondrules from the unequilibrated L, L(LL) and LL ordinary chondrites (UOCs) NWA 5206, NWA 8276, MET 96503, MET 00452, MET 00526, NWA 7936 and QUE 97008 were selected, which are of petrologic types 3.00–3.15 and were thus least metamorphosed after formation. Magnesium and Al isotopes were measured in-situ by Secondary Ion Mass Spectrometry (SIMS) using a CAMECA 1280 ims. 26Mg excess from in-situ decay of 26Al correlating with 27Al/24Mg has been detected in the mesostasis of all but one chondrule. The initial Al isotopic compositions (26Al/27Al)0 and 26Mg/24Mg ratios (δ26Mg0∗) deduced from internal mineral isochron regressions range from (9.5 ± 2.8) × 10−6 to (3.1 ± 1.2) × 10−6 and −0.020 ± 0.028‰ to 0.011 ± 0.039‰, respectively. The corresponding chondrule ages (ΔtCAI), calculated relative to calcium-aluminum-rich inclusions (CAIs) using the canonical 26Al/27Al = (5.23 ± 0.13) × 10−5, are between 1.76-0.27+0.36 and 2.92-0.34+0.51 Ma and date the melt formation and thus primary chondrule formation from dust-like precursors or reprocessing of older chondrules. The age range agrees with those acquired with different short-lived chronometers and with published 26Al-26Mg ages, the majority of which were obtained for chondrules from the Bishunpur and Semarkona meteorites, although no chondrule with (26Al/27Al)0 > 10−5 was found.Chondrules in single chondrite samples or between different chondrite groups show no distinct age distributions. The initial 26Al/27Al of the oldest chondrules in the L(LL)/LL and L chondrite samples are identical within their 1σ uncertainties and yield a mean age of 1.99-0.08+0.08 Ma and 1.81-0.10+0.11 Ma, respectively. The oldest chondrules from six of the seven studied samples record a mean age of 1.94-0.06+0.07 Ma. Since heating events in the protoplanetary disk could have partially reset the Al-Mg systematics in pre-existing chondrules and this would have shifted recorded 26Al-26Mg ages toward younger dates, the oldest mean age of 1.81-0.10+0.11 Ma recorded in L chondrite chondrules is interpreted to date the rapid and punctuated onset of chondrule formation. The density distribution of chondrule ages from this study, which comprises the largest single dataset of OC chondrule ages, combined with published ages for chondrules from ordinary and carbonaceous chondrites reveals major age peaks for OC chondrules at 2.0 and 2.3 Ma. Chondrules in ordinary and carbonaceous chondrites formed almost contemporaneously (with a possible distinction between CC groups) in two chemically distinct reservoirs, probably in density-enriched regions at the edges of Jupiter’s orbit. The young formation ages of chondrules suggest that they do not represent precursors but rather by-products of planetesimal accretion.

Evidence of a Proton Halo in 23Al: A Mean Field Analysis

We have studied the nuclear structure properties like binding energy, charge radius, quadrupole deformation parameter for various isotopes of Al from the valley of stability to drip line region using the well known relativistic mean field formalism (RMF) with NL3 parameter set. We have compared our results with experimental data and found reasonable agreement. Further, we have taken spherical and deformed RMF densities to estimate the reaction dynamics of $^{23-28}$Al isotopes as projectiles and $^{12}$C as target by conjunction in Glauber model. The estimated results are also compared with the experimental data. The analysis of angular elastic differential and one proton removal cross sections are also studied with Glauber model many body system to investigate the structural feature of $^{23}$Al. The evidence of enhanced total reaction cross section, higher value of rms radius, narrow longitudinal momentum distribution and small proton separation energy of $^{23}$Al support its proton halo structure.

Effect of deformation on structure and reaction of Al isotopes using relativistic mean field densities in Glauber model

We have examined the ground state properties of Al isotopes towards the proton rich side from A = 22 to 28 using the well known relativistic mean field (RMF) formalism with NLSH parameter set. The calculated results are compared with the predictions of finite range droplet model and experimental data. The calculation is extended to estimate the reaction cross section for $$^{22-28}$$ Al as projectiles with $$^{12}$$ C as target. The incident energy of the projectiles are taken as 950 MeV/nucleon, for both spherical and deformed RMF densities as inputs in the Glauber model approximation. Further investigation of enhanced values of total reaction cross section for $$^{23}$$ Al and $$^{24}$$ Al in comparison to rest of the isotopes indicates the proton skin structure of these isotopes. Specifically, the large value of root mean square radius and total reaction cross section of $$^{23}$$ Al could not be ruled out the formation of proton halo.

Neutrino nucleosynthesis in core-collapse Supernova explosions

The neutrino-induced nucleosynthesis (v process) in supernova explosions of massive stars of solar metallicity with initial main sequence masses between 15 and 40 M⨀ has been studied. A new extensive set of neutrino-nucleus cross-sections for all the nuclei included in the reaction network is used and the average neutrino energies are reduced to agree with modern supernova simulations. Despite these changes the v process is found to contribute still significantly to the production of the nuclei 7Li, 11B, 19F, 138La and 180Ta, even though the total yields for those nuclei are reduced. Furthermore we study in detail contributions of the v process to the production of radioactive isotopes 26Al, 22Na and confirm the production of 92Nb and 98Tc.