Uncertainties In Physics Research Articles

Self-Direction in Physics Graduate Education: Insights for STEM from David J. Rowe’s Career-Long Methods

The ability to self-direct a research program determines graduate degree completion. Yet, research on incompletion of science, technology, engineering, and mathematics (STEM) graduate programs assumes students’ present level of self-direction adequate and neglects to recognize a lack of self-directed learning (SDL) as key. This essay explores SDL for STEM, presenting the work of theoretical nuclear physicist David J. Rowe as a key example of applying a process of SDL in practice. Rowe focused on this challenge of physics graduate education by promoting SDL through the type of research flow that has been found to bring the greatest satisfaction to researchers regarding their insights. Strategies he explored involved his space, time, open mindedness and theoretical contributions with students and in collaboration with colleagues. A self-directed learner himself, Rowe developed methods of mentoring for encouraging physics graduate students to recognize symmetry as valuable in identifying solutions to problems quickly—helping students take the lead in finding insightful resolutions to complex, multidimensional, mathematical physics uncertainties. These strategies for supporting SDL in this context are examined here, with the use of narrative research to interpret the texts and conversations exchanged with the author. The process of SDL developed by Rowe is presented with recommendations on how Rowe’s methods may be modeled to improve self-direction in STEM graduate education more widely.

The Consequences of Surface-Exchange Coefficient Uncertainty on an Otherwise Highly Predictable Major Hurricane

Abstract In addition to initial conditions, uncertainty in model physics can also influence the practical predictability of tropical cyclones. In this study, the influence that various magnitudes of uncertainty in the surface exchange coefficients of momentum (Cd) and enthalpy (Ck) can have on an otherwise highly predictable major hurricane (Hurricane Patricia) is compared with that resulting from climatological environmental initial condition uncertainty and the intrinsic limit for this case. As the systematic uncertainty in Cd and Ck is reduced from 40% to 1%, the simulated uncertainty in the intensity and structure is substantially reduced and approaches the intrinsic limit when uncertainty is reduced to 1%. In addition, the forecasted intensity and structure uncertainty only becomes less than that resulting from climatological environmental initial condition uncertainty once the systematic uncertainty in Cd and Ck is reduced to ∼10%, highlighting the strong influence of model error in limiting TC predictability. If Cd and Ck are perturbed stochastically, instead of systematically, it is shown that the influence on the simulated intensity and structure is negligible and nearly identical to the intrinsic limit, regardless of the magnitude of the stochastic Cd and Ck perturbations. While the magnitude of the stochastic Cd and Ck perturbations are comparable to the systematic perturbations, the stochastic perturbations are shown to not substantially perturb the time-integrated inner-core fluxes of momentum or enthalpy that predominantly determine simulated tropical cyclone intensity. Last, it is shown that the kinetic energy error growth behavior varies with the radius, azimuthal wavenumber, and ensemble design. Significance Statement The air–sea energy exchange beneath hurricanes is highly uncertain but strongly influences intensity. In this study, the influences of different magnitudes of surface-exchange coefficient uncertainty on the simulated intensity of an intense hurricane is compared with that resulting from environmental initial condition uncertainty and the intrinsic predictability limit. The main takeaway is that current surface-exchange coefficient uncertainties result in larger intensity uncertainty than environmental initial condition uncertainty, and substantial improvements in predictions are possible if current surface-exchange coefficient uncertainties are reduced. Furthermore, it is shown that randomly perturbing the surface-exchange coefficients at each point in space and time is not the best approach to account for the influences of this uncertain physical process on hurricane prediction because it has minimal influence on the simulated intensity.

Measurement of the Mo100(α,xn) cross section at weak r -process energies

The weak $r$ process in neutrino-driven winds following a core-collapse supernova is thought to contribute to the cosmic abundances of the first $r$-process peak elements between Se and Ag. Sensitivity studies have found that the early nucleosynthesis in the weak $r$ process is primarily driven by $(\ensuremath{\alpha},xn)$ reactions due to the high temperatures, and that current nuclear physics uncertainties in the $(\ensuremath{\alpha},xn)$ rates result in significant uncertainties of the calculated abundances. The weak $r$-process path proceeds several nuclei away from stability where $(\ensuremath{\alpha},xn)$ reaction cross sections have not yet been measured. In this paper we report the $^{100}\mathrm{Mo}(\ensuremath{\alpha},xn)$ cross section (between 8.9 and 13.2 MeV in the center of mass, corresponding to 3.5--6.8 GK) in inverse kinematics using the Multi-Sampling Ionization Chamber (MUSIC) detector at the Argonne Tandem Linac Accelerator System (ATLAS) facility. With this first measurement of the $^{100}\mathrm{Mo}(\ensuremath{\alpha},xn)$ cross section, we have demonstrated the ability of MUSIC to measure $(\ensuremath{\alpha},xn)$ cross sections for $A$ up to 100, therefore paving the way for further measurements with radioactive beams at ATLAS or the Facility for Rare Isotope Beams.

Radiation hydrodynamics modelling of kilonovae withSNEC

ABSTRACTWe develop a method to compute synthetic kilonova light curves that combine numerical relativity simulations of neutron star mergers and the SNEC radiation–hydrodynamics code. We describe our implementation of initial and boundary conditions, r-process heating, and opacities for kilonova simulations. We validate our approach by carefully checking that energy conservation is satisfied and by comparing the SNEC results with those of two semi-analytic light-curve models. We apply our code to the calculation of colour light curves for three binaries having different mass ratios (equal and unequal mass) and different merger outcome (short-lived and long-lived remnants). We study the sensitivity of our results to hydrodynamic effects, nuclear physics uncertainties in the heating rates, and duration of the merger simulations. We find that hydrodynamics effects are typically negligible and that homologous expansion is a good approximation in most cases. However, pressure forces can amplify the impact of uncertainties in the radioactive heating rates. We also study the impact of shocks possibly launched into the outflows by a relativistic jet. None of our models match AT2017gfo, the kilonova in GW170817. This points to possible deficiencies in our merger simulations and kilonova models that neglect non-LTE effects and possible additional energy injection from the merger remnant and to the need to go beyond the assumption of spherical symmetry adopted in this work.

Development of a “nature run” for observing system simulation experiments (OSSEs) for snow mission development

Abstract Snow is a fundamental component of global and regional water budgets, particularly in mountainous areas and regions downstream that rely on snowmelt for water resources. Land surface models (LSMs) are commonly used to develop spatially distributed estimates of snow water equivalent (SWE) and runoff. However, LSMs are limited by uncertainties in model physics and parameters, among other factors. In this study, we describe the use of model calibration tools to improve snow simulations within the Noah-MP LSM as the first step in an Observing System Simulation Experiment (OSSE). Noah-MP is calibrated against the University of Arizona (UA) SWE product over a Western Colorado domain. With spatially varying calibrated parameters, we run calibrated and default Noah-MP simulations for water years 2010-2020. By evaluating both simulations against the UA dataset, we show that calibration decreases domain averaged temporal RMSE and bias for snow depth from 0.15 to 0.13 m and from -0.036 to -0.0023 m, respectively, and improves the timing of snow ablation. Increased snow simulation performance also improves estimates of model-simulated runoff in four of six study basins, though only one has statistically significant improvement. Spatially distributed Noah-MP snow parameters perform better than default uniform values. We demonstrate that calibrating variables related to snow albedo calculations and rain-snow partitioning, among other processes, is a necessary step for creating a nature run that reasonably approximates true snow conditions for the OSSEs. Additionally, the inclusion of a snowfall scaling term can address biases in precipitation from meteorological forcing datasets, further improving the utility of LSMs for generating reliable spatiotemporal estimates of snow.

Sensitivity Study of Type-I X-ray Bursts to Nuclear Reaction Rates

Type-I X-ray bursts are frequently occurring thermonuclear runaways on the surface of an accreting neutron star. The different nuclear reactions that empower the cataclysmic event play a key role in accurately comparing theoretical models and observations. We investigate the effect of the uncertainties in the nuclear reactions using a ONEZONE model for a set of different compositions and accretion rates that are within the range of the standard observed burst sources. A combination of a full-reaction network and a semi-analytic model is used to obtain the conditions at the time of X-ray burst ignition via simulating the settling process of the accreted material. We then evaluate the sensitivity of the X-ray burst model by varying the proton and alpha-induced reaction rates in JINA REACLIBV2.2 within representative nuclear physics uncertainties.

Accuracy of environmental tracers and consequences for determining the Type Ia supernova magnitude step

Type Ia Supernovae (SNe Ia) are standardizable candles that allow us to measure the recent expansion rate of the Universe. Due to uncertainties in progenitor physics, potential astrophysical dependencies may bias cosmological measurements if not properly accounted for. The dependency of the intrinsic luminosity of SNe Ia with their host-galaxy environment is often used to standardize SNe Ia luminosity and is commonly parameterized as a step function. This functional form implicitly assumes two-populations of SNe Ia. In the literature, multiple environmental indicators have been considered, finding different, sometimes incompatible, step function amplitudes. We compare these indicators in the context of a two-populations model, based on their ability to distinguish the two populations. We show that local Hα-based specific star formation rate (lsSFR) and global stellar mass are better tracers than, for instance, host galaxy morphology. We show that tracer accuracy can explain the discrepancy between the observed SNe Ia step amplitudes found in the literature. Using lsSFR or global mass to identify the two populations can explain all other observations, though lsSFR is favoured. As lsSFR is strongly connected to age, our results favour a prompt and delayed population model. In any case, there exists two populations that differ in standardized magnitude by at least 0.121 ± 0.010 mag.

Development of a dynamic event tree (DET) to analyze SBO accident in VVER-1000/V446 nuclear reactor

Probabilistic safety assessment (PSA) is the main approach currently applied in safety assessment of nuclear power plants to calculate the core damage frequency (CDF). The conventional event tree/fault tree methodology, adopted in current PSA studies, has weaknesses such as nonrealistic modeling of operator and recovery actions, inability for functional reliability modelling of passive safety systems, using predetermined timing and order of accident sequences without any interaction of system responses, insensitivity of the system failure to uncertainties in the process physics and consequently its output is not comprehensive for safety considerations, risk management and decision making tasks. In this study to overcome these bottlenecks, a dynamic approach based on dynamic event tree (DET) is applied to calculate the CDF for the station blackout (SBO) accident in VVER-1000/V446 nuclear reactor. To implement the DET, deterministic and probabilistic models are developed using the plant data and the characteristics of the SBO accident. These models are then run simultaneously to investigate the time of operator actions, AC power supply recovery, and the availability of safety systems on the accident progression and consequences. The results show that the value of CDF calculated with DET is equal to 1.97e-6 (yr−1). The results also illustrates that the DET can provide useful insights concerning potential risk contributors and the effectiveness of operator and recovery actions.

The intermediate neutron capture process

Context. Carbon-enhanced metal-poor (CEMP) r/s-stars show surface-abundance distributions characteristic of the so-called intermediate neutron capture process (i-process) of nucleosynthesis. We previously showed that the ingestion of protons in the convective helium-burning region of a low-mass low-metallicity star can explain the surface abundance distribution observed in CEMP r/s stars relatively well. Such an i-process requires detailed reaction network calculations involving hundreds of nuclei for which reaction rates have not yet been determined experimentally. Aims. We investigate the nuclear physics uncertainties affecting the i-process during the asymptotic giant branch (AGB) phase of low-metallicity low-mass stars by propagating the theoretical uncertainties in the radiative neutron capture cross sections, as well as the 13C(α,n)16O reaction rate, and estimating their impact on the surface-abundance distribution. Methods. We used the STAREVOL code to follow the evolution of a 1 M⊙ [Fe/H] = − 2.5 model star during the proton ingestion event occurring at the beginning of the AGB phase. In the computation, we adopt a nuclear network of 1160 species coupled to the transport processes and different sets of radiative neutron capture cross sections consistently calculated with the TALYS reaction code. Results. It is found that considering systematic uncertainties on the various nuclear ingredients affecting the radiative neutron capture rates, surface elemental abundances are typically predicted within ±0.4 dex. The 56 ≲ Z ≲ 59 region of the spectroscopically relevant heavy-s elements of Ba-La-Ce-Pr as well as the r-dominated Eu element remain relatively unaffected by nuclear uncertainties. In contrast, the inclusion of the direct capture contribution impacts the rates in the neutron-rich A ≃ 45, 100, 160, and 200 regions, and the i-process production of the Z ≃ 45 and 65–70 elements. Uncertainties in the photon strength function also impact the overabundance factors by typically 0.2–0.4 dex. Nuclear level densities tend to affect abundance predictions mainly in the Z = 74 − 79 regions. The uncertainties associated with the neutron-producing reaction 13C(α,n)16O and the unknown β-decay rates are found to have a low impact on the overall surface enrichment. Conclusions. The i-process nucleosynthesis during the early AGB phase of low-metallicity low-mass stars remains sensitive to nuclear uncertainties, substantially affecting theoretical predictions of still unknown radiative neutron capture cross sections. Improved descriptions of direct neutron capture based on shell model calculations or experimental constraints from (d, p) reactions could help to decrease the uncertainties in the estimated rates. Similarly, constraints on the photon strength functions and nuclear level densities, for example through the Oslo method, in the neutron-rich region of A ≃ 100 and 160 would increase the predictive power of the present simulations.

Uncertainties in the18F(p,α)15O reaction rate in classical novae

Context.Direct observation ofγ-ray emission from the decay of18F ejected in classical nova outbursts remains a major focus of the nuclear astrophysics community. However, modeling the abundance of ejected18F, and thus the predicted detectability distance of aγ-ray signal near 511 keV emitted from these transient thermonuclear episodes, is hampered by significant uncertainties in our knowledge of the key18F(p,α) reaction rate.Aims.We analyze uncertainties in the most recent nuclear physics experimental results employed to calculate the18F(p,α) reaction rate. Our goal is to determine which uncertainties have the most profound influence on the predicted abundance of18F ejected from novae in order to guide future experimental works.Methods.We calculated a wide range of18F(p,α) reaction rates using theR-Matrix formalism, which allowed us to take all interference effects into account. Using a selection of 16 evenly spaced rates over the full range, we performed 16 new hydrodynamic nova simulations.Results.We have performed one of the most thorough theoretical studies of the impact of the18F(p,α) reaction in classical novae to date. The18F(p,α) rate remains highly uncertain at nova temperatures, resulting in a factor of ∼10 uncertainty in the predicted abundance of18F ejected from nova explosions. We also found that the abundance of18F may be strongly correlated with that of19F.Conclusions.Despite numerous nuclear physics uncertainties affecting the determination of the18F(p,α) reaction rate, dominated by unknown interference signs between 1/2+and 3/2+resonances, future experimental work should focus on firmly and precisely determining the directly measurable quantum properties of the subthreshold states in the compound nucleus19Ne near 6.13 and 6.29 MeV.

Kilonovae Across the Nuclear Physics Landscape: The Impact of Nuclear Physics Uncertainties on r-process-powered Emission

Abstract Merging neutron stars produce “kilonovae”—electromagnetic transients powered by the decay of unstable nuclei synthesized via rapid neutron capture (the r-process) in material that is gravitationally unbound during inspiral and coalescence. Kilonova emission, if accurately interpreted, can be used to characterize the masses and compositions of merger-driven outflows, helping to resolve a long-standing debate about the origins of r-process material in the Universe. We explore how the uncertain properties of nuclei involved in the r-process complicate the inference of outflow properties from kilonova observations. Using r-process simulations, we show how nuclear physics uncertainties impact predictions of radioactive heating and element synthesis. For a set of models that span a large range in both predicted heating and final abundances, we carry out detailed numerical calculations of decay product thermalization and radiation transport in a kilonova ejecta with a fixed mass and density profile. The light curves associated with our models exhibit great diversity in their luminosities, with peak brightness varying by more than an order of magnitude. We also find variability in the shape of the kilonova light curves and their color, which in some cases runs counter to the expectation that increasing levels of lanthanide and/or actinide enrichment will be correlated with longer, dimmer, redder emission.

Determination of lattice physics properties and uncertainties in a solid fuel molten salt cooled assembly using OpenMC

The desire for reducing our carbon footprint is driving significant interest in advanced nuclear reactors to produce energy. One promising technology is the Fluoride Salt-Cooled High-Temperature Reactor (FHR) which provides both electricity and high temperatures for use in process heat applications. The reactor technology considered in this work is a Generation IV design that uses TRISO particles uniformly embedded in fuel stripes within the fuel plates and liquid salt as coolant. The fuel design and conditions are the same as those used in a recent OECD/NEA FHR Benchmark. This paper reports the multiplication factor, fission reaction rate, and neutron spectrum for different cases from that benchmark study. A unique contribution of this work is the assessment of nuclear data uncertainty impact on the Figures of Merit used in the FHR benchmark. The OpenMC Monte Carlo code and perturbed nuclear data files from the TENDL-2017 library were utilized in these analyses. This work is part of the ongoing international efforts to explore and identify the applicability of current methods and codes for FHR simulations and molten salt reactors in general.

The impact of baryons on cosmological inference from weak lensing statistics

ABSTRACT As weak lensing surveys are becoming deeper and cover larger areas, information will be available on small angular scales down to the arcmin level. To extract this extra information, accurate modelling of baryonic effects is necessary. In this work, we adopt a baryonic correction model, which includes gas both bound inside and ejected from dark matter (DM) haloes, a central galaxy, and changes in the DM profile induced by baryons. We use this model to incorporate baryons into a large suite of DM-only N-body simulations, covering a grid of 75 cosmologies in the Ωm–σ8 parameter space. We investigate how baryons affect Gaussian and non-Gaussian weak lensing statistics and the cosmological parameter inferences from these statistics. Our results show that marginalizing over baryonic parameters degrades the constraints in Ωm–σ8 space by a factor of 2–5 compared to those with baryonic parameters fixed. We also find that combining the lensing power spectrum and peak counts can break the degeneracy between cosmological and baryonic parameters and mitigate the impact of the uncertainty in baryonic physics.

Legal Uncertainty in the context of the Foundations of Criminal Justice Transformation

Based on the analysis of the history of legal science and law enforcement practice, the paper considers the prerequisites for the conceptualization of the phenomenon of uncertainty in law. The author offers a historical and rational reconstruction of the transition from the everyday and practical experience of understanding uncertainty to the concept that allows us to formulate the principles of lawmaking and law enforcement that prohibit uncertainty in the law and court decisions. The author explicates the difference between the conceptualization of the phenomenon of uncertainty in the Russian legal literature and similar literature of the English-speaking world, where three different concepts are used to denote it: indeterminacy, vagueness and uncertainty. The paper analyzes the difficulties that arise in the implementation of the desire to integrate the system of Russian law into the legal space of the European Union, where the principle of legal certainty is one of the main instruments of integration. The author analyzes in detail the assessment of prospects and the significance of the principle of legal certainty in the practice of implementing the idea of the rule of law, and considers the paradoxes that arise in this case.Examples from the practice of the European Court of Human Rights, when certain decisions are criticized because of non-compliance by lawmakers with the principle of legal certainty, confirm the essential importance of ideological and value bases in the systems of modern law. The paper examines the significance of the philosophical and theoretical-conceptual grounds for the inclusion of the general scientific concept of uncertainty in the private scientific methodology of legal research. The differences in the interpretation of the phenomenon of uncertainty in linguistics, physics, economics, philosophy, logic and other sciences are determined. It is concluded that it is necessary to attract funds and methods of interdisciplinary research for the further development of the theory of legal uncertainty.

Theoretical Predictions of Surface Light Element Abundances in Protostellar and Pre-Main Sequence Phase

Theoretical prediction of surface stellar abundances of light elements–lithium, beryllium, and boron–represents one of the most interesting open problems in astrophysics. As well known, several measurements of 7Li abundances in stellar atmospheres point out a disagreement between predictions and observations in different stellar evolutionary phases, rising doubts about the capability of present stellar models to precisely reproduce stellar envelope characteristics. The problem takes different aspects in the various evolutionary phases; the present analysis is restricted to protostellar and pre-Main Sequence phases. Light elements are burned at relatively low temperatures (T from ≈2 to ≈5 million degrees) and thus in the early evolutionary stages of a star they are gradually destroyed at different depths of stellar interior mainly by (p, α) burning reactions, in dependence on the stellar mass. Their surface abundances are strongly influenced by the nuclear cross sections, as well as by the extension toward the stellar interior of the convective envelope and by the temperature at its bottom, which depend on the characteristics of the star (mass and chemical composition) as well as on the energy transport in the convective stellar envelope. In recent years, a great effort has been made to improve the precision of light element burning cross sections. However, theoretical predictions surface light element abundance are challenging because they are also influenced by the uncertainties in the input physics adopted in the calculations as well as the efficiency of several standard and non-standard physical processes active in young stars (i.e. diffusion, radiative levitation, magnetic fields, rotation). Moreover, it is still not completely clear how much the previous protostellar evolution affects the pre-Main Sequence characteristics and thus the light element depletion. This paper presents the state-of-the-art of theoretical predictions for protostars and pre-Main Sequence stars and their light element surface abundances, discussing the role of (p, α) nuclear reaction rates and other input physics on the stellar evolution and on the temporal evolution of the predicted surface abundances.

Do Multi‐Model Ensembles Improve Reconstruction Skill in Paleoclimate Data Assimilation?

AbstractReconstructing past climates remains a difficult task because pre‐instrumental observational networks are composed of geographically sparse and noisy paleoclimate proxy records that require statistical techniques to inform complete climate fields. Traditionally, instrumental or climate model statistical relationships are used to spread information from proxy measurements to other locations and to other climate variables. Here ensembles drawn from single climate models and from combinations of multiple climate models are used to reconstruct temperature variability over the last millennium in idealized experiments. We find that reconstructions derived from multi‐model ensembles produce lower error than reconstructions from single‐model ensembles when reconstructing independent model and instrumental data. Specifically, we find the largest decreases in error over regions far from proxy locations that are often associated with large uncertainties in model physics, such as mid‐ and high‐latitude ocean and sea‐ice regions. Furthermore, we find that multi‐model ensemble reconstructions outperform single‐model reconstructions that use covariance localization. We propose that multi‐model ensembles could be used to improve paleoclimate reconstructions in time periods beyond the last millennium and for climate variables other than air temperature, such as drought metrics or sea ice variables.

Probing hybrid stars with gravitational waves via interfacial modes

One of the uncertainties in nuclear physics is whether a phase transition between hadronic nuclear matter to quark matter exists in supranuclear matter equations of state. Such a feature can be probed via gravitational-wave signals from binary neutron star inspirals that contain information of the induced tides. The dynamical part of the tides is caused by the resonance of pulsation modes of stars, which causes a shift in the gravitational-wave phase. In this paper, we investigate the dynamical tides of the interfacial mode ($i$-mode) of spherical degree $l=2$, a non-radial mode caused by an interface associated with a quark-hadron phase transition inside a hybrid star. In particular, we focus on hybrid stars with a crystalline quark matter core and a fluid hadronic envelope. We find that the resonant frequency of such $i$-modes typically ranges from 300Hz to 1500Hz, and the frequency increases as the shear modulus of the quark core increases. We next estimate the detectability of such a mode with existing and future gravitational-wave events from the inspiral waveform with a Fisher analysis. We find that GW170817 and GW190425 have the potential to detect the $i$-mode if the quark-hadron phase transition occurs at sufficiently low pressure and the shear modulus of the quark matter phase is large enough. We also find that the third-generation gravitational-wave detectors can further probe the $i$-mode with intermediate transition pressure. This finding opens a new, interesting direction for probing the existence of quark core inside a neutron star.

On the Maximum Mass of Neutron Stars and GW190814

Abstract Motivated by the recent discovery of a compact object with mass in the range 2.5–2.67 M ⊙ in the binary merger GW190814, we revisit the question of the maximum mass of neutron stars (NSs). We use a Markov Chain Monte Carlo approach to generate about two million phenomenological equations of state with and without first-order phase transitions. We fix the crust equation of state and only assume causality at higher densities. We show how a strict upper bound on the maximum NS mass can be inferred from upcoming observation of NS radii and masses. The derived upper bounds depend only on relativity and causality, so it is not affected by nuclear physics uncertainties. We show how a lower limit on the maximum mass of NSs, in combination with upcoming measurements of NS radii by LIGO/Virgo and NICER, would constrain the equation of state of dense matter. Finally, we discuss the implications for GW190814.

Monte Carlo variations as a tool to assess nuclear physics uncertainties in nucleosynthesis studies

The propagation of uncertainties in reaction cross sections and rates of neutron-, proton-, and α-induced reactions into the final isotopic abundances obtained in nucleosynthesis models is an important issue in studies of nucleosynthesis and Galactic Chemical Evolution. We developed a Monte Carlo method to allow large-scale postprocessing studies of the impact of nuclear uncertainties on nucleosynthesis. Temperature-dependent rate uncertainties combining realistic experimental and theoretical uncertainties are used. From detailed statistical analyses uncertainties in the final abundances are derived as probability density distributions. Furthermore, based on rate and abundance correlations an automated procedure identifies the most important reactions in complex flow patterns from superposition of many zones or tracers. The method already has been applied to a number of nucleosynthesis processes.

Cross-section measurements to low-lying excited final states in the Mg24(α,p)Al*27(γ) reaction as an energy source for x-ray bursts

Energy production in Type Ia x-ray bursts depends on a number of nuclear reactions that become efficient in a hot environment (up to 2 GK). Model sensitivity studies have been performed in an effort to better identify the reactions that have the largest effect, but these efforts are hampered by the high level of complexity of the astrophysical model and large nuclear physics uncertainties. In a recent study, the $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction was found to significantly affect the energy generation in x-ray bursts. This manuscript reports the first study of the $^{24}\mathrm{Mg}(\ensuremath{\alpha},{p}_{1,2}\ensuremath{\gamma})^{27}\mathrm{Al}$ reaction at energies relevant for x-ray bursts. The branches to the $^{27}\mathrm{Al}$ excited states increase to a small degree the estimates of the total astrophysical $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction rate.