Multi-channel R-matrix analysis of CNO cycle reactions

The CNO cycle is the main process for hydrogen burning in stars somewhat more massive than the Sun. The reaction cross sections at Gamow energies are typically in the femto to pico-barn range and are consequently very difficult to measure experimentally. The CNO reaction rates are based on extrapolations of experimental data from higher energies. We are developing a multi-channel R-matrix code (AZURE) to provide a new and more comprehensive tool for fitting experimental data and making extrapolations to lower energies in all reaction and scattering channels. The 14N(p,γ )15O reaction is the slowest reaction of the CNO cycle and thus it determines the energy production rate of CNO burning. Furthermore, this reaction plays an important role in the determination of Globular Cluster age, since the position of the turnoff point, at which the GC stars escape from the Main Sequence, is powered by the onset of the CNO burning, whose bottleneck is the 14N(p, γ )15O. We have made a reanalysis of the most recent experimental data on the ground state and the 6.18 MeV transitions. The ratio of the cross sections of the 15N(p, γ )16O and 15N(p,α)12C reactions determines how much catalytic material passes to higher CNO cycles and has an effect on the production of heavier elements, particularly 16O and 17O. Simultaneous analysis of both reactions for all channels suggests that the ratio σγ/σα is smaller than previously reported

Measurement of the resonance at ER=1422 keV in Ar36(p,γ)37K

A new resonance at ER=1422 keV has been found in the reaction Ar36(p,γ)37K. From its measured resonance strength of ωγ=(6.0±1.5)×10-4 eV the proton partial width Γp can be calculated. Our data suggest a value of Γγ/Γp40 for the ratio of γ to proton partial width for the corresponding state at Ex=3241 keV in K37. We find that the corrected distribution of Gamow-Teller strength below the isobaric analog state as obtained from the β-delayed proton decay of Ca37 is in agreement with the results inferred from the Cl37(p,n)37Ar reaction

Uncertainty contributions to low-flow projections in Austria

The main objective of the paper is to understand the contributions to the uncertainty in low-flow projections resulting from hydrological model uncertainty and climate projection uncertainty. Model uncertainty is quantified by different parameterisations of a conceptual semi-distributed hydrologic model (TUWmodel) using 11 objective functions in three different decades (1976–1986, 1987–1997, 1998–2008), which allows for disentangling the effect of the objective function-related uncertainty and temporal stability of model parameters. Climate projection uncertainty is quantified by four future climate scenarios (ECHAM5-A1B, A2, B1 and HADCM3-A1B) using a delta change approach. The approach is tested for 262 basins in Austria. The results indicate that the seasonality of the low-flow regime is an important factor affecting the performance of model calibration in the reference period and the uncertainty of Q95 low-flow projections in the future period. In Austria, the range of simulated Q95 in the reference period is larger in basins with a summer low-flow regime than in basins with a winter low-flow regime. The accuracy of simulated Q95 may result in a range of up to 60 % depending on the decade used for calibration. The low-flow projections of Q95 show an increase of low flows in the Alps, typically in the range of 10–30 % and a decrease in the south-eastern part of Austria mostly in the range −5 to −20 % for the climate change projected for the future period 2021–2050, relative the reference period 1978–2007. The change in seasonality varies between scenarios, but there is a tendency for earlier low flows in the northern Alps and later low flows in eastern Austria. The total uncertainty of Q95 projections is the largest in basins with a winter low-flow regime and, in some basins the range of Q95 projections exceeds 60 %. In basins with summer low flows, the total uncertainty is mostly less than 20 %. The ANOVA assessment of the relative contribution of the three main variance components (i.e. climate scenario, decade used for model calibration and calibration variant representing different objective function) to the low-flow projection uncertainty shows that in basins with summer low flows climate scenarios contribute more than 75 % to the total projection uncertainty. In basins with a winter low-flow regime, the median contribution of climate scenario, decade and objective function is 29, 13 and 13 %, respectively. The implications of the uncertainties identified in this paper for water resource management are discussed

Integrated impact modelling of climate change and adaptation policies on land use and water resources in Austria"

Climate change is a major driver of land use and ecosystems. Changes in climatic conditions will affect the quality and quantity of water resources. Autonomous adaptation by farmers can influence the compliance with the good ecological and chemical status according to the EU Water Framework Directive. We present results from an integrated impact modelling framework (IIMF) to analyze policy options for planned adaptation in agricultural land use and sustainable management of land and water resources until 2040. The IIMF consists of the bio-physical process model EPIC, the regional land use optimization model PASMA[grid], the quantitative precipitation/runoff TUW model, and the surface water emission model MONERIS. Stakeholder driven scenarios facilitate multi-actor knowledge transfer. Climate change scenarios are combined with socio-economic and policy pathways. The latter include water protection measures on fertilization management, soil and crop rotation management. The results show that the selected climate change and policy scenarios impact average agricultural gross margins by ±2%. However, regional impacts are more severe particularly under assumptions of decreasing precipitation patterns. The water protection policies can alleviate pressures compared to the business as usual scenario but do not lead to sufficient conditions in all watersheds. To conclude, the IIMF is able to capture the interfaces between water quality and land use and to cover multiple policy and climate scenarios. However, despite efforts to increase the robustness of data and model interfaces, uncertainties need to be tackled in subsequent studies

Measurement of 25Mg(p; gamma)26Al resonance strengths via gamma spectrometry

The COMPTEL instrument performed the first mapping of the 1.809 MeV photons in the Galaxy, triggering considerable interest in determing the sources of interstellar 26Al. The predicted 26Al is too low compared to the observation, for a better understanding more accurate rates for the 25Mg(p; gamma)26Al reaction are required. The 25Mg(p;gamma)26Al reaction has been investigated at the resonances at Er= 745; 418; 374; 304 keV at Ruhr-Universitat-Bochum using a Tandem accelerator and a 4piNaI detector. In addition the resonance at Er = 189 keV has been measured deep underground laboratory at Laboratori Nazionali del Gran Sasso, exploiting the strong suppression of cosmic background. This low resonance has been studied with the 400 kV LUNA accelerator and a HPGe detector. The preliminary results of the resonance strengths will be reported.Comment: Accepted for publication in Journal of Physics

The multifaith campus: Transforming colleges and universities for spiritual engagement

Dafina Lazarus Stewart, Michael M. Kocet, and Sharon Lobdell explore what college and university campuses would look like if transformed to promote and sustain religious and secular pluralism and interfaith cooperation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83741/1/20049_ftp.pd

The Cross Section of 3He(3He,2p)4He measured at Solar Energies

We report on the results of the \hethet\ experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak ($E_{\rm 0}$=22 keV). The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the \hethet\ reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted $S_{\rm b}(E_{\rm 0})$ value for bare nuclides (=5.40 MeV b).Comment: 18 pages, 10 postscript figures, Calculations concerning hypothetical resonanz added, Submitted to Phys. Rev. C., available at this URL: HTTP://www.lngs.infn.it/lngs/htexts/luna/luna.htm

Constraining the S factor of 15N(p,g)16O at Astrophysical Energies

The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338 <Ep < 1028 keV) can dramatically effect the extrapolation to energies of astrophysical interest. To facilitate a reliable extrapolation the 15N(p,g)16O reaction has been remeasured covering the energy range from Ep=1800 keV down to 130 keV. The results have been analyzed in the framework of a multi-level R-matrix theory and a S(0) value of 39.6 keV b has been found.Comment: 15 pages, 9 figure

First measurement of the 14N(p,gamma)15O cross section down to 70 keV

In stars with temperatures above 20*10^6 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p,gamma)15O reaction. Deep underground in Italy's Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4pi BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90 - 300 *10^6 K, for the first time with negligible impact from extrapolations

Theoretical Evaluation of the Reaction Rates for 26Al(n,p)26Mg and 26Al(n,a)23Na

The reactions that destroy 26Al in massive stars have significance in a number of astrophysical contexts. We evaluate the reaction rates of 26Al(n,p)26Mg and 26Al(n,a)23Na using cross sections obtained from the codes EMPIRE and TALYS. These have been compared to the published rates obtained from the non-smoker code and to some experimental data. We show that the results obtained from EMPIRE and TALYS are comparable to those from non-smoker. We also show how the theoretical results vary with respect to changes in the input parameters. Finally, we present recommended rates for these reactions using the available experimental data and our new theoretical results