The impact of global nuclear mass model uncertainties on rr-process abundance predictions

Rapid neutron capture or `$r$-process' nucleosynthesis may be responsible for half the production of heavy elements above iron on the periodic table. Masses are one of the most important nuclear physics ingredients that go into calculations of $r$-process nucleosynthesis as they enter into the calculations of reaction rates, decay rates, branching ratios and Q-values. We explore the impact of uncertainties in three nuclear mass models on $r$-process abundances by performing global monte carlo simulations. We show that root-mean-square (rms) errors of current mass models are large so that current $r$-process predictions are insufficient in predicting features found in solar residuals and in $r$-process enhanced metal poor stars. We conclude that the reduction of global rms errors below $100$ keV will allow for more robust $r$-process predictions.Comment: 5 pages, 3 figures, invited talk at the 15th International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), to appear in EPJ Web of Conference

THE INFLUENCE OF WATER TEMPERATURE AND FLOW ON YEAR CLASS STRENGTH OF TWAITE SHAD (ALOSA FALLAX FALLAX) FROM THE RIVER SEVERN, ENGLAND.

Year class strength (YCS) was estimated for the 25 year period between 1972 and 1996. The index (YCS) was based on the mean number of six year old female fish caught per tide (1972-1991) in a net fishery at the start of the freshwater phase of their spawning migration, or predicted from juvenile data (1992-1996). The variation in recruitment as measured by the coefficient of variation for the 20 year period (1972 to 1991) was 124.5 %. There was good spawning success in 1976 and 1989 and particularly poor recruitment in the periods 1977 to 1981 and 1985 to 1988. Since 1990 recruitment has remained relatively stable. Water temperature was positively correlated to YCS with mean July temperature explaining the greatest proportion of the variance in YCS (67 %), followed by August (48 %), June (31 %) and October (20 %) ; May and September temperatures did not significantly explain the variation in YCS. Flow in the months June to August were significantly inversely correlated with YCS, with the greatest proportion of the variability explained by August flows (41 %), followed by flows in July (36 %) and June (25 %). Flows in May, September and October were not significantly correlated with YCS. Combining environmental variables in a multiple regression indicated that mean daily temperature between June and August accounted for 77.1 % of the variability in year class strength. The inclusion of flow did not increase significantly the amount of variation explained

The sensitivity of r-process nucleosynthesis to the properties of neutron-rich nuclei

About half of the heavy elements in the Solar System were created by rapid neutron capture, or r-process, nucleosynthesis. In the r-process, heavy elements are built up via a sequence of neutron captures and beta decays in which an intense neutron flux pushes material out towards the neutron drip line. The nuclear network simulations used to test potential astrophysical scenarios for the r-process therefore require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for thousands of nuclei far from stability. Only a small fraction of this data has been experimentally measured. Here we discuss recent sensitivity studies that aim to determine the nuclei whose properties are most crucial for r-process calculations.Comment: 8 pages, 4 figures, submitted to the Proceedings of the Fifth International Conference on Fission and Properties of Neutron-Rich Nuclei (ICFN5

Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios

In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are built up via a sequence of neutron captures and beta decays that involves thousands of nuclei far from stability. Though we understand the basics of how the r-process proceeds, its astrophysical site is still not conclusively known. The nuclear network simulations we use to test potential astrophysical scenarios require nuclear physics data (masses, beta decay lifetimes, neutron capture rates, fission probabilities) for all of the nuclei on the neutron-rich side of the nuclear chart, from the valley of stability to the neutron drip line. Here we discuss recent sensitivity studies that aim to determine which individual pieces of nuclear data are the most crucial for r-process calculations. We consider three types of astrophysical scenarios: a traditional hot r-process, a cold r-process in which the temperature and density drop rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International Nuclear Physics Conference (INPC) 201

VARIATION IN THE AGE AT FIRST SPAWNING OF FEMALE TWAITE SHAD (ALOSA FALLAX FALLAX) FROM THE RIVER SEVERN, ENGLAND.

The mean age of maturity of female Alosa fallax fallax based on annual samples ranged from 4.28 to 5.26 years, with an overall mean ± 95 % CI of 4.80 ± 0.021 years. The mean age at first spawning was determined for the 1973 – 1992 year classes and ranged from 4.41 years to 5.40 years. A significant power relationship existed between the mean age at first spawning and the combined biomass of the 0-2 and 0-3 age groups (P < 0.05), explaining 40.7 % and 31.6 % of the variability in the age at which a year class matures. The relationship between maturity and biomass indicates that the onset of maturity was related to density-dependent processes and fish, that matured early had significantly faster growth rates compared to those that matured later (P < 0.05). The findings suggest that the immature fish at sea congregate in a fairly restricted area where it is likely that the older year classes impact younger ones. The fact that the relationship between maturity and the biomass of various components of the stock breaks down after the age of four may relate to the onset of maturity, as the mature fish enter the rivers to spawn and are effectively isolated from the main population

Isomerization Mechanism in Hydrazone-Based Rotary Switches: Lateral Shift, Rotation, or Tautomerization?

Two intramolecularly hydrogen-bonded arylhydrazone (aryl = phenyl or naphthyl) molecular switches have been synthesized, and their full and reversible switching between the E and Z configurations have been demonstrated. These chemically controlled configurational rotary switches exist primarily as the E isomer at equilibrium and can be switched to the protonated Z configuration (Z-H^+) by the addition of trifluoroacetic acid. The protonation of the pyridine moiety in the switch induces a rotation around the hydrazone C═N double bond, leading to isomerization. Treating Z-H^+ with base (K_(2)CO_3) yields a mixture of E and “metastable” Z isomers. The latter thermally equilibrates to reinstate the initial isomer ratio. The rate of the Z → E isomerization process showed small changes as a function of solvent polarity, indicating that the isomerization might be going through the inversion mechanism (nonpolar transition state). However, the plot of the logarithm of the rate constant k vs the Dimroth parameter (E_T) gave a linear fit, demonstrating the involvement of a polar transition state (rotation mechanism). These two seemingly contradicting kinetic data were not enough to determine whether the isomerization mechanism goes through the rotation or inversion pathways. The highly negative entropy values obtained for both the forward (E → Z-H^+) and backward (Z → E) processes strongly suggest that the isomerization involves a polarized transition state that is highly organized (possibly involving a high degree of solvent organization), and hence it proceeds via a rotation mechanism as opposed to inversion. Computations of the Z ↔ E isomerization using density functional theory (DFT) at the M06/cc-pVTZ level and natural bond orbital (NBO) wave function analyses have shown that the favorable isomerization mechanism in these hydrogen-bonded systems is hydrazone–azo tautomerization followed by rotation around a C–N single bond, as opposed to the more common rotation mechanism around the C═N double bond

The impact of nuclear masses near N=82N=82 on rr-process abundances

We have performed for the first time a complete $r$-process mass sensitivity study in the $N=82$ region. We take into account how an uncertainty in a single nuclear mass propagates to influence important quantities of neighboring nuclei, including Q-values and reaction rates. We demonstrate that nuclear mass uncertainties of $\pm0.5$ MeV in the $N=82$ region result in up to an order of magnitude local change in $r$-process abundance predictions. We identify key nuclei in the study whose mass has a substantial impact on final $r$-process abundances and could be measured at future radioactive beam facilities.Comment: 7 pages, 3 figures, submitte