Nucleosynthesis of Nickel-56 from Gamma-Ray Burst Accretion Disks

We examine the prospects for producing Nickel-56 from black hole accretion disks, by examining a range of steady state disk models. We focus on relatively slowly accreting disks in the range of 0.05 - 1 solar masses per second, as are thought to be appropriate for the central engines of long-duration gamma-ray bursts. We find that significant amounts of Nickel-56 are produced over a wide range of parameter space. We discuss the influence of entropy, outflow timescale and initial disk position on mass fraction of Nickel-56 which is produced. We keep careful track of the weak interactions to ensure reliable calculations of the electron fraction, and discuss the role of the neutrinos.Comment: 10 pages, 9 figure

Explosive Nucleosynthesis of Weak r-Process Elements in Extremely Metal-Poor Core-Collapse Supernovae

There have been attempts to fit the abundance patterns of extremely metal-poor stars with supernova nucleosynthesis models for the lighter elements than Zn. On the other hand, observations have revealed that the presence of EMP stars with peculiarly high ratio of "weak r-process elements" Sr, Y and Zr. Although several possible processes were suggested for the origin of these elements, the complete solution for reproducing those ratios is not found yet. In order to reproduce the abundance patterns of such stars, we investigate a model with neutron rich matter ejection from the inner region of the conventional mass-cut. We find that explosive nucleosynthesis in a high energy supernova (or "hypernova") can reproduce the high abundances of Sr, Y and Zr but that the enhancements of Sr, Y and Zr are not achieved by nucleosynthesis in a normal supernova. Our results imply that, if these elements are ejected from a normal supernova, nucleosynthesis in higher entropy flow than that of the supernova shock is required.Comment: 27pages, 15figures; ApJ accepte

Estimates of Stellar Weak Interaction Rates for Nuclei in the Mass Range A=65-80

We estimate lepton capture and emission rates, as well as neutrino energy loss rates, for nuclei in the mass range A=65-80. These rates are calculated on a temperature/density grid appropriate for a wide range of astrophysical applications including simulations of late time stellar evolution and x-ray bursts. The basic inputs in our single particle and empirically inspired model are i) experimentally measured level and weak decay information, ii) estimates of matrix elements for allowed experimentally-unmeasured transitions based on the systematics of experimentally observed allowed transitions, and iii) estimates of the centroids of the GT resonances motivated by shell model calculations in the fp shell as well as by (n,p) and (p,n) experiments. Transitions involving Fermi resonances (isobaric analog states) are also included and dominate the rates for many interesting proton rich nuclei for which an experimentally-determined ground state lifetime is unavailable. To compare our results with more detailed shell model based calculations we also calculate weak rates for nuclei in the mass range A=60-65 for which Langanke and Martinez-Pinedo have provided rates. The typical deviation in the electron capture and B- decay rates for these ~30 nuclei is less than a factor of two or three for a wide range of temperature and density appropriate for pre-supernova stellar evolution. We also discuss some subtleties associated with the partition functions used in calculations of stellar weak rates and show that the proper treatment of the partition functions is essential for estimating high temperature beta decay rates. Partition functions based on un-converged Lanczos calculations can result in estimates of high temperature beta decay rates that are systematically low.Comment: Tables of rates for nuclei in the mass range A=66-110 are available from J. Prue

Prospects for obtaining an r-process from Gamma Ray Burst Disk Winds

We discuss the possibility that r-process nucleosynthesis may occur in the winds from gamma ray burst accretion disks. This can happen if the temperature of the disk is sufficiently high that electron antineutrinos are trapped as well as neutrinos. This implies accretion disks with greater than a solar mass per second accretion rate, although lower accretion rates with higher black hole spin parameters may provide viable environments as well. Additionally, the outflow from the disk must either have relatively low entropy, e.g. around s = 10, or the initial acceleration of the wind must be slow enough that it is neutrino and antineutrino capture as opposed to electron and positron capture that sets the electron fraction.Comment: 8 pages, submitted to Nucl. Phys. A as part of the Nuclei in Cosmos 8 proceeding

On the Contribution of Gamma Ray Bursts to the Galactic Inventory of Some Intermediate Mass Nuclei

Light curves from a growing number of Gamma Ray Bursts (GRBs) indicate that GRBs copiously produce radioactive Ni moving outward at fractions of the speed of light. We calculate nuclear abundances of elements accompanying the outflowing Ni under the assumption that this Ni originates from a wind blown off of a viscous accretion disk. We also show that GRB's likely contribute appreciably to the galactic inventory of 42Ca, 45Sc, 46Ti, 49Ti, 63Cu, and may be a principal site for the production of 64Zn.Comment: 11 pages, 1 figur

Learning IoT without the "I" - Educational Internet of Things in a Developing Context

To provide better education to children from different socio-economic backgrounds, the Thai Government launched the "One Tablet PC Per Child" (OTPC) policy and distributed 800,000 tablet computers to first grade students across the country in 2012. This initiative is an opportunity to study how mobile learning and Internet of Things (IoT) technology can be designed for students in underprivileged areas of northern Thailand. In this position paper, we present a prototype, called OBSY (Observation Learning System) which targets primary science education. OBSY consists of i) a sensor device, developed with low-cost open source singled-board computer Raspberry Pi, housed in a 3D printed case, ii) a mobile device friendly graphical interface displaying visualisations of the sensor data, iii) a self-contained DIY Wi-Fi network which allows the system to operate in an environment with inadequate ICT infrastructure

Nucleosynthesis in High-Entropy Hot-Bubbles of SNe and Abundance Patterns of Extremely Metal-Poor Stars

There have been suggestions that the abundance of Extremely Metal-Poor (EMP) stars can be reproduced by Hypernovae (HNe), not by normal supernovae (SNe). However, recently it was also suggested that if the innermost neutron-rich or proton-rich matter is ejected, the abundance patterns of ejected matter are changed, and normal SNe may also reproduce the observations of EMP stars. In this letter, we calculate explosive nucleosynthesis with various Ye and entropy, and investigate whether normal SNe with this innermost matter, which we call "hot-bubble" component, can reproduce the abundance of EMP stars. We find that neutron-rich (Ye = 0.45-0.49) and proton-rich (Ye = 0.51-0.55) matter can increase Zn/Fe and Co/Fe ratios as observed, but tend to overproduce other Fe-peak elements. In addition to it, we find that if slightly proton-rich matter with 0.50 <= Ye < 0.501 with s/kb ~ 15-40 is ejected as much as ~ 0.06 Msolar, even normal SNe can reproduce the abundance of EMP stars, though it requires fine-tuning of Ye. On the other hand, HNe can more easily reproduce the observations of EMP stars without fine-tuning. Our results imply that HNe are the most possible origin of the abundance pattern of EMP stars.Comment: 10 pages, 3 figures, Accepted to ApJL; modified reference

Event-by-event study of prompt neutrons from 239Pu(n,f)

Employing a recently developed Monte Carlo model, we study the fission of 240Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies up to 2 MeV.Comment: 17 pages, 20 figure