Experimental study of Ar 38 +α reaction cross sections relevant to the Ca 41 abundance in the solar system

In massive stars, the Ca41(n,α)Ar38 and K41(p,α)Ar38 reactions have been identified as the key reactions governing the abundance of Ca41, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the Ca41(n,α)Ar38 reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse Ar38(α,n)Ca41 and Ar38(α,p)K41 reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV Ar38 beam and He4 as the active-gas target. Both excitation functions were measured simultaneously in the energy range of 6.8≤Ec.m.≤9.3 MeV. Using detailed balance the Ca41(n,α)Ar38 and K41(p,α)Ar38 reaction rates were determined, which suggested a 20% increase in the Ca41 yield from massive stars

The First Magnetic Fields

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars is discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early generation of stars or active galactic nuclei can be dispersed into the intergalactic medium.Comment: Accepted for publication in Space Science Reviews. Pdf can be also downloaded from http://canopus.cnu.ac.kr/ryu/cosmic-mag1.pd

Reaction rate for carbon burning in massive stars

Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5-4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate

Study of the Alm 26 (d,p) Al 27 Reaction and the Influence of the Al 26 0+ Isomer on the Destruction of Al 26 in the Galaxy

The existence of Al26 (t1/2=7.17×105 yr) in the interstellar medium provides a direct confirmation of ongoing nucleosynthesis in the Galaxy. The presence of a low-lying 0+ isomer (Al26m), however, severely complicates the astrophysical calculations. We present for the first time a study of the Al26m(d,p)Al27 reaction using an isomeric Al26 beam. The selectivity of this reaction allowed the study of â.,"=0 transfers to T=1/2, and T=3/2 states in Al27. Mirror symmetry arguments were then used to constrain the Al26m(p,γ)Si27 reaction rate and provide an experimentally determined upper limit of the rate for the destruction of isomeric Al26 via radiative proton capture reactions, which is expected to dominate the destruction path of Al26m in asymptotic giant branch stars, classical novae, and core collapse supernovae

Probing the Single-Particle Character of Rotational States in F 19 Using a Short-Lived Isomeric Beam

A beam containing a substantial component of both the Jπ=5+, T1/2=162 ns isomeric state of F18 and its 1+, 109.77-min ground state is utilized to study members of the ground-state rotational band in F19 through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2+ band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei

How well do we understand the reaction rate of C burning?

Carbon burning plays a crucial role in stellar evolution, where this reaction is an important route for the production of heavier elements. A particle-γ coincidence technique that minimizes the backgrounds to which this reaction is subject and provides reliable cross sections has been used at the Argonne National Laboratory to measure fusion cross-sections at deep sub-barrier energies in the 12C+12C system. The corresponding excitation function has been extracted down to a cross section of about 6 nb. This indicates the existence of a broad S-factor maximum for this system. Experimental results are presented and discussed

Reaction rate for carbon burning in massive stars

Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5-4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries