Progress on nuclear reaction rates affecting the stellar production of 26Al

The radioisotope 26Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26Al in these astrophysical objects, including (but not limited to) 25Mg(p, ¿)26Al, 26Al(p, ¿)27Si, and 26Al(n, p/a). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work.Postprint (published version

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Unbound States of \u3csup\u3e32\u3c/sup\u3eCl relevant for Novae

The 31S(p,γ?)32Cl proton-capture reaction is expected to be the dominant breakout pathway of the SiP cycle, which is important for understanding nucleosynthesis in some novae [1]. At novae temperatures, the 31S(p,γ?)32Cl reaction rate is dominated by 31S+p resonances. Discrepancies in the 32Cl resonance energies were reported in previous measurements [1, 2]. We used the 32S(3He,t)32Cl charge-exchange reaction to produce unbound states in 32Cl and determine their excitation energies by detecting tritons at the focal plane of the Enge Spectrograph at the Yale University\u27s Wright Nuclear Structure Laboratory. Proton branching ratios were determined by detecting the decay protons coming from the residual 32Cl states using a silicon array in the spectrometer\u27s target chamber. The improved energy values of excited levels in 32Cl and measurements of the proton-branching ratios should significantly improve our understanding of the 31S(p,γ?)32Cl reaction rate. © Copyright owned by the author(s

Studying the (α, p)-process in X-ray bursts using radioactive ion beams

In type I X-Ray Bursts (XRBs) the nuclear flow is driven towards the proton-drip line by the triple-α reaction, the (α, p)-process, and the rp-process. Along the nucleosynthetic path, the reaction flow can be stopped at so-called waiting-point nuclei. The low Qpγ value of a waiting-point nucleus leads to (p; γ)-(γ, p) equilibrium causing the flow to stall and await a β decay. However, if the temperature is high enough the competing (α, p) reaction can bypass the waiting point. This can have significant effects on the final elemental abundances, energy output, and observables such as double-peaked luminosity profiles. In the intermediate mass region 22Mg, 26Si, 30S, and 34Ar have been identified as possible candidates for waiting-point nuclei in XRBs. A method to study the (α, p)-process on intermediate mass waiting-point nuclei has been developed whereby the time-inverse reaction is studied in inverse kinematics using radioactive ion beams produced by the in-flight method at the ATLAS facility at Argonne National Laboratory. The three reactions p(29P,26Si)a, p(33Cl, 30S)a, and p(37K,34Ar)a have been studied for the first time to determine cross sections for 26Si(α, p) 29P, 30S(α, p)33Cl, and 34Ar(α, p)37K, respectively. The results and future plans will be discussed. © Copyright owned by the author(s)

The \u3csup\u3e33\u3c/sup\u3eS(p,γ)\u3csup\u3e34\u3c/sup\u3eCl reaction in classical nova explosions

The analysis of microscopic grains within primitive meteorites has revealed isotopic ratios largely characteristic of the conditions thought to prevail in various astrophysical environments. Recently, several grains have been identified with isotopic signatures similar to those predicted within the ejecta of nova explosions on oxygen-neon white dwarfs. A possible smoking gun for a grain of nova origin is a large 33S abundance: nucleosynthesis calculations predict as much as 150 times the solar abundance of 33S in the ejecta of oxygen-neon novae. This overproduction factor may, however, vary by factors of at least 0.01 - 3 because of uncertainties in the 33S(p,γ)34Cl reaction rate over nova temperatures. In addition, better knowledge of this rate would help with the interpretation of nova observations over the S-Ca mass region, and contribute towards the firm establishment of a nucleosynthetic endpoint in these phenomena. Finally, constraining this rate may help to finally confirm or rule out the decay of an isomeric state of 34Cl (Ex = 146 keV, t1/2 =32 min) as a source for observable gamma-rays from novae. Direct examinations of the 33S(p,γ)34Cl reaction in the past have only identified resonances down to Er = 434 keV. At nova temperatures, lower-lying resonances could certainly play a dominant role. Several recent, complementary studies dedicated to improving our knowledge of the 33S(p,γ)34Cl rate, using both indirect methods (measurement of the 34S( 3He,t)34Cl and 33S(3He,d) 34Cl reactions with the Munich Q3D spectrograph) and direct methods (in normal kinematics at CENPA, University of Washington, and in inverse kinematics with the DRAGON recoil mass separator at TRIUMF) are presented here. Our results affect predictions of sulphur isotopic ratios in nova ejecta (e.g. 32S/33S) that may be used as diagnostic tools for the nova paternity of grains. © ?Copyright owned by the author(s)

X-ray burst studies with the JENSA gas jet target

When a neutron star accretes hydrogen and helium from the outer layers of its companion star, thermonuclear burning enables the αp-process as a break out mechanism from the hot CNO cycle. Model calculations predict (α, p) reaction rates significantly affect both the light curves and elemental abundances in the burst ashes. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target enables the direct measurement of previously inaccessible (α,p) reactions with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory (NSCL), USA. JENSA is going to be the main target for the Recoil Separator for Capture Reactions (SECAR) at the Facility for Rare Isotope Beams (FRIB). Commissioning of JENSA and first experiments at Oak Ridge National Laboratory (ORNL) showed a highly localized, pure gas target with a density of ∼1019 atoms per square centimeter. Preliminary results are presented from the first direct cross section measurement of the 34Ar(α, p)37 K reaction at NSCL

X-ray Burst Studies with the JENSA Gas Jet Target

When a neutron star accretes hydrogen and helium from the outer layers of its companion star, thermonuclear burning enables the αp-process as a break out mechanism from the hot CNO cycle. Model calculations predict (α, p) reaction rates significantly affect both the light curves and elemental abundances in the burst ashes. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target enables the direct measurement of previously inaccessible (α,p) reactions with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory (NSCL), USA. JENSA is going to be the main target for the Recoil Separator for Capture Reactions (SECAR) at the Facility for Rare Isotope Beams (FRIB). Commissioning of JENSA and first experiments at Oak Ridge National Laboratory (ORNL) showed a highly localized, pure gas target with a density of ∼1019 atoms per square centimeter. Preliminary results are presented from the first direct cross section measurement of the 34Ar(α, p)37 K reaction at NSCL

X-ray burst studies with the JENSA gas jet target

When a neutron star accretes hydrogen and helium from the outer layers of its companion star, thermonuclear burning enables the αp-process as a break out mechanism from the hot CNO cycle. Model calculations predict (α, p) reaction rates significantly affect both the light curves and elemental abundances in the burst ashes. The Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target enables the direct measurement of previously inaccessible (α,p) reactions with radioactive beams provided by the rare isotope re-accelerator ReA3 at the National Superconducting Cyclotron Laboratory (NSCL), USA. JENSA is going to be the main target for the Recoil Separator for Capture Reactions (SECAR) at the Facility for Rare Isotope Beams (FRIB). Commissioning of JENSA and first experiments at Oak Ridge National Laboratory (ORNL) showed a highly localized, pure gas target with a density of ∼1019 atoms per square centimeter. Preliminary results are presented from the first direct cross section measurement of the 34Ar(α, p)37 K reaction at NSCL