Three-Dimensional Structure of the Corona During WHPI Campaign Rotations CR-2219 and CR-2223

Differential emission measure tomography (DEMT) and white light (WL) tomography were applied to study the three-dimensional (3D) structure of the global solar corona for two Whole Heliosphere and Planetary Interactions campaign periods, Carrington rotations 2219 and 2223. With DEMT, Solar Dynamics Observatory/Atmospheric Imaging Assembly images were used to reconstruct the 3D coronal electron density and temperature in the range of heliocentric distance 1.02–1.25 R⊙. With WL tomography, Solar and Heliospheric Observatory/Large Angle and Spectrometric COronagraph-C2 images were used to reconstruct the 3D electron density in the range of heliocentric distance 2.5–6.0 R⊙. The two periods were also simulated with the 3D-magneto-hydrodynamic Alfvén Wave Solar Model (AWSoM), and its results compared in detail with the reconstructions. The DEMT analysis reveals a 20% less dense and 20% hotter corona than for rotations corresponding to the solar cycle 23/24 deep minimum. The electron density and temperature of the AWSoM model agree with DEMT results within 10% and 20%, respectively, while its electron density overestimates results of WL tomography up to 75%. The slow (fast) component of the terminal wind speed of the model is found to be associated with field lines characterized by larger (smaller) values of the tomographic density and temperature at the coronal base. DEMT reconstructions reveal the coronal plasma to be ubiquitously characterized by temperature variability of up to ≈45% over spatial scales of order ∼104 km. Taking into account this level of fine-structure by global models may be consequential for their predictions on wave propagation in the corona.Key PointsTomographic analysis of Whole Heliosphere and Planetary Interactions rotations indicate a corona 20% less dense and 20% hotter compared to rotations of the SC 23/24 solar minimumThe model density and temperature agree with extreme ultraviolet tomography results within 20% and overestimates up to 75% the density from white light tomographyThe wind model slow/fast component is associated with field lines characterized by larger/lower tomographic electron density and temperaturePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172932/1/jgra57223.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172932/2/jgra57223_am.pd

Three‐Dimensional Structure of the Corona During WHPI Campaign Rotations CR‐2219 and CR‐2223

International audienceDifferential emission measure tomography (DEMT) and white light (WL) tomography were applied to study the three‐dimensional (3D) structure of the global solar corona for two Whole Heliosphere and Planetary Interactions campaign periods, Carrington rotations 2219 and 2223. With DEMT, Solar Dynamics Observatory/Atmospheric Imaging Assembly images were used to reconstruct the 3D coronal electron density and temperature in the range of heliocentric distance 1.02–1.25 R ⊙ . With WL tomography, Solar and Heliospheric Observatory/Large Angle and Spectrometric COronagraph‐C2 images were used to reconstruct the 3D electron density in the range of heliocentric distance 2.5–6.0 R ⊙ . The two periods were also simulated with the 3D‐magneto‐hydrodynamic Alfvén Wave Solar Model (AWSoM), and its results compared in detail with the reconstructions. The DEMT analysis reveals a 20% less dense and 20% hotter corona than for rotations corresponding to the solar cycle 23/24 deep minimum. The electron density and temperature of the AWSoM model agree with DEMT results within 10% and 20%, respectively, while its electron density overestimates results of WL tomography up to 75%. The slow (fast) component of the terminal wind speed of the model is found to be associated with field lines characterized by larger (smaller) values of the tomographic density and temperature at the coronal base. DEMT reconstructions reveal the coronal plasma to be ubiquitously characterized by temperature variability of up to ≈45% over spatial scales of order ∼10 4 km. Taking into account this level of fine‐structure by global models may be consequential for their predictions on wave propagation in the corona

Beyond the acceptance limit of DRAGON: The case of the 6Li(α,γ)10B^6Li(\alpha,\gamma )^{10}B reaction

Radiative capture reactions play a pivotal role for our understanding of the origin of the elements in the cosmos. Recoil separators provide an effective way to study these reactions, in inverse kinematics, and take advantage of the use of radioactive ion beams. However, a limiting factor in the study of radiative capture reactions in inverse kinematics is the momentum spread of the product nuclei, which can result in an angular spread larger than the geometric acceptance of the separator. The DRAGON facility at TRIUMF is a versatile recoil separator, designed to study radiative capture reactions relevant to astrophysics in the A ∼ 10–30 region. In this work we present the first attempt to study with DRAGON a reaction, 6 Li( α,γ ) 10 B, for which the recoil angular spread exceeds DRAGON’s acceptance. Our result is in good agreement with the literature value, showing that DRAGON can measure resonance strengths of astrophysically important reactions even when not all the recoils enter the separator

Radiative Alpha Capture on 7Be with DRAGON at Energies Relevant to the \varvec{\nu } p-Process

International audienceThe origin of the p-nuclei, has been a long-standing puzzle in nuclear astrophysics. The $\nu$ p-process is a candidate for the production of the light p-nuclei, but it presents high sensitivity to both supernova dynamics and nuclear physics. It has been recently shown that the breakout from pp-chains through the$^{7}$Be $(\alpha ,\gamma )^{11}$C reaction, which occurs prior to $\nu$ p-process, can significantly influence the reaction flow, and subsequently the production of p-nuclei in the $90<{\text {A}}<110$ region. Nevertheless, this reaction has not been studied well yet in the relevant temperature range - T = 1.5–3 GK. To that end, the first direct study of important resonances of the$^{7}$Be $(\alpha ,\gamma )^{11}$C reaction with unknown strengths using DRAGON was recently performed at TRIUMF. The reaction was studied in inverse kinematics using a radioactive$^{7}$Be (t$_{1/2}$  = 53.24 d) beam provided by ISAC-I and two resonances above the$^{11}$C $\alpha$ -separation energy - Q$_{\alpha } = 7543.62$  keV - were measured. The experimental details, in particular how the recoil transmission and BGO efficiencies were accounted for considering the large cone angle for this reaction, will be presented and discussed alongside some preliminary results

Energy Acceptance of the St. George Recoil Separator

Radiative alpha-capture, (α,γ) , reactions play a critical role in nucleosynthesis and nuclear energy generation in a variety of astrophysical environments. The St. George recoil separator at the University of Notre Dame's Nuclear Science Laboratory was developed to measure (α,γ) reactions in inverse kinematics via recoil detection in order to obtain nuclear reaction cross sections at the low energies of astrophysical interest, while avoiding the γ -background that plagues traditional measurement techniques. Due to the γ ray produced by the nuclear reaction at the target location, recoil nuclei are produced with a variety of energies and angles, all of which must be accepted by St. George in order to accurately determine the reaction cross section. We demonstrate the energy acceptance of the St. George recoil separator using primary beams of helium, hydrogen, neon, and oxygen, spanning the magnetic and electric rigidity phase space populated by recoils of anticipated (α,γ) reaction measurements. We find the performance of St. George meets the design specifications, demonstrating its suitability for (α,γ) reaction measurements of astrophysical interest

Experimental measurement of the 12C+16O fusion cross sections at astrophysical energies

The total cross sections of the 12C+16O fusion have been experimentally determined at low energies to investigate the role of this reaction during late stellar evolution burning phases. A high-intensity oxygen beam was produced by the 5MV pelletron accelerator at the University of Notre Dame impinging on a thick ultra-pure graphite target. Protons and γ-rays were measured simultaneously in the center-of-mass energy range from 3.64 to 5.01 MeV, using strip silicon and HPGe detectors. Statistical model calculations were employed to interpret the experimental results. A new broad resonance-like structure is observed for the 12C+16O reaction, and a decreasing trend of its S-factor towards low energies is found

Experimental measurement of the

The total cross sections of the 12C+16O fusion have been experimentally determined at low energies to investigate the role of this reaction during late stellar evolution burning phases. A high-intensity oxygen beam was produced by the 5MV pelletron accelerator at the University of Notre Dame impinging on a thick ultra-pure graphite target. Protons and γ-rays were measured simultaneously in the center-of-mass energy range from 3.64 to 5.01 MeV, using strip silicon and HPGe detectors. Statistical model calculations were employed to interpret the experimental results. A new broad resonance-like structure is observed for the 12C+16O reaction, and a decreasing trend of its S-factor towards low energies is found

Precision half-life measurement of 11C^{11}\mathrm{C}: The most precise mirror transition Ft\mathcal{F}t value

Background: The precise determination of the Ft value in T=1/2 mixed mirror decays is an important avenue for testing the standard model of the electroweak interaction through the determination of Vud in nuclear β decays. C11 is an interesting case, as its low mass and small QEC value make it particularly sensitive to violations of the conserved vector current hypothesis. The present dominant source of uncertainty in the C11Ft value is the half-life. Purpose: A high-precision measurement of the C11 half-life was performed, and a new world average half-life was calculated. Method: C11 was created by transfer reactions and separated using the TwinSol facility at the Nuclear Science Laboratory at the University of Notre Dame. It was then implanted into a tantalum foil, and β counting was used to determine the half-life. Results: The new half-life, t1/2=1220.27(26) s, is consistent with the previous values but significantly more precise. A new world average was calculated, t1/2world=1220.41(32) s, and a new estimate for the Gamow-Teller to Fermi mixing ratio ρ is presented along with standard model correlation parameters. Conclusions: The new C11 world average half-life allows the calculation of a Ftmirror value that is now the most precise value for all superallowed mixed mirror transitions. This gives a strong impetus for an experimental determination of ρ, to allow for the determination of Vud from this decay