Session EG: Nuclear Astrophysics: Stellar and Big Bang Nucleosynthesis

Extracting the scattering parameters from $^3$He-$^4$He elastic scattering using Effective Field Theory

The $^3He(\alpha,\gamma)^7Be$ reaction is one of the prime reaction in Big Bang nucleosynthesis as well as in solar-fusion pp chain. Accurate input for solar-fusion models requires extrapolation of experimental data on this reaction to energies; roughly between 20 to few hundred keV's. Also, the scattering parameters for this reaction affect the shape of extrapolant S(E)[1]. We study the elastic scattering of $^3He$ by $^4He$ in the lab energy range 1.0-5.7 MeV to constrain these parameters. We take $^7Be$ as cluster of $^3He$ and $^4He$ as degrees of freedom. We employ Effective Field Theory(EFT) upto next-to-leading order(NLO) to study s- and p-waves with strong interaction included. The relevant scattering amplitudes are the same as those of the modified effective range expansion upto $O(k^2) (O(k^4))$ in the s(p)-waves. We generate s- and p-wave phase shifts and also fit the cross section to study the impacts of imposing constrains available from $^7$Be bound states and extract s(p) wave effective scattering length(volume) and effective range. [1]Zhang et. al, S-factor and Scattering parameters from $^3He+^4He \rightarrow ^7Be+\gamma$ data. arXiV:1811.07611v1 [nucl-th] [2]Mohr et.al, Phys. Rev. C \textbf{48} 3 (1993) [3]Barnard et.al, Nucl. Phys. \textbf{50} (1984) 640   

Elastic scattering of $^{\mathrm{3}}$He$+\alpha $ with SONIK.

Elastic scattering of $^{\mathrm{3}}$He$+\alpha $ is essential for a theoretical and phenomenological understanding of $^{\mathrm{3}}$He($\alpha $,$\gamma )^{\mathrm{7}}$Be, a key reaction in big bang nucleosynthesis and solar neutrino physics. Elastic scattering data for $^{\mathrm{3}}$He$+\alpha $ can be used in a phenomenological $R$-matrix analysis to extrapolate the $^{\mathrm{3}}$He($\alpha $,$\gamma )^{\mathrm{7}}$Be astrophysical $S$-factor ($S_{\mathrm{34}})$ to solar energies. The flux predictions for $^{\mathrm{7}}$Be and $^{\mathrm{8}}$B solar neutrinos depend critically on $S_{\mathrm{34}}$. Thus, it is important to improve the accuracy and precision of $S_{\mathrm{34}}$ at solar energies. The existing $\alpha (^{\mathrm{3}}$He,$^{\mathrm{3}}$He)$\alpha $ data do not extend to low energies and lack the precision required to constrain the extrapolation of $S_{\mathrm{34}}$ to solar energies. A new measurement of $\alpha (^{\mathrm{3}}$He,$^{\mathrm{3}}$He)$\alpha $ was performed using Scattering of Nuclei in Inverse Kinematics (SONIK) scattering chamber, a windowless, extended gas target surrounded by an array of 30 doubly-collimated silicon charged particle detectors situated at TRIUMF, ISAC-I. The measurement was performed at 9 energies with 0.873$\le E$[$^{\mathrm{3}}$He]$\le $5.462 MeV covering an angular range of 22.5$^{\mathrm{o}}\le \theta_{\mathrm{lab}}\le $135$^{\mathrm{o}}$. Experimental techniques and preliminary results from the experiment will be discussed.   

Measurements of the Astrophysical S Factor of ${ }^{12}C$\textbf{(}$\alpha $\textbf{,}$\gamma $\textbf{)}${ }^{16}{\rm O}$\textbf{Reaction}

E. TSENTALOVICH \textit{MIT-Bates Laboratory,} \textit{E-mail: tsentalovich@bates.mit.edu} A measurement of the astrophysical S factor of ${ }^{12}C$ ($\alpha $,$\gamma ){ }^{16}{\rm O}$ reaction is proposed using the inverse ${ }^{16}{\rm O}(\gamma $,$\alpha ){ }^{12}C$ reaction. The proposed experiment uses electron beam to produce Bremsstrahlung photons and allows an extension of the range of measurements down to $E_{c.m.} =$ 0.6 - 0.7 MeV.   

Constraining Sodium Production in Globular Clusters Using the $^{23}$Na$(^3$He$,d)^{24}$Mg Reaction

Globular clusters consist of hundreds of thousands of stars gravitationally bound in a relatively small radius ($\sim 10$ pc). Over the last few decades, intense observational study has revealed that globular clusters are comprised of multiple stellar populations each with distinct chemical signatures.\footnote{R. Gatton, E. Carretta, A. Bragaglia, \textbf{AAPR} 20, 2012} The star-to-star Na-O anticorrelation is the most pervasive of these so called abundance anomalies, and is theorized to be the result of stellar material undergoing hydrogen burning at $50 \text{-} 100$ MK. Unfortunately, many thermonuclear reaction rates suffer from large uncertainties at these temperatures, thereby limiting our understanding of nucleosynthesis in globular clusters. Among these rates one of the most critical is the sodium destroying reaction $^{23}$Na$(p, \gamma)^{24}$Mg. Using the Enge Split-pole Spectrograph at Triangle Universities Nuclear Laboratory (TUNL), we have measured the transfer reaction $^{23}$Na$(^3$He$,d)^{24}$Mg. Excitation energies, spin-parities, and spectroscopic factors were extracted for states of interest improving our estimates of the $^{23}$Na$(p, \gamma)$ reaction rate, and thus constraining sodium destruction in stellar material.   

Investigation of High-Lying (Alpha, Gamma) Resonances in 22Ne through One-Neutron Transfer in Inverse Kinematics at TIGRESS

In asymptotic giant branch (AGB) stars, 22Ne plays an important role in several nucleosynthesis processes, with its production competing with the synthesis of 19F through the so called `poisoning reaction', and the following transfer into 25Mg acting as the main neutron sources for the heavy element s-process, affecting the reaction rates of numerous isotopes. In this contribution, we discuss a recent neutron transfer experiment done at TRIUMF in November 2018, directly populating 22Ne, allowing for high resolution measurements of the resonance energies with the SHARC silicon detector, coupled to the HPGe detector array TIGRESS for accurate measurement of the characteristic gamma rays. We will then present the method of using the angular distribution of these newly measured gamma rays and protons to determine the spins of the resonance states, allowing for further constraint on the reaction cross-section.   

Alpha-capture reaction rates for $^{22}$Ne($\alpha$,n) and $^{22}$Ne($\alpha$,$\gamma$) via sub-Coulomb $\alpha$-transfer and its effect on final abundances of s-process isotopes.

The $^{22}$Ne($\alpha$,n) reaction is a very important neutron source reaction for the slow neutron capture process (s-process) in asymptotic giant branch stars. Direct measurements are extremely difficult to carry out at Gamow energies due to the extremely small reaction cross section. The large uncertainties introduced when extrapolating direct measurements at high energies down to the Gamow energies can be overcome by determining the partial $\alpha$-width of the relevant states in indirect measurements. This can be done using $\alpha$-transfer reactions at sub-Coulomb energies to reduce the dependence on optical model parameters. The $\alpha$-transfer reaction of $^{22}$Ne($^6$Li,d)$^{26}$Mg was carried out at the Cyclotron Institute at Texas A$\&$M University to study this reaction. It appears that the widths of the near $\alpha$-threshold resonances of $^{26}$Mg are quite different for similar $^{22}$Ne($^6$Li,d) reactions carried out previously using different higher energies. This discrepancy affects the final reaction rate of the $^{22}$Ne($\alpha$,n) reaction, and the rate of the competing $^{22}$Ne($\alpha$,$\gamma$) reaction, thus affecting the final abundances of the s-process isotopes.   

Experimental Challenges for Measuring $^{14}$N$(\alpha , \gamma) ^{18}$F in Inverse Kinematics

Recoils from the $^{14}$N$(\alpha,\gamma)^{18}$F reaction were recently detected for the first time using the St. George recoil mass separator. This reaction is the first in the $^{14}$N$(\alpha,\gamma)^{18}$F$(\beta^+\nu)^{18}$O$(\alpha,\gamma)^{22}$Ne$(\alpha,n)$ chain which produces s-process neutrons in TP-AGB, massive helium burning, and carbon burning stars. Recoil mass separation is a technique to study such reactions in inverse kinematics by detection of the recoil nuclei from these reactions. This is effectively done using a helium gas-jet target (HIPPO), an ion optics transport line which includes a Wien filter velocity selector (St. George), and a time-of-flight vs. energy detection system. The recent characterization of the ion optics and reconstruction of the HIPPO helium gas-jet target have allowed for the first detection of $^{18}$F recoils. The preliminary results of this commissioning experiment and the experimental challenges of using the recoil separator will be presented, along with the ongoing and proposed improvements to HIPPO that will allow future measurements with St. George.   

First detection of $^{18}$F from the $^{14}$N$(\alpha , \gamma)^{18}$F reaction with the St. George recoil mass separator

The St. George recoil mass separator at the University of Notre Dame has successfully observed its first recoils from the reaction $^{14}$N$(\alpha , \gamma)^{18}$F studied in inverse kinematics. The cross section of this reaction contributes to the abundance of $^{22}$Ne which is a neutron source for the s-process in TP-AGB, massive helium burning and carbon burning stars via the $^{22}$Ne$(\alpha , n)^{25}$Mg reaction. The kinematics and cross section of $^{14}$N$(\alpha , \gamma)^{18}$F at low energies make it an ideal candidate for commissioning experiments of St.\ George and the characterization of the focal plane detector. The St. George ion optics separates the $^{14}$N beam and sends the $^{18}$F recoils into a particle identification detection system. The identification uses the time-of-flight versus residual energy approach. The particle identification system was developed for the St.\ George recoil mass separator, in collaboration with Indiana University South Bend. Preliminary results of the first nuclear reaction measured with St.\ George will be presented.