Session B1: Nuclear Astrophysics II

Further Exploration of the $^{33}$S($\alpha $,p)$^{36}$Cl Reaction Cross Section

Short-lived radionuclides (SLRs) are extant from the Early Solar System (ESS) and useful for dating products of ESS processes. The SLR $^{36}$Cl was potentially produced by solar energetic particles incident on gas and dust in the protoplanetary disk. Measurement of the cross section of the reaction $^{33}$S($\alpha $,p)$^{36}$Cl, which contributes significantly to the abundance of $^{36}$Cl, is an important input in solar irradiation models regarding the determination of elemental abundances, and is thus of great interest. In a previous measurement performed by Bowers et al. (2013), the cross section of this reaction was studied using a combination of activation of a $^{4}$He gas cell and analyzing the produced $^{36}$Cl via Accelerator Mass Spectrometry (AMS) over an energy range of 0.7 -- 2.42 MeV/A. The result of this measurement was a significantly higher yield of $^{36}$Cl than predicted by Hauser-Feshbach cross section calculations. In light of the paper by Mohr (2013), the same activation was repeated at the University of Notre Dame at intermediate energies to study the cross section further, using the same combination of activation and AMS. The results of this measurement will be presented.   

Low Energy $^{\mathrm{20}}$Ne(p,$\gamma )^{\mathrm{21}}$Na Direct Capture Cross-Section Measurement

In stars whose stellar temperatures is greater than 0.05GK, hydrogen burning can proceed via the NeNa cycle. This cycle contributes to the synthesis of Ne, Na, and Mg isotopes. Direct capture and the high energy tail of a subthreshold resonance dominate the stellar reaction rate for $^{\mathrm{20}}$Ne(p,$\gamma )^{\mathrm{21}}$Na, which is the first reaction in the NeNa cycle[1]. A recent study of the low-energy direct capture cross-section was performed at the University of Notre Dame using the 5MV accelerator and the newly refurbished Rhinoceros extended gas target [2]. Preliminary results from this campaign will be presented and discussed. [1] C. Rolfs et al., Nuclear Physics A241, 480 (1975). [2] C. Rolfs et al., NIM 157, 19 (1978).   

Measurement of the $^{\mathrm{1}}$H($^{\mathrm{17}}$F, $\alpha )^{\mathrm{14}}$O cross section at TWINSOL

The $^{\mathrm{14}}$O($\alpha $, p)$^{\mathrm{17}}$F reaction is one of the main probable breakout routes, which lead to the rp-process from the hot-CNO cycle, converting the initial CNO elements into heavier elements. Although many indirect measurements have been done to determine the resonant rates of this reaction, reaction rates can be incorrect by orders of magnitude by utilizing different methods. Furthermore, there is short of directly measured cross section data at the energy of astrophysical interest. The $^{\mathrm{1}}$H($^{\mathrm{17}}$F, $\alpha )^{\mathrm{14}}$O reaction, the time-inverse of the $^{\mathrm{14}}$O($\alpha $, p)$^{\mathrm{17}}$F$_{\mathrm{g.s.}}$ reaction, will be studied using a radioactive $^{\mathrm{17}}$F beam at TWINSOL. The (p, $\alpha )$ reaction cross sections will be measured over the energy range of interest for X-ray bursts. Finally, the $^{\mathrm{14}}$O($\alpha $, p)$^{\mathrm{17}}$F$_{\mathrm{g.s.}}$ reaction can be determined from detailed balance. This talk will introduce the preparations for the coming experiment.   

Timing Resolution and Detection Efficiency of the St. George Detector System

The St. George recoil mass separator at the University of Notre Dame will be used to study $(\alpha,\gamma)$ reactions of astrophysical interest. A detection system was developed for the St. George recoil mass separator, in collaboration with Indiana University South Bend, that will utilize energy and time-of-flight to separate reaction products from residual unreacted beam particles. The detection system utilizes uses two microchannel plate (MCP) detectors, which register timing measurements, and a silicon strip detector is used to measure the ion’s kinetic energy. The performance of the detection system will be presented.   

The Design of SSNAP a Solenoid Spectrometer for Use with TwinSol

Nucleon transfer reactions can be used to elucidate many nuclear astrophysics processes. By carrying out and observing these reactions in a laboratory environment our understanding of these processes can be improved. The Solenoid Spectrometer for Nuclear AstroPhysics (SSNAP) is a new helical orbit spectrometer being designed at the University of Notre Dame. Designed around a strip of on-axis position sensitive silicon detectors along the length of the second TwinSol solenoid; SSNAP will be sensitive to the charged light ions produced in these reactions. Through the detection and measurement of these charged light ions the properties of the heavy residual nuclei can be understood. The current progress in the design and of simulations will be presented. This research was supported by the National Science Foundation.   

Studying a Potential Calibration Reaction for NIF

Measurements have been made for the reaction $^{\mathrm{10}}$B(p,$\gamma )^{\mathrm{11}}$C. Investigating this is the first step in utilizing the reaction $^{\mathrm{10}}$B(p,$\alpha )^{\mathrm{7}}$Be as a potential calibration for the National Ignition Facility (NIF). NIF is able to create conditions within the same temperature range that exist during hydrogen burning in a star, a process by which nucleosynthesis occurs. Be-7 has a half-life of 53.2 days, long enough to gather and study before it decays but short enough to have decayed in several months, which makes its reaction a suitable candidate for calibration. There is a 10 keV resonance that dominates the low energy cross section of both $^{\mathrm{10}}$B(p,$\alpha )^{\mathrm{7}}$Be and the ground state $^{\mathrm{10}}$B(p,$\gamma )^{\mathrm{11}}$C. In addition, a higher energy resonance at 600 keV is shared by both reactions. The two resonances interfere, as they have the same spin-parity 5/2$+$, and their levels are not constrained enough by data to allow for reliable extrapolation to the lower energies that correspond to the temperature range of NIF. The measurement of $^{\mathrm{10}}$B(p,$\gamma )^{\mathrm{11}}$C is sensitive to the gamma partial width as well as the alpha width of these levels and will better determine these resonances, allowing for more confident extrapolation.   

Spectroscopic strengths of low-lying levels in $^{\mathrm{18}}$Ne

Much effort has been made to understand the origins of $^{\mathrm{18}}$F. Due to its relatively long half-life (\textasciitilde 2 hours) it is a likely source of the 511 keV gamma line often seen as novae envelopes begin to become transparent. It is likely produced through the beta decay of $^{\mathrm{18}}$Ne, which is itself produced (largely) through the $^{\mathrm{17}}$F(p,$\gamma )$ reaction. Understanding the direct capture contribution to the $^{\mathrm{17}}$F(p,$\gamma )$ reaction is important to accurately model it. As such, the spectroscopic strengths of low-lying states in $^{\mathrm{18}}$Ne are needed. At the University of Notre Dame a measurement of the $^{\mathrm{17}}$F(d,n) reaction has been performed using a beam produced with TwinSol. The neutrons were detected using a combination of VANDLE and UMDSA arrays. Data will be shown and preliminary results discussed. Work supported by the National Science Foundations and the DOE Office of Nuclear Physics.   

Li : a cosmological problem from a nuclear physics perspective.

The primordial abundance discrepancy in the lithium 7 between the prediction from the cosmological observations, like the cosmic microwave background, and the stellar abundances is one of the main astrophysical sources of concern for big bang nucleosynthesis. While various solutions are proposed, the focused of this work is on a nuclear origin. This motivated the study of 7Li(alpha,gamma)11B. The 5U accelerator of the Nuclear Science laboratory at the University of Notre Dame was used to accelerate a alpha beam on a LiF target. The Ge-detectors Online Array for Gamma Ray Spectroscopy in Nuclear astrophysics (Georgina) was used to detect gamma rays from three resonances at 401, 814 and 953 keV in 11B. Preliminary results will be presented.