Since 1999, the TRIUMF-ISAC facility has been providing rare isotope beams for nuclear physics experiments. The three pillars of the program are nuclear structure, nuclear astrophysics, and fundamental symmetries. This article reviews highlights of each of these aspects of the ISAC science program, including tests of the collective behaviors, first explained by Bohr, Mottelson and Rainwater, at the limits of nuclear stability, and future prospects with the ARIEL facility at TRIUMF.

https://iopscience.iop.org/article/10.1088/0031-8949/91/9/093002/pdf

The TRIUMF-ISAC facility: two decades of discovery with rare isotope beams

The unknown thermonuclear rate of the 30P(p, γ)31S reaction at classical-nova temperatures currently prohibits the accurate modeling of nova nucleosynthesis in the A ⩾ 30 region. This is hindering the calibration of nova thermometers based on observed O/S, S/Al, O/P, and P/Al abundance ratios in nova ejecta, the calibration of a meter to probe mixing at the core-envelope interface in novae based on the observed Si/H abundance ratio, and the identification of candidate pre-solar nova grains found in primitive meteorites based on laboratory measurements of their 30Si/28Si isotopic ratios. Each of these diagnostics could address key questions in our understanding of classical novae if the 30P(p, γ)31S rate were known. We review progress on the determination of the 30P(p, γ)31S rate leading to a critical assessment of current interpretations of published data and prospects for future work.

The 30P(p, γ)31S reaction in classical novae: progress and prospects

The DRAGON recoil mass separator at TRIUMF exists to study radiative proton and alpha capture reactions, which are important in a variety of astrophysical scenarios. DRAGON experiments require a data acquisition system that can be triggered on either reaction product (γ-ray or heavy ion), with the additional requirement of being able to promptly recognize coincidence events in an online environment. To this end, we have designed and implemented a new data acquisition system for DRAGON, which consists of two independently triggered readouts. Events from both systems are recorded with timestamps from a 20 MHz clock that are used to tag coincidences in the earliest possible stage of the data analysis. Here we report on the design, implementation, and commissioning of the new DRAGON data acquisition system, including the hardware, trigger logic, coincidence reconstruction algorithm, and live time considerations. We also discuss the results of an experiment commissioning the new system, which measured the strength of the E
 c.m. = 1113 keV resonance in the 20
 Ne(p, γ)21
 Na radiative proton capture reaction.

Design and commissioning of a timestamp-based data acquisition system for the DRAGON recoil mass 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.

/pdf/energy-acceptance-of-the-st-george-recoil-separator-7zt1i6g6j8.pdf

Energy acceptance of the St. George recoil separator

The asymptotic normalization coefficients of the bound states ${J}^{\ensuremath{\pi}}=({0}_{1}^{+},{2}_{1}^{+},{4}_{1}^{+},{2}_{2}^{+})$ in $^{18}\text{O}$ are extracted from the peripheral neutron transfer reaction $^{13}\text{C}$$(^{17}\text{O}$$,^{18}\text{O}$$)^{12}\text{C}$. They are then converted to their mirror states in $^{18}\text{Ne}$, which are further used to evaluate the astrophysical $S$ factor for the proton capture reaction $^{17}\text{F}$($p$,$\ensuremath{\gamma}$)$^{18}\text{Ne}$. The elastic-scattering cross sections have been measured in both incoming and outgoing channels in order to extract the optical potentials needed for distorted-wave-Born-approximation calculations. The $S$ factor is found to be ${S}_{1\ensuremath{-}17}(0)=2.17\ifmmode\pm\else\textpm\fi{}0.37$ keV b. The contribution of the direct capture rate to this reaction is estimated, and its consequences on the production of $^{18}\text{F}$ at stellar energies in ONe novae are discussed.

Astrophysical reaction rate for F17 ( p , γ ) Ne18 from the transfer reaction C13 ( O17 , O18 ) C12

The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the γ-ray observable radioisotope 18F, produced in novae. However, no successful measurement of this reaction exists and the rate used is calculated from incomplete information on the contributing resonances. Of the two resonances thought to play a significant role, one has a radiative width estimated from the assumed analogue state in the mirror nucleus, 19F. The second does not have an analogue state assignment at all, resulting in an arbitrary radiative width being assumed. Here, we report the first successful direct measurement of the 18F(p,γ)^19Ne reaction. The strength of the 665 keV resonance (Ex=7.076  MeV) is found to be over an order of magnitude weaker than currently assumed in nova models. Reaction rate calculations show that this resonance therefore plays no significant role in the destruction of ^{18}F at any astrophysical energy.

/pdf/measurement-of-radiative-proton-capture-on-f-18-and-4ri6v6s67l.pdf

Measurement of Radiative Proton Capture on F-18 and Implications for Oxygen-Neon Novae

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Measurement of Radiative Proton Capture on F-18 and Implications for Oxygen-Neon Novae