Papers
Ab initio many-body calculation of the 7Be(p, γ )8B radiative capture
We apply the ab initio no-core shell model/resonating group method (NCSM/RGM) approach to calculate
the cross section of the 7Be(p,γ )8B radiative capture. This reaction is important for understanding the
solar neutrino flux. Starting from a selected similarity-transformed chiral nucleon–nucleon interaction
that accurately describes two-nucleon data, we performed many-body calculations that simultaneously
predict both the normalization and the shape of the S-factor. We study the dependence on the number
of 7Be eigenstates included in the coupled-channel equations and on the size of the harmonic oscillator
basis used for the expansion of the eigenstates and of the localized parts of the integration kernels. Our
S-factor result at zero energy is on the lower side of, but consistent with, the latest evaluation.
Journal: Physics Letters B
Recoil separators for radiative capture using radioactive ion beams
Radiative capture reactions involving the fusion of hydrogen or helium are ubiquitous in the stellar history of the universe, and are some of the most important reactions in the processes that govern nucleosynthesis and energy generation in both static and explosive scenarios. However, radiative capture reactions pose some of the most difficult experimental challenges due to extremely small cross sections.
With the advent of recoil separators and techniques in inverse kinematics, it is now possible to measure radiative capture reactions on very short-lived radioactive nuclei, and in the presence of high experimental backgrounds. In this paper we review the experimental needs for making measurements of astrophysical importance on radiative capture reactions. We also review some of the important historical advances in the field of recoil separators as well as describe current techniques and performance milestones, including descriptions of some of the separators most recently working at radioactive ion beam facilities, such as DRAGON at TRIUMF and the DRS at the Holifield Radioactive Ion Beam Facility.We will also summarize some of the scientific highlight measurements at the RIB facilities.
Journal: European Physical Journal A
Measurement of Radiative Proton Capture on 18F and Implications for Oxygen-Neon Novae
The rate of the 18F(p,g)19Ne reaction affects the final abundance of the gamma-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,g)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 18F at any astrophysical
energy
Journal: Phys. Rev. C
Strength of the Ec.m. = 1113 keV resonance in 20Ne(p, γ) 21Na
The 20Ne(p, γ)21Na reaction is the starting point of the NeNa cycle, which is an important process for the production of intermediate mass elements. The Ec.m. = 1113 keV resonance plays an important role in the determination of stellar rates for this reaction since it is used to normalize experimental direct capture yields at lower energies. The commonly accepted strength of this resonance, ωγ = 1.13±0.07 eV, has been misinterpreted as the strength in the center-of-mass frame when it is actually the strength in the laboratory frame. This has motivated a new measurement of the Ec.m. = 1113 keV resonance strength in 20Ne(p, γ)21Na using the DRAGON recoil mass spectrometer. The DRAGON result, 0.972 ± 0.11 eV, is in good agreement with the accepted value when both are calculated in the same frame of reference.
Journal: Phys. Rev. C, Brief Reports
MESA MODELS OF CLASSICAL NOVA OUTBURSTS:
THE MULTICYCLE EVOLUTION AND EFFECTS OF
CONVECTIVE BOUNDARY MIXING
Novae are cataclysmic variables driven by accretion of H-rich material onto a
white-dwarf (WD) star from its low-mass main-sequence binary companion. New
time-domain observational capabilities, such as the Palomar Transient Factory
and Pan-STARRS, have revealed a diversity of their behaviour that should be
theoretically addressed. Nova outbursts depend sensitively on nuclear physics
data, and more readily available nova simulations are needed in order to effectively
prioritize experimental effort in nuclear astrophysics. In this paper we use
the MESA stellar evolution code to construct multicycle nova evolution sequences
with CO WD cores. We explore a range of WD masses and accretion rates as well
as the effect of different cooling times before the onset of accretion. In addition,
we study the dependence on the elemental abundance distribution of accreted
material and convective boundary mixing at the core-envelope interface. Models
with such convective boundary mixing display an enrichment of the accreted envelope
with C and O from the underlying white dwarf that is commensurate with
observations. We compare our results with the previous work and investigate a
new scenario for novae with the 3He-triggered convection.
Journal: Astrophysical Journal
One fewer solution to the cosmological lithium problem
Data from a recent 9Be(3He,t )9B measurement are used to rule out a possible solution to the cosmological lithium problem based on conventional nuclear physics.
Journal: Physical Review C
MESA AND NUGRID: A FRAMEWORK FOR MODELLING OF NOVAE EXPLOSIONS AND NUCLEOSYNTHESIS
We present a new framework for 1D numerical simulations of novae explosions and nucleosynthesis. It combines the powers of the state-of-the-art MESA stellar evolution code and NuGrid post-processing nucleosynthesis code. It is designed to be used by any interested researcher or student. To make it easy to run the codes and their visualization tools by a non-expert, the framework will include user- friendly shell scripts and detailed instructions on how to use them. It is shown that our framework allows to compute the evolution of CO novae through several consecutive explosions. The framework will soon be extended to include ONe novae and mixing between the accreted envelope and underlying white dwarf.
Journal: In preparation
Novae in a test-tube: Investigating the 21Na(ρ,γ)22Mg reaction at TRIUMF's ISAC facility
The 21Na(ρ,γ)22Mg reaction is expected to play an important role in the synthesis of intermediate mass elements in Oxygen-Neon novae. The first direct measurement of the rate of this reation was completed using the DRAGON recoil mass separator at TRIUMF's ISAC facility. The energy of one resonance important in the reaction was measured to be Ec.m.=728.1 ± 1.2 keV, and its resonance strength was determined to be ωγ= 254 ± 16stat ± 44sys meV.
Journal:
Solar fusion cross sections II: the pp chain and CNO cycles
The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.
Journal: Review of Modern Physics, vol. 83, Issue 1, pp. 195-246
Development of detection systems for low-energy heavy ions at DRAGON
The new DRAGON facility at TRIUMF is designed to measure alpha and proton capture reactions with radioactive ion beams in inverse kinematics. For nucleo-synthesis in astrophysical scenarios, the relevant energies lie in the 0.15-1 MeV/u range, where very low cross sections are expected. Therefore the separation of the recoil products from the beam particles will be a difficult task. This pare focuses on the end detectors, which will be used to distinguish recoils from beam particles at the end of the DRAGON separator.
Journal: Nuclear Physics A
