Research by the FRIB Charge-Exchange Group
We study the spin-isospin response of nuclei to learn about the isovector properties of nuclei and nuclear matter, with applications in astrophysics and neutrino physics
Weak interactions in Astrophysics
S800 Spectrograph and Gretina used in (t,3He+gamma) experiments. (Image by S. Noji)
We employ charge-exchange reactions to extract Gamow-Teller strength distributions from which electron-capture rates in astrophysical environments can be deduced. The model-independent extraction of Gamow-Teller strength is possible because of a well-established proportionality between Gamow-Tellet strength and charge-exchange reactions at beam energies of ~100 MeV/u. Since charge-exchange reactions are not restricted by the reaction Q-value, they can be used to probe the response not accessible in direct electron-capture/beta decay.
The main reaction for probing stable targets has been the (t,3He) reaction and the (d,2He) reaction in inverse kinematics was recently developed to probe unstable isotopes. The data are used to improve our electron capture rate library. Read more...
Probing the isovector response of unstable nuclei
Understanding the spin-isospin response of unstable nuclei is key for testing and improving theoretical model of the strong nuclear force, the isospin structure of nuclei, and for constraining weak interaction rates of importance for nuclear astrophysics. The charge-exchange group developed the (p,n) charge-exchange reaction in inverse kinematics, which required the construction of the low-energy neutron detector array (LENDA) and, in collaboration with Ursinus College, a liquid Hydrogen target. The (7Li,7Be) reaction in inverse kinematics was developed by using the Segmented Germanium Array. More recently, the group worked together with the Active-Target Time Projection Chamber (AT-TPC) collaboration to use the AT-TPC to measure (d,2He) charge-exchange reactions in inverse kinematics. These experiments use the S800 Spectrograph for detecting and identifying the heavy residues. The (p,n), (7Li,7Be), and (d,2He) experimental techniques at medium beam energies for studying unstable isotopes were first developed by our group.
LENDA and the Ursinus-NSCL liquid hydrogen target at the S800 (top) and the AT-TPC at the S800 (below). Images by S. Noji.
Simultaneously extracted isovector spin-transfer and non-spin-transfer excitation energy spectra in the 12C(10Be,10B+gamma) reactions
Isovector giant resonances
Isovector giant resonances are collective excitations of nuclei in which the proton and neutron fluids oscillate out of phase. Their characteristics, such as excitation energies and widths, provide information about the bulk properties of nuclear matter and the nuclear equation of state. The study of isovector giant resonances is important for understanding the role of isospin and asymmetries between proton and neutron matter, which is, for example, important for understanding neutron rich matter, e.g. in neutron stars. Our focus has been on developing the (10Be,10B+gamma) reaction as a novel tool for studying the isovector giant monopole resonance. By using this reaction, the spin-transfer and non-spin transfer responses can be separated in a single experiment.
Gamow-Teller strengths and Level densities
The understanding of Gamow-Teller strength distributions is important for applications in neutrino physics, including for the development of neutrino detectors, constraining matrix elements for neutrinoless double beta decay, and astrophysical neutrino reaction rates. Our group utilizes charge-exchange reactions at FRIB and RCNP, Osaka, to provide necessary data and constraints. Recently, we have started the development of the charge-exchange Oslo method for extracting level densities and gamma-ray strength functions from charge-exchange data as well. This will allow for extracting Gamow-Teller strengths, level densities, and gamma-ray strength functions in a single experiment. The first results will be published soon.
High-resolution 150Nd(3He,t) spectra obtained at RCNP, Osaka, for constraining the matrix element of neutrinoless double beta decay of 150Nd to 150Sm