Nuclear Physics Seminar: Bryce Frentz & John Wilkinson, University of Notre Dame


Location: zoom

An investigation of the astrophysically important 14N(p,γ)15O reaction

Bryce Frentz, Physics Graduate Student
University of Notre Dame

The CNO cycle is responsible for ~1% of solar energy production and ~2% of the solar neutrino flux via the ß-decay of 13N and 15O. The amount of 15O in the sun’s core depends critically on the 14N(p,γ) 15O reaction rate, which, as the cycle’s bottleneck, dictates the abundances of elements in the cycle. Recently, the first measurements of the solar neutrino flux were made by the BOREXINO group, finding rates discrepant with those extrapolated from low-energy cross section measurements. The main uncertainties in extrapolating the 14N(p,γ) 15O reaction rate to the Gamow window are the width of the subthreshold state at 6.79 MeV in 15O, and the capture cross section to both the ground state and the state at 6.17 MeV. In this talk, efforts to address these uncertainties, undertaken both at Notre Dame and the CASPAR facility, will be presented. First, new measurements of the 14N(p,γ) 15O reaction at proton energies ranging from 270-1070 keV at CASPAR and at energies 800-1200 keV at Notre Dame, using the Sta. Ana accelerator, will be shown. This talk will also detail our investigation of the lifetime of the 6.79 MeV state in 15O with the Doppler Shift Attenuation Method at the NSL. Our investigation shows a sub-femtosecond lifetime for the 6.79 MeV state and this result was cross validated with lifetime measurements for the 5.18 and 6.17 MeV states in 15O.


Heavy-Ion Production of Theranostic 149Tb for Potential Medical Applications

John Wilkinson, Physics Graduate Student
University of Notre Dame

Theranostics is an emerging field of nuclear medicine that uses radioisotopes to simultaneously image and treat disease. This is typically done by having one decay mode be useful for imaging and a second type of decay used to irradiate cells. One possible theranostic isotope, 149 Tb, performs therapeutic and diagnostic functions with simultaneous alpha and positron decay modes. As a very proton-rich nucleus, 149 Tb (t1/2  = 4.12 h) is restricted to accelerator production and isotope harvesting, with clinical work in close proximity. To date, it has only been produced for clinical tests by a light ion spallation reaction at a high-energy nuclear physics facility.  We propose an alternate production method using a heavy-ion reaction close to the Coulomb barrier. In this study 89 Y(63 Cu,x) 149 X was investigated as an indirect production pathway for all A=149 isobars. The preliminary yield data for 149 Tb and other reaction products measured by offline gamma spectroscopy are compared to predictions from the PACE4 fusion-evaporation code. A near-symmetric fission yield is also observed.

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