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Low-energy 23Al β-delayed proton decay and 22Na destruction in novae


  Moshe Friedman [1,2]  ,  Tamas Budner [1,3]  ,  David Pérez-Loureiro [1,4]  ,  Emanuel Pollacco [5]  ,  Chris Wrede [1,3]  ,  Jordi José [6,7]  ,  Alex Brown [1,3]  ,  Marco Cortesi [1]  ,  Cathleen Fry [1,3]  ,  Brent Glassman [1,2]  ,  Joe Heideman [4]  ,  Molly Janasik [1,3]  ,  Michael Roosa [1,3]  ,  Jordan Stomps [1,3]  ,  Jason Surbrook [1,3]  ,  Pranjal Tiwari [1,3]  
 [1] National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321, USA
[2] Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem, Israel 91904
[3] Department of Physics and Astronomy Michigan State University, East Lansing, Michigan 48824-1321, USA
[4] Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee , 37996 USA
[5] IRFU, CEA, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France
[6] Departament de Fı́sica, Escola d’Enginyeria de Barcelona Est, Universitat Politècnica de Catalunya, Av./ Eduard Maristany 10, E-08930 Barcelona, Spain
[7] Institut d’Estudis Espacials de Catalunya, Ed. Nexus-201, C/ Gran Capità 2-4, E-08034 Barcelona, Spain

Classical novae are energetic and common thermonuclear astrophysical explosions on the surface of a white dwarf that is accreting hydrogen-rich material from a companion star. Space-based observations of 1275-keV γ-rays from 22Na produced in nova explosions are expected to provide direct constraints on nova models. Previously and currently deployed instruments may have been on the cusp of detecting 22Na and more sensitive future missions are being planned.

22Na production in novae is strongly dependent on the rate of the destructive 22Na(p, γ) reaction, and, in particular, on the strength of a single resonance at center-of-mass energy of 204-keV. Two direct measurements of this resonance strength differ by a factor of 3.2. Another way to determine the strength is to combine measurements of the proton branching ratio Γp/Γ of the resonance with its lifetime. This can be done using the 23Al(β+p)22Na decay. However, such a measurement is challenging due to the low proton branching ratio from the 204-keV state, and the overwhelming β+ background at that energy

The GADGET assembly is a new detection system, comprised of gas-filled charged-particle detector surrounded by the Segmented Germanium Array. The detector is designed to measure protons and heavier charged particles with high efficiency, while maintaining low ionization from β particles. GADGET was recently used to measure the aforementioned branching ratio at NSCL.

We report a factor of 5 lower branching ratio compared to the most recent literature value. This new value was used in conjunction with literature lifetime to study the effect on the 22Na yield from typical ONe novae. In a series of new hydrodynamic simulations of nova outbursts we found that the inconsistencies in the 22Na has increased to a factor of 3.8, corresponding to a factor of ∼ 2 in the maximum detectability distance.