Measurement of the beta decay of ²⁶P to determine classical nova ²⁶Al production in the Milky Way galaxy

Observation across the Milky Way of a 1809-keV γ-ray characteristic of ²⁶Al decay provides direct evidence for ongoing nucleosynthetic production of ²⁶Al. Although massive stars and supernovae are likely to be the primary sites for ²⁶Al production, classical novae may also contribute a significant portion of the total amount of Galactic ²⁶Al. At peak nova temperatures of approximately 0.4 GK, the rate of the ²⁵Al(p,γ)²⁶Si reaction, which bypasses ²⁶Al production and therefore places an upper limit on the amount of ²⁶Al contributed by novae to Galactic abundances, is likely dominated by a single 3⁺ resonance. Constraining the energy and strength of this resonance is therefore critical to determining the ²⁵Al(p,γ)²⁶Si reaction rate. We have used a radioactive ²⁶P beam produced at the National Superconducting Cyclotron Laboratory to populate the 3+ state via beta decay, and have observed first evidence for its γ decay branch, the last piece of information needed to calculate the resonance strength. We find the 3⁺ state to have a resonance energy of E_r = 414.9 ± 0.6 (stat) ± 0.3 (syst) ± 0.6 (lit.) keV and a resonance strength of ωγ = 23 ± 6 (stat) ⁺¹¹ -10 (lit.) meV. We have also used hydrodynamic nova simulations to model ²⁶Al production and we find that novae may contribute up to 0.6 solar masses of the Galactic ²⁶Al - 38% of the total Galactic ²⁶Al abundance.