Search for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26 Al and 22 Na 1-3 . While γ rays from the decay of the former radioisotope have been observed through-out the Galaxy, 22 Na remains untraceable. The half-life of 22 Na (2.6 yr 4 ) would allow the observation of its 1.275 MeV γ -ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus 5 . The 22 Na( p, γ ) 23 Mg 5 reaction remains the only source of large uncertainty about the amount of 22 Na ejected. Its rate is dominated by a single reso- nance on the short-lived state at 7785.0(7) keV in 23 Mg 6 . In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the 23 Mg states, combining magnetic and highly-segmented tracking γ -ray spectrometers, places strong limits on the amount of 22 Na produced in novae, explains its non-observation to date in γ rays (flux < 2.5×10 −4 ph.cm −2 s −1 7 ), and constrains its detectability with future space-borne observatories.