Kinetic computations of the thermonuclear burning in the one-zone hydrogen-rich envelope were used to obtain a possible range of radioactive nuclei abundance in CO and ONeMg nova ejecta. The total amount of radioactive N, O and F isotopes in the envelope is approximately equal to the amount of dwarf CO matter admixed in the process of the accretion and/or outburst. The fraction of synthesised {18}F is 0.1-1% by mass.

We calculated light curves of annihilation line of the short-lived NOF isotopes and studied effects of the variation of envelope parameters and expansion kinematics (free expansion and wind). Light curves are highly sensitive to the degree of mixing of radioactive isotopes in the envelope. The presence of only one per cent of unmixed matter in the outer layer leads to the strong suppression of the first luminosity peak related to radioactive N and O isotopes. The second luminosity peak from {18}F decays is suppressed if the fraction of the outer unmixed layer exceeds 10%.

We propose to use observations of annihilation line flux of {18}F with CGRO or (in future) with INTEGRAL and independent observational estimate of {18}O mass in the ejected envelope, for the diagnostics of the degree of mixing and the mass of synthesised {18}F in novae. Calculations of the amount of synthesised {22}Na and {26}Al are compared with upper limits from gamma-ray observations.