All other isotopes of aluminium are radioactive. Probably the most secure of such is 26Al, that has a half-lifetime of 717,000 yrs: when it had been present together with secure 27Al from the interstellar medium from which the Solar Method fashioned (believe that to are already produced by stellar nucleosynthesis also), https://johnnyjaqes.activosblog.com/36135683/indicators-on-sheds-and-garages-you-should-know