Ionisation cooling in FFAG's

A structure for dissipating heat by natural convection, intended for being provided on the periphery of packaging for transporting and/or storing radioactive materials, the structure having two adjacent half-structures each comprising primary fins which are parallel and angled relative to a height direction of the structure, the primary fins of the two half-structures forming, in pairs, fins of the general shape of an inverted V when the packaging is arranged vertically with the bottom thereof oriented downwards.