Une radioactivité bénéfique à très faible dose ?

STANFORD –L'accident nucléaire de Fukushima et ses conséquences suscitent une montagne de commentaires et de spéculations. Malheureusement une grande partie du débat souffre d'un défaut d'informations et pose problème.

A moins de 20 kilomètres de la centrale, en certains endroits le niveau de radioactivité a été multiplié par 400. De la radioactivité a été détectée dans du lait, du poisson et des légumes de la région et plusieurs pays ont interdit leur importation. A Tokyo, à 225 kilomètres de là, l'eau du robinet a été déclarée impropre à la consommation pour les bébés. Quelles conclusions tirer de ces informations ?

Le niveau de radiation est relativement peu dangereux pour la santé si l'on ne se trouve pas dans les environs immédiats de la centrale. La plus grande partie de la radioactivité provient de l'iode 131, ce qui n'est pas très inquiétant. Premièrement cet isotope a une période très courte (seulement 8 jours), sa radioactivité décroît donc rapidement (en 10 semaines son niveau représente moins de 0,1% de son niveau initial). Deuxièmement, sa présence indique que c'est le réacteur qui est à l'origine des radiations, et non les barres de combustible usagée qui comporte des radio-isotopes beaucoup plus dangereux et de période bien plus longue. Troisièmement, il existe un antidote efficace pour les personnes exposées, c'est l'iode non radioactif, facilement disponible sous forme solide ou liquide. Il bloque l'absorption de l'iode radioactif par la thyroïde.

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