Always keeping in mind, of course, that the radiation level for your average, ordinary, everyday banana is about 100 Bq/kg.
Always keeping in mind that bananas are irrelevant to discussions in which cesium and other nuclear waste products are present. For one tiny little example, the human body won’t take up more than a tiny amount of radioactive potassium whereas there is no limit to the amount of radioactive cesium it will uptake - important, basic differences which render the whole banana gimmick a waste of time.