the half life of iodine 131 is 8 days. if a patient is given a dosage of iodine 131 for radioactive therapy, initially the radioactive activity of the patient will be quite high (so high that the patient may have to be quarantined for public safety). how long does it take (assuming all the iodine remains inside the patient) before the radioactive activity from the patient decreases down to 5% of the original value? explain your reasoning.