The physical half life of radioactive iodine 131 is

RADIOACTIVE IODINE The stable isotope of iodine is 127I. Its radioactive isotope of medicinal impoance is: 131I physical half-life of iodine 131 is 8 days. Mech of action:- 131I emits X-rays as well as b paicles. latter are utilized for their destructive effect on thyroid cells. 131I is concentrated by thyroid, incorporated in colloid--emits radiation from within the follicles. The b paicles penetrate only 0.5-2 mm of tissue. The thyroid follicular cells are affected from within, undergo pyknosis and necrosis followed by fibrosis when a sufficiently large dose has been administered, without damage to neighbouring tissues. Ref:- kd tripathi; pg num:-255