ke a ta ft 4 SG Qj on iJ ~~ ead ~~ a Tne wnole-body reteation of an element of activity taken up at time r_ ip wit re (t - t) . : : . 23 r. S is the systemic whole-body retention for 39, ‘The activity taken up at dt and remaining at t is U (rt) t C(t - 1) dt. dt is