Stopwatch on the world

Feature Novel of Deadly Menace
Every member of the UN received the note which said: ... Give us peace within a month or I shall destroy the earth utterly. And only two men believed the sender to be capable of carrying out his threat—two men, bucking red-tape, trying to find the terribly sincere atomic physicist, Chetzisky, before the deadline!
Chetzisky held the world in his hand. Would the United Nations act to end war, or was the world doomed?
EXTRACTS, HOSPITAL CASE HISTORY No. 3007:
Patient admitted 11:45 A.M. in coma and severe shock. Pulse weak. Temperature 95. White cell count less than 2,000. Blood draining off into tissues, indicating generalized purpura. Immediate whole blood transfusions given.
DIAGNOSIS: Radiation illness. Exposure considered lethal. Probably about 1,000 roentgens.
2:30 P.M. White cell count now down to 500. Response to aureomycin treatment favorable.... 3:10 P.M. Hematocrit reading remains high at 101.... 3:55 P.M. Lab reports show karyorrhexis developing swiftly as more and more cells are ionized by 'hot' isotopes in patient's body.... 4:40 P.M. Geiger counter set up at bedside to check progressive radioactivity of the human atomic pile.... 5:10 P.M. Guided by hematocrit readings, blood transfusions increased, supplemented by albumen.... 5:50 P.M. Patient conscious. Suffers violent spasms of pain. Morphine barely suffices. He appears thoughtful, moves head weakly....
With a great effort I turn my head and see the sun going down behind the color-splashed ridges of the Coastal range. It's the last sunset I shall ever see and the end of a day that a mad-man with an atomic stopwatch meant to be your last.
Every cell inside me seems a glowing coal. The geiger counter clicks off a slow, steady staccato. Suddenly I find my body arching itself convulsively in a wracking outbreak of pain. There is the quick sharpness of a needle in my arm and mercifully I am numb.
Armstrong, his giant frame hunched over in the chair, watches me with a suffering look new to those hard, cold eyes of his. A good man and a loyal friend. If he weren't as stubborn and resolute as a bull-dog, you might not be sitting down to your supper tonight.