The use of the atomic bomb near the end of the war turned Pauling in a new direction. As one who had long worked on the structure of molecules, both normal and abnormal, on their behavior in the human body, and on their transmission through heredity, he took an immediate and intense interest in the potentially malignant effects of nuclear fallout on human molecular structures, as well as in the forces of blast and fire released by an exploding bomb.
In the political climate of the time, with the Cold War with Russia in its early stages and Senator McCarthy and the House Un-American Activities committee hunting communists everywhere, Pauling's anti-war activities brought him floods of criticism. His public stand made Pauling the target of an internal investigation at Caltech, as well as governmental harassment and attacks in the press. In 1952, the State Department refused to renew Pauling's passport. the official reason was that his travels ``would not be in the best interest of the United States." The world scientific community was outraged.
In 1958, on January 15, he presented to the UN the celebrated petition signed by 9,235 scientists from many countries in the world protesting further nuclear testing. In that same year he published No More War!, a book which presents the rationale for abandoning not only further use and testing of nuclear weapons but also war itself, and which proposes the establishment of a World Peace Research Organization within the structure of the UN to "attack the problem of preserving the peace".
When the Soviet Union announced a resumption of nuclear testing in August, 1961, after the nuclear powers had voluntarily withheld testing for three years, Pauling redoubled his efforts to convince the Russian, American, and British leaders of the necessity of a test ban treaty. He spoke as a man of science.
The Nuclear Test Ban Treaty, outlawing all but underground nuclear testing, was signed in July, 1963, and went into effect on October 10, 1963, the same day on which the Norwegian Nobel Committee announced that the Peace Prize reserved in the year 1962 was to be awarded to Linus Pauling. He died in 1994.