[3] In February 1946, Halperin was arrested and accused of espionage in Canada, in connection with the defection of Igor Gouzenko, a Soviet cipher clerk, which occurred in Ottawa in September 1945.

[4] Gouzenko's defection and subsequent investigation showed that the Soviet Union was carrying on large-scale spying in Canada and the United States, including nuclear weapons espionage.

After some arduous questioning and confinement lasting several weeks, under a Royal Commission appointed by Justice Minister Louis St-Laurent, followed by a trial in early 1947, Halperin was eventually cleared and freed.

Halperin was awarded an honorary doctorate of laws from Queen's in 1989, and was made a Member of the Order of Canada, both for his humanitarian work.

[7] Halperin was elected a Fellow of the Royal Society of Canada in 1953, and won the Henry Marshall Tory Medal in 1967.