What two countries supported the project that Louis Slotin died working on?
Louis Slotin: Louis Alexander Slotin (1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who worked on the Manhattan Project. Louis Slotin:  He received a lethal dose of radiation and died of acute radiation syndrome nine days later. Manhattan Project:  It was led by the United States with the support of the United Kingdom and Canada.
the United Kingdom and Canada