Question: What two countries supported the project that Louis Slotin died working on?

Context paragraphs:
International reactions to the Saffron Revolution: International reaction to the 2007 Burmese anti-government protests ranges from support of the protestors through neutrality to support of the State Peace and Development Council, the ruling junta.  While most countries supported the protests and urged the Myanmar's State Peace and Development Council ruling military Junta to implement far-reaching reforms, several key countries, such as the People's Republic of China and India maintained commitment to the notion of noninterference.  A number of protests against the Burmese Government's crackdown have been held worldwide.

France–United Kingdom relations: France–United Kingdom relations are the relations between the governments of the French Republic and the United Kingdom of Great Britain and Northern Ireland (UK).  The historical ties between the two countries are long and complex, including conquest, wars, and alliances at various points in history.  The Roman era saw both areas, except Scotland and Northern Ireland, conquered by Rome, whose fortifications exist in both countries to this day, and whose writing system introduced a common alphabet to both areas; however, the language barrier remained.  The Norman conquest of England in 1066 decisively shaped English history, as well as the English language.  In the medieval period, the countries were often bitter enemies, with both nations' monarchs claiming control over France.  The Hundred Years' War stretched from 1337 to 1453 resulting in French victory.  Britain and France fought a series of five major wars , culminating in the Coalition victory over Napoleon in 1815.  After that there were some tensions, but peace generally prevailed and as the 19th century progressed, the relationship became better.  Closer ties between the two began with the 1904 Entente cordiale, particularly via the alliances in World War I and World War II, wherein both countries fought against Germany, and in the latter conflict British armies helped to liberate occupied France from the Nazis.  Both nations opposed the Soviet Union during the Cold War and were founding members of NATO.  In recent years the two countries have experienced a quite close relationship, especially on defence and foreign policy issues; the two countries tend, however, to disagree on a range of other matters, most notably the European Union.  The British press relishes the chance to refer to France and Britain as "historic rivals" or emphasize the perceived ever-lasting competition that still opposes the two countries.

Demon core: The demon core was a 6.2 kg subcritical mass of plutonium measuring 89 mm in diameter, roughly the size of a softball, best known for its involvement in two criticality accidents.  The core was slated for use in a third World War II nuclear bomb, but remained in use for testing after Japan's surrender.  It was designed with a small safety margin to ensure a successful explosion of the bomb.  The device briefly went supercritical when it was accidentally placed in supercritical configurations during two separate experiments intended to guarantee the core was indeed close to the critical point.  The incidents happened at the Los Alamos laboratory in 1945 and 1946, and resulted in the acute radiation poisoning and subsequent deaths of scientists Harry Daghlian and Louis Slotin.  After these incidents the spherical plutonium core was referred to as the "demon core".

Unification of Romania and Moldova: The unification of Romania and Moldova (Romanian: "Unirea Republicii Moldova cu România" ) is a popular concept in the two countries beginning with the late 1980s, during the dissolution of the Soviet Union.  The Romanian Revolution in 1989 and the independence of Moldova in 1991 further contributed to the development of a movement for the unification of the two Romanian-speaking countries.  The question of reunification is recurrent in the public sphere of the two countries, often as a speculation, both as a goal and a danger.  The idea, while widespread in Romania, is only supported by a minority in Moldova.

Michael Lista: Michael Lista (born September 1, 1983) is a Canadian poet.  He is the author of "Bloom", a book of poems about Canadian Manhattan Project physicist Louis Slotin.  He writes a monthly column on poetry for "The National Post" and lives in Toronto.

Brazil–United States Treaty: The Brazil–United States Treaty was a military assistance agreement signed in 1952 in Rio de Janeiro between the two countries, with the goal of defending the Western Hemisphere.  Military relations between the United States and Brazil date back to World War II, when Brazil supported the Allied effort in the invasion of Italy in 1942.  Brazil provided troops for the invasion.  On January 3, 1952, The Brazilian government issued decree 30363 establishing new government regulations.  These new regulations allowed for the return of foreign capital that was invested in Brazil and profit remittances on that capital.  Shortly after, representatives from the United States and representatives from Brazil started to negotiate a bilateral military assistance agreement in Rio de Janeiro on January 3, 1952.  The document outlining the agreement between the two countries would be signed on March 15, 1952.  The agreement went into effect on May 19, 1952.  During the time of the negotiations, Major General Charles L. Mullins, Jr. negotiated a separate military plan with the Brazilian Government.  The plan was approved on March 14, 1952 by the Secretary of Defense Lovett.  In a private ceremony on March 15, 1952 United States Major General Mullins and Brazilian General Monteiro signed the military plan that outlined a common defense between the two nations.  The agreement allowed major weapons and training by the United States military to the Brazilian military.  This tenuous alliance governed the two nations bilateral ties during the events of the Cold War.  However, the alliance was short lived, and suffered several major blows between the two nations during the military coup in Brazil in 1964.  During this time the United States still provided military support and training to the side that supported the United States.

Malawi–Mozambique relations: Malawi–Mozambique relations refers to the current and historical relationship between the countries of Malawi and Mozambique.  As Malawi shares a large border with Mozambique, much of the substance of their foreign relations pertain to the border separating the two nations.  Both of the sovereign states have amicably agreed that lacustrine borders on Lake Malawi remain the largest priority between the two countries, as the exploitation of natural resources within the waters of Lake Malawi remain an issue the two countries continue to resolve.  The moment considered an act of generosity and sympathy within the two countries relations is when, during the Mozambique Civil War, Malawi housed over one million Mozambican refugees between 1985 and 1995.  After this gesture, Malawian relations with Mozambique crumbled under the tenure of Bingu wa Mutharika, notoriously reaching a nadir when Malawian police launched a raid into Mozambique's territory.

Louis Slotin: Louis Alexander Slotin (1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who worked on the Manhattan Project.  During World War II, Slotin conducted research at Los Alamos National Laboratory.  He performed experiments with uranium and plutonium cores to determine their critical mass values.  On 21 May 1946, Slotin was conducting a demonstration when he accidentally initiated a fission reaction, which released a burst of hard radiation.  He received a lethal dose of radiation and died of acute radiation syndrome nine days later.  Slotin was the second person to die from a criticality accident, following the death of Harry Daghlian, who had been exposed to radiation by the same core that killed Slotin.  Slotin was publicly hailed as a hero by the United States government for reacting quickly and preventing his accident from killing any colleagues.  He was later criticized for failing to follow protocol during the experiment.

Manhattan Project: The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons.  It was led by the United States with the support of the United Kingdom and Canada.  From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers.  Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs.  The Army component of the project was designated the Manhattan District; "Manhattan" gradually superseded the official codename, Development of Substitute Materials, for the entire project.  Along the way, the project absorbed its earlier British counterpart, Tube Alloys.  The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US $2 billion (about $ in 2016 dollars).  Over 90% of the cost was for building factories and to produce fissile material, with less than 10% for development and production of the weapons.  Research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada.

Alvin C. Graves: Alvin Cushman Graves (November 4, 1909 – July 19, 1965) was an American nuclear physicist who served at the Manhattan Project's Metallurgical Laboratory and the Los Alamos Laboratory during World War II.  After the war, he became the head of J (Test) Division at Los Alamos, and was director or assistant director of numerous nuclear weapons tests during the 1940s and 1950s.  Graves was badly injured in the 1946 laboratory criticality accident in Los Alamos that killed Louis Slotin, but recovered.

Supporting paragraphs: Louis Slotin Manhattan Project
Answer: the United Kingdom and Canada