Louis Alexander Slotin ( ; 1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who took part in the Manhattan Project. Born and raised in the North End of Winnipeg, Manitoba, Slotin earned both his Bachelor of Science and Master of Science degrees from the University of Manitoba, and his doctorate in physical chemistry at King's College London in 1936. Afterwards, he joined the University of Chicago as a research associate to help design a cyclotron.
In 1942, Slotin was invited to participate in the Manhattan Project, and subsequently performed experiments with uranium and plutonium cores to determine their critical mass values. After World War II, he continued his research at Los Alamos National Laboratory in New Mexico. On 21 May 1946, he accidentally triggered a supercritical nuclear chain reaction, which released a burst of hard radiation. He was rushed to the hospital and died nine days later on 30 May. Slotin had become the second fatal victim of a criticality accident in history, following Harry Daghlian, who had died of a related accident with the same plutonium "demon core" the previous year.
Slotin was hailed as a hero by the United States government for reacting quickly enough to prevent the deaths of his colleagues. However, Slotin had ignored safety protocols for the experiment causing the accident. Therefore, some physicists stated that Slotin's behavior preceding the accident was reckless and that his death was preventable. The accident and its aftermath have been dramatized in several fictional and non-fictional accounts.
Early life
Louis Slotin was the first of three children born to Israel and Sonia Slotin, Yiddish-speaking Jewish refugees who had fled the pogroms of Russia to Winnipeg, Manitoba. He grew up in the North End neighborhood of Winnipeg, an area with a large concentration of Eastern European immigrants. From his early days at Machray Elementary School through his teenage years at St. John's High School, Slotin was academically exceptional. His younger brother, Sam, later remarked that his brother "had an extreme intensity that enabled him to study long hours."
At age 16, Slotin entered the University of Manitoba to pursue a degree in science. During his undergraduate years, he received a University Gold Medal in both physics and chemistry. Slotin received a B.Sc. degree in geology from the university in 1932 and a M.Sc. degree in 1933. With the assistance of one of his mentors, he obtained a fellowship to study at King's College London under the supervision of Arthur John Allmand,
King's College London
While at King's College London, Slotin distinguished himself as an amateur boxer by winning the college's amateur bantamweight boxing championship. Later, he gave the impression that he had fought for the Spanish Republic and trained to fly a fighter with the Royal Air Force. Author Robert Jungk recounted in his book Brighter than a Thousand Suns: A Personal History of the Atomic Scientists, an early history of the Manhattan Project, that Slotin "had volunteered for service in the Spanish Civil War, more for the sake of the thrill of it than on political grounds. He had often been in extreme danger as an anti-aircraft gunner." During an interview years later, Sam stated that his brother had gone "on a walking tour in Spain" and he "did not take part in the war" as previously thought. the University of Chicago accepted Slotin as a research associate. There, he gained his first experience with nuclear chemistry, helping to build the first cyclotron in the midwestern United States. The job paid poorly and Slotin's father had to support him for two years. From 1939 to 1940, Slotin collaborated with Earl Evans, the head of the university's biochemistry department, to produce radiocarbon (carbon-14 and carbon-11) from the cyclotron.
Slotin might have been present at the start-up of Enrico Fermi's "Chicago Pile-1", the first nuclear reactor, on 2 December 1942; the accounts of the event do not agree on this point. During this time, he also contributed to several papers in the field of radiobiology. His expertise on the subject garnered the attention of the United States government, and as a result he was invited to join the Manhattan Project, an effort to develop an atomic bomb. Scientists referred to this flirting with the possibility of a nuclear chain reaction as "tickling the dragon's tail", based on a remark by physicist Richard Feynman comparing the experiments to "tickling the tail of a sleeping dragon". On 16 July 1945, Slotin assembled the core for Trinity, the first detonated atomic device, and became known as the "chief armorer of the United States" for his expertise in assembling nuclear weapons. Slotin received two small circular lead and silver commemorative pins for his work on the project. A dose of 1 Gy (≈100 roentgen) can cause nausea and vomiting in 10% of cases, but is generally survivable.
Harry Daghlian's death
On 21 August 1945, laboratory assistant Harry Daghlian, one of Slotin's close colleagues, was performing a criticality experiment when he accidentally dropped a heavy tungsten carbide brick onto a plutonium–gallium alloy bomb core, later nicknamed demon core, which would later also kill Slotin. The 24-year-old Daghlian was irradiated with a large dose of neutron radiation. Later estimates suggested that this dose might not have been fatal on its own, but he then received additional delayed gamma radiation and beta burns while disassembling his experiment.
Planned return to teaching
After World War II, Slotin expressed growing disdain for his personal involvement in the project. He remarked, "I have become involved in the Navy tests, much to my disgust."
By Slotin's own unapproved protocol, the shims were not used. The top half of the reflector was resting directly on the bottom half at one point, while 180 degrees from this point a gap was maintained by the blade of a flat-tipped screwdriver in Slotin's hand. The size of the gap between the reflectors was changed by twisting the screwdriver. Slotin, who was given to bravado, became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans and cowboy boots in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing the test in that manner. Scientists referred to this flirtation with a nuclear chain reaction as "tickling the dragon's tail", based on a remark by physicist Richard Feynman.
At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a "prompt critical" reaction and a burst of hard radiation. By 25 May 1946, four of these seven men had been discharged from the hospital. The United States Army physician responsible for the Los Alamos base hospital, Captain Paul Hageman, said that Slotin's, Graves's, Kline's and Young's "immediate condition is satisfactory." Slotin died at 11 a.m. on 30 May, in the presence of his parents. He was buried in the Shaarey Zedek Cemetery in Winnipeg on 2 June 1946. Graves, who was standing the closest to Slotin, also developed acute radiation sickness and was hospitalized for several weeks. He survived, although he lived with chronic neurological and vision problems. Young also suffered from acute radiation syndrome, but recovered. By 28 January 1948 Graves, Kline and Perlman sought compensation for damages suffered during the incident. Graves settled his claim for $3,500 (or about $ today, adjusted for inflation).
Three of the observers eventually died of conditions that are known to be promoted by radiation: Graves of a heart attack twenty years later at age 55, Cieslicki of acute myeloid leukemia nineteen years later at age 42, and Young of aplastic anemia and bacterial infection of the heart lining, twenty-nine years later, at age 83. Some of the deaths may have been a consequence of the incident. Louis Hempelman, M.D., a consultant to the Los Alamos Scientific Laboratory, believed that it is not possible to establish a causal relation between the incident and the specifics of the death from such a small sample. After the accident, it needed time to cool. It was therefore rescheduled for the third test of the series, provisionally named Charlie, but this was cancelled due to the unexpected level of radioactivity after the underwater Baker test and the inability to decontaminate the target warships. The core was eventually melted down and its material reused in a later core.
Radiation dosage
thumb|right|300px|A sketch used by doctors to determine the amount of radiation to which each person in the room had been exposed during the excursion
thumb|right|300px|A drawing based on the above sketch.
The radiation doses received in these two accidents are not known with any accuracy. A large part of the dose was due to neutron radiation, which could not be measured by dosimetry equipment of the day. The available film badges were not worn by personnel during the accident, and badges that were supposed to be planted under tables in case of disasters like these were not found. Disaster badges hung on the walls provided some useful data about gamma radiation.
A "tentative" estimate of the doses involved was made in 1948, based on dozens of assumptions, some of which are now known to be incorrect. In the absence of personal dosimetry badges, the study authors relied on measurements of sodium activation in the victims' blood and urine samples as their primary source of data. This activation would have been caused by neutron radiation, but they converted all doses to equivalent doses of gamma or X-ray radiation. They concluded that Daghlian and Slotin had probably received doses equivalent to and , respectively, of gamma rays. Minimum and maximum estimates varied from about 50% to 200% of these values. The authors also calculated doses equivalent to a mix of soft 80 keV X-rays and gamma rays, which they believed gave a more realistic picture of the exposure than the gamma equivalent. In this model, the equivalent X-ray doses were much higher, but would be concentrated in the tissues facing the source, whereas the gamma component penetrated the whole body. Slotin's equivalent dose was estimated to be 1930 R (roentgen) of X-ray with 114 R of gamma, while Daghlian's equivalent dose was estimated to be 480 R of X-ray with 110 R of gamma. Based on citations and supporting reasoning, the most reliable estimate may be a 1978 Los Alamos memo which suggested 10 Gy(n) + 1.14 Gy(γ) for Slotin and 2 Gy(n) + 1.1 Gy(γ) for Daghlian. These doses are consistent with the symptoms they experienced.
On 14 June 1946, the associate editor of the Los Alamos Times, Thomas P. Ashlock, penned a poem entitled "Slotin – A Tribute":