Louis Slotin

• 1. Introduction

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  At 3:20 on the afternoon of the 21st of May 1946, Louis Slotin stood in a laboratory at Los Alamos. The air around him suddenly glowed blue. Everyone in the room felt a wave of heat roll across them. Slotin tasted something sour, and his left hand burned fiercely. Within days, the world would be asking what had happened in that room. Slotin was a Canadian physicist and chemist who had helped build the first atomic weapons. Was he a hero, or did he bring about his own death? Physicists would argue about it for decades. What was he doing with a plutonium core while colleagues looked on? Who warned him to stop? And how did a scientist who longed to go back to teaching end up in that room at all?

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• 2. Winnipeg and London

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  Louis Alexander Slotin was born on the 1st of December 1910 in Winnipeg, Manitoba, the eldest of three children. His parents, Israel and Sonia Slotin, spoke Yiddish and had fled the pogroms of Russia. The family lived in the North End, a district crowded with immigrants from Eastern Europe. Louis excelled at Machray Elementary School and later at St. John's High School. His younger brother Sam recalled that Louis "had an extreme intensity that enabled him to study long hours."

  At 16, Slotin entered the University of Manitoba to study science. He collected a University Gold Medal in physics and another in chemistry. He took a B.Sc. in geology in 1932 and an M.Sc. in 1933. A mentor then helped him win a fellowship to King's College London. There he worked under Arthur John Allmand, who chaired the chemistry department and specialized in applied electrochemistry and photochemistry.

  In London, Slotin won the college's amateur bantamweight boxing championship. He also let people believe he had fought for the Spanish Republic and trained to fly a fighter with the Royal Air Force. Author Robert Jungk repeated the Spanish story in Brighter than a Thousand Suns. Jungk wrote that Slotin volunteered "more for the sake of the thrill of it than on political grounds," and faced danger as an anti-aircraft gunner. Sam later set the record straight in an interview. Louis had gone on "a walking tour in Spain" and "did not take part in the war."

  In 1936, Slotin earned his Ph.D. in physical chemistry at King's College London. His thesis, "An Investigation into the Intermediate Formation of Unstable Molecules During some Chemical Reactions," won a prize. He then spent six months in Dublin as a special investigator for Great Southern Railways. His task was testing the Drumm nickel-zinc rechargeable batteries used on the Dublin-Bray line. That job was short, and his next move would take him across the Atlantic.

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• 3. From Cyclotron to Los Alamos

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  The University of Chicago accepted Slotin as a research associate in 1937, after Canada's National Research Council turned down his application. There he helped build the first cyclotron in the American Midwest, which gave him his first taste of nuclear chemistry. The pay was so poor that his father had to support him for two years.

  From 1939 to 1940, Slotin worked with Earl Evans, head of the university's biochemistry department. Together they used the cyclotron to produce radioactive carbon, both carbon-14 and carbon-11. With carbon-11, the pair showed that plant cells can turn carbon dioxide into carbohydrates, a process called carbon fixation.

  Accounts disagree on whether Slotin was present on the 2nd of December 1942, when Enrico Fermi started Chicago Pile-1, the first nuclear reactor. He did contribute to several papers on radiobiology. That expertise caught the attention of the United States government, which invited him into the Manhattan Project, the effort to build an atomic bomb. He worked on plutonium production under Eugene Wigner, a future Nobel laureate, first in Chicago and then at Oak Ridge National Laboratory in Tennessee. In December 1944, he moved to Los Alamos National Laboratory in New Mexico and joined Robert Bacher's bomb physics group.

  At Los Alamos, Slotin's work was criticality testing, first with uranium in experiments run by Otto Robert Frisch and later with plutonium cores. The tests brought lumps of fissile material close to the point where a chain reaction sustains itself. The goal was to learn each lump's critical mass. Physicist Richard Feynman compared it to "tickling the tail of a sleeping dragon." Scientists adopted the phrase "tickling the dragon's tail."

  On the 16th of July 1945, Slotin assembled the core for Trinity, the first atomic device ever detonated. His expertise earned him the nickname "chief armorer of the United States." He received two small circular commemorative pins, made of lead and silver, for the work.

  In the winter of 1945-46, Slotin startled colleagues by repairing an instrument 6 ft underwater inside the Clinton Pile while it was running. He chose that over waiting one more day for a shutdown. He wore no dosimetry badge, yet his dose was estimated at no less than 100 roentgen. That is roughly 1 Gy, a level that causes nausea and vomiting in about 10 percent of people but is generally survivable. The next time he skipped a precaution, the dose would not be survivable.

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• 4. The Demon Core

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  On the 21st of August 1945, laboratory assistant Harry Daghlian was running a criticality experiment. Daghlian was one of Slotin's close colleagues. He accidentally dropped a heavy tungsten carbide brick onto a 6.2 kg bomb core made of a plutonium-gallium alloy. The core would later be nicknamed the demon core. Daghlian, who was 24, absorbed a large dose of neutron radiation. Later estimates suggested that dose alone might not have killed him. But he then took delayed gamma radiation and beta burns while taking his experiment apart. He collapsed with acute radiation poisoning and died 25 days later in the Los Alamos base hospital.

  After the war ended, Slotin spoke with growing disgust about his part in the project. "I have become involved in the Navy tests, much to my disgust," he remarked. He felt stuck, explaining, "I am one of the few people left here who are experienced bomb putter-togetherers." What he wanted was to return to the University of Chicago and resume teaching and research in biophysics and radiobiology. To free himself, he began training Alvin C. Graves to take over his role at Los Alamos. Graves would soon stand closer to Slotin than anyone else in the room.

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• 5. The Screwdriver Method

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  Two half-spheres of beryllium, a metal that reflects neutrons, were set around a plutonium core 3.5 in across. It was the same 6.2 kg core that had irradiated Daghlian. The experiment demonstrated one of the first steps of a fission reaction. Slotin gripped the upper 9-inch hemisphere, which measures 228.6 mm, with his left hand through a thumb hole at its top. A screwdriver blade in his other grip held the two halves apart. Twisting the screwdriver changed the size of the gap.

  The standard protocol called for shims between the halves. If the halves closed completely, a critical mass could form instantly, and a lethal power excursion would follow. Slotin skipped the shims, using a method nobody had approved. The top half rested directly on the bottom half at one point. On the opposite side, 180 degrees away, the screwdriver blade kept a gap open.

  Slotin was given to bravado. He had run the test almost a dozen times, often in his trademark blue jeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly warned Slotin and others that they would be "dead within a year" if they kept performing it that way.

  Then the screwdriver slipped, and the upper hemisphere fell. The result was a "prompt critical" reaction and a burst of hard radiation. Slotin jerked his hand upward, lifting the hemisphere and dropping it to the floor, which ended the reaction. By then he had already absorbed a lethal dose of neutron radiation.

  The dosimetry badges sat in a locked box about 100 ft from the reaction, and nobody in the room was wearing one. Slotin asked Dr. Raemer E. Schreiber to take the badges from the lead box and place them on the critical assembly. The request told investigators nothing about the doses received. It also put Schreiber at what one report called "great personal risk" of further exposure. That same report concluded that heavy radiation may cause vertigo and leave a person "in no condition for rational behavior." As soon as Slotin left the building, he vomited. His colleagues rushed him to the hospital, where nine days would prove that nothing could be done.

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• 6. Nine Days

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  Numerous volunteers offered blood for transfusions, but Slotin's condition could not be treated. The Army flew his parents from Winnipeg at its own expense, and they reached his bedside four days after the accident. By the fifth day, he was getting rapidly worse.

  Over the next four days, Slotin endured what one account calls an "agonizing sequence of radiation-induced traumas." These included severe diarrhea, reduced urine output, swollen hands, erythema, intestinal paralysis and gangrene. He developed "massive blisters on his hands and forearms." A medical expert described the internal radiation burns across his body as a "three-dimensional sunburn." By the seventh day, he had periods of "mental confusion." His lips turned blue, and he was placed in an oxygen tent. He suffered "a total disintegration of bodily functions" and slipped into a coma. Slotin died at 11 a.m. on the 30th of May, with his parents present. He was buried in Shaarey Zedek Cemetery in Winnipeg on the 2nd of June 1946.

  Six other men had been in the room: Alvin Cushman Graves, Samuel Allan Kline, Marion Edward Cieslicki, Dwight Smith Young, Theodore P. Perlman and Pvt. Patrick J. Cleary. Graves, who stood closest to Slotin, developed acute radiation sickness and spent several weeks in hospital. He survived but lived with chronic neurological and vision problems. Young also suffered acute radiation syndrome and recovered.

  On the 28th of January 1948, Graves, Kline and Perlman sought compensation for their injuries. Graves settled his claim for $3,500. Three of the observers later died of conditions that radiation is known to promote. Graves died of a heart attack twenty years later at age 55. Cieslicki died of acute myeloid leukemia nineteen years later at 42. Young died of aplastic anemia and a bacterial infection of the heart lining twenty-nine years later at 83.

  Louis Hempelman, a consultant to the Los Alamos Scientific Laboratory, argued that so small a sample cannot establish a causal link. His publicly available report included personal medical information that he had earlier refused to give Cieslicki himself, during Cieslicki's final illness.

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• 7. Counting the Dose

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  No one has ever measured exactly what Slotin and Daghlian absorbed. Most of the dose came from neutrons, which the dosimeters of the day could not record. The film badges were not being worn. The badges meant to sit under tables in case of disasters were never found. Only disaster badges hanging on the walls produced useful data, and only about gamma radiation.

  In 1948, researchers made a "tentative" estimate that rested on dozens of assumptions, some now known to be wrong. With no personal badges to read, they relied on sodium activation in blood and urine samples, which neutron radiation causes. They converted every dose to a gamma or X-ray equivalent. They concluded that Daghlian and Slotin probably received doses equal to 290 rem and 880 rem of gamma rays. Minimum and maximum estimates ranged from about 50% to 200% of those values.

  The authors also modeled a mix of soft 80 keV X-rays and gamma rays, which they thought gave a more realistic picture. For Slotin, this mix came to 1930 R of X-ray with 114 R of gamma. For Daghlian, it came to 480 R of X-ray with 110 R of gamma. The X-ray share would concentrate in tissue facing the source, while gamma penetrated the whole body. Five hundred rem is usually a fatal exposure for humans.

  Modern dosimetry works differently, using weighting factors and absorbed doses rather than roentgen. Recent documents interpret Slotin's dose anywhere from 287 rad to 21 Sv. The most reliable estimate may be a 1978 Los Alamos memo. It gave 10 Gy of neutron radiation plus 1.14 Gy of gamma for Slotin, and 2 Gy of neutron plus 1.1 Gy of gamma for Daghlian. Those figures fit the symptoms both men suffered.

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• 8. Hero or Reckless

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  On the 14th of June 1946, Thomas P. Ashlock, associate editor of the Los Alamos Times, published a poem titled "Slotin - A Tribute." It opened with the line "May God receive you, great-souled scientist!"

  The official story credited Slotin's quick reaction, taken at immediate risk to his life, with saving the men working beside him from certain death. Graves endorsed that account at the time. Graves, like Slotin, had shown little concern for nuclear safety, and he later alleged that fallout risks were "concocted in the minds of weak malingerers."

  Decades later, Schreiber spoke out publicly. He argued that Slotin had used improper and unsafe procedures that endangered the others in the laboratory along with himself. Robert B. Brode had reported hearsay to the same effect back in 1946. Some physicists concluded that Slotin's behavior was reckless and that his death was preventable.

  After the accident, Los Alamos ended all hands-on critical assembly work. Later criticality testing used remotely controlled machines, such as the "Godiva" series, with the operator at a safe distance.

  The core had been intended for Able, a detonation in the Crossroads series of nuclear weapons tests. Slotin's experiment was said to be the last before detonation, a final demonstration that the core could go critical. The core needed time to cool, so it was rescheduled for the third test, provisionally named Charlie. Charlie was cancelled after the underwater Baker test left unexpected radioactivity and the target warships could not be decontaminated. The core was eventually melted down, and its material was reused in a later core.

  The 1947 film The Beginning or the End shows a scientist assembling the Hiroshima bomb who dies after contact with radioactive material. Dexter Masters's 1955 novel The Accident is a fictional account of the last days of a nuclear scientist with radiation poisoning. In the 1989 film Fat Man and Little Boy, John Cusack plays Michael Merriman, a fictional character based on Slotin. The Louis Slotin Sonata, a 2001 off-Broadway play, was directed by David P. Moore.

  In 1948, Slotin's colleagues at Los Alamos and the University of Chicago started the Louis A. Slotin Memorial Fund. It paid for physics lectures by distinguished scientists such as Robert Oppenheimer, Luis Walter Alvarez and Hans Bethe, and it lasted until 1962. In 2002, an asteroid discovered in 1995 was named 12423 Slotin in his honour.

  According to Weinberg and Wigner, Slotin was the first to propose calling a certain interval of reactivity a dollar. At zero, a chain reaction sustains itself. At one dollar, the slowly released delayed neutrons are no longer needed to keep it going, and the reaction becomes prompt critical. Stable nuclear reactors operate between zero and a dollar. Excursions and nuclear explosives operate above it. A hundredth of a dollar is called a cent.

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