Stephen Schwartz Profile picture
Aug 21, 2021 8 tweets 3 min read Read on X
76 years ago tonight at Los Alamos, 24-year-old graduate student and Manhattan Project physicist Harry Daghlian, Jr., was conducting a risky criticality experiment alone when he accidentally dropped a 4.4 kg (9.7 lb) tungsten carbide brick on a 6.2 kg (13.7 lb) plutonium core.
The brick increased neutron reflectivity back into the core, instantly causing it to go supercritical and flood the wooden shack with radiation. Although Daghlian quickly pushed the extra brick off the core with his right hand, he still received an estimated dose of 510 rem.
Daghlian was taken to the Los Alamos hospital and his symptoms were treated. As he slowly and painfully succumbed to acute radiation poisoning, he methodically described his condition to observing doctors. He died 25 days later, the Manhattan Project's first radiation fatality.
Army Private Robert Hemmerly was on guard duty that night in the shack as Daghlian performed his last experiment, but he was seated about 12 feet away with his back turned, reading a newspaper. The 29-year-old saw a bright blue flash and received an estimated dose of 50 rem.
Although Hemmerly's white blood cell count was elevated for a few days and he felt more tired than usual for about two months, he did not suffer from radiation sickness. He fathered two more children in 1947 and 1948 and died from acute myelogenous leukemia in 1978, at age 62.
Nine months to the day after Harry Daghlian's accident, another Los Alamos physicist conducting a similar criticality experiment with the same plutonium core suffered the same fate. The so-called "demon core" was subsequently melted down and reused.
Left: Herbert Lehr and Daghlian load the assembled plutonium core of the "Gadget" into a Plymouth sedan to drive it to the Trinity shot tower on July 13, 1945.

Right: Louis Slotin (standing left) and Daghlian (seated) help to fully assemble the "Gadget" before the Trinity test.
Here's another remarkable photo of Slotin and Lehr standing in the canvas tent at the base of the shot tower next to the now uncovered tamper plug containing the 13.6-pound core of the "Gadget" prior to its insertion into the casing.

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More from @AtomicAnalyst

Oct 3, 2023
Today in 1986, 680 miles NE of Bermuda, the Soviet Yankee 1-class ballistic missile submarine K-219 was on patrol when seawater leaked into a missile tube, triggering an explosion of the missile’s volatile liquid fuel that killed three sailors and crippled the submarine.


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Under very dangerous conditions, the crew managed to shut down the submarine’s reactors and stabilize it. Captain Igor Britanov was ordered to have the K-219 towed by freighter 4,300 miles to its homeport of Gadzhiyevo (near Murmansk), but it flooded and sank three days later. Image
The K-219—including its two nuclear reactors, 16 submarine-launched ballistic missiles, and 32-48 thermonuclear warheads—sank in 18,000 feet of water to the bottom of the Hatteras Abyssal Plain. Image
Read 10 tweets
Sep 29, 2023
This afternoon in 1957, in the closed city of Chelyabinsk-65 near Kyshtym in the Southern Urals, a stainless steel tank holding 70-80 tons of highly-radioactive waste left over from processing plutonium for nuclear weapons exploded, releasing 20 million curies of radioactivity. Image
While the explosion was chemical in nature (much of the liquid waste evaporated over time, leaving behind a volatile dry mixture of sodium nitrate and sodium acetate), a brief nuclear criticality may have initiated it. The explosion’s size has been estimated at 5-100 tons of TNT.
The explosion completely destroyed the tank and damaged two adjacent ones. About 90 percent of the radioactive waste fell to the ground in the immediate vicinity of the tank, while about 10 percent was lofted by the wind in a plume up to 1 kilometer high and 300 kilometers long. Image
Read 9 tweets
Sep 19, 2023
Today in 1980 at about 3:00am, the highly-volatile liquid fuel of a nuclear-armed Titan II ICBM exploded inside an underground silo 3.3 miles north-northeast of Damascus, Arkansas, and approximately 50 miles north of the capital of Little Rock, destroying the missile and silo.

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The explosion—which occurred more than 8 hours after a worker accidentally dropped a large socket, puncturing a fuel tank—killed Sr. Airman David Livingston, 22, destroyed the missile and silo, and hurled its 9-Mt W53 warhead through the 740-ton silo doors and ~100 feet away.


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Note also the unintentionally ironic, below-the-fold headline in the St. Louis Post-Dispatch that day, beneath the article about the catastrophic accident: “Would Use A-Bomb If Necessary To Defend U.S., Carter Warns.” Image
Read 7 tweets
Sep 17, 2023
Today in 1955, a specially-modified B-36 bomber—the NB-36H—made its first test flight out of Carswell AFB, Texas, carrying (but not powered by) an operational 1-Megawatt air-cooled nuclear reactor. It would make 46 additional flights over Texas and New Mexico through March 1957. Image
The NB-36H flew directly over Lake Worth, the principal water source for Fort Worth. A B-50 carrying specially-trained paratroopers escorted each test flight. Had the NB-36H crashed, they would jump into the impact zone to prevent any unauthorized entry.
A 12-ton lead-and-rubber-shielded cockpit with windows 10-12 inches thick protected the flight crew from the otherwise lethal amount of radiation emanating from the reactor hanging in the bomb bay. Special water pockets installed aft of the cockpit also absorbed radiation.
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Read 20 tweets
Sep 14, 2023
OTD in 1954—for its ninth nuclear test—the USSR staged a live-fire nuclear wargame ~600 mi. SE of Moscow near Totskoye. At 9:33am (local), a 40-kt atomic bomb exploded 1,150 feet in the air between two groups of soldiers, some just 2 miles from the blast.
The roughly 45,000 soldiers were then ordered into mock battle under highly radioactive conditions for the remainder of the day. Most had no protective equipment and were not warned about the dangers. Some who were issued gas masks removed them in the oppressive 115F (46C) heat.
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Exposures that day were reportedly ten times the maximum allowable level for US soldiers for an entire year. The 1,000,000 people who lived within 100 miles of the blast were given no warning at all. For more about this “monstrous” exercise, see: washingtonpost.com/archive/politi…
Read 10 tweets
Sep 11, 2023
On September 11, 2001, US Strategic Command was one week into its annual Global Guardian nuclear command and control exercise. Bombers had been armed with nuclear weapons, ICBMs and several SSBNs were on alert, and three E-4B command posts were airborne. omaha.com/local/on-strat…
Which is why, when Air Force One landed at Barksdale Air Force Base, Louisiana (taking President George W. Bush from Sarasota, Florida, to Offutt Air Force Base, Nebraska, and, eventually, back to Washington, DC), this is the first thing that happened: politico.com/magazine/story…
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In 2016, @warkin and @rwindrem reported that three dozen live nuclear weapons were loaded aboard strategic bombers at three US Air Force bases that day. The other bases were almost certainly Minot AFB in North Dakota and Whiteman AFB in Missouri. nbcnews.com/storyline/9-11…
Read 9 tweets

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