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The demon core was a spherical subcritical mass of plutonium in diameter, manufactured during World War II by the United States nuclear weapon development effort, the Manhattan Project, as a fissile core for an early atomic bomb. The core was prepared for shipment as part of the third nuclear weapon to be used in Japan, but when Japan surrendered, the core was retained at Los Alamos for testing and potential later use. It was involved in two criticality accidents at the Los Alamos Laboratory on August 21, 1945, and May 21, 1946, each resulting in a fatality. Both experiments were designed to demonstrate how close the core was to criticality with a tamper, but in each case, the core was accidentally placed into a critical configuration. Physicists Harry Daghlian and Louis Slotin suffered acute radiation syndrome (ARS) and died soon after, while others present in the lab were also exposed. The core was melted down in summer 1946 and the material recycled for use in other cores. The demon core (like the second core used in the bombing of Nagasaki) was, when assembled, a solid sphere measuring in diameter. It consisted of three parts: two plutonium-gallium hemispheres and a ring, designed to keep neutron flux from "jetting" out of the joined surface between the hemispheres during implosion. The core of the device used in the Trinity Test at the Alamogordo Bombing and Gunnery Range in July did not have such a ring. The refined plutonium was shipped from the Hanford Site in Washington state to the Los Alamos Laboratory; an inventory document dated August 30 shows Los Alamos had expended "HS-1, 2, 3, 4; R-1" (the components of the Trinity and Nagasaki bombs) and had in its possession "HS-5, 6; R-2", finished and in the hands of quality control. Material for "HS-7, R-3" was in the Los Alamos metallurgy section, and would also be ready by September 5 (it is not certain whether this date allowed for the unmentioned "HS-8s fabrication to complete the fourth core).

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Atomic bombings of Hiroshima and Nagasaki

On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki. The bombings killed between 129,000 and 226,000 people, most of whom were civilians, and remain the only use of nuclear weapons in an armed conflict. Japan surrendered to the Allies on 15 August, six days after the bombing of Nagasaki and the Soviet Union's declaration of war against Japan and invasion of Japanese-occupied Manchuria. The Japanese government signed the instrument of surrender on 2 September, effectively ending the war.

Prompt criticality

In nuclear engineering, prompt criticality describes a nuclear fission event in which criticality (the threshold for an exponentially growing nuclear fission chain reaction) is achieved with prompt neutrons alone and does not rely on delayed neutrons. As a result, prompt supercriticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while nuclear reactors rely on delayed neutrons or external neutrons to achieve criticality.

Plutonium

Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric.

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The present article presents the mechanical characterization of the fuel rods oscillator developed for the purposes of the COLIBRI experimental program in CROCUS. COLIBRI aims at investigating the radiation noise related to fuel vibrations. The main motiva ...

2020

Thermodynamics, structure, and charge state of hydrogen-vacancy complexes in delta-plutonium

Michael Frederick Francis

Hydrogen-vacancy complexes can form in a material due to the exothermic binding of hydrogen atoms to vacancy sites. We explore the structure and electronic properties of hydrogen-vacancy complexes in delta-Pu using a density functional theory supercell app ...

American Physical Society2014

Stress-modulated composition in the vicinity of dislocations in nearly lattice matched AlxIn1-x N/GaN heterostructures: A possible explanation of defect insensitivity

Nicolas Grandjean, Jean-François Carlin, Marco Cantoni, Eric Feltin, Pierre Stadelmann, Anas Mouti, Jean-Luc Rouvière

Evidence of composition fluctuations around threading dislocations at scales ranging from atomic distances to tens of nanometers is provided by z-contrast imaging, strain measurement, and energy dispersive x-ray spectroscopy in AlxIn1-x N/GaN heterostructu ...

2011

Explores two-dimensional neuron models, Type I and Type II, discussing firing thresholds and Hopf bifurcation.