nuclear physics


Operation Dominic - Sunset (1962)

The Soviet Union had abrogated the 34 month old de facto nuclear testing moratorium on 1 September 1961 by initiating an unprecedented series of atmospheric nuclear tests. The initial U.S. response was to commence its own test series (Operation Nougat) two weeks later. Nougat was an underground series however, restricted to very low yield devices.

Numerous atmospheric tests, many at high yield, were of course on the drawing board at the weapons labs, some carried over from planning for previous test series. The Dominic Sunset test successfully reached the full design yield with a yield-to-weight ratio of 4.06 kt/kg. The vapor cloud rose to over 60,000 feet.

Nuclear detonations produced high above the ground do not create mushroom clouds. The heads of the clouds themselves consist of highly radioactive particles, primarily the fission products, and are usually dispersed by the wind, though weather patterns (especially rain) can produce problematic nuclear fallout.

Nuclear explosions are often accompanied by short-lived vapor clouds known variously as “Wilson clouds”, condensation clouds, or vapor rings. The low pressure region causes a sharp drop in temperature, causing moisture in the air to condense in a shell surrounding the explosion. When the pressure and temperature return to normal, the Wilson cloud dissipates.

Cherenkov radiation - faster than light in a meduim.

Vavilov-Cherenkov radiation is electromagnetic radiation emitted when a charged particle (in this case the electron) passes through an electrically polarizable medium at a speed greater than the phase velocity of light in that medium - in cherenkov radiation, electrons are emitted faster than than the speed light travels in water.

light travels through water at 0.75c (thats 75% the speed of light in a vacuum). Matter can be accelerated beyond this speed  during nuclear reactions and in particle accelerators.

Cherenkov radiation is used in particle physics to identify types of particles. One could measure the velocity of an electrically charged elementary particle by the properties of the Cherenkov light it emits in a certain medium. If the momentum of the particle is measured independently, the mass of the particle can be computed by its momentum and velocity, and with this identify the particle.

The radiant blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after the Soviet scientist and Nobel Prize winner Pavel Alekseyevich Cherenkov, who discovered it in 1958 through experiment.



Nov. 1, 1952: First Hydrogen Bomb Test

Ivy Mike was the codename given to the first test of a thermonuclear device, in which part of the explosive yield comes from nuclear fusion. It was detonated on November 1, 1952 by the United States on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy. The device was the first full test of the Teller-Ulam design, a staged fusion bomb, and was the first successful test of a hydrogen bomb.

The blast created a crater 6,240 feet (1.9 km) in diameter and 164 feet (50 m) deep where Elugelab had once been; the blast and water waves from the explosion (some waves up to twenty feet high) stripped the test islands clean of vegetation, as observed by a helicopter survey within 60 minutes after the test, by which time the mushroom cloud and steam were blown away. Radioactive coral debris fell upon ships positioned 35 miles (48 km) from the blast, and the immediate area around the atoll was heavily contaminated for some time. Produced by intensely concentrated neutron flux about the detonation site were two new elements, einsteinium and fermium.

The nuclear explosion was photographed by high-speed rapatronic cameras less than 1 millisecond after detonation. Developed by Dr. Harold Edgerton in the 1940s, the rapatronic photographic technique allowed nuclear explosion’s fireball growth to be recorded on film. The exposures were often as short as 10 nanoseconds, and each rapatronic camera would take exactly one photograph.

We May All Be Made of Stardust, But What Makes Stardust?

Most of my followers should know that the atoms that comprise your body and just about everything around you were forged in stars. If you didn’t know this I urge you to spend more time avidly watching Cosmos.

But how does this process actually occur? The secret lies in nuclear fusion which is essentially the opposite to fission (which causes radioactive decay). Fusion is simply the combination of two nuclei into one larger nuclei. In the process a large amount of energy is released. The energy that is released is what powers stars and gives you sunlight.  The cornerstone of this process lies in a property called binding energy, which is essentially the energy that holds together an atom’s nucleus. The important thing is to relate this to the mass of nucleus by referring to it as “binding energy per nucleon” (protons and neutrons essentially). Of all the elements iron has the highest binding energy per nucleon which means that combining atoms smaller than iron releases energy, whilst combining atoms that are larger requires an energy input. Heavier elements than iron are typically only produced during supernovas (a remnant of which is pictured above) which also have the effect of distributing the atoms in shells or jets.


The promising development of Compact Fusion at Lockheed Martin - Skunk Works.

More, elsewhere:


Meet the youngest person on Earth to achieve nuclear fusion

Taylor Wilson built his first bomb when he was 10 years old. Four years later, he became the thirty-second person on Earth to ever build a working nuclear fusion reactor.

“I would say someone like [Taylor] comes along maybe once in a generation,” says Kristina Johnson, who, when she met Taylor, was serving as the Under Secretary of Energy at the U.S. Department of Energy. “He’s not just smart; he’s cool and articulate. I think he may be the most amazing kid I’ve ever met.”

And after reading this incredible profile on Taylor, penned by Popular Science’s Tom Clynes, we’re inclined to agree — though calling Taylor “smart” may just be the understatement of the century.

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The Advanced Test Reactor

The Advanced Test Reactor (ATR) is a research reactor at the Idaho National Laboratory, located east of Arco, Idaho. This reactor is primarily designed and used to test materials to be used in other, larger-scale and prototype reactors.

Test reactors are very different in appearance and design from commercial, nuclear power reactors. Commercial reactors are large, operate at high temperature and pressure, and require a large amount of nuclear fuel. Because of their large size and stored energy, commercial reactors require a robust “containment structure” to prevent the release of radioactive material in the event of an emergency situation. A typical commercial reactor has a volume of 48 cubic meters with 5400 kg of uranium at 288 °C (550 °F) and 177 atm. By contrast, the ATR does not require a large containment structure—it has a volume of 1.4 cubic meters, contains 43 kg of uranium, and operates at 60 °C (140 °F) and 26.5 atm (conditions similar to a water heater).

The ATR core is designed to be as flexible as possible for research needs. It can be brought online and powered down safely as often as necessary to change experiments or perform maintenance. The reactor is also powered down automatically in the event of abnormal experimental conditions or power failure.

The reactor is a virtual “time machine.” Part of the uniqueness of the ATR rests with its capability to produce an extremely high neutron flux that duplicates years of exposure of materials experienced in a commercial nuclear reactor’s radiation environment in a matter of weeks or months. Its core design allows many experiments to be conducted simultaneously, with each experiment receiving a different and carefully controlled level of radiation.

The blue glow is the Cherenkov light that is emitted by the electrons from beta decay going on in the nuclear fuel. This characteristic blue glow is due to Cherenkov radiation. It is named after Russian scientist Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to detect it experimentally. A theory of this effect was later developed within the framework of Einstein’s special relativity theory by Igor Tamm and Ilya Frank, who also shared the Nobel Prize.

Image credit: Idaho National Laboratory


On the Shelves in Oxford, or rather On the Grass in Oxford this week, we have five new Very Short Introductions!

Robert A. Segal’s Myth: A Very Short Introduction looks at the origins of the study of myths, and how they have been applied to the arts and sciences. In Psychoanalysis: A Very Short Introduction, Daniel Pick offers a lucid, lively, and wide-ranging survey of psychoanalysis. Similarly, in Byzantium: A Very Short Introduction, Peter Sarris introduces the reader to the unique fusion of Roman political culture, Greek intellectual tradition and Christian faith that took place in the imperial capital of Byzantium. Frank Close’s Nuclear Physics: A Very Short Introduction provides an accessible introduction to this complex field, showing how nuclear physics brings the science of the stars to Earth. Last but not least, Robert J. Allison’s The American Revolution: A Very Short Introduction is a brisk, accessible, and vivid introduction to arguably the most important event in the history of the United States - the American Revolution.

Written by experts in the field, these Very Short Introductions offer concise, intelligent and manageable introductions to a diverse range of subjects. See what you will discover…

Photos by Amelia Carruthers for Oxford University Press.


The Rapid Action Electronic camera is a high-speed camera capable of recording a still image with an exposure time as brief as 10 nanoseconds. It was developed by Harold Edgerton in the 1940s and was first used to photograph the rapid changing matter in nuclear explosions within milliseconds of ignition. For a film-like sequence of high-speed photographs, arrays of up to 12 cameras were deployed, with each camera carefully timed to record a different time frame. Each camera was capable of recording only one exposure on a single sheet of film, so in order to create time-lapse sequences, banks of 4 to 10 cameras were set up to take photos in rapid succession.