Today’s Bombs, Making a Bomb


Bombs are bigger today.

One kiloton was originally defined as the explosive equivalent of 1000 tons of TNT. This definition was found to be imprecise and so the term was redefined to be the release of 10^12 calories of explosive energy. The largest weapon ever tested was a 50 megaton (Mt) (1 megaton = 1000 kilotons) weapon that the Soviets exploded 3.5 kilometers above Novaya Zemlya on October 30, 1961. For comparison, the total tonnage of bombs dropped during World War II was approximately two Mt, and during the Vietnam War it was approximately 6.3 Mt.

Both the US and Russia have bombs in the Mt range, Pakistan and India have bombs in the 15 – 20 kT range.

Although nuclear weapons are radioactive and this will eventually cause cancers later, the important issue is the size of the bombs that one plane can carry. For example, the bombing of Dresden involved les than 3 kt of bombs, and many, many planes.

Nuclear Winter

A few decades back, nuclear winter was considered to be a possible result of a superpower nuclear war. So much dust is kicked into the air, it’s like being hit by a major meteorite (such as occurred 65 million years ago, killing the dinosaurs and a whole bunch of other species). The original assumption was thousands of Mt in nuclear weapons leading to a dramatic decrease in the Earth’s temperature. However, the people involved in the original calculations were not bomb experts, they also assumed a flat Earth, and generally, it is now believed that a nuclear war of this magnitude would produce some cooling of the Earth during the day due to all the dust, a warming during the night because the heat can’t escape, for a short period of time. It is no longer thought to be a major consequence of an all out nuclear war.

Terrorists and the bomb

Back to Bodansky:

Currently nuclear war between the major nuclear powers (the US and Russia) and the intermittently threats of an India-Pakistan both appear remote.

The most imminent threat for the United States, and perhaps for the world as a whole, appears to be from the possible use of single weapons by terrorist groups.

A 1-kt bomb could kill half of people from thermal burns within 610 meters (0.4 miles). Additionally, people as far away as 790 meters (0.5 miles) could receive an absorbed dose of 4 grays (Gy). Of 23 Chernobyl victims receiving doses between 4 and 6 Gy, 7 died. A ground level explosion could create heavy local fallout: up to 4 Gy for a distance of 5.5 km (3.4 miles) downwind.

Because much of the dose is due to very short-lived radionuclides, the rate falls very rapidly with time–by approximately a factor 10 when the time increases by a factor of 7. Thus, at 7 h, the dose rate is 10% of the 1-h level, at 49 h, it is 1% of the 1-h level.

Preferences on bomb designs are shifting.

It is considerably easier to make a bomb using enriched uranium than to make one using with plutonium, and uranium may be becoming the material of choice for countries or groups that want to build a bomb with minimal effort and chance of detection.

This is because the spontaneous fission rates for Pu is larger, so a more complicated means is needed to combine the subcritical masses to make a supercritical mass. More on this in the next post.

Also in this series
Part 1 Nuclear Bombs, Nuclear Energy, and Terrorism
Part 3 Making Bombs from Nuclear Waste
Part 4 Terrorist Targets
Part 5 Nuclear Proliferation—International Treaties
Part 6 The Bomb Spreads
Part 7 Nuclear Power and the Weapons Threat
Part 8 Wrapup on Nuclear Power Series

Comments are closed.