Global Nuclear Politics
Department of Politics, University of York, Autumn term 2020-21
Background briefing for lecture 1: The Nuclear Age
This background note is designed to give you an overview of how nuclear
weapons work and how they were first invented. For further background reading,
see Andrew Futter, The Politics of Nuclear Weapons, ch. 2 ’What are nuclear
weapons?’ and ch. 3 ‘Testing, defining and delivering nuclear weapons’.
1. What is a nuclear weapon?
The first nuclear weapons were atomic bombs. They produce immense levels of
energy from the splitting, or fissioning, of atomic nuclei. Only certain chemical
elements undergo fission, and then only certain types, or isotopes, of those
elements. Uranium-235 and plutonium-239 are the two fissile materials used in
nuclear weapons. Uranium-235 is a rare form of uranium found in uranium ore
that is mined in a number of countries. Plutonium is an artificial and exotic
element that does not occur naturally. It is made by ‘burning’ uranium fuel in a
nuclear reactor. The first nuclear reactors were invented in order to make
plutonium for use in the US nuclear weapons programme, the Manhattan Project,
in World War II.
When an atom is split it releases neutrons (the core of an atom is made of
protons and neutrons) and some of its mass is converted into energy. Einstein’s
famous E=mc2 equation where ‘e’ is the amount of energy released, ‘m’ is the
amount of mass converted to energy and ‘c’ speed of light (a massive number,
especially when squared) means that a when tiny amount of mass is converted
into energy through the fission process, the amount of energy released is very
large.
The neutrons released from a fissioned uranium or plutonium atom hit other
atoms and cause them to fission and so on. This is called a chain reaction. A
nuclear detonation is an uncontrolled chain reaction involving billions of
reactions in a fraction of second, which results in the release of a huge amount
of energy in a very short space of time from a relatively small mass of material.
1
, The amount of material you need to ensure an uncontrolled chain reaction is
called the critical mass. The critical mass for uranium-235 is 56kg. A material
called a tamper, such as uranium-238, can be used to increase the proportion of
neutrons that cause fission to occur. This can reduce the critical mass to around
14kg. The critical mass for plutonium-239 is 11kg. This can be brought down to
3-4 kg.
You can watch a short video on nuclear fission here. You can read a factsheet on
the production of plutonium here.
The second type of nuclear weapon is a thermonuclear weapon, also known as a
hydrogen bomb, H-bomb, or fusion bomb. The physics here is a bit different. The
energy produced is an order of magnitude bigger than that produced by an
atomic, or fission, bomb. A thermonuclear bomb produces all this energy through
nuclear fusion: the fusing together of atomic nuclei of hydrogen (hence ‘H-
bomb’). Fusing atomic nuclei together requires temperatures and pressures
greater than those found at the centre of the sun. The only way to do this is to
use a fission weapon to create those conditions. A thermonuclear weapon is
therefore a two-stage weapon. The first stage is a regular fission weapon that
‘ignites’ the thermonuclear fuel to release tremendous amounts of energy in a
thermonuclear explosion.
You can watch a short video explaining nuclear fusion here.
Because you can use as much thermonuclear fuel as you like, the amount of
energy you can produce is practically unlimited. The fission bomb that detonated
above Hiroshima exploded with a yield of around 15 kilotons (kt) equivalent of
TNT. That’s 15,000 tons of TNT going off all at once. The first thermonuclear
weapon ever tested by the US in 1952 codenamed ‘Ivy Mike’ detonated with an
explosive yield of 10 megatons. That’s 10 million tons of TNT. The largest
weapon ever tested was the Soviet ‘Tsar Bomba’ in 1957. It was detonated at a
height of 10km and produced an explosive yield of 57 megatons. Its shockwave
2
Department of Politics, University of York, Autumn term 2020-21
Background briefing for lecture 1: The Nuclear Age
This background note is designed to give you an overview of how nuclear
weapons work and how they were first invented. For further background reading,
see Andrew Futter, The Politics of Nuclear Weapons, ch. 2 ’What are nuclear
weapons?’ and ch. 3 ‘Testing, defining and delivering nuclear weapons’.
1. What is a nuclear weapon?
The first nuclear weapons were atomic bombs. They produce immense levels of
energy from the splitting, or fissioning, of atomic nuclei. Only certain chemical
elements undergo fission, and then only certain types, or isotopes, of those
elements. Uranium-235 and plutonium-239 are the two fissile materials used in
nuclear weapons. Uranium-235 is a rare form of uranium found in uranium ore
that is mined in a number of countries. Plutonium is an artificial and exotic
element that does not occur naturally. It is made by ‘burning’ uranium fuel in a
nuclear reactor. The first nuclear reactors were invented in order to make
plutonium for use in the US nuclear weapons programme, the Manhattan Project,
in World War II.
When an atom is split it releases neutrons (the core of an atom is made of
protons and neutrons) and some of its mass is converted into energy. Einstein’s
famous E=mc2 equation where ‘e’ is the amount of energy released, ‘m’ is the
amount of mass converted to energy and ‘c’ speed of light (a massive number,
especially when squared) means that a when tiny amount of mass is converted
into energy through the fission process, the amount of energy released is very
large.
The neutrons released from a fissioned uranium or plutonium atom hit other
atoms and cause them to fission and so on. This is called a chain reaction. A
nuclear detonation is an uncontrolled chain reaction involving billions of
reactions in a fraction of second, which results in the release of a huge amount
of energy in a very short space of time from a relatively small mass of material.
1
, The amount of material you need to ensure an uncontrolled chain reaction is
called the critical mass. The critical mass for uranium-235 is 56kg. A material
called a tamper, such as uranium-238, can be used to increase the proportion of
neutrons that cause fission to occur. This can reduce the critical mass to around
14kg. The critical mass for plutonium-239 is 11kg. This can be brought down to
3-4 kg.
You can watch a short video on nuclear fission here. You can read a factsheet on
the production of plutonium here.
The second type of nuclear weapon is a thermonuclear weapon, also known as a
hydrogen bomb, H-bomb, or fusion bomb. The physics here is a bit different. The
energy produced is an order of magnitude bigger than that produced by an
atomic, or fission, bomb. A thermonuclear bomb produces all this energy through
nuclear fusion: the fusing together of atomic nuclei of hydrogen (hence ‘H-
bomb’). Fusing atomic nuclei together requires temperatures and pressures
greater than those found at the centre of the sun. The only way to do this is to
use a fission weapon to create those conditions. A thermonuclear weapon is
therefore a two-stage weapon. The first stage is a regular fission weapon that
‘ignites’ the thermonuclear fuel to release tremendous amounts of energy in a
thermonuclear explosion.
You can watch a short video explaining nuclear fusion here.
Because you can use as much thermonuclear fuel as you like, the amount of
energy you can produce is practically unlimited. The fission bomb that detonated
above Hiroshima exploded with a yield of around 15 kilotons (kt) equivalent of
TNT. That’s 15,000 tons of TNT going off all at once. The first thermonuclear
weapon ever tested by the US in 1952 codenamed ‘Ivy Mike’ detonated with an
explosive yield of 10 megatons. That’s 10 million tons of TNT. The largest
weapon ever tested was the Soviet ‘Tsar Bomba’ in 1957. It was detonated at a
height of 10km and produced an explosive yield of 57 megatons. Its shockwave
2
