# Physics Definitions

• Created by: Georgia
• Created on: 14-04-13 13:20

## Random

Can't predict which nucleus will decay and when.

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## Decay Constant

The probability that one atom will decay per unit time.

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## Half Life

The time taken for the decay rate (activity) to fall to half its original value.

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## Activity

The number of nuclei of the isotope that disintergrate per second.

OR,

The rate of change of the number of nuclei of the isotope.

(1 Bequerel = 1 Disintergration per second)

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## Isotope

Atoms of the same element that have the same number of protons but a different number of neutrons.

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## The Atomic Mass Unit

u, is defined as one twelfth of the mass of one atom of carbon-12.

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## Binding Energy of a Nucleus

The energy required to completely separate the nucleus into its individual nucleons.

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## Mass Defect

The mass of a nucleus is always less than the total mass of its constituent nucleons. This difference is called the Mass Defect.

Any nucleus has a mass defect which, when concerted to its energy equivalent, is equal to the binding energy of that nucleus.

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## Fission

Occurs when a large nucleus, such as that of Uranium, splits into two much smaller nuclei.

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## Fusion

Takes place when two nuclei combine to form a bigger nucleus.

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## Moderator

A material that slows down fast neutrons (produced by fission process) without absorbing them.

Suitable materials: Carbon in the form of Graphite, Heavy Water (Deuterium Oxide).

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## Control Rods

Absorb surplus neutrons before they cause further fission.

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## Specific Heat Capacity

The heat energy, in joules, required to increase the temperature of 1kg of that substance by 1K.

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## Latent Heat of Fusion

The heat required to change the state of 1kg of the material from solid to liquid without a change in termperature.

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## Latent Heat of Vaporisation

The heat required to change the state of 1kg if the material from liquid to vapour (gas) without a change in temperature.

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## Boyle's Law

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume.

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## Charles' Law

For a fixed mass of gas at a constant pressure, the volume is directly proportional to the absolute temperature.

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## Pressure Law

For a fixed mass of gas at constant volume, the pressure is directly proportional to the absolute temperature.

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