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UNIVERSITY OF CAMBRIDGE
DEPARTMENT OF ENGINEERING
4M16 NUCLEAR POWER COURSE
BASIC PRINCIPLES
Introduction
The objective of this course is to give a basic introduction to nuclear energy and the principles of
physics which underlie the production of power from nuclear sources. Questions of health physics,
safety and waste production will also be discussed.
Terminology
Isotopes denoted by:
Z
AI
often simplified to
IA
eg U235, Pu239
where:
Mass Number A: is total number of heavy particles in the nucleus (nucleons)
Atomic Number Z: is the number of protons
Neutron Number N: is the number of neutrons
A = N + Z
Radioactive Decay
Alpha (α): the release of a helium nucleus, usually accompanied by gamma (γ) rays which
are a form of electromagnetic radiation
Mass number falls by 4, atomic number falls by 2
Beta (β): the emission of a negative particle equivalent to an electron by the transformation
of a neutron into a proton
Neutron = proton + beta (–) particle + neutrino
Mass number is unchanged, atomic number increases by 1
Beta positive decay is possible though less common
Proton = neutron + beta (+) particle + neutrino
Mass number is unchanged, atomic number falls by 1
Beta decay is again usually accompanied by gamma rays
Gamma (γ): emission is electromagnetic radiation and if alone there is no change in mass
atomic or neutron numbers.
Neutron emission also occurs in some nuclear reactions and is critical to the generation of
electricity by nuclear energy.
Basic Decay Equations
N = N0 exp(–λt)
where N is number of nuclei at time t
N0 is number at time 0
λ is the decay constant
