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Physicss Physics A Level Physics Home Revision hut
Radioactivity
Radioactive materials have unstable nuclei which try to
 “decay”into more stable nuclei. They do this by emitting
particles from their nucleus.
 There are two types of particle, Alpha and Beta.
 Alpha Decay α
 Some elements decay by emitting alpha  particles.  These
 consist of 2 protons and 2 neutrons (the same as a helium
 nucleus). Radium decays to Radon by alpha emission.
226
88 Ra
222
86
Rn 2 α (note. the top number is the atomic mass (protons + neutrons) and the bottom number is the atomic number ( number of protons)) Beta Decay β Some elements decay by emitting beta particles. This is when a neutron changes to proton and an electron. The proton stays in the nucleus but the electron is emitted as a beta particle. Carbon 14 decays to Nitrogen by beta emission.
14
6 C 7 N β 0
-1
Gamma emission γ
After alpha or beta particles have been emitted the
 nucleus can remain in an “exited state. The protons
 and neutrons are rearranged resulting in γ emission.
 Gamma emission is not in the form of particles, it is
high energy electomagnetic radiation.
Penetration by alpha,beta particles
and Gamma rays
 Alpha particles  are the least penetrating and are
easily stopped by a sheet of paper and only
 travel a few cm in air
 Beta particles can pass through paper but can be
stopped by a thin sheet of aluminium and can
 travel several metres in air
 Gamma rays are very penetrating and are only stopped
by many cm of lead.