GCSE Physics Edexcel P3 Topic 3

These are revision notes I made myself. I got A* in the Physics GCSE exam and 80 UMS (full marks) in the P3 exam using only these notes.

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P3 Topic 3: Production, uses and risks of ionising radiation from radioactive sources
In an atom, as said before, the number of protons and electrons are the same. Atoms with different numbers
of neutrons but are the same element are called isotopes.
An atom is electrically neutral as equal number of positive protons as negative electrons.
Ion: an atom which has lost or gained electrons and so has a net charge eg. Na2+
The particles found in the nucleus are called nucleons.
All atoms of a particular element have the same number of protons. This number is called the atomic number
or proton number of the element.
The number of neutrons in an atom can vary; the mass number or the nucleon number is the total number of
protons and neutrons in the nucleus.
Relative mass and charge
Sub atomic particles Relative Mass Relative charge
Proton 1 +1
Neutron 1 0
Electron 1/1840 or 0 -1
Positron 1/1840 or 0 +1
Alpha, Beta and Gamma radiation
Alpha Beta Gamma
4 0
What is it? A helium nucleus, 2 He An electron -1 e Electromagnetic radiation
Is it fast, slow, heavy or Slow and heavy Light and fast No mass, very fast
Is it ionising? Strongly ionising Moderately ionising Weakly ionising
How penetrating is it and Stopped by paper, skin Stopped by thin metal Stopped by thick lead or
what stops it? etc. very thick concrete
This is the antiparticle of an electron. The only difference is they are positively charged. They all have the
same properties as electrons, otherwise.
Neutron radiation
Neutrons are more penetrating than alpha or beta and sometimes even more penetrating than gamma.
They are not directly ionising but they can be absorbed by the nuclei of atoms in the substances they pass
Absorbing a neutron can make a nucleus radioactive, which then can make the nucleus ionising and as a result,
neutrons are sometimes referred to as `indirectly ionising'.
Neutrons are best absorbed by light nuclei. Hydrogen is the lightest of them all so hydrogen rich substances
such as water, polyethene and concrete are used for neutron radiation shields.
As well as this, thick lead is often added to the neutron radiation shielding to shield against possible gamma
radiation as well.
Beta minus (-) decay
In - decay a neutron becomes a proton plus an electron. Beta minus radiation consists of a stream of high
energy electrons which are ionising.

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Beta plus (+) decay
In + decay a proton becomes a neutron plus a positron. Positron decay decreases the atomic number by one
but leaves the mass number unaffected.
Alpha radiation
Each alpha particle is made up of two protons and two neutrons. They are not very penetrating but they are
very ionising. They are very large compared with beta particles so are easily capable of dislodging electrons
from atoms. However, this mean they lose energy quickly so have a limited range.…read more

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An isotope which lies above the curve has too many neutrons to be stable. An isotope which lies under the
curve has too little neutrons to be stable.
The N=Z curve stops when the proton number goes about 82 as all isotopes are unstable above this number.
When there are:
Too many neutrons: Beta-minus decay occurs which is the emission of an electron from the nucleus.…read more

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Tracers in Medicine
The radioactive isotopes used in tracers always have short half lives.
The tracer is injected into the patient or swallowed. An external detector follows its progress as it moves
around the body. The radiation emitted can be used by a computer to create an image to show where the
strongest reading of radiation is coming from.
Some examples of isotopes used:
o Iodine-131 is a very common one which is absorbed by the thyroid gland.…read more

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Internal and external radiation
Tumours can be treated with internal radiation or external radiation. External radiation uses high-energy
X-rays or gamma rays to destroy the cancer cells. The radiation is closely focused on the tumour but it is
inevitable that some healthy cells may be damaged.
Internal radiation uses an implant of a radioactive substance. This method gives a high dose of radiation to a
small part of the body, so damage to normal tissue surrounding the tumour is limited.…read more


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