1. P2 - Physics
Radiation

2. P2 – Physics - Aims
(HIGHER TIER ONLY) – to explain how the Rutherford and Marsden scattering experiment led to the ‘plum pudding’ model of the atom being replaced by the nuclear model

3. P2 – Physics - Structure of the atom
A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it…
Ernest Rutherford, British scientist:
I did an experiment (with my colleagues Geiger and Marsden) that proved this idea was wrong. I called it the “Scattering Experiment”

4. P2 – Physics - The Rutherford Scattering Experiment
Alpha particles (positive charge, part of helium atom)
Thin gold foil
Most particles passed through, 1/8000 were deflected by more than 900
Conclusion – the atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.

5. P2 – Physics - The structure of the atom
ELECTRON – negative, mass nearly nothing
PROTON – positive, same mass as neutron (“1”)
NEUTRON – neutral, same mass as proton (“1”)

6. P2 – Physics - The structure of the atom
Particle
Relative Mass
Relative Charge
Proton 1 +1
Neutron
Electron -1
MASS NUMBER = number of protons + number of neutrons He 2 4
SYMBOL
PROTON NUMBER = number of protons

7. P2 – Physics - Radiation
In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no net electrical charge
All atoms of a particular element have the same number of protons
Atoms of different elements have different numbers of protons
Atoms of the same element that have different numbers of neutrons are called isotopes

8. O 8 16 O 8 17 O 8 18 P2 – Physics - Isotopes
An isotope is an atom with a different number of neutrons:
Notice that the mass number is different. How many neutrons does each isotope have? O 8 16 O 8 17 O 8 18
Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.
A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.

9. P2 – Physics - Background Radiation
13% are man-made
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power

10. P2 – Physics - Types of radiation
1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 ______ – the nucleus of a ______ atom)
Unstable nucleus
New nucleus
Alpha particle
2) Beta () – an atom decays into a new atom by changing a neutron into a _______ and electron. The fast moving, high energy electron is called a _____ particle.
Beta particle
Unstable nucleus
New nucleus
3) Gamma – after  or  decay surplus ______ is sometimes emitted. This is called gamma radiation and has a very high ______ with short wavelength. The atom is not changed.
Words – frequency, proton, energy, neutrons, helium, beta
Unstable nucleus
New nucleus
Gamma radiation