Experiment Name:
Atomic Physics
IGCSE Single Science
Revision Book - Section 5
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Name: _________________________________
Teacher: _________________________________
Syllabus Content_______________________________
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Syllabus Details________________________________
5.1 Radioactivity
5.1 (a) Detection of radioactivity
Core
• Show awareness of the existence of background radiation
Background radiation
• Radiation is all around us
• Some of the main sources of background radiation are…
o Rocks – e.g. granite
o Outer space
o Building materials
o Radon gas in the air
• Radon gas is a problem when it collects in houses
• Describe the detection of α-particles, β –particles and γ -rays (β + are not included: β particles will be taken to refer to β –)
Geiger – Muller Tube
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• Radiation enters the tube
• The radiation ionises the argon gas
• The positive ions go to the cathode and the electrons go to the anode
• This causes a tiny current to flow
• The current is amplified and detected on a counter
NOTES PAGE
Photographic Film
• Photographic film can be used to detect radiation
• Radiation makes photographic film turn black
• This only lets you know if there was radiation after you develop the film
5.1 (b) Characteristics of the three kinds of emission
Core
• State that radioactive emissions occur randomly over space and time
Radioactive emission:
• This occurs randomly over space and time
• You can not predict which nucleus will decay and when
• State, for radioactive emissions:
– their nature
– their relative ionising effects
– their relative penetrating abilities
|Property |Alpha |Beta |Gamma |
| | | | |
|Nature |Helium nuclei |High energy electron from |Electromagnetic radiation |
| |(2 protons and 2 neutrons) |the nucleus | |
|~Ionising power |High |Medium |Low |
|Penetration (absorbed by) |Low (paper) |Medium (5mm Al) |High (Thick lead) |
|Charge |+2ve |-ve |None |
• Describe their deflection in electric fields and magnetic fields
|Emission |Effect of electric field |Effect of magnetic field |
|Alpha particle |Deflected towards negative parallel to |Deflected perpendicular to the magnetic |
| |field |field |
|Beta particle |Deflected towards positive parallel to |Deflected perpendicular to the magnetic |
| |field |field |
|Gamma radiation |No effect |No effect |
• Interpret their relative ionizing effects
• Alpha particles have a strong ionizing effect as they have 2 positive charges per particle
• Beta particle have a medium ionizing effect as they have 1 negative charge per particle
• Gamma rays are weakly ionizing as they have no charge
NOTES PAGE
5.1 (c) Radioactive decay
Core
• State the meaning of radioactive decay, using equations (involving words or symbols) to represent changes in the composition of the nucleus when particles are emitted
Alpha decay…. Example….
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In alpha decay…
• An alpha particle is lost from the nucleus of an atom
• The number of protons reduces by 2
• The number of neutrons reduces by 2
o The nucleon number reduces by 4
o The proton number reduces by 2
Beta decay… Example….
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In Beta decay…
• A high energy electron is lost from the nucleus
• One Neutron changes into a proton
o The proton number increases by 1
o The nucleon number does not change
Gamma decay… Example….
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In Gamma decay…
• The atom goes from a high energy state to a low energy state
• There is no change to the proton number or the nucleon number
5.1 (d) Half-life
Core
• Use the term half-life in simple calculations, which might involve information in tables or decay curves
Half life…
• The time taken for half of a particular radioactive isotope to decay
• Example…
o If the half time of Carbon 14 is 5600 years
o After 5600 years 1/2 the atoms have not decayed
o After 11200 (2 x 5600) ¼ of the atoms have not decayed
NOTES PAGE
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• The activity of a radioactive isotope decreases with time
• This type of curve is called an exponential curve
5.1 (e) Safety precautions
Core
• Describe how radioactive materials are handled, used and stored in a safe way
SAFE USAGE AND STORAGE OF RADIOACTIVE MATERIALS….
• Radioactive materials produce emissions that are highly ionizing
• These emissions can ionize the skin and organs of humans, so causing birth defects, cancer and burns
• These materials must be handled so that these emission do are not incident on the people working with them
o Storage – Often under water as the water absorbs the emissions well
o Handling – Within fume cupboards and often using robots
o Usage – Within closed environments (with thick highly absorbing walls)
o Waste disposal – Still a big issue but increasingly stored deep underground
NOTES PAGE
5.2 The nuclear atom
5.2 (a) Atomic model
Core
• Describe the structure of an atom in terms of a nucleus and electrons
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Supplement
• Describe how the scattering of α-particles by thin metal foils provides evidence for the nuclear atom
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NOTES PAGE
|Observation |Conclusion |
|Most particles pass straight through the gold leaf |Gold is predominantly empty space |
|~1:8000 are repelled back |Gold has small positively charged nuclei |
|Some are repelled through large angles |The nucleus has a large positive charge |
5.2 (b) Nucleus
Core
• Describe the composition of the nucleus in terms of protons and neutrons
• Use the term proton number Z
• Use the term nucleon number A
Use the term nuclide and use the nuclide notation X
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5.2 (c) Isotopes
Supplement
• Use the term isotope
ISOTOPE: Nuclides with the same number of protons but different number of neutrons
• Give and explain examples of practical applications of isotopes
• Carbon dating – Using the decay of carbon 14 the age of old organic materials can be calculated
o The percentage of carbon 14 in the air is stable and known
o The percentage of carbon 14 in trees is kept constant by photosynthesis
o When trees or plants are cut down and stop photosynthesising the carbon 14 in them decays
o By calculating the percentage of carbon 14 present in old organic artefacts (wooden tools, etc), and knowing the half life of carbon 14, the age of the artefacts can be calculated
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