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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