P2.6- Radioactivity

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How did a packet of uranium salts form the image of a key on the film developed by Henri Becquerel?
The uranium salts sent out radiation. This passed around the key that was sitting on top of the film, but it was blocked by the key.
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What prize was Marie Curie awarded for the discovery of polonium and radium?
The 1911 Nobel Prize
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What is likely to have caused Marie Curie to fall ill with leukaemia?
Radiation poisoning from the radioactive materials she worked with
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Name a device which can be used to detect radioactivity.
A Geiger counter
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Name the three types of radiation given out by radioactive substances. In each case, give the symbol.
1) alpha radiation, α 2) beta radiation, β 3) gamma radiation, γ
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Which type of radiation can be stopped using a sheet of paper?
alpha radiation
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Why do the unstable nuclei of radioactive substances emit radiation?
To become stable
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What term is used to describe the emission of radiation from an atom?
Radioactive decay
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Why do we say that the emission of radiation is a random event?
Because we can’t tell when an unstable nucleus will decay
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Where can background radiation come from?
The environment, from space or from devices such as X-ray machines
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What famous discovery did Ernest Rutherford make in 1913?
The discovery of the nucleus
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What experiments did he use to prove his discovery?
Alpha particle scattering experiments
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How did Rutherford deduce that the nuclei of atoms are positively charged?
Because (positively charged) alpha particles were repelled by the nuclei, and like charges repel, therefore the nuclei must be positively charged.
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How did Rutherford deduce that the atomic nucleus is much smaller than the atom?
Because most alpha particles pass through the atom without deflection
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Give three reasons why Rutherford’s nuclear model was quickly accepted.
1) It agreed with measurements that Geiger and Marsden had made in their experiments. 2) It explained radioactivity in terms of the changes that happen to an unstable nucleus when radiation is emitted. 3) It predicted the existence of the neutron.
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Describe the ‘plum pudding’ atomic model.
Some scientists thought that the atom consisted of positively charged matter, evenly spread out, with electrons buried inside, similar to plums in a plum pudding.
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Why did Rutherford’s experiments disprove the plum pudding model?
The plum pudding model couldn’t explain why some alpha particles were scattered through large angles by atoms.
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How is a charged particle formed?
A charged particle is formed when an atom loses or gains electrons.
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What is a charged particle called?
An ion
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What does the ‘atomic number’ refer to?
The number of protons in a nucleus
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What symbol is the atomic number given?
Z
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What are isotopes?
Atoms of the same element with different numbers of neutrons.
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What name is given to the number of protons and neutrons in a nucleus?
The mass number
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What does an alpha particle consist of?
Two protons and two neutrons
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What happens in the nucleus when a beta particle is created?
A neutron in the nucleus changes into a proton and a β particle (electron). The β particle is instantly emitted at high speed.
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Write down (1) the relative mass and (2) the relative charge of a β particle.
1) Relative mass is effectively zero. 2) Relative charge is -1.
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When does γ radiation take place in the nucleus?
After an α or β particle has been emitted
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What are the properties of γ radiation?
γ radiation is uncharged and has no mass.
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What happens to the number of protons and neutrons in the nucleus after γ radiation has been emitted?
They are unchanged.
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Describe the two steps that should be used to find the count rate due to a radioactive source using a Geiger counter.
1) Measure the background count rate. 2) Measure the count rate with the source in place, and subtract the background count rate from this to find the source count rate.
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How can we test the range of the source in the air?
By moving the Geiger tube away from the source until the count rate due to the source drops to zero.
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How does gamma radiation move through air?
It spreads out without being absorbed.
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What is a β particle?
A fast-moving electron
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Why are α particles deflected in the opposite direction to β particles?
Because α radiation consists of positively charged particles while β radiation consists of negatively charged particles
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Why are α particles harder to deflect than β particles?
Because α particles have a much greater mass than β particles
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What does gamma radiation consist of?
Electromagnetic radiation
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What other type of field other than an electric field could be used to deflect radiation?
A magnetic field
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When an alpha particle passes through an electric field, what can be said about the force deflecting it, compared to a beta particle?
It is twice as great.
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Why is this?
Because the charge of an alpha particle is twice that of a beta particle
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What is ionisation?
Ionisation is when radiation from a radioactive substance knocks electrons out of other atoms, causing them to become charged.
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Why can ionisation be a danger when radiation passes through a living thing?
Ionisation in a living cell can damage or kill the cell. Damage to the genes inside a cell can be passed on if the cell generates more cells.
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Which type of radiation is more dangerous in the body and why?
Alpha radiation because it has a greater ionising effect than beta or gamma radiation
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What do we mean by the ‘activity’ of a radioactive isotope?
The number of atoms that decay per second
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How do we measure the count rate due to a sample?
By using a Geiger counter to measure the number of counts per second
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What can you say about the average time taken for the count rate to fall by a half?
It is always the same.
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What do we mean by ‘half-life’?
The average time it takes for the number of nuclei of a radioactive isotope in a sample to half
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After one half-life, what will have happened to the count rate?
It will have halved.
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Why do we say that radioactivity is a random process?
Because we can’t predict when an individual atom will decay
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Why can we predict how many atoms will decay in a certain time?
Because there are (usually) a very large number of atoms in a sample
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What two factors need to be considered when choosing a radioactive substance for a particular job?
1) The half-life of the substance 2) The type of radiation given out
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When is automatic thickness monitoring used?
When making metal foil
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How does an automatic thickness monitor know when the foil is too thick?
The amount of β radiation penetrating the material drops and so the detector reading drops.
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The amount of β radiation penetrating the material drops and so the detector reading drops.
The detector sends a signal to the rollers, which then increase the pressure on the sheet, making it thinner again.
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What are radioactive tracers used for?
To track the flow of a radioactive substance though a system
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Radioactive iodine is used as a radioactive tracer in patients with suspected blocked kidneys. Give three reasons for choosing radioactive iodine.
1) Its half-life is a few days, so it lasts long enough for the test to be done but decays almost completely after a few weeks. 2) It decays into a stable product. 3) It emits gamma radiation, so it can be detected outside the body.
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What are (1) carbon dating and (2) uranium dating used for?
What are (1) carbon dating and (2) uranium dating used for?
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Which has a longer half-life: radioactive carbon or uranium?
Uranium
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What is measured during carbon dating?
The count rate from the wood
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What needs to be measured during uranium dating?
The number of atoms of uranium and lead
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Other cards in this set

Card 2

Front

What prize was Marie Curie awarded for the discovery of polonium and radium?

Back

The 1911 Nobel Prize

Card 3

Front

What is likely to have caused Marie Curie to fall ill with leukaemia?

Back

Preview of the front of card 3

Card 4

Front

Name a device which can be used to detect radioactivity.

Back

Preview of the front of card 4

Card 5

Front

Name the three types of radiation given out by radioactive substances. In each case, give the symbol.

Back

Preview of the front of card 5
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