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Physics > 6. Radioactivity > Flashcards

6. Radioactivity Flashcards

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1
Q

Give an approximation for the radius of an atom

A

1 x 10⁻¹⁰

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2
Q

What are the three subatomic constituents of an atom?

A
  • Proton
  • Neutron
  • Electron
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3
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus.

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4
Q

Approximately what proportion of the total radius of an atom is the radius of the nucleus?

A

1 / 10,000

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5
Q

Describe the arrangement of protons, neutrons, and electrons in an atom.

A
  • Protons and neutrons are found in the atom’s nucleus.
  • Electrons are found in discrete energy levels orbiting around the nucleus in electron shells.
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6
Q

What type of charge does the nucleus of an atom have? Why?

A

Positive charge.
- The nucleus contains protons and neutrons.
- Protons have a positive charge.
- Neutrons have no charge.

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7
Q

Give two ways that an atom’s electron arrangement can be changed.

A
  • Absorbing electromagnetic radiation.
  • Emitting electromagnetic radiation.
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8
Q

Explain how an atom’s electron arrangement changes when it absorbs EM radiation.

A
  • Electrons move to higher energy levels.
  • They move away from the nucleus.
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9
Q

Explain how an atom’s electron arrangement changes when it emits EM radiation.

A
  • Electrons move to a lower energy level.
  • They move towards the nucleus.
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10
Q

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

A
  • The number of protons is equal to the number of electrons.
  • Protons and electrons have equal and opposite charges, so charges cancel out.
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11
Q

What do all forms of the same element have in common?

A

The number of protons.

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12
Q

What is the name given to the number of protons in an atom?

A

Atomic number

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13
Q

What is an atom’s mass number?

A

The total number of protons plus neutrons in the atom.

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14
Q

What is an isotope of an atom?

A

An atom of an element that has a different number of neutrons, but the same number of protons.

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15
Q

What property differs between isotopes of an element?

A

The mass of the atom.

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16
Q

How do atoms turn into positive ions?

A
  • They lose one or more of their outer electrons.
  • Electrons are negatively charged, so the resultant charge of the atom is positive.
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17
Q

What are the relative masses of a proton, neutron, and electron?

A

Proton: 1
Neutron: 1
Electron: 1/2000

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18
Q

What are the relative charges of a proton, neutron, and electron?

A

Proton: +1
Neutron: 0
Electron: -1

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19
Q

State four types of nuclear radiation.

A
  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
20
Q

What is meant by background radiation?

A
  • Radiation that is always present.
  • It is in very small amounts and so not harmful.
21
Q

Give four sources of background radiation.

A
  • Rocks
  • Cosmic rays from space
  • Nuclear weapon testing
  • Nuclear accidents
22
Q

How do you measure and detect background radiation?

A
  • Photographic film
  • Geiger-Muller counter
23
Q

How is photographic film used to measure radiation?

A

A photographic film turns dark when it absorbs radiation. This is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes. Therefore the workers know when they have been exposed to too much radiation.

24
Q

How are Geiger-Muller tubes used to measure radiation?

A

When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation. The frequency of the pulse depends on how much radiation is present. A high frequency would mean the tube is absorbing a large amount of radiation.

25
Q

What constitutes of an alpha particle?

A
  • Two protons and two neutrons.
  • It is the same as a helium nucleus.
26
Q

What is the range of an alpha particle through air?

A

A few centimetres (normally in the range of 2-10cm)

27
Q

What will block beta radiation?

A
  • A thin sheet of aluminium.
  • Several metres of air.
28
Q

What will block gamma radiation?

A
  • Several centimetres of lead
  • A few metres of concrete
29
Q

Which type of radiation is most ionising?

A

Alpha radiation

30
Q

Which type of radiation is least ionising?

A

Gamma radiation

31
Q

How does gamma emission affect the mass/charge of an atom?

A

Both mass and charge remain unchanged.

32
Q

Describe the plum-pudding model of the atom.

A

A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it.

33
Q

Prior to the discovery of the electron, what was believed about the atom?

A

The atom was believed to be indivisible.

34
Q

Which experiment led to the plum-pudding model being discarded?

A

Rutherford’s alpha-scattering experiment.

35
Q

What is the name given to the currently accepted model of the atom?

A

The Bohr Model

36
Q

Describe Rutherford’s experiment

A
  • Alpha particles (charge +2) were fired at a thin sheet of gold foil.
  • Most particles went straight through.
  • Some particles were deflected by small angles (<90⁰)
  • A few particles were deflected by large angles (>90⁰)
37
Q

What are the conclusions of Rutherford’s experiment?

A
  • Most of an atom is empty space.
  • The nucleus has a positive charge.
  • Most of the mass is concentrated in the nucleus.
38
Q

What happens in the process of beta plus decay?

A

A proton turns into a neutron and a positron (in order to conserve charge).

39
Q

What is the process called when a neutron changes into a proton and an electron?

A

Beta minus decay.

40
Q

When alpha decay occurs, what happens to the atomic number and the mass number of the atom?

A
  • The atomic number decreases by 2.
  • The mass number decreases by 4.
  • A new element is made since the atomic number has changed.
41
Q

What effect does beta minus decay have on the mass number and atomic number of an atom?

A
  • The mass number stays the same as the total number of neutrons and protons hasn’t changed (one has just turned into the other).
  • The atomic number increases since there is one more proton.
42
Q

Define the activity of an unstable nucleus.

A

Activity is the rate at which a source of unstable nuclei decays.

43
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

44
Q

What is count-rate?

A

The number of radioactive decays per second for a radioactive source.

45
Q

Give an example of a detecter that may be used to measure count-rate.

A

Geiger-Muller tube

46
Q

Describe the nature of radioactive decay.

A
  • Random.
  • Which nuclei decays and when is determined only by chance.
  • It is impossible to predict which nuclei will decay and when.
47
Q

Define the half-life of a radioactive isotope.

A
  • The time it takes for the number of unstable nuclei in a substance to halve.
  • The time it takes for the count rate from a sample to fall to half its initial level.

Physics (13 decks)

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