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Physics GCSE > Radioactivity > Flashcards

Radioactivity Flashcards

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1
Q

Describe the plum pudding model of the atom

A

Thompson believed that the mass of an atom was spread evenly.
He described the atom as negatively charged particles swimming in a positively charged sea

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2
Q

Describe the results Rutherford’s team obtained when they fired alpha particles at gold foil

A

Most of the particles went straight through the foil but a few bounced back (one in 20,000 deflected at an angle greater than 90°)

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3
Q

Explain what results Rutherford‘s team would’ve expected if the plum pudding model was correct

A

All of the alpha particles would’ve gone straight through because the positive charge wouldn’t have been concentrated enough to send them back

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4
Q

Describe the model that Rutherford suggested following this experiment

A

All of the mass and positive charge are in a extremely small volume (nucleus) ‘most of the atom is empty space’

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5
Q

How does Rutherford’s model explain the results of the experiment

A

The particles are unlikely to hit the nucleus so most go straight through but some are repelled by the very concentrated nucleus

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6
Q

What does giving energy to atoms do to the electrons

A

Giving an atom energy excites the electrons moving them up into higher energy levels (shells)

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7
Q

What happens when the electrons de-excite

A

The electrons will return to their lower orbits emitting a particular frequency of the EM radiation which is what we see as a particular colour of light

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8
Q

Why do we see different colours of light from the metals when put under the flame (practice investigating exciting of electrons)

A

They are created by the different positions of electron shells (distances from each other) creating different frequencies when de-excited

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9
Q

What is ionisation

A

The atom receives so much energy that an electron escapes 

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10
Q

What is phosphorescence

A

The material is phosphorescent if it has absorbed some electromagnetic energy and then emits it much later

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11
Q

What is fluorescence

A

A material is fluorescent if it is absorbs some electromagnetic energy and then emits it straight away

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12
Q

What is radioactive radiation

A

Free electrons (BETA PARTICLES) or really high energy EM waves (GAMMA RAYS) or parts of atoms (ALPHA PARTICLES) that are given off

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13
Q

What is background radiation

A

The radioactive radiation that is always all around us- given off every day materials

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14
Q

What do you use to measure background radiation

A

A Geiger-Müller tube 

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15
Q

What is a Geiger-Müller tube

A

GM tube is a hollow cylinder field with gas at a low-pressure.
The tube has a thin mica window at one end

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16
Q

What is a ‘decay’

A

A single atoms nucleus falling apart- that’s what produces the radioactive radiation

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17
Q

What does it mean when you hear a beep from a GM tube

A

Somewhere an atom has fallen apart

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18
Q

What should you always account for before measuring radiation

A

Background radiation

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19
Q

What is 1 becquerel (1Bq) of activity equal to

A

1 decay per second

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20
Q

What causes a greater number of counts in a GM tube

A

The greater the level of radiation, the more ionisation in the tubes, so the greater the number of counts

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21
Q

What happens inside a GM tube

A

Tube is connected to a circuit, with an electrode on the inner edge of the tube and an electrode put in up the middle. Ionising radiation enters a chamber, ionising the air. The ions flow across the gap between the edge and the middle, allowing a current to flow for a moment. The counter connected to the tube beeps.

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22
Q

An isotope is described as radioactive if…

A

The nucleus of atoms of that isotope are unstable and will fall apart at some point

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23
Q

The point at which one particular unstable nucleus will fall apart is…

A

Totally random

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24
Q

What are the three different types of radioactive radiation

A

Alpha
Beta (also something very similar called a positron)
Gamma

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25
Q

What is the relative atomic mass of an alpha particle

A

4

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26
Q

What is the relative atomic mass of a beta particle

A

Negligible (1/1835)

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27
Q

What is the relative atomic mass of a positron

A

Negligible (1/1835)

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28
Q

What is the relative atomic mass of a gamma ray

A

0

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29
Q

What is an alpha particle made from

A

Two protons and two neutrons

30
Q

What is a beta particle made from

A

It’s just a free electron that was made in the nucleus

31
Q

What is a positron made of

A

Exactly like an electron except it is positively charged

32
Q

What is a gamma ray made from

A

A ray of pure energy (EM wave)

33
Q

What is the relative charge of an alpha particle

A

+2

34
Q

What is the relative charge of a beta particle

A

-1

35
Q

What is the relative charge of a positron

A

+1

36
Q

What is the relative charge of a gamma ray

A

0

37
Q

What is the ionisation ability of an alpha particle

A

Highly Ionising

38
Q

What is the ionisation ability of a beta particle

A

Moderately ionising

39
Q

What is the ionisation ability of a positron

A

Likely to annihilate very quickly

40
Q

What is the ionisation ability of a gamma ray

A

Low ionising

41
Q

What is the range in air of an alpha particle

A

Very short: about 10 cm

42
Q

What is the range in air of a beta particle

A

Medium: about 1 m

43
Q

What is the range in air of a positron

A

Likely to annihilate very quickly

44
Q

What is the range in air of a gamma ray

A

Very long: unlimited in air

45
Q

What is the penetration range of an alpha particle

A

Very short: stopped by thin paper

46
Q

What is the penetration range of a beta particle

A

Medium: stopped by a few mm of aluminium

47
Q

What is the penetration range of a positron

A

Likely to annihilate very quickly

48
Q

What is the penetration range of a gamma ray

A

Very long: possibly stopped by many cm of lead or >1 m of concrete

49
Q

What did Henri Becquerel and Marie Curie discover

A

They figured out how to measure the intensity of radioactivity and soon found other radioactive elements
Marie curie created the term ‘radioactivity’ to describe the phenomena in 1896

50
Q

What did Rutherford then find after the discoveries in 1896

A

He carried out tests and discovered two types of radiation by putting different materials between the radioactive substance and a detector (alpha and beta)

51
Q

What is the symbol used for an alpha particle

A

4 (α)

2

52
Q

What is the symbol used for a beta particle

A

0 (ß)

-1

53
Q

What is the symbol used for a positron

A

0 (ß)

+1

54
Q

What is the symbol used for a gamma ray

A

0 (Y)

0

55
Q

What is half-life

A

Half life of a radioisotope is the time taken for the number of undecayed nuclei to reduce by half

56
Q

Why are radioactive materials dangerous

A

The radiation that is emitted from a radioisotope is ionising…
this means that if an atom in one of your cells absorbs the energy in the radiation, that atom will be altered…
altering the electron make up of an atom within a cell will alter the chemical reactions and bonding in that cell …
which will result in a change in what to the cell does

57
Q

What is a dangerous half life

A

If the half life is very short (seconds or less) or if it is very long (thousands of years+) there won’t be many decays per second (activity will be lower) so you won’t receive a big dose from it

58
Q

What is irradiation

A

Irradiation is when something receives a dose of radioactive radiation. It happens for as long as the object is exposed to radioactive material

59
Q

What is contamination

A

Contamination is when a radioactive material is transferred into or onto an object.
For as long as that material is present the object will then get irradiated

60
Q

What are uses of alpha radiation

A

Smoke detectors & paper production

61
Q

What are the uses of beta radiation

A

Manufacturing aluminium foil (determines the thickness)

62
Q

What are the uses of positron radiation

A

PET scans

63
Q

What are the uses of gamma radiation

A

Sterilisation
radiotherapy
industrial traces (says where there are holes in a pipeline)

64
Q

Most radioactive sources give off ONE OF alpha, beta or positron but then ALSO give off gamma rays. Why do they give off gamma rays?

A

They do this when the nucleus rearranges and releases some spare energy after the initial decay.

65
Q

How do smoke detectors work using alpha particles

A

Alpha particles from source IONISE AIR between two metal plates, causing a current to flow around a circuit. Smoke absorbs alpha particles, the ionising doesn’t happen so much and the current drops. The alarm sounds

66
Q

Radiotherapy can be “internal” or “external”. In each case, explain the process.

A

External: gamma rays fired in from outside the body, from changing angles focussed on the position of the cancerous cell.
Internal: a radioactive source is ingested by the patient so that it ends up next to/in the cancer.

67
Q

How is photographic film used to detect different types of radiation

A

Film blackens in presence of radiation. Put film behind different absorbers (paper, aluminium, lead) to find out which type of radiation is present.

68
Q

How does sterilisation and irradiating food work using gamma rays

A

Gamma rays fired at the food kill the bacteria on them, greatly reducing the speed of bacterial growth

69
Q

What are tracers and how do they work

A

A source that emits gamma rays is ingested (swallowed, injected) by the patient.
The source moves around the body, emitting gamma rays that get out of the patient and are picked up by a sensor.
The computer attached to the sensor can then map the body.

70
Q

Why are gamma rays used for tracers

A

They are less likely to be absorbed by the cells and cause harm

71
Q

PET scanners use a different kind of tracer- How does a PET scanner work

A
  1. The patient is injected with a radioactive substance that undergoes ß+/ positron decay (the tracer)
  2. The tracer is attached to a molecule that collects in a tumour
  3. When nuclei in the tracer decay, they emit positrons
  4. When a positron meets an electron they are both destroyed and to gamma rays are emitted
  5. The PET scanner detects the gamma rays and calculates where the radiation came from
  6. The PET scan and moves around the patient to detect lots of pairs of gamma rays
  7. A computer builds up an image of the inside of the patient

Physics GCSE (17 decks)

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