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Physics > SP6 Radioactivity > Flashcards

SP6 Radioactivity Flashcards

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1
Q

Describe the structure of an atom

A

Neutrons and protons make positive nucleus. Electrons orbit nucleus in shells

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2
Q

Where is most of the mass of an atom found?

A

In the nucleus

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3
Q

What is the gold foil experiment?

A

1909, Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil. Most particles went through the sheet, some were defected more than they had expected, and a few were deflected back the way they had come - this proved that most of the mass of the atom was concentrated at the centre of the nucleus

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4
Q

Define isotope

A

Isotopes of an element are atoms with the same number of protons (atomic number) but a different number of neutrons (mass number)

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5
Q

Why do atoms have no overall charge?

A

Because there is an equal number of negative electrons and positive protons

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6
Q

Define an ion

A

Ions are electrically charged particles formed when atoms lose or gain electrons

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7
Q

Define ionisation

A

Ionisation is the addition or removal of an electron to create an ion

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8
Q

When can electrons change orbit?

A

An inner electron can move up to a higher energy level if it absorbs EM radiation with the right amount of energy

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9
Q

Define background radiation

A

is the low level radiation that’s around us all the time

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10
Q

List sources of background radiation

A

foods, building materials, cosmic rays, rocks

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11
Q

Radiation precautions

A

lead-lined boxes, standing behind barriers, gloves, long-handle tongs, protective suits

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12
Q

How can photographic film detect radioactivity?

A

Photographic film goes darker when it absorbs radiation, just like it does when it absorbs visible light. The more radiation the film absorbs, the darker it is when it is developed

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13
Q

Define a Geiger-Muller Tube

A

The Geiger-Muller tube is a device that detects radiation. It gives an electrical signal each time radiation is detected. These signals can be converted into clicking sounds, giving a count rate in clicks per second or per minute

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14
Q

List 5 types of radiation

A

alpha, beta, gamma, neutron, positron

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15
Q

Define an alpha particle

A

Alpha particles are helium nuclei

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16
Q

Define a beta particle

A

Beta particles can be electrons or positrons

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17
Q

Describe the nature of gamma radiation

A

After a nucleus has decayed, it undergoes nuclear rearrangement and releases some energy - gamma rays released by the nucleus carry away this energy

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18
Q

Penetration of alpha, beta and gamma

A

Alpha - few cm in air / absorbed by paper
Beta - few m in air / absorbed by sheet of aluminium
Gamma - far in air / absorbed by thick sheets of lead / concrete

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19
Q

Ionisation of alpha, beta and gamma

A

Alpha - strongly ionising
Beta - moderately ionising
Gamma - weakly ionising

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20
Q

Describe the process of beta-minus decay

A

A neutron changes into a proton and an electron

  • mass number = doesn’t change
  • atomic number = increases by 1
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21
Q

Describe the process of beta-plus decay

A

A proton changes into a neutron and a positron

  • mass number = doesn’t change
  • atomic number = decreases by 1
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22
Q

Describe the process of alpha decay

A

When a nucleus emits an alpha particle, it loses 2 protons and 2 neutrons

  • mass number = decreases by 4
  • atomic number = decreases by 2
23
Q

Define the process of neutron emission

A

When a nucleus emits a neutron

  • mass number = decreases by 1
  • atomic number = stays the same
24
Q

Describe the process of gamma rays radiation

A

A way of getting rid of excess energy from an atom. The nucleus goes from an excited state to a more stable state by emitting a gamma ray

  • mass number = stays the same
  • atomic number = stays the same
25
Q

Define half-life

A

The half-life is the average time taken for the number of radioactive nuclei in an isotope to halve

26
Q

Define a long half-life

A

means the activity falls more slowly because most of the nuclei don’t decay for a long time

27
Q

The activity of a radioactive sample is measured as 640Bq. 2hrs later, it has fallen to 40Bq. Find it’s half life

A

1) Count how many half-lives it took to fall to 40Bq

Initial - 640 First - 320 Second - 160 Third - 80 Fourth - 40

2) Calculate the half-life of the sample

Two hours is 4 half-lives so 2hrs/4 = 30mins

28
Q

Radioactivity in smoke alarms

A

Alpha radiation is placed in smoke alarm, close to two electrodes. The source causes ionisation and a current of charged particles to flow. If there is smoke, it will absorb the charged particles, stopping the current and sounding the alarm

29
Q

Radioactivity in irradiating food

A

Food can be irradiated by a high dose of gamma rays which will kill all microbes

30
Q

Radioactivity in sterilisation

A

Medical equipment can be sterilised using gamma rays instead of being boiled which can damage equipment

31
Q

Radioactivity in tracers and thickness gauges

A

Gamma emitting tracers are used in industry to detect leaks in underground pipes.

Beta is used in thickness control - you direct radiation through the stuff being made and put a detector on the other side. When the amount of detected radiation changes, it means the material is coming out too thick or thin

32
Q

List 3 uses of radiation

A

Cancer diagnosis / treatment, irradiation, sterilisation, tracers, thickness control, smoke alarms

33
Q

How do dangers of radiation depend on half-life?

A

A long half-life means that nearby areas are exposed to radiation for (millions of) years which is dangerous

34
Q

Contamination with radioactive substances

A

Contaminating atoms might decay, releasing radiation which could cause harm.

35
Q

Irradiation with radioactive substances

A

Objects near a radioactive source are irradiated by it - this means they are exposed to it

36
Q

Harmful effects of ionising radiation

A
  • enter living cells and ionise atoms and molecules within them which can lead to tissue damage
  • lower doses tend to cause minor damage without killing cells
  • can penetrate the body and get to other delicate organs
37
Q

Why must isotopes used in PET scanners have to be produced nearby?

A

They have short half-lives, so must be made near hospitals so they don’t run out

38
Q

Define PET scanners in diagnosis

A

A technique used to show tissue or organ function, and can be used to diagnose medical conditions

39
Q

External radiation while treating tumours

A

Gamma rays can be aimed at the tumour, as these are able to penetrate through the patients body.

40
Q

Internal radiation while treating tumours

A

A radioactive material is placed inside the body into or near a tumour . Alpha particles are strongly ionising, so can cause damage to nearby areas

41
Q

How does PET scans identify cancer tumours?

A

it shows metabolic activity in tissues as cancer cells have a much higher metabolism than healthy cells

42
Q

Describe the fission of U-235

A

A slow-moving neutron is fired at a large, unstable nucleus of uranium-235. The neutron is absorbed by the nucleus making the atom split. When the U-235 atom splits, it forms two new lighter elements and energy is released.

43
Q

Define a chain reaction

A

Each time a uranium atom splits up, it spits out 2/3 neutrons, which can hit other uranium nuclei causing them to split also and so on

44
Q

How is a chain reaction controlled in a power station?

A

By Boron control rods that limit the rate of fission by absorbing excess neutrons

45
Q

How is thermal energy converted to electrical energy in a chain reaction?

A

Energy released by fission is transferred to thermal energy store of moderator. This is then transferred to thermal energy store of cooler. Then to the thermal energy store of cold water passing through a boiler. This causes water to boil and energy to be transferred to the kinetic energy store of steam.

This energy is then transferred to kinetic energy store of a turbine, then to kinetic energy store of a generator. The energy is transferred away from the generator electrically

46
Q

Define nuclear fusion

A

Two light nuclei collide at a high speed and join (fuse) to create a larger, heavier nucleus. The heavier nucleus doesn’t have as much mass as the two separate light nuclei did. Some of the mass of the lighter nuclei is converted to energy

47
Q

What is nuclear fusion the energy source for?

A

stars

48
Q

What is the difference between fusion and fission?

A

Fusion is the opposite of fission

49
Q

Why does fusion need high temp. and pressures?

A

Because the positively charged nuclei have to get very close to fuse, so the strong force due to electrostatic repulsion has to be overcome.

50
Q

Why do the conditions of fusion stop fusion power stations being built?

A

No material can withstand the high temperatures - it would just vaporise. So fusion reactors are really hard and expensive to build and use.

51
Q

Advantages to nuclear power to generate electricity

A
  • pretty safe way to generate electricity
  • very reliable
  • clean source of energy
  • huge amounts of energy produced from small amount of nuclear material
52
Q

Disadvantages to nuclear power to generate electricity`

A
  • negative public perception
  • waste disposed unsafely
  • long radioactive half-lives
  • risk of leaks
  • high costs
53
Q

List 3 types of nuclear reaction

A

Nuclear decay, fission, fusion

Physics (9 decks)

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