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Physics- P2 > P2.5 What happens when radioactive substances decay, uses and dangers > Flashcards

P2.5 What happens when radioactive substances decay, uses and dangers Flashcards

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1
Q

Describe the relative size of the nucleus compared to the rest of the atom

A

nucleus is tiny, but it makes up most of the mass of the atom.

rest of the atom is mostly empty space

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2
Q

What are the relative masses in an atom?

A

proton- 1

neutron- 1

electron- very small

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3
Q

What are the relative electric charges in an atom?

A

proton- +1

neutron- 0 (no charge)

electron- -1

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4
Q

In an atom, the number of electrons is equal to the number of….

A

protons

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5
Q

What overall charge does an atom have?

A

no charge

as the number on electrons is equal to the number of protons

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6
Q

When are ions formed?

A

if an atom loses or gains electrons

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7
Q

What do atoms of the same element always have the same number of?

A

protons

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8
Q

What is an isotope?

A

different atomic forms of the same element, which have the same number of protons but a different number of neutrons

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9
Q

What does the atomic number show?

A

the total number of protons in an atom

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10
Q

What does the mass number show?

A

The total number of protons and neutrons in an atom

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11
Q

What are radioactive substances?

A

substances that give out radiation from the nuclei of their atoms all the time whatever happens to them

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12
Q

Radioactive decay is a ………. process

A

random

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13
Q

Where does background radiation come from?

A

air, food, building materials, rocks

radiation from space- cosmic rays (mostly come from the sun)

man-made sources- fall out from nuclear weapons, nuclear accidents, dumped nuclear waste

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14
Q

Describe the structure of alpha particles

A

2 neutrons and 2 protons, the same as a helium nucleus

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15
Q

Describe the structure of beta particles

A

an electron

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16
Q

Describe the structure of gamma radiation

A

electromagnetic waves

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17
Q

What are some properties of alpha particles?

A

big and heavy so relatively slow moving

therefore do not penetrate very far into materials- stopped quickly even travelling through air

Because of their size they are strongly ionising

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18
Q

What does it mean if a particle was ‘ionising’?

A

the particle bashes into lots of atoms and knock electrons off them before they slow down. This creates lots of ions

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19
Q

What are some properties of beta particles?

A

Move quite fast and are quite small

penetrate moderately into materials

have a long range in air

moderately ionising

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20
Q

What are some properties of Gamma rays?

A

opposite of alpha particles

penetrate far into materials with out being stopped

pass straight through air

means they are weakly ionising as they tend to pass through rather than colliding with atoms

have no mass or charge

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21
Q

What are alpha particles stopped by?

A

paper

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22
Q

What are beta particles stopped by?

A

aluminium

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23
Q

What are gamma particles stopped by?

A

thick lead

24
Q

What is the charge of an alpha particle?

A

positive

2 protons, 2 neutrons

25
Q

What is the charge of a beta particle?

A

negative

it is an electron

26
Q

Describe what happens when alpha, beta and gamma radiations travel through a magnetic field?

A

both alpha and beta are deflected in opposite directions because of their opposite charge.

Alpha particles have a larger charge than beta particles so feel a greater force in magnetic and electric fields. BUT they are deflected less because they have a much greater mass.

Gamma radiation is an EM wave and has no charge so does not get deflected at all.

27
Q

Describe the basic structure of an atom

A

a small central nucleus composed of protons and neutrons surrounded by electrons

28
Q

What does the extent of the harmful effects of radiation depend on?

A

how much exposure you have from the radiation

the energy and penetration of the radiation, since some types are more hazardous than others

29
Q

What type(s) of radiation are most dangerous outside the body? WHY?

A

beta and gamma

as they can penetrate far into materials so can damage delicate organs.

Alpha is less dangerous as it can not penetrate into the skin

30
Q

What type(s) of radiation are most dangerous inside the body?

A

Alpha

as alpha sources do their damage in a very localised area.

Beta and gamma are less dangerous inside the body because they mostly pass straight out without doing much damage.

31
Q

Describe how radiation is dangerous

A

alpha, beta and gamma radiation can enter living cells and collide with molecules.

These collisions are called ionisation and they damage or destroy the molecules

This can cause cancer

32
Q

What measures can be taken to reduce the exposure to nuclear radiations?

A

in experiments, use radioactive sources for as short time as possible so exposure is kept to a minimum

handle with tongs- never allow skin contact

hold the source at arms length- decrease the amount of radiation that hits you, especially for alpha particles as they do not travel far in air

Store radioactive sources in a lead box as lead absorbs all 3 types of radiation- also wear lead aprons and stand behind lead screens

33
Q

What is a use of alpha radiation?

A

Smoke Detectors

weak source of alpha radiation is placed in the detector, close to 2 electrodes

The source causes ionisation, and a current flows between the 2 electrodes

If there is a fire then smoke will absorb the radiation so the current stops and the alarm sounds

34
Q

Describe a use of beta and gamma radiation in tracers in medicine

A

certain radioactive isotopes can be injected into people and their progress around the body can be followed using and external detector

A computer shows where the strongest reading is coming from - eg used to indicate if the thyroid gland is taking in iodine as it should

must be gamma or beta emitters (not alpha) so that radiation passes out of the body.

THEY SHOULD HAVE A SHORT HALF LIFE so that the radioactivity inside the patient quickly disappears- less ionisation

35
Q

Describe how gamma rays are used to treat cancer

A

high doses of gamma will kill living cells so can be used to kill cancerous cells

gamma rays have to be directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells

36
Q

Describe how gamma rays can be used in the sterilisation of food and surgical instruments

A

Food can be exposed to a high dose of gamma rays which will kill all microbes- keep food fresh for longer

food is not radioactive afterwards

medical instruments can be sterilised in the same way

Advantage over boiling is that is does not involve high temperatures- cheaper, food is not damaged

37
Q

What is the half-life of a radioactive isotope?

A

the average time it takes for the number of nuclei in a radioactive isotope sample to halve,

or

the time it takes for the count rate from a sample containing the isotope to fall to half its initial level

38
Q

Describe the plum pudding model

A

They used to believe that atoms were spheres of positive charge with tiny electrons stuck in them

39
Q

Who proved the plum pudding theory wrong?

A

Rutherford and Marsden

40
Q

What were the results of Rutherford’s and Marsden’s experiment and how did this prove the plum pudding model wrong?

A

1) Most alpha particles passed straight through the gold foil
- suggests most of the atom is empty space

2) Some alpha particles passed through but were deflected by varying amounts - Suggests an atom has a positive centre (alpha particles deflected as are positive)
3) Some alpha particles cam straight back- Suggests the positive centre is very dense

41
Q

Describe Rutherford’s and Marsden’s experiment and what did they expect to happen?

A

fired a beam of alpha particles at thin gold foil

expected the particles would be slightly deflected by the electrons in the plum pudding model (thought overall charge of an atom is positive)

42
Q

What does it mean if a radioactive sample has a short half life?

A

radioactivity falls quickly, because lots of the nuclei decay quickly

43
Q

What does it mean if a radioactive substance has a long half life?

A

radioactivity falls slowly because most of the nuclei don’t decay for a long time.

44
Q

Which 2 types of radiation can pass through a sheet of card?

A

beta and gamma

45
Q

Which type of radiation has the greatest range in air?

A

gamma

46
Q

If a radioactive source is stored in a freezer, why does the radiation emitted from the source not decrease?

A

As nothing you do to a radioactive substance changes the rate of decay

47
Q

Suggest why a person may receive a higher than average dose of radiation from background sources

A
  • frequent flying
  • living at high altitude
  • having more than the average number of x rays
  • working in a nuclear power station
48
Q

Name some manmade sources of background radiation

A

nuclear power stations

nuclear weapons

nuclear accidents

49
Q

Why are readings of background radiation in a room always different?

A

as radioactive decay is a random process

50
Q

How many protons and how many neutrons are there in an alpha particle?

A

2 protons

2 neutrons

51
Q

How do you balance an equation in which a substance emits a beta particle?

A

0

+1

52
Q

How do you balance an equation in which a substance emits an alpha particle?

A
  • 4

- 2

53
Q

When a substance decays and releases a beta particle, why does the atomic number of that substance increase by one?

A

Because for every beta particle emitted, a neutron turns to a proton in the nucleus

54
Q

Inside what part of a power station is an isotope produced by radioactive decay produced?

A

reactor

55
Q

How do you know beta radiation was emitted?

A

atomic number increases by 1

because a neutron becomes a proton

mass number does not change

56
Q

Explain the risk to a patient of using a radioactive substance as a medical tracer

A

radiation causes ionisation

that may then harm healthy cells (cause cancer)

57
Q

suggest why doctors use radioactive substances for medical diagnosis even though there is a risk

A

benefit is greater than the risk

Physics- P2 (6 decks)

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