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Physics > SP6 Radioactivity > Flashcards

SP6 Radioactivity Flashcards

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1
Q

What’s the particle theory / kinetic theory

A

Is the model that helps explain properties of liquids and gases and solids

Particles usually represented with spheres

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2
Q

When do chemical reactions occur

A

When atoms in substances become joined in different ways

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3
Q

What did J.J Thomson do

A

Carried out experiments to show atoms contain much smaller subatomic particles called elections - these have a negative charge and hardly any mass

Described as a pudding made of positron charged material with negatively charged electrons (plums) scattered through it

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4
Q

What did Ernest Rutherford do

A

Carried out experiments involving a study of what happened when positively charged subatomic particles (alpha particles) passes through various substances

He discovered most of a particles went through gold foil but a few bounces back - the plum pudding model could not explain this

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5
Q

What did Rutherford change about the plum pudding model

A

Suggested atoms were mostly space with most of mass in the central nucleus with a positive charge and electrons around the nucleus and so would allow some particles to be deflected by a small amount

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6
Q

What the radius of a nucleus

A

1 X 10^-15 m radius

1 X 10^-10 for the atom so atom itself 100,000 times bigger than nucleus inside it

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7
Q

What are nucleons

A

Particles in nucleus

They are protons or neutrons

Protons have a mass of 1 and neutrons a mass of 1

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8
Q

What’s the atomic number

A

The proton number = number of electrons too

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9
Q

What’s the mass number or nucleon number

A

The total number of protons and neutrons in the nucleus

Numbers of neutrons can vary

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10
Q

What are isotopes

A

Two atoms of the same element have different mass numbers as a result of different numbers of neutrons

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11
Q

Tell me about electrons shells

A

Electrons can only exist in certain orbits around the nucleus

Each electron shell is at a different energy level so If ask atom absorbs energy an electron can move to a higher orbit

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12
Q

When does an atom emit light

A

When an atom emits energy it moves to a lower orbit and emits visible light of a particular wavelength

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13
Q

What’s the emission spectrum

A

It’s different for each element

An electron can move down 1 sheep at a time, even 2, maybe 3 or more at a time so different wavelengths are produced which show up on emission spectrum

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14
Q

What’s the absorption spectrum

A

The visible spectrum that passes through an atom

The wavelengths of light that neon gas absorb are the same wavelengths it emits

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15
Q

What did Niels Bohr amend about Rutherfords model of the atom

A

Suggesting electrons can only be in certain shells around the nucleus and can’t be in between so that’s why they are lines on emission and absorption spectra

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16
Q

When does ionisation happen

A

When an atom gains so much energy one or more of the electrons can escape from the atom all together

Radiation that causes electrons to escape is called ionising radiation

This means it has a positive charge as there are more protons so it’s a positive ion

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17
Q

What’s backround radiation

A

We are constantly being exposed to ionising radiation at a low level, from space and naturally radioactive substances in the environment

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18
Q

What are the sources of backround radiation

A

49% radon gas - produced by rocks that contain small amounts of uranium- it diffuses into the air and can build up in houses. Rock type varies so does amount of radon

15% medical 
13% ground and buildings
12% cosmic rays
10% food and drink 
1% nuclear and other
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19
Q

What are cosmic rays

A

High energy charged particles from the sun and other stars

They are stopped by the upper atmosphere but some still reach the surface

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20
Q

How can radioactivity be detected using photographic film

A

It becomes darker and darker as more radiation reaches it

However the film has to be developed in order to measure the amount of radiation (the dose)

Dosimeters are often work to check how much radiation they have been exposed to (badge)

Newer dosimeters use materials that change colour without needing to be developed

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21
Q

How can the radioactivity or a source be measured

A

Using a Geiger müller (GM) tube

Radiation passing through the tube ionises the gas inside it and allows a short pulse of current to flow

The tube can be connected to a counter to count the pulses of current or the GM tube may give a click each time radiation is detected

The count rate is the number of clicks per second or minute

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22
Q

What do scientists do before they measure radioactivity of a source

A

They need to measure the backround radiation first by taking several readings and finding the mean - the mean value is then subtracted from the measurements!!

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23
Q

What’s the nucleus of a radioactive substance like

A

It’s unstable so it fan easily change or decay

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24
Q

Tell me about decay

A

When it occurs radiation is emitted which causes the nucleus to lose energy and become more stable - it’s a random process and you can’t predict it

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25
Q

What are alpha particles

A

Alpha particles contain two protons and two neutrons
- just like nucleus of helium atom

They have a relative mass of 4 with no electrons

Charge of +2

Can be written as fish symbol / weird a

Or 4 with 2 under and He by the side

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26
Q

Tell me about Beta particles

A

They are high energy, high speed electrons

They have a relative mass of 1/1835 and a charge of -1 they can be written as a welter B with a - minus sign top right corner of it

Or 0 with -1 under and e next to it

The electrons that are beta particles come from the nuclei of atoms when a neutron transforms into a proton

Beta particles do not ionise the atoms as they leave them

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27
Q

Tell me about positrons

A

They are high energy high speed particles with the same mass as electrons but a charge of +1

They can be written as B^+ or 0 with +1 under and e

Opposite to beta particles

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28
Q

Tell me about gamma rays

A

written as weird y

They are a high frequency electromagnetic waves (they travel at the speed of light)

They don’t have an electric charge

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29
Q

Tell about neutrons is radioactive decay

A

Neutrons can also be emitter from an unstable nucleus

They have a relative mass of 1 and no electric charge

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30
Q

What type of radiation are positrons, gamma rays, beta particles and alpha particles

A

Ionising radiation

So they can all penetrate materials

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31
Q

Tell me about Alpha particles passing through materials

A

They are emitted at high speeds
Due to this and their high relative mass, they transfer a lot of energy and so are good at ionising atoms they encounter

Each time they ionise an atom they lose energy - since they produce many ions in a short distance, they lose energy quickly and have a SHORT PENETRATION DOSTANCE

THEY CAN BE STOPPED BU PAPER

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32
Q

How far can alpha particles travel

A

Can be stopped by a few centimetres in air

Very ionising

Can be stopped by a sheet of paper

33
Q

Tell about beta particles being ionising

A

Beta particles are much less ionising than alpha particles so it can penetrate further in to matter

34
Q

What can stop beta particles

A

Will travel a few metres in air

Moderately ionising

Can be stopped by 3mm thick aluminium

35
Q

Tell me how ionising gamma rays are

A

They can penetrate much further in to matter they are about 10 times less ionising than beta particles and can penetrate matter easily

36
Q

What can stop gamma rays

A

They will travel a few km in air

Weakly ionising

Need thick lead or several metres of concrete to stop them

They can use gamma rays to check the inside of lorries to help prevent movement of illegal goods

37
Q

How can an atom become a different element

A

When an unstable nucleus changes and emits particles, the atomic number can change

If this happens to atoms becomes a different element

Eg when alpha is emitted th mass number goes down 4 and atomic number by 2

38
Q

When happens to a neutron in beta decay

A

A neutron changes in to a proton and electron

The electron is ejected from the atom. Atomic number increase by 1 mass number don’t change

Beta particle is the electron

39
Q

What happens in positron decay

A

A proton becomes a neutron and a positron

The atomic number goes down by 1 by mass number don’t change

40
Q

What happens with gamma radiation

A

Nuclei may lose energy as gamma radiation when the subatomic particles in the nucleus are rearranged which helps makes them more stable

41
Q

What’s a nuclear equation

A

Shows what’s happened during radioactive decay

The equation must be balanced and the total mass number and total charges must be the Same on both sides

Look page 101 (just like a half equation in chemistry ish)

42
Q

What did Marie curie do

A

Made important discoveries with radioactivity

Before dangers were known - notebooks are still radioactive

43
Q

What’s the ACTIVITY of any radioactive substance

A

The number of decays per second and is measured in becquerels )Bq£

One becquerel is one nuclear decay each second

44
Q

What’s the half life of a radioactive substance

A

It’s the time taken for half the unstable nuclei in a sample of a radioactive isotope to decay

We can’t predict individual nucleus because it’s a random process

However the half life does allow us to predict the activity of a large number of nuclei

The half life is the same for any mass of a particular isotope

Wh Carbon-14 is 5730 years

45
Q

The more stable a nuclei a sample of a substance contains the lower its…

A

Activity

The half life of an isotope is therefor also a measure of how long it takes tor the activity to halve

I

46
Q

How can half like be recorded

A

It can be found by recording the activity of a sample over a period of time

47
Q

Take a break

A

;)

48
Q

How can gamma rays be used to kill microorganisms

A

Some bacteria also cause food poisoning, food can be irradiated by gamma rays to kill bacteria
- makes it safer to eat do you can store it for longer

Also surgical instruments need to be sterilised to kill microorganisms- heat Them but plastic ones are irradiated with gamma rays

49
Q

Tell me about tracers

A

Radioactive isotopes can be used as tracers - a gamma source added to water is used to detect leaks in water pipes buried underground

Where ther is a leak the water flows into the surrounding earth. A Geiger-müller tube following the path of the pipe will detect higher levels of radiation where there is a leak

50
Q

How can radioactivity be used for cancer tracers

A

It can be used a tracer in the body to find cancer

Similar to a leaking pipe

51
Q

How can radioactivity be used to check thickness of paper

A

A detector is below he paper and a beta source on other side

If paper is too thin more beta particles penetrate the paper and the detector records a higher count rate and so rollers to squash paper reduces force to make it thick and oppose happens when paper too thick

52
Q

Tell me about using radioactivity for smoke alarms

A

It contains a source of alpha particles, there’s a gap in an electrical circuit between 2 electrically charged plates and alpha Partjcles ionise air and attract move to opposite charge plate and allow a small electrical current to flow

When smoke gets in to gap - air is not ionises as smoke particles slow down jons and so alarm sounds when the current drops below a certain level

53
Q

What can ionising radiation do to your skin m8 this ain’t difficult

A

Damage your tissue - reddened skin from radiation burns

Small amount over long time can damage DNA in a cell - may cause cancer - if they occur in gametes they can be passed on to the next generation; not all mutations harmful and cells often capable of repairing damage if the dose is low

54
Q

Why are radioactive sources always handled with tongs

A

The intensity of radiation decreases with distance from the source, risk can further be redirected by not pointing sources at people and storing them in lead lined containers

55
Q

Tell me about radiation in hospital

A

Small doses

Sources with shortest half life used - minimise time patient is exposed

56
Q

What’s irradiation

A

When someone is exposed to radiation from a nearby radioactive martial - once they move away the irradiation stops

57
Q

Whats contamination

A

If they inhale, touch or ingest radioactive material - radiation will continue until material has decayed or is removed which isn’t always possible

Water and soils can be contaminated and spread in the food chain - many people concerned with accidents in nuclear power stations

58
Q

Tell me about radioactive tracers - how they work

With gamma

A

The tracer often contains a radioactive isotope attached to molecules that will be taken up by particular organs in the body - the tracer emits gamma rays

It can be ingested, inhaled or injected into blood or organ

Gamma cameras detect the tracer

59
Q

What can tracers be used for with gamma

A

They find sources of internal bleeding - gamma camera detect highest areas of gamma radiation when bleeding is occcuring

Gamma cameras also detect tumours - radioactive glucose molecules because cancer cells are very active and uptake glucose more quickly than other cells

60
Q

Give me an example of a radioactive isoptope

A

Technetium-99m is attached to a drug that collects in the brain

61
Q

Tell me about using tracers with positrons

A

A tracer emits a positron, when this meets an electron both the electron and positron are destroyed and 2 gamma rays are emitted in opposite directions

The detector in a PET scanner moves around the patient building up a set of images showing where the the different amounts of gamma radiation are coming from

62
Q

Why must radioactive isotopes used in tracers have a short half life

A

So other parts of the body are affected as little as possible - since they lose there reactivity quickly they must be made close to a hospital and are often used within or even minutes of productions

63
Q

Why are cancer cells more susceptible to being killed by radiation

A

They divide more rapidly than cells in the body and are so more susceptible

64
Q

What’s internal radiotherapy

A

It uses a beta emitter placed close or in a tumour and the patient stays in the room alone whilst source in place

Doesn’t always require surgery

65
Q

What’s external radiotherapy

A

Uses Beams of gamma rags or x Rays or protons directed at the tumour from outside the body

Serveral lower strength beams may be directed from different directions so that only the tumour absorbs a lot of the energy

66
Q

What are the two types of nuclear reaction that are used as a source of energy on a large scale

A

Nuclear fission

Nuclear fusion

67
Q

Tell me simply what’s nuclear fission

A

Large nuclei such as uranium-235 break up to form smaller nuclei and release energy
Fission reactions are used in nuclear power stations

68
Q

Tell me simply what nuclear fusion is

A

Two small nuclei join together to from larger nucleus, fusion reactions release energy inside the sun

69
Q

Tell me some pros of nuclear fuels

A

They store a lot more energy per kilogram than any other type of fuel, this makes them useful for naval ships and submarines

Nuclear fuels don’t burn and don’t need air to allow them to release energy and don’t produce co2 - most energy is used in power stations to generate electricity

Although uranium is non renewable but supplies estimated for over 200 years - much longer than other non renewable fuel

70
Q

Tell me about radioactive waste

A

They do produce waste that will stay radioactive for millions of years - it’s also expensive to treat - sealed in concrete or glass and buried safely

Parts of a nuclear power station become radioactive as it is used and this makes it very difficult to decommission (dismantle safely)

71
Q

Tell me about nuclear fission

A

Uranium 235 nucleus absorbs a nucleus and then splits into 2 smaller daughter nuclei - which are radioactive.
2 or more neutrons are released and both neutrons and nuclei store a lot of kinetic energy, energy also transferred by heating

If neutrons released are absorbed by other uranium 235 nuclei become unstable and release more nuetrons and so on

It’s an uncontrolled nuclear chain reaction

72
Q

What are fuel rods

A

In a nuclear reactor the the fuel is made into fuel rods - at high speeds neutrons leave the fuel rods and are slowed down to increase chance they will be absorbed by any other uranium nuclear

Inside a reactor core, fuel rods are inserted into holes in a material called a moderator which slows down the neutrons

73
Q

What’s a moderator

A

Holes in a material to slow down nuetrons in nuclear fission

74
Q

How is the chain reaction nuclear fission controlled

A

Using control rods - which contain elements thag absorb nuetrons

They are placed in the reactor core, if rate of fission needs to increase, control rods moved out of the core and vice versa

When the control rods are fully lowered into the core, the chain reaction stops and the reactor shuts down

75
Q

How is electricity generated from nuclear fission

A

Energy released from the core is transferred to a coolant - which is lumped through the reactor, coolant can be water, gas or a liquid metal

The hot coolant is pumped by a heat exchanger where it’s used to make steam which drives a turbine which turns a generator to produce electricity

76
Q

Tell me about nuclear fusion

A

Occurs when smaller nuclei combine to form larger ones, the mass of the larger one is slightly less than 2 smaller nuclei - lost mass due to converted energy

77
Q

Tell me about fusion in the sun

A

Hydrogen nuclei combine to form helium

Hydrogen-2 deuterium and hydrogen-3 tritium have to be forced together , the protons are positively charged and like charges repel; electrostatic repulsion

Sun has strong gravity so very high pressure in centre - so nuclei close together to be more likely to fuse + higher temps and so some can overcome electrostatic repulsion and fuse

78
Q

Why aren’t we doing nuclear fusion on earth

A

A useful fusion reactor needs fusion to happen faster than it does in the sun

Very difficult to reproduce very high pressures on earth, so temperature needs to be very high - hotter then the sun so we can’t do this on earth or at least to make it efficient

Difficult to sustain extreme temps and pressures required - so far no experimental reactors have produced more energy than has been put in

79
Q

Would fusion or fission reactors produce more energy

A

Fusion theoretically would produce more energy

Helium produced is not radioactive, but any materials used to contain fusion reactions do become radioactive - but far less problems with disposing radioactive waste from fusion reactors than fission

Physics (13 decks)

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