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Physixs > P6- Radioactivity > Flashcards

P6- Radioactivity Flashcards

1
Q

How can radiation that is emitted be detected?

A

With a Geiger Muller tube, which measiures the count rate in counts per minute, or second.

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2
Q

What do atoms consist of?

A

A nucleus, made up of protons and neutrons, surrounded by electrons

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3
Q

What is the atomic number of an atom?

A

The number of protons.

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4
Q

What does the atomic number define?

A

What the element is (eg. a carbon atom always has 6 protons)

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5
Q

What charge does the nucleus of an element have?

A

Positive

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6
Q

What is the mass number of an atom?

A

The number of protons plus the neutrons - the mass of the nucleus

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7
Q

What are isotopes?

A

Atoms of an element with the same number of protons but a different number of neutrons. Most elements have isotopes but only one or two stable ones - the others are unstable and radioactive.

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8
Q

How many stable isotopes does an atom have?

A

Usually only one or two. The rest are unstable and radioactive, meaning they give out nuclear radiation.

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9
Q

What are the four types of radiation?

A

Alpha, beta, gamma and neutron

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10
Q

What is an alpha particle?

A

Two neutrons and two protons - the same as helium. They have a relative mass of 4 and a charge of +2. They are relatively big, heavy and slow moving.

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11
Q

What is a beta particle?

A

An electron, with virtually no mass and a charge of -1. They move quite fast and are relatively small. For every beta particle emitted, a neutron turns to a proton in the nucleus.

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12
Q

What is a gamma ray?

A

After emitting an alpha or beta particle, the nucleus might need to get rid of some extra energy. It does this by emitting a gamma ray - a type of electromagnetic wave. Gamma rays have no mass or charge. They are just energy, so the don’t change the element of the nucleus when they are emitted.

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13
Q

What is neutron radiation?

A

If a nucleus contains a lot of neutrons, it may just throw one out, making the element an isotope.

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14
Q

What happens when radiation travels through a material?

A

It can collide with the material’s atoms, which slows down or stops the radiation. This means that the radiation can only penetrate so far into a material before it’s absorbed.

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15
Q

What does the range of radiation depend on?

A

The range of radiation depends on the type of radiation and the material it’s travelling through.

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16
Q

What are the different ranges of the different radiation types?

A

Gamma - longest range

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17
Q

What is count rate?

A

The number of radioactive particles that reach a detector in a given time. The further the radiation has to travel, the higher the chance it will be absorbed by the material it is travelling through. This means the count rate decreases the further the detector is from the radioactive source.

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18
Q

What can be used to block the different radiation types?

A

Alpha - paper
Beta - aluminium
Gamma - thick lead/concrete

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19
Q

What happens to the mass/atomic number when an alpha particle is emitted?

A

The mass number decreases by 4, as it loses two protons and two neutrons. The atomic number decreases by 2, as it has 2 less protons.

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20
Q

What happens to the mass/atomic number when a beta particle is emitted?

A

The mass number doesn’t change, as it has lost a neutron but gained a proton. The atomic number increases by 1 as it has one more proton.

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21
Q

What happens to the mass/atomic number when a gamma ray is emitted?

A

The mass number and the atomic number don’t change.

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22
Q

How do electrons sit in an atom?

A

In different energy levels, or shells. Each energy level is a different distance from the nucleus.

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23
Q

How does an electron move up one or more energy levels in an atom?

A

If it absorbs electromagnetic radiation with the right amount of energy. When it does move up, it moves to a partially filled (or empty) shell and is said to be “excited”.

24
Q

What happens when an electron moves back to its original energy level?

A

It falls back to its original energy level, and in doing so it loses the same amount of absorbed energy. The energy is carried away by EM radiation.

25
Q

What does it mean if an atom is ionised?

A

If an outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom entirely. It is now a free electron and the atom is said to have been ionised.

26
Q

How is nuclear radiation involved in ionisation?

A

Alpha, beta and gamma radiation can ionise atoms, and so can also be called ionising radiation. The ionisation power is different for different ionising radiations.

27
Q

What is the different ionisation power of the different ionising radiation types?

A

Gamma - lowest ionisation power

28
Q

What does bacquerels (Bq) measure?

A

The number of nuclei that decay in a second.

29
Q

How can you detect radiation emitted from a decaying nucleus?

A

A Geiger Muller tube, which measures count rate in counts per minute or second.

30
Q

What is the half-life of a substance?

A

The half-life of a source is the average time taken for its activity (or count rate) to halve. It can also be thought of as the average time taken for half of the remaining unstable nuclei to decay.

31
Q

What do different half-lifes mean?

A

A long half-life means the activity falls more slowly because most of the nuclei don’t decay for a long time.

32
Q

How do low doses of ionising radiation affect cells?

A

Lower doses of ionising radiation can damage living cells by causing mutations to the DNA. This can cause the cell to divide uncontrollably - cancer.

33
Q

How do high doses of ionising radiation affect cells?

A

Higher doses tend to kill cells completely, which causes radiation sickness if a lot of cells are blasted at once.

34
Q

What are the dangers of ionising radiation outside of the body?

A

Alpha is much less dangerous outside of the body as it cannot penetrate skin.

35
Q

What are the dangers of ionising radiation inside the body?

A

Beta and gamma are less dangerous inside the body as they are less ionising - gamma will mostly pass straight out without doing much damage.

36
Q

What is irradiation and the risk of irradiation?

A

If the radiation from a radioactive source reaches an object, it is irradiated. The risk of irradiation from a source is how likely it is that an object will be irradiated by the source. It depends on the distance from the source and the type of radiation.

37
Q

Why does alpha radiation have a lower risk of irradiation than gamma radiation?

A

Alpha has a shorter range in materials compared to gamma radiation and so the irradiation risk is lower.

38
Q

What is contamination and the risk of contamination?

A

If a radioactive source ends up on or in an object, the object is contaminated. The contamination risk is how likely it is that an object could get contaminated; if a radioactive source is solid, there’s no contamination risk for an object that doesn’t touch the source. However, if it is a gas, then it could move and come into contact with the object, increasing the contamination risk.

39
Q

What is the difference between contamination and irradiation?

A

Irradiation is temporary - if the source is taken away, any irradiation caused stops. Contamination lasts for longer - if the original source is taken away, the atoms causing contamination are left behind.

40
Q

What is important when looking for the right radioactive source to use?

A

You have to find a balance between a source that has a high enough activity to be useful but won’t be dangerous for too long.

41
Q

How is gamma radiation used for tracers?

A

Tracers can be injected or ingested to see how parts of the body are working. They need a relatively short half-life (a few hours, so that it doesn’t damage the patient but so that it exists long enough for the job). Gamma radiation can penetrate tissue, so eventually pass out of the body and are detected.

42
Q

How is radiation used to treat cancer?

A

High doses of radiation can kill living cells, so it is used to treat cancer.
The radiation is directed carefully and at a specific dosage (depending on the size and type of tumour, and size and age of patient), so that it kills cancer cells without damaging too many normal cells.
However, a fair amount of damage still affects the normal cells which makes the patient feel ill.

43
Q

How is cancer treated externally?

A

Using gamma rays - they are focused on the tumour using a wide beam. The patient stays still and the beam is rotated around them with the tumour at the centre. This minimises the exposure of normal cells to radiation, and it is given in doses with time between for the healthy cells to be repaired or replaced.

44
Q

How is cancer treated internally?

A

Implants containing beta-emitters are placed next to or inside the tumour. The beta particles damage the cells in the tumour but have a short enough range that the damage to healthy tissue is limited. Alpha emitters can also be injected into a tumour - they are strongly ionising, so they do lots of damage to the cancer cells.

45
Q

What is nuclear fission?

A

A type of nuclear reaction that is used to release energy from large and unstable nuclei, such as uranium or plutonium, by splitting them into smaller nuclei.

46
Q

How can nuclear fission occur?

A

Spontaneously (the fission is unforced and happens by itself), or by absorbing a neutron (if a nucleus absorbs a neutron then it becomes unstable and splits).

47
Q

What is the product of nuclear fission?

A

When a large nucleus splits it forms two new smaller nuclei, and possibly a few neutrons. A nucleus splitting gives out a lot of energy - some of this energy is transferred to the kinetic energy stores of the fission products. There is also a lot of extra energy which is carried away by gamma radiation.

48
Q

How can nuclear fission lead to a chain reaction?

A

Nuclear fission of uranium can happen if a neutron is absorbed into a uranium nucleus. This addition of a neutron makes the nucleus unstable, which causes it to split. Everytime it splits, it spits out 2 or 3 neutrons, some of which may be absorbed by other nuclei for the same process. This creates a chain reaction.

49
Q

How do nuclear power stations utilise chain reactions?

A

They generate electricity from them, using uranium or plutonium as fuel. The energy which is released in the chain reaction is used to heat water to make steam, which is used to drive a steam turbine connected to an electricity generator.

50
Q

What’s the main problem with nuclear power?

A

The disposal of the nuclear waste. The products left over after fission are highly radioactive with long half-lifes, and are difficult and expensive to dispose of safely.

51
Q

What is nuclear fusion?

A

When two light nuclei join to create a larger nucleus. For example, two hydrogen nuclei can fuse to form a helium nucleus. It releases a lot of energy (more than fission).

52
Q

What creates the large amount of energy in nuclear fusion?

A

The difference in mass between the original nuclei and the new nucleus. The total mass of the original nuclei is larger than the mass of the new nucleus. The extra mass is converted into energy and carried away by radiation.

53
Q

Why do people want to create fusion reactors?

A

Fusion creates no radioactive waste, and there’s plenty of hydrogen to use as fuel.

54
Q

Why are fusion reactors difficult to produce?

A

Fusion only happens at extremely high temperatures (10,000,000 degrees Celsius) and high pressures. Therefore, there are a few experimental reactors but none of them are generating electricity yet.

55
Q

What is emission spectra?

A

Colours of light that are emitted from an energy source at very specific wavelengths/frequencies, and none inbetween.

56
Q

What is absorption spectra?

A

A normal colour spectrum with very specific wavelengths missing.

Physixs (8 decks)

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