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Physics > Topic 4: Radioactivity > Flashcards

Topic 4: Radioactivity Flashcards

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1
Q

What did Rutherford do in is experiment? - What did he predict would happen?

A

Fired alpha particles at a thin sheet of gold foil
He predicted that most particles would go straight through, and some may be slightly deflected, BUT, this was not entirely the case as some came straight back

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2
Q

What did Rutherford conclude about the atom from his experiment?

A

Atom is mostly empty space
Most of the mass in an atom is concentrated at the centre in a nucleus
Nucleus in an atom has a positive charge

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3
Q

What happens when an electron absorbs Electromagnetic Radiation?

A

Inner electron moves up to a higher energy level, away from the nucleus, if it absorbs EM radiation with the right amount of energy
When it moves up it is said to be ‘excited’
The electron will then fall back to its original energy level and emit the same amount of energy it absorbed. The energy is carried away by EM radiation
(VISIBLE LIGHT)

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4
Q

What’s ionising radiation?

A

Any radiation that can knock electrons from atoms

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5
Q

What are the types of ionising radiation?

A

Alpha, Beta (+and-), gamma

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6
Q

What are the features of an alpha particle/radiation?

A
  • Alpha radiation is when an Alpha particle is emitted from nucleus
  • 2 protons, 2 neutrons
  • Strongly ionising (their large size easily knocks off electrons)
  • Low penetration power
  • Only travel a few cm in air
  • Absorbed by a thin sheet of paper
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7
Q

What are the features of a Beta+ particle/radiation?

A
  • beta plus particle is a fast-moving POSITRON (antiparticle of the electron)
  • Moderately ionising
  • Smaller range in air than beta minus because when a positron hits an electron, the two destroy eachother and produce gamma rays (called annihilation)
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8
Q

What does it mean by the positron being an antiparticle to the electron?

A
  • Positron has the same mass as the electron, but a +1 charge
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9
Q

Why do positrons have a smaller range in air?

A

When they hit an electron, they annihilate

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10
Q

What are the features of a Beta- particle/radiation?

A
  • fast moving electron released by the nucleus
  • Virtually no mass
  • Relative charge -1
  • Moderately ionising (smaller than alpha)
  • Range in air of a few metres
  • Absorbed by approx. 5mm thick aluminium sheet
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11
Q

What are the features of gamma rays/radiation?

A
  • Energy released by a decaying nucleus
  • High penetration power (absorbed by thick lead sheets)
  • Weakly ionising (passes through rather than collide with atoms)
  • Long range in air
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12
Q

What’s an isotope?

A

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

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13
Q

What can radioactive substances emit when they decay?

A

Alpha, beta, gamma, neutrons

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14
Q

During alpha decay, what maths do you have to apply?

A

Mass number - 4
Atomic number - 2

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15
Q

During Beta-minus decay, what maths do you have to apply?

A

Mass number + 0
Atomic number + 1

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16
Q

During Positron emission, what maths do you have to apply?

A

Mass number + 0
Atomic number - 1

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17
Q

During neutron emission, what maths do you have to apply?

A

Mass number - 1
Atomic number + 0

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18
Q

Explain how nucleuses can become more stable

A

Gamma rays get rid of excess energy from an atom
The nucleus goes from an excited state to a more stable state by emitting a gamma ray

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19
Q

Which particle in the nucleus decays during beta decay?

A

Neutrons

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20
Q

Describe what happens during radioactive decay

A

Radioactive substances spit out one or more types of ionising radiation

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21
Q

What’s a Half-life?

A

The average time taken for the number of radioactive nuclei in an isotope to halve

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22
Q

What’s the activity?

A

The rate at which a source decays

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23
Q

What is activity measured with?

A

Geiger-Muller tube
- Clicks each time it detects radiation

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24
Q

What’s photographic film?

A

More radiation it’s exposed to, the darker it gets

25
Q

What does a source with a short half life mean for the activity?

A

The activity falls quickly, because the nuclei are very UNSTABLE and rapidly decay

26
Q

Are sources with short half lives dangerous?

A

Yes, they emit a a high amount of radiation at the start and quickly become safe

27
Q

What does a source with a long half life mean?

A

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

28
Q

Are sources with long half lives dangerous?

A

They can be because they release small amounts of radiation for a long time. It’s dangerous because areas are exposed to radiation for millions of years

29
Q

Explain what happens each time a radioactive nucleus decays

A

Each time a radioactive nucleus decays, one or more radioactive nucleus disappears. As the unstable nuclei all steadily disappear, the activity as a whole decreases

30
Q

What’s activity measured in?

A

Becquerels
1Bq = One decay per second

31
Q

Radiation is completely _______

A

Random

32
Q

What’s background radiation?

A

Low-level radiation that’s around us all the time

33
Q

What sources does background radiation come from?

A
  • Radioactivity of naturally occurring unstable isotopes which are all around us (in the air, some food, building materials and some rocks)
  • Radiation from space known as cosmic rays (Sun) - Earth’s atmosphere mostly protects us from much of this radiation
  • Radiation due to human activity (fallout from nuclear explosions/nuclear waste) - only a tiny proportion of total background radiation
34
Q

What’s the absorbed radiation dose?

A

The absorbed radiation dose is the amount of radiation you are exposed to (and so the amount of energy your body absorbs)

35
Q

What’s Irradiation? - how can the effects be reduced?

A
  • Objects near a radioactive source are irradiated by it (exposed to it)
  • Irradiation doesn’t make things radioactive
  • Effects can be reduced by keeping sources in lead-lined boxes, standing behind barriers or being in a different room. Medical staff who work with radiation use photographic film badges to monitor their exposure
36
Q

What’s Contamination? - how it be prevented?

A
  • If unwanted radioactive atoms get onto an object, it is said to be contaminated
  • These contaminating atoms may then decay which releases radiation (could cause harm)
  • Once a person is contaminated, they are at risk of harm until the contamination is removed or all the radioactive atoms have decayed
  • To prevent contamination: Gloves and tongs used when handling sources to avoid particles getting stuck to your skin, industrial workers ay wear protective suits to stop them breathing in the particles
37
Q

What are the dangers of radiation entering living cells?

A
  • When radiation enters living cells, it can ionise atoms and molecules in them leading to tissue damage
  • Lower doses of radiation cause minor damage without killing the cells. This can give rise to mutant cells which divide uncontrollably leading to cancer
  • higher doses kill cells completely causing radiation sickness (vomiting, hair loss, tiredness) if a lot of cells get killed at once
38
Q

What are the most dangerous forms of radiation when outside the body? - why?

A

Beta and Gamma
- They can penetrate the body and get to delicate organs

39
Q

What is the most dangerous form of radiation when inside the body? - why?

A

Alpha
- Alpha particles are strongly ionising so they do their damage in a very localised area

40
Q

Are radioactive sources safer if the half-life is longer or shorter? - explain why

A
  • lower the activity, the safer the radioactive source is to be around
  • Sources with shorter half-lives become safer faster, because the activity falls much faster
  • Even if a source with a long half-life has a lower initial activity, the source with a shorter half-life will become safer after a certain period of time
41
Q

How do smoke alarms work?

A
  • Weak source of alpha radiation is placed in a smoke detector close to two electrodes
  • The source causes ionisation (alpha particles are strongly ionising) and a current of charged particles flows
  • If there is a fire then smoke will absorb the charged particles which stops the current meaning that the alarm sounds
42
Q

How is food and medical equipment sterilised?

A
  • Food and medical equipment can be irradiated with a high dose of gamma rays
  • This kills all microbes
  • So, the food doesn’t go bad as quickly and medical equipment is sterilised
  • the radioactive source for this must be a very strong emitter of gamma rays with a long half-life so that it doesn’t need replacing often
43
Q

Why is irradiation a good method of sterilisation?

A
  • Unlike boiling, it doesn’t involve high temperatures
  • Fresh fruit and plastic instruments can be sterilised without being damaged
44
Q

How do tracers work? - what type of radiation should be used?

A
  • Medical tracer is injected into/swallowed by a patient and its progress around the body is followed using an external detector
  • Can be used to detect and diagnose medical conditions like cancer
  • Isotopes taken into body must be beta or gamma (never alpha as its highly ionising so it will cause damage), so that radiation passes out of the body without doing too much damage. They should have a short half-lifer so the radioactivity inside the patient quickly disappears
45
Q

How is radiation used for thickness control?

A
  • beta radiation used
  • direct radiation at the stuff being made (e.g. paper) and place a detector on the other side connected to a control unit
  • when the amount of detected radiation changes, it means the (e.g. paper) is coming out too thick or thin, so the control unit adjusts the rollers to give the correct thickness
  • must be a beta source because the paper will partially block the radiation - if all or none of it goes through, the reading won’t change as the thickness changes
46
Q

What does PET stand for? (PET scanning)

A

Positron emission tomography

47
Q

What are PET scans used for?

A

Diagnosing medical conditions

48
Q

How do PET scans identify cancer? (BASIC ANSWER)

A

They can identify active cancer tumours by showing metabolic activity in tissue
Cancer cells have a much higher metabolism than healthy cells

49
Q

Explain what happens during a PET scan.

A

1) Inject patient with a substance used by the body e.g. glucose, containing a positron-emitting radioactive isotope with a short half-life so it acts as a tracer. The tracer moves through the body to the organs over an hour
2) Positrons emitted by the isotope meet electrons in an organ and annihilate. This emits high energy gamma rays in opposite directions that are detected. Detectors around the body detect each pair of gamma rays - the tumour will lie along the same path as each pair. By detecting at least 3 pairs, the location of the tumour can accurately be found by triangulation
3) The distribution of radioactivity matches up with metabolic activity because more of the radioactive substance injected (e.g. glucose) is taken up and used by cells with an increased metabolism (doing more work)

50
Q

Should isotopes used in PET scanning have long or short half-lives?

A

Short half-lives
- They need to be made close to where they’ll be used (some hospitals have their own cyclotron to make the isotopes on-site
- Otherwise, if they have to be transported over a large distance, their activity could be too low by the time they arrive at the hospital

51
Q

What’s Nuclear Fission?

A

Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei, energy is released (from uranium or plutonium)

52
Q

Explain what happens during Nuclear Fission

A

1) Slow moving neutron fired at large unstable nucleus (often Uranium-235). The neutron is absorbed by the nucleus, making the atom more unstable which causes it to split
2) When the atom splits, it forms two new lighter elements called daughter nuclei and energy in the form of gamma rays is released
3) All the new nuclei is radioactive
4) Each time uranium atom splits up, it also spits out two or three neutrons which can hit another uranium nuclei, causing them to split as well - this repeats as a CHAIN REACTION

53
Q

Why does nuclear fission in reactors have to be carefully controlled - and how are they controlled?

A
  • Neutrons released by fission have a lot of energy and if the chain reaction is left unchecked, large amounts of energy will be released in a short time as a runaway reaction which could lead to an explosion
  • Uranium fuel rods are placed in a moderator (e.g. graphite) to slow downing the fast-moving neutrons
  • Control rods (usually boron) are lowered into the reactor in between the fuel rods to limit rate of fission by absorbing excess neutrons
  • This creates a steady rate of nuclear fission where one new neutron produces another fission
54
Q

Explain how nuclear power stations can generate electricity

A
  • Nuclear power stations create controlled chain reactions
  • Nuclear fission produces heat which turns water to steam
  • the steam powers a turbine which generates electricity
55
Q

What are nuclear power stations powered by?

A

Nuclear Reactors

56
Q

What’s nuclear fusion? - explain what happens

A
  • Nuclear fusion is the joining of two light nuclei when they collide at high speed to create a larger, heavier nucleus
  • The heavier nucleus does not have as much mass as the two separate, light nuclei did because some of the mass of the lighter nuclei is converted to energy and released
57
Q

Give an example of nuclear fusion

A

Hydrogen nuclei can fuse to produce a helium nucleus

58
Q

What’s the main problem with nuclear fusion?

A
  • requires really high pressures and temperatures because the positively charged nuclei have to get very close to fuse, so the strong force due to electrostatic repulsion has to be overcome
  • it takes more power to get up to the temperature required than the reactor can produce
59
Q

What are the pros and cons of nuclear power?

A

PROs:
- Very reliable
- Reduces need for fossil fuel which are running out
- Doesn’t contribute to global warming
CONs:
- Some people see it as dangerous
- Waste products from nuclear fission have very long half-lives meaning that they’ll be radioactive for many many many years
- Leaks

Physics (9 decks)

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