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Phys Paper 1 > P7: Radioactivity > Flashcards

P7: Radioactivity Flashcards

1
Q

What is the basic structure of an atom?

A

Central nucleus containing neutral neutrons and positive protons, with negative electrons that orbit in energy levels around it
Nearly all of the mass of the atom is concentrated in the nucleus

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2
Q

What is the scale/size of an atom?

A

Radius = ~ 1x10-¹°
Nucleus radius = 1/10 000 radius of atom

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3
Q

How does the energy in energy levels differ depending on their distance from the nucleus?

A

Energy levels which are further away have higher energy

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4
Q

How can electrons change energy levels?

A

If an atom gains electromagnetic radiation, an electron can move to a higher energy level - the atom can now emit the electromagnetic radiation, and the electron returns to its original energy level

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5
Q

What do the numbers next to the elements mean?

A

Small number = proton and electron number (atomic number)
Big number = relative atomic mass (protons + neutrons)

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6
Q

What is an isotope?

A

Different versions of the same element with different numbers of neutrons

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7
Q

What is an ion?

A

An atom that has gained or lost an electron to gain a positive (lose) or negative (gain) charge

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8
Q

After the electrons were discovered, what was the new atomic model presented?

A

The plum pudding model - a ball of positive charge with negative electrons embedded in it

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9
Q

What experiment proved the existence of a positive nucleus?

A

The alpha-scattering experiment

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10
Q

Describe the alpha scattering experiment

A

A piece of gold foil was rolled to just a few atoms thick (that’s why it was chosen).
Then, positive alpha particles were fired at it.
Observations deducted that most alpha particles passed through the gold foil without changing direction, sometimes they were slightly deflected and other times they were directly deflected backwards

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11
Q

Why did the alpha-scattering experiment disprove the plum-pudding model?

A

Most of the alpha particles went through the foil - meaning the atom is mostly empty space.
As some of the atoms were deflected, the centre of the atom must have a positive charge as it deflected the positive particles.
Some particles bounced straight back - meaning the mass of the atom is concentrated in the centre

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12
Q

What was the new atomic model proposed?

A

The nuclear model - a positive nucleus surrounded by mostly empty space with tiny orbiting electrons

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13
Q

What were other additions to the nuclear model?

A

Energy levels, proposed by Bohr
Neutrons, proposed by Chadwick

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14
Q

What is the process of radioactive decay?

A

The process of an unstable nucleus giving out radiation to stabilise itself

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15
Q

What is the nature of radioactive decay?

A

It’s random - scientist cannot predict when it will happen

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16
Q

What is activity and what are its units?

A

The rate at which a source of unstable nuclei decay.
Its measured in Becquerel (Bq), where 1 Bq = 1 decay per second

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17
Q

How is activity measured?

A

Using a Geiger-Muller tube - the count-rate is the number of decays recorded each second by a detector

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18
Q

What are the 4 types of radiation?

A

Alpha radiation
Beta radiation
Gamma radiation
Neutron

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19
Q

What is the structure of an alpha particle?

A

A single helium nucleus - 2 protons and 2 neutrons

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20
Q

What is the structure of a beta particle?

A

A single electron that has been ejected from the nucleus at high speed

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21
Q

How is a beta particle made?

A

It is formed when a neutron in the nucleus changes into a proton and an electron - which is then released

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22
Q

What is the structure of gamma radiation?

A

Gamma rays - a type of electromagnetic radiation from the nucleus

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23
Q

What is the range of alpha particles in air?

A

5cm
They are large, meaning they can’t travel far in air before colliding with it and being stopped

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24
Q

What is the range of beta particles in air?

A

1 m

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25
Q

What is the range of gamma rays in air?

A

~ 1km

26
Q

What material stops alpha particles?

A

A sheet of paper

27
Q

What stops beta particles?

A

A few mm of aluminium

28
Q

What stops gamma rays?

A

Several cm of lead

29
Q

What is ionising power?

A

When radiation collides with atoms, it causes them to lose electrons (form ions)

30
Q

Describe the ionising power of each of the forms of radiation

A

Alpha - strongly ionising
Beta - relatively ionising
Gamma - weakly ionising

31
Q

What are the rules for alpha decay?

A

Atomic number decreases by 2
Mass number decreases by 4

32
Q

What are the rules for beta decay?

A

Atomic increases by 1
Mass number remains the same

33
Q

What is the half-life of a radioactive isotope?

A

The time it take for the number of nuclei of the isotope in the sample to halve
sample =! a single atom
It is also the time it takes for the count rate (activity) from a sample containing the isotope to fall to half its initial level

34
Q

What is irradiation?

A

Exposing an object to nuclear radiation (it does not become radioactive)
e.g. gamma radiation is used for sterilisation

35
Q

What is radioactive contamination?

A

When unwanted radioactive isotopes end up on other materials

36
Q

What are the dangers of ionising radiation?

A

The risk of cancer is increased

37
Q

What precaution can be taken against alpha radiation?

A

Wear gloves

38
Q

What precautions can be taken against beta and gamma radiation?

A

Lead apron
Shielding (using lead walls and lead-glass screen)

39
Q

What precaution can be taken against all types of radiation?

A

Radiation monitor to measure how much radiation has been received - if it’s too much, then the person will know not to work with radioactive isotopes

40
Q

What precaution can be taken against all types of radiation?

A

Radiation monitor to measure how much radiation has been received - if it’s too much, then the person will know not to work with radioactive isotopes

41
Q

How dangerous is alpha contamination?

A

Very - alpha radiation is very strongly ionising, but easily stopped by dead cells on the skin surface. It can be dangerous if inhaled or swallowed,
(thus they cannot escape the body and crash into living cells, damaging their DNA)

42
Q

How dangerous is beta contamination?

A

Relatively - it’s quite ionising and enter the body through the skin

43
Q

How dangerous is gamma radiation?

A

Meh - Weakly ionising, passes straight through the body

44
Q

How dangerous is gamma radiation?

A

Meh - Weakly ionising, passes straight through the body

45
Q

What is background radiation?

A

A measure of the level of the ionising radiation in the environment of a particular location

46
Q

What are the natural sources of background radiation?

A

Radioactive rocks e.g. granite
Cosmic rays e.g. supernovae

47
Q

What are the man-made source of background radiation?

A

Nuclear accidents e.g. at power stations
Nuclear testing

48
Q

What can affect your exposure to nuclear radiation?

A

Your location and occupation

49
Q

What are the units for dose of radiation?

A

Sieverts (Sv)/ millisievert (mSv)

50
Q

What are some uses of radiation in medicine?

A

To explore internal organs and
To control or
Destroy unwanted tissue

51
Q

How is radioactive iodine used to explore the thyroid gland?

A

The patient drinks radioactive iodine which emits gamma radiation. The thyroid gland is found in the neck and it absorbs iodine to make hormones.
The gamma radiation leaves the body and can be detected. If a scan shows that the gland has absobed too much or too little, doctors can diagnose the condition.

52
Q

What is a tracer?

A

Injected radioactive sources that can make tissues show up through a medical imaging process

53
Q

What are the issues/ specifics of using radioactive tracers?

A

They must use weakly ionising radiation (beta/ gamma)
They must emit radiation that can be detected outside the body (beta/ gamma)
It must not decay into another radioactive isotope
Must have a short half life so it’s not present in the body for a long time

54
Q

What is radiotherapy?

A

Destroying cancer tissue with ionising radiation
Gamma radiation is used, they pass through the body and destroy the tumour

55
Q

What is the problem with radiotherapy?

A

It can also destroy healthy tissue

56
Q

What is nuclear fission?

A

The splitting of a large, unstable nucleus by the absorption of a neutron

57
Q

What happens during nuclear fission?

A

When a neutron hits a nucleus, it forms 2 daughter nuclei of roughly equal size, 2-3 neutrons and a gamma ray + energy, all fission products have kinetic energy.
The released neutrons can now hit more uranium nuclei and trigger fission again, and again, releasing enormous energy.

58
Q

What is a chain reaction?

A

When the fission of one nucleus results in the fission of other nuclei, and theirs results in the fission of more nuclei.

59
Q

How is energy generated in a nuclear reactor?

A

Using a controlled chain reaction
(explosion in a weapon is caused by an uncontrolled chain reaction)

60
Q

What is nuclear fusion?

A

Two light nuclei joining together to form one heavier nucleus
- some of the mass of the nuclei is converted to energy and released as radiation and heat

Phys Paper 1 (8 decks)

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