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Physics 9-1 iGCSE Oxford AQA > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

What is the radius of an atom?

A

1 × 10^−10 m

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2
Q

Provide some evidence for the distribution of mass in the atom

A

Scattering of alpha particles by thin metal foil

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3
Q

What happens to an electron if it gains energy by absorbing EM radiation?

A

They can move to higher energy level = further away from nucleus

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4
Q

What happens to an electron if it releases EM radiation?

A

It will move to lower energy level = that’s closer to nucleus

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5
Q

What happens if one or more electrons leaves an atom?

A

Atom becomes positively charged ion

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6
Q

What is an isotope?

A

Atoms with same no. of protons (same atomic number & same charge on nucleus) BUT different no. of neutrons (different mass number)

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7
Q

Do all elements have isotopes?

A

Yes

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8
Q

How many roughly stable isotopes do each element have?

A

1-2

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9
Q

What is radioactive decay?

A

When unstable isotopes decay into other elements & give out radiation as they try to become more stable

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10
Q

What can unstable isotopes also release when they decay?

A

Can release neutrons (n)

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11
Q

What is ionising radiation?

A

Radiation that knocks electrons off atoms, forming positive ions

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12
Q

What does the ionising power of a radiation source mean?

A

How easily it can knock electrons off atoms (forming positive ions)

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13
Q

What do radiation substances release?

A

Radioactive substances spit out one or more types of ionising radiation (e.g. beta, gamma, alpha)

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14
Q

Where is radiation given off in a radioactive substance

A

From the nuclei of their atoms

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15
Q

Why can’t you predict exactly which nucleus in a

sample will decay next, or any one of them will decay?

A

Radioactive decay is entirely random

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16
Q

How can radiation can be measured?

A

By using a Geiger-Muller tube and counter

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17
Q

How does Geiger-Muller tube and counter measure radiation?

A

Records the count-rate i.e. Number of radiation counts reaching it per second

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18
Q

What can half-life be used for?

A

Used to find rate at which a source decays - its ACTIVITY

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19
Q

What is activity measured in?

A

Becquerels, Bq (where 1 Bq is 1 decay per second)

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20
Q

Each time radioactive nucleus decays (to become stable nucleus), what happens to its activity?

A

Its activity as a whole will decrease

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21
Q

Do older sources emit more or less radiation?

A

Older sources emit less radiation

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22
Q

Why can’t we measure how long exactly it will take for a nucleus to decay?

A

The activity never reaches 0

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23
Q

What is half-life?

A
  • The time taken for the number of radioactive nuclei in an isotope to halve
  • The time it takes for the count rate from a sample containing the isotope to fall to half its initial level
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24
Q

What does it mean if a source has a short half-life?

A

The activity will fall quickly

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25
Q

Why would a source have a short half-life?

A

Because nuclei are very unstable and rapidly decay

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26
Q

Why are sources with short half-life dangerous?

A

Because they emit a high amount of radiation at start

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27
Q

What is good thing about sources with a short half-life

A

Can quickly become safe

28
Q

What does it mean if a source has a long half-life?

A

Its activity falls more slowly = releases small

amounts of radiation for long time

29
Q

Why would a source have a long half-life?

A

Because most of nuclei don’t decay for a long time

30
Q

Why are sources with long half-life dangerous?

A

Nearby areas are exposed to radiation for (millions of) years

31
Q

What do nuclear equations show?

A

Are a way of showing radioactive decay by using element symbols

32
Q

What is the form nuclear equations are written in?

A

atom before decay → atom(s) after decay + radiation emitted

33
Q

What is the golden rule to remember when writing nuclear equations?

A

The total mass and atomic numbers must be equal on both sides

34
Q

What happens to an atoms atomic number and mass number when it emits an alpha particle?

A

Its atomic number reduces by 2 and its mass number reduces by 4

35
Q

Why does the charge of the nucleus decrease when an atom emits an alpha particle?

A

Its atomic number reduced by 2 = a proton is positively charged and a neutron is neutral

36
Q

How can an alpha particle be written as in a nuclear equation?

A

As a helium nucleus - see mind map for answer

37
Q

Write out the nuclear equation for Uranium-238 which gives off thorium-234 and an alpha particle

A

See mind map for answer

38
Q

What happens to an atom when beta decay occurs?

A

A neutron in nucleus turns in a proton and releases a

fast-moving electron (beta particle)

39
Q

Why does the charge of the nucleus increase (become positive) when an atom emits a beta particle?

A

The number of protons in nucleus has increased by 1

40
Q

Why does the mass of the nucleus not change during beta decay?

A

Because the nucleus has lost a neutron and gained a proton during beta decay ∴ mass of nucleus doesn’t change (protons and neutrons have same mass)

41
Q

How can a beta particle be written as in a nuclear equation?

A

See mind map for answer

42
Q

Write out the nuclear equation for Carbon-14 which gives off nitrogen-14 and a beta particle

A

See mind map for answer

43
Q

How does a nucleus get rid of excess energy?

A

By releasing it as gamma rays

44
Q

Do gamma rays change the atomic mass or atomic number of an atom?

A

No

45
Q

How can gamma radiation be written as in a nuclear equation?

A

See mind map for answer

46
Q

Practice Question on Half-life:
The initial activity of a sample is 640 Bq. Calculate the final activity as a percentage of the initial activity after 2 half-life.

A

= 25% (see mind map for working out)

47
Q

What are alpha particles?

A

Helium Nuclei

48
Q

What is alpha radiation?

A

When an alpha particle (α) is emitted from nucleus

49
Q

What is an α-particle made up of (i.e. its no. of neutrons and protons)?

A

2 neutrons and 2 protons (like a helium nucleus)

50
Q

What is the charge of an alpha particle?

A

2+

51
Q

How far can an alpha particle travel in air?

A

Only can travel a few cm in air

52
Q

What will absorb an alpha particle?

A

A sheet of paper

53
Q

How ionising are alpha particles and why?

A

Strongly ionising because of their size

54
Q

Give an example how alpha radiation can be used in a home

A

Alpha radiation can be used in a smoke detector. It ionises the air particles, causing current to flow. If there’s smoke in the air, it bind to the ions = meaning current stops and the alarm sounds.

55
Q

What is a beta particle?

A

Beta particle (β) is a fast-moving electrons released by nucleus

56
Q

How much mass does a beta particle have?

A

Virtually has no mass

57
Q

What is the charge of a beta particle?

A

Charge of -1

58
Q

How ionising are beta particles?

A

Moderately ionising

59
Q

How far can a beta particle travel in the air?

A

A few meters

60
Q

What will absorb a beta particle?

A

A sheet of aluminium (around 5 mm thick)

61
Q

How can beta radiation be used (if a beta particle is moderately penetrating)?

A

Beta emitters are used to test the thickness of sheets of metal as particles are not immediately absorbed by material (like alpha radiation & do not penetrate as far as gamma rays). ∴ Slight variations in thickness affect the amount of radiation passing through the sheet.

62
Q

What are gamma rays (γ)?

A

Waves of electromagnetic radiation released by nucleus

63
Q

What the penetration of gamma rays and how far will it travel in the air?

A

They penetrate far into materials without being stopped and will travel a long distance through air

64
Q

What is a gamma ray’s charge?

A

Has no charge

65
Q

How ionising are gamma rays and why?

A

Weakly ionising because they tend to pass through rather than collide with atoms

66
Q

What will absorb a gamma ray?

A

Absorbed by thick sheets of lead or meters of concrete

Physics 9-1 iGCSE Oxford AQA (12 decks)

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