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Physics > Topic 6 - radioactivity > Flashcards

Topic 6 - radioactivity Flashcards

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1
Q

Isotope

A

Element with the same number of protons but a different number of neutrons

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2
Q

Ionising

A

Causes an atom to lose or gain electrons

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3
Q

Unstable atoms

A

Wrong number of protons to neutrons causing it to emit radiation in the form of energy or mass

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4
Q

Stable atom

A

Have the right balance of neutrons to protons

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5
Q

Radiation

A

Emission of mass or energy

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6
Q

Rutherfords gold leaf experiment of alpha particles. Observations:

A

Most alpha particles passed through
Some got detected
A few bounced back

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7
Q

Conclusions of Rutherfords gold leaf experiment

A

Atom is mostly empty space
There was a positive charge at the centre
The mass was concentrated at the centre

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8
Q

How is an ion formed?

A

If an electrons absorbs enough energy it will make up all the shells and leave the atom

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9
Q

What radioactive particles are emitted from an unstable atom?

A

Alpha =α. Beta= β. Gamma= γ and neutron radiation

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10
Q

What is background radiation?

A

Radiation that is naturally occurring all the time

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11
Q

Sources of background radiation

A

Food, rocks, medical, food.

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12
Q

Main source in the uk for background radiation

A

Radon gas, nuclear power stations + space

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13
Q

What is a Geiger - Müller tube?

A

Detects ionising radiation when a charged particle (from an ionised atom) completes a circuit.

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14
Q

How do you accurately measure the radioactivity of an object?

A

1) take 3 readings of background radiation in the room without object being present. Find the average.
2) take 3 readings with object present + find average.
3) subtract background radiation reading from average reading of object

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15
Q

Bohr’s model of the atom

A

Passed high current through gases + they emitted light - set number of colours. If only certain frequencies (colours) are present then electrons only moving between set energy levels. -> electrons shells must be set distances from nucleus.

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16
Q

What is half life?

A

The time taken for the activity of a radioactive substance to reduce by a half.

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17
Q

Can you predict half life?

A

No, it’s unpredictable + random. You can’t say which nucleus will decay or when. You can’t cause it to decay or slow down.

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18
Q

What are the dangers of ionising radiation?

A

If alpha, beta or gamma ionise the nuclei in the atoms that make up your DNA your cells can mutate and cause cancer

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19
Q

Contamination

A

The source of radiation is on or in you

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20
Q

Irradiation

A

The source of radiation is near you

21
Q

Safety measures when dealing with types of radiation

A

Barriers + distance. Eg long handled tongs, gloves, using sources with short half life

22
Q

What is the approximate size of an atom?

A

x10-^10m

23
Q

Describe the atom

A

A positively charged nucleus with protons + neutrons surrounded by negatively charged electrons. Almost all mass in nucleus

24
Q

What is the relative mass of a proton?

A

1

25
Q

What is the relative charge of a proton?

A

+1

26
Q

What is the relative mass of a neutron?

A

1

27
Q

What is the relative charge of a neutron?

A

0

28
Q

What is the relative mass of an electron?

A

1/2000

29
Q

What’s the relative charge of an electron?

A

-1

30
Q

How is an atom neutral?

A

Because the number of protons equals the number of electrons

31
Q

What happens to electrons when there is an absorption or emission of electromagnetic radiation?

A

They can move up to a higher energy level if it absorbs EM radiation with right amount of energy. It then quickly falls back + emit same amount of energy absorbed + often visible light is released

32
Q

What is an alpha particle?

A

They’re helium nuclei. They have two neutrons + two protons.

33
Q

Describe how ionising + penetrable alpha particles are

A

They don’t penetrate very far into materials + stopped quickly. Travel few cm in air + absorbed by paper.
Due to their size they’re highly ionising

34
Q

What is a beta particle?

A

Beta minus is an electron emitted from nucleus.

Beta plus is a positron from nucleus (the antiparticle of the electron)

35
Q

Describe how ionising and penetrable beta particles are

A

They’re moderately ionising. Beta minus have range in air of few meters + absorbed by 5mm aluminium
Positrons have smaller range as when they hit electron the two destroy each other + produce gamma rays.

36
Q

What are gamma rays?

A

Waves of EM radiation released by the nucleus that carry away this energy.

37
Q

Describe how ionising and penetrable gamma rays are

A

They penetrate far into materials without being stopped + travel long distance in air.
Weekly ionising as they pass though rather than collide with atoms
Absorbed by thick lead or concrete.

38
Q

Describe the process of β– decay

A

A neutron becomes a proton plus an electron

39
Q

Describe the process of β+ decay

A

A proton becomes a neutron plus an electron

40
Q

What is the unit of activity of a radioactive isotope?

A

Becquerel, Bq

41
Q

Explain the effect of alpha decay on the charge + mass of an atom

A

The mass number decreases by 4

The atomic number decreases by 2

42
Q

Explain the effect of beta minus decay on the charge + mass of an atom

A

Neutron changes into a protons + electron so:
Mass number doesn’t change as it lost neutron but gained proton
Atomic number increases by 1

43
Q

Explain the effect of beta plus decay on the mass + charge of an atom

A

Mass number doesn’t change as it’s lost a proton but gained a neutron
Atomic number decreases by 1 as it has one less proton

44
Q

Explain the effect of neutron emission on the mass + charge of an atom

A

Mass number decreases by 1

Atomic number stays the same

45
Q

Explain the effect of gamma radiation on the charge and mass of an atom

A

Gamma rays agents rid of excess energy from an atom

Mass + atomic numbers stay the same gayer gamma ray has been emitted

46
Q

What happens to nuclei that have undergone radioactive decay?

A

They often undergo nuclear rearrangement with a loss of energy as gamma radiation

47
Q

How does the radioactivity of a source decrease over time?

A

Each time radioactive nucleus decays one more radioactive nucleus disappears. As unstable nuclei steadily disappear, activity as a whole will decrease.

48
Q

What is half life?

A

The time taken for half the undecayed nuclei to decay.

Physics (11 decks)

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