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Physics Flashcards - OCR 21st Century > P5 - Radioactive Materials > Flashcards

P5 - Radioactive Materials Flashcards

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1
Q

Describe the structure of a nucleus

A

Describe the structure of a nucleus

The nucleus is positively charged and is
made of protons (positive) and neutrons
(neutral).

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2
Q

What are the relative charges of protons,

electrons and neutrons?

A

What are the relative charges of protons, electrons
and neutrons?

Protons: +1
Electrons: -1
Neutrons: 0

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3
Q

What are the relative masses of protons,

electrons and neutrons?

A

What are the relative masses of protons, electrons
and neutrons?

Protons: 1
Electrons: 0 (0.0005)
Neutrons: 1

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4
Q

Give an estimate for the radius of an

atom

A

Give an estimate for the radius of an atom

1x10⁻10m

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5
Q

Describe the arrangement of electrons in

an atom

A

Describe the arrangement of electrons in an atom

Electrons are arranged at different
energy levels, different distances from
the nucleus.

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6
Q

How can electrons arrangement

change?

A

How can electron arrangement change?

If an atom absorbs EM radiation,
electrons can move to higher energy
levels or leave the atoms entirely.

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7
Q

Describe Dalton’s atomic model

A

Daltons atomic model

Everything is made of tiny spheres
atoms) which could not be divided into
anything smaller.
(1800

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8
Q

Describe JJ Thompson’s atomic model

A

Describe JJ Thompson’s atomic model

The Plum Pudding Model: the overall 
charge of an atom is neutral, so it 
consists of a positive sphere (“pudding”) 
with embedded negative electrons.
(1897)
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9
Q

Describe Rutherford’s experiment

A

Describe Rutherford’s experiment
● Alpha particles (charge +2) were fired at a thin
sheet of gold foil.
● Most particles went straight through.
● Some particles were deflected by small angles
(< 90º).
● A few particles were deflected by large angles
(> 90º).

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10
Q

What are the conclusions of Rutherford’s

experiment?

A 
What are the conclusions of Rutherford’s 
experiment?
● Most of an atom is empty space.
● The nucleus has a positive charge.
● Most of the mass is concentrated in 
the nucleus.
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11
Q

Describe Rutherford’s atomic model

A

Describe Rutherford’s atomic model

There is a positive nucleus at the centre 
of an atom, with negative electrons 
existing in a “cloud”/region around the 
nucleus.
(1913)
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12
Q

Describe Bohr’s atomic model

A

Describe Bohr’s atomic model

Bohr’s model was very similar to the 
Rutherford model, but he described 
electrons as existing in fixed 
orbitals/shells/energy levels around the 
nucleus.
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13
Q

What is an isotope?

A

What is an isotope?

Atoms of the same element, with the
same number of protons, but a different
number of neutrons so therefore different
masses.

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14
Q

What do all atoms of the same element

share?

A

What do all atoms of the same element share?

The same number of protons (atomic
number).

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15
Q

When is an atom neutral?

A

When is an atom neutral?

When proton number = electron number.

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16
Q

When does radioactive decay occur?

A

When does radioactive decay occur?

When an atomic nucleus is unstable; it
gives off radiation to become more
stable.

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17
Q

Define activity

A

Define activity

The rate of decay of a source of unstable
nuclei; the number of decays per
second.

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18
Q

What is activity measured in?

A

What is activity measured in?

Becquerels, Bq

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19
Q

Define count rate

A

Define count rate

The number of decays per second.

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20
Q

How can count rate be measured?

A

How can count rate be measured?

Using a Geiger-Muller Tube.

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21
Q

Describe α (ALPHA) radiation

A 
Describe α (ALPHA) radiation
● 1 particle is 2 protons, 2 neutrons 
(same as a helium nucleus).
● Highly ionising.
● Weakly penetrating (blocked by ~5cm 
of air).
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22
Q

Give the equation for an α (ALPHA) particle

A

Give the equation for a α (ALPHA) particle

α 4/2 (SEARCH IT)

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23
Q

Describe ß (BETA) radiation

A 
Describe ß (BETA) radiation
● 1 particle is a single electron.
● Medium ionising effect.
● Medium penetration (blocked by 
~50cm of air or a sheet of metal).
24
Q

Give the equation for a ß (BETA) particle

A

Give the equation for a ß (BETA) particle

ß0/-1 SEARCH IT

25
Q

Describe γ (GAMMA) radiation

A 
Describe γ (GAMMA) radiation
● Weakly ionising.
● Highly penetrating (blocked by several 
cm of lead).
● Electromagnetic radiation (no 
particles).
26
Q

Give the equation for γ (GAMMA) radiation

A

Give the equation for γ (GAMMA) radiation
γ0/0 SEARCH IT
γ radiation is an EM wave.

27
Q

Define half life

A

Define half life

Half life is the time taken for the number
of radioactive nuclei to halve, or the time
taken for the count rate/activity to halve.

28
Q

Why can the decay of a single nucleus

not be predicted?

A

Why can the decay of a single nucleus not be
predicted?

Radioactive decay is a random process.

29
Q

How is net decline calculated?

A

How is net decline calculated?

Net decline = initial number - number after n half lives
Or
Net decline = initial number - (initial number x (½)ⁿ)

30
Q

What are the risks of ionising radiation to

people?

A

What are the risks of ionising radiation to people?

It can damage living cells, causing them
to die or mutate and become cancerous.

31
Q

What is contamination?

A

What is contamination?

Unwanted radioactive atoms found on
materials.

32
Q

What is irradiation?

A

What is irradiation?

Exposing an object to nuclear radiation,
without making it radioactive.

33
Q

What is a use of irradiation?

A

What is a use of irradiation?

Sterilisation; medical tools are irradiated
to kill bacteria.

34
Q

Give 3 practical applications of

radioactive materials

A

Give 3 practical applications of radioactive materials

● Medical tracers
● Radiotherapy
● Smoke alarms

35
Q

Give an example of a medical tracer

A

Give an example of a medical tracer

Technetium

36
Q

Why is technetium used as a medical

tracer?

A

Why is technetium used as a medical tracer?

It has a half life of 6 hours and decays into a safe
isotope which can be excreted, making it safe for
use in the body.

It releases only gamma radiation so is weakly
ionising and can pass easily through body tissue
without damaging it.

37
Q

What kind of radiation is used for

radiotherapy?

A

What kind of radiation is used for radiotherapy?

Gamma radiation

38
Q

Explain the process of radiotherapy

A

Explain the process of chemotherapy

● Gamma emitters direct gamma rays
onto specific areas with cancerous
cells.
● The cells absorb the radiation and die.

39
Q

What kind of radiation is used in smoke

alarms?

A

What kind of radiation is used in smoke detectors?

Alpha radiation

40
Q

Give an isotope used in smoke alarms

A

Give an isotope used in smoke alarms

Americium

41
Q

How do smoke alarms work?

A

How do smoke alarms work?

Alpha radiation is emitted into the air,
reaching a detector and completing the
circuit. If smoke is present, it blocks alpha
radiation so it does not reach the detector
and the circuit is broken, causing an alarm
to sound.

42
Q

What factors need to be considered in

choosing radiation type?

A

What factors need to be considered in choosing
radiation type?

● Ionising ability.
● Penetration (alpha should not be used 
in the body, as it is blocked by skin so 
will be trapped inside).
● Half life.
43
Q

What is a nuclear fuel?

A

What is a nuclear fuel?

A radioactive material that releases
energy during changes in the nucleus.

44
Q

What is nuclear fission?

A

What is nuclear fission?

The splitting of a large and unstable
nucleus.

45
Q

How does fission occur?

A

How does fission occur?

When a nucleus absorbs a neutron.

46
Q

What is produced by fission?

A

What is produced by fission?

2 smaller nuclei, 2-3 neutrons and 
gamma rays (energy).
47
Q

Explain how a fission chain reaction occurs

A

Explain how a fission chain reaction occurs

When a nucleus absorbs a neutron and
decays, it produces neutrons which can
cause other nuclei to decay.

48
Q

Give 2 examples of nuclear fuel for

fission

A

Give 2 examples of nuclear fuel for fission

● Uranium
● Plutonium

49
Q

What other form of energy is released by

fission?

A

What other form of energy is released by fission?

Kinetic energy; the daughter nuclei move
away with kinetic energy.

50
Q

What is fusion?

A

What is fusion?

When two small nuclei fuse to form a
heavier nucleus and release energy.

51
Q

How do the masses of the reactants and

products compare in fusion?

A

How do the masses of the reactants and products
compare in fusion?

The sum of the masses of the two nuclei
which react is more than the mass of the
heavier nucleus that is formed.
(total mass decreases)

52
Q

Why does mass decrease in nuclear

fusion?

A

Why does mass decrease in nuclear fusion?

Some mass is converted into energy,
released as radiation.

53
Q

Give an example of where fusion occurs

A

Give an example of where fusion occurs

In stars (e.g. the sun)

54
Q

Why is fusion currently not a viable

energy source?

A

Why is fusion currently not a viable energy source?

There is no design yet which
accomplishes positive net energy; so far,
fusion always uses more energy than it
gives out.

55
Q

Give an example of a nuclear fusion

reaction

A

Give an example of a nuclear fusion reaction

Two hydrogen nuclei fusing to form a
new helium nucleus.

Physics Flashcards - OCR 21st Century (12 decks)

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