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Physics > Radioactivity > Flashcards

Radioactivity Flashcards

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1
Q

What are the 3 types of radiation

A

Alpha, Beta and Gamma

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2
Q

What is alpha radiation

A

The emission of an alpha particle

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3
Q

What is an alpha particle

A

2 protons and 2 neutrons

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4
Q

What is beta radiation

A

The emission of a beta particle

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5
Q

What is a beta particle

A

A fast moving electron

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6
Q

What is gamma radiation

A

A gamma wave

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7
Q

What is a gamma wave

A

A high energy EM wave

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8
Q

Properties of alpha radiation

A

Range of 3cm in air
Stopped by paper/skin
Heavily ionising
Slow
Deflected by E and B fields

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9
Q

Properties of Beta radiation

A

Range of 1m in air
Stopped by 1-3mm aluminium
Moderately ionising
Fast
Deflected by E and B fields

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10
Q

Properties of Gamma radiation

A

Infinite range in air
Stopped by thick lead
Lightly ionising
Speed of light
Not deflected by E and B fields

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11
Q

How do alpha beta and gamma radiation interact with E fields

A

Opposite charges attract

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12
Q

How do alpha beta and gamma radiation interact with B fields

A

Fleming’s Left Hand Rule

Conventional current flows in the same direction as positive charge motion

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13
Q

Dangers of ionising radiation

A

Damages living cells

Cell DNA is damaged either directly or by creating ions/free radicals that react with DNA

Damaged DNA may cause cells to divide and grow uncontrollably, causing a tumour that may be cancerous

High doses kill living cells outright

Cell mutations and cancerous growth occur at both high and low doses

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14
Q

Precautions to observe with ionising radiation

A

No source must be allowed to come into contact with skin

Solid sources must be transferred using tongs, a glove-box or robot - minimum exposure

Liquid, gas and solids in powder form must be in sealed container - can’t be inhaled. spilt on hands or drunk

Radioactive sources should not be used for longer than necessary

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15
Q

What are the 2 methods of detection

A

Cloud Chamber and Geiger Tube

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16
Q

How does a cloud chamber work

A

Contains air saturated with water at a very low temperature

Alpha/Beta particles will ionise the air and the water molecules will be attracted to the ions, creating a track of minute condensed water droplets

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17
Q

Describe alpha particle tracks in a cloud chamber

A

Straight, radiating from source
Tracks from given isotope of same length
Same range/ionising power/energy

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18
Q

Describe beta particle tracks in a cloud chamber

A

Wispy tracks because beta particles are easily deflected by air molecules
Less easy to see than alpha particle tracks
because beta particles are less ionising

19
Q

How does a Geiger Tube work

A

Sealed tube that contains argon gas at low pressure

Thin mica window at end allows alpha and beta particles to enter

A metal rod down the centre of tube is at a positive potential with respect to the tube walls - E field in tube

When an alpha or beta particle enters the tube, it ionises all gas particles along its track

Negative ions attracted to rod - positive to tube walls

Ions accelerate - collide with more gas particles - creating more ions

20
Q

How does detection work in a Geiger Tube

A

Many ions created in short time and discharged at electrodes

Pulse of charge travels around circuit for each discharge - causing a voltage pulse across R - which is recorded as a single count

21
Q

How does absorption work in a Geiger Tube

A

Geiger tube and counter used to investigate absorption by different materials

Number of counts in a given time measured and used to calculate count rate by dividing by time

Before the count rate is examined, the count rate due to background ration must be measured

Count rate is then measured with absorber between source and tube, and background count rate subtracted from it

By using absorbers of the same material but different thickness, the effect of absorber thickness can be investigated

Number of counts in a given time measured and used to calculate count rate by dividing by time

22
Q

Define Transmutation

A

Name given to the process by which an unstable nucleus decays and becomes a new nucleus

Parent nucleus becomes a daughter nucleus

The daughter nucleus itself may be unstable and decay to another nucleus

The process continues until a stable nucleus is formed

Nucleon number, atomic number, mass/energy are all conserved during a transmutation

23
Q

Desribe Alpha Decay

A

Energy is released during an alpha decay owing to the mass deficit between mass of parent nucleus, and the sum of masses of daughter nucleus and alpha particle

Helium nucleus is emitted

24
Q

What happens during Beta Minus decay

A

An electron and anti neutrino are emitted

25
Q

What emits Beta Minus Radiation

A

Nuclei that have too many neutrons for stability

26
Q

What happens during Beta plus decay

A

A positron and neutrino are emitted

27
Q

What emits Beta plus radiation

A

Nuclei that have too many protons for stability

28
Q

What happens during Gamma decay

A

The emission of a y photon

Doesn’t change the number of protons or neutrons but allows the nucleus to lose energy

Only happens if daughter nucleus is formed in an excited state - following an alpha or beta emission or electron capture

If daughternucleus stays in the excited state for one time - it can be separated from the parent nucleus

Thus a source of only gamma radiation is produced

29
Q

Look at NZ graphs

A

Ok

30
Q

Define Half Life

A

Average time taken for half the number of unstable nuclei in a sample to decay

31
Q

Formula for mass remaining after half life

A

0.5^n x Initial mass

Where n is number of half lives

32
Q

Define radioactive activity

A

Number of nuclei that decay every second l

Unit Bq

1 Bq = 1 decay per second

33
Q

Formula for Activity (A)

A

A = lambda x N

Lambda is decay constant
N is number of nuclei

34
Q

Nature of decay

A

Random and spontaneous

35
Q

Alpha Decay Equation

A

A A-4 4
X -> Y + He
Z Z-2 2

36
Q

Beta Decay Equation

A

A A 0
X -> Y + e + anti electron neutrino
Z Z+1 -1

37
Q

Gamma Decay Equation

A

A A
X -> X + Gamma ray
Z Z

38
Q

Formula for half life

A

lambda t1/2 = ln(2)

39
Q

Model Exponential decay

A

Delta N / Delta t = -lambda x N

N = N0 x e^-lambda x t

  • Start with a given number of undecayed nuclei N0
  • Choose a very small interval of time, which must be very small compared with the half-life of the isotope so that we can assume activity does not change significantly
  • Calculate number of nuclei decaying with the equation Delta N = Delta t x lambda x N
  • Calculate the number of undecayed nuclei in the source at the end of the period by subtracting delta N from the previous value of N
40
Q

Limitations to carbon dting

A

Assumes ratio of carbon-14 atoms:carbon-12 atoms has stayed constant over time

41
Q

Explain carbon dating

A

Carbon-14:Carbon-12 nuclei in atmospheric carbon is almost constant at 1.3x10^-12 - same ratio in all living things

Once an organism dies, it stops taking in carbon, whilst the amount of carbon-14 it contains continues to decay

Activity from carbon-14 is proportional to undecayed carbon-14 nuclei

42
Q

Why can we not use carbon-14 to dare rocks on the Earth to meteors

A

Formed during the creation of the Solar System

Half-life is not long enough for these ages

Use rubidium-87 instead which emits beta minus particles

43
Q

Formula for decrease in activity with time

A

A = A0 x e^-lambda x t

A0 is the activity at time t

44
Q

Formula for decrease in undecayed nuclei with time

A

N = N0 x e^-lambda x t

N0 is the number of undecayed nuclei at time t

Physics (19 decks)

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