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physics a - level > Nuclear Physics (1): Radioactivity > Flashcards

Nuclear Physics (1): Radioactivity Flashcards

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1
Q

What was proposed by Ernest Rutherford?

A

The nuclear model of the atom

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2
Q

Describe the set up of Rutherfords experiment

A

He knew that some isotopes were unstable and so emitted radiation. He knew that alpha radiation consisted of fast moving, positively charged particles.

His experiment was done in an evacuated chamber, with an alpha source directed at a thin layer of metal foil. The alpha particles scattered by the by the metal foil were detected by a detector which could be moved around at a constant distance from the point of impact of the beam on the metal foil.

He measured the number of alpha particles reaching the detector per minute for different angles of deflection

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3
Q

What is the order of the nuclear diameter?

A

x10^-15

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4
Q

What are the 3 scenarios that occurred when the alpha particles were fired at the thin metal foil?

A
  1. Most Alpha particles passed straight through
  2. Some Alpha particles were deflected slightly
  3. Some Alpha particles were deflected by more than 90 degrees
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5
Q

What was Rutherfords conclusion made from the fact that most alpha particles passed straight through the thin metal foil?

A
  • Atoms are mostly empty space
  • Nuclei are very small
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6
Q

What was Rutherfords conclusion made from the fact that some alpha particles deflected slightly by the thin metal foil?

A
  • Nucleus very small
  • Repulsion has occurred, therefore the nucleus is positively charged
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7
Q

What was Rutherfords conclusion made from the fact that some alpha particles were deflected by more than 90 degrees by the thin metal foil?

A
  • Nucleus is massive
  • Nucleus is dense
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8
Q

Why must the foil used in Rutherfords experiment by very thin?

A

As otherwise the alpha particles will be scattered more than once, altering the results of the experiment

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9
Q

What is the probability that an alpha particle is deflected by more that 90 degrees?

A

1 in 10,000

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10
Q

What is the probability that an alpha particle is deflected by more than 90 degrees by a foil of n layers of atoms?

A

1 in 10,000n

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11
Q

What was the theorised structure of the nucleus before Rutherfords experiments?

A

The Plum Pudding Model - where protons are distributed evenly throughout the atom

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12
Q

What are the 3 types of radiation you need to know about?

A
  1. Alpha
  2. Beta
  3. Gamma
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13
Q

What are the ionising properties of alpha, beta and gamma radiation relative to each other?

A

Alpha - MOST
Beta - Moderately ionising
Gamma - LEAST

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14
Q

What are the penetrating properties of alpha, beta and gamma radiation relative to each other?

A

Alpha - LEAST
Beta - Moderately penetrating
Gamma - MOST

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15
Q

What is alpha radiation stopped by?

A
  • A few cm of air
  • Sheet of paper
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16
Q

What is beta radiation stopped by?

A
  • 5mm of aluminium
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17
Q

What is gamma radiation stopped by?

A
  • Significantly reduced by several cm of lead
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18
Q

What is gamma radiation comprised of?

A

High energy photons

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19
Q

How can the charges of the different types of radiation by shown?

A

Firing a beam of radioactive particles through a magnetic field:
- Gamma photons will stay straight
- Alpha particles will be deflected in one direction
- Beta particles will be deflected in the opposite direction but by MORE as beta particles are much lighter

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20
Q

What apparatus is used to investigate the ionising effect of radiation? Describe briefly how it works

A

Ionisation chamber and picoammeter

The ionisation chamber contains air at atmospheric pressure. The picoammeter is connected to the central electrode and the wall electrode of the ionisation chamber.

A source is directed into the ionisation chamber causing ions to be created which are attracted to the oppositely charged electrodes where they are discharged. As a result electrons pass through the picoammeter. The current produced through the picoammeter is proportional to the number of ions per second created in the chamber.

Alpha radiation - Produce the strongest currents as long as the source is not too far away from the chamber
Beta radiation - moderately strong currents
Gamma radiation - Weak currents

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21
Q

Describe the set up of a cloud chamber and briefly how it works

A

SET UP:
- Contains air saturated with a vapour at very low temperatures

HOW IT WORKS:
- Due to ionisation of the air an alpha or beta particle leaves a visible track of condensation as the ionising particles trigger the formation of droplets

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22
Q

Why does gamma radiation not produce a track in a cloud chamber?

A

As it is very weakly ionising

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23
Q

What do the tracks produced by alpha particles in a cloud chamber look like?

A
  • Straight easily visible tracks
  • All the same length -> indicating that all alpha particles have the same range
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24
Q

What do tracks produced by beta particles in a cloud chamber look like?

A
  • Wispy tracks that are easily deflected by air molecules
  • The tracks are less easy to see as beta particles are less ionising
25
Q

Describe a simple set up and method for investigating absorption by different materials for the types of radiation

A

EQUIPMENT:
- Source in sealed container
- Absorber material
- Geiger tube connected to a geiger counter

METHOD
- Measure the count rate, which is the number of counts in a given time detected by the geiger tube
- Before the source is tested you need to determine the count rate due to background radiation
- Then measure the count rate at a set distance (minus the background radiation) Followed by with an absorber.
- By using absorbers of different thicknesses you can investigate the effect of the absorber thickness on the count rate

NB: the longer you do each of your readings over, the better

NNB: The same set up is used for proving the inverse square law for gamma radiation except an absorber isn’t needed and you re simply altering the distance of the gamma source from the tube. You can also use it to determine the ranges of all the types of radiation in air.

26
Q

What is another word for ‘penetrating ability’ of radiation?

A

Range

27
Q

For a given source what energies do the alpha particles emitted have?

A
  • Energies are the same for all alpha particles emitted for a given source
28
Q

For a given source what energies do the beta particles emitted have?

A
  • Energies vary up to a maximum for a given source due to the neutrino also being emitted
29
Q

For a given source what energies do the gamma photons emitted have?

A
  • Energies are the same for all gamma photons emitted for a given source
30
Q

What law does the range of gamma radiation depend on?

A

The inverse square Law where:

I (intensity) = k/x^2

31
Q

What type of radiation is used in fire alarms?

A

Alpha radiation

32
Q

What is the definition of intensity of a source of radiation?

A

The radiation energy per unit second passing normally through a unit area

33
Q

Derivation of the inverse square law for gamma radiation

A

For a point source that emits n gamma photons per second the intensity = nhf

At a distance r from the source, all the photons emitted from the point source pass through a total area of 4(pi)r^2

Therefore:

I = nhf/4(pi)r^2
I = k/r^2

where k = nhf/4(pi)

34
Q

What is the charge of a nuclide AZ X?

A

+Ze (where e is the charge of the proton)

35
Q

What are some short term health impacts of exposure to ionising radiation?

A
  • Radiation poisoning
  • Skin burns
  • Nausea
36
Q

What are some long term health impacts of exposure to ionising radiation?

A
  • Destroys cell membranes causing cells to die
  • Cause cell mutation or rapid cell growth -> cancer
  • Death
37
Q

What should you do in the lab when handling ionising radiation?

A
  • Keep the source in a lead lined container
  • Place a warning sign on the door
  • Direct the source downwards
  • Put the source away as soon as you have used it
  • Solid sources should be transferred using handling tools such as tongs to ensure the user is as far away from the source as possible
38
Q

What piece of apparatus is used to measure the amount of radiation received?

A

Film badge

39
Q

What is the term for the amount of radiation received by a person?

A

Their dosage

40
Q

What is dosage measured in?

A

Sieverts, Sv

41
Q

What is background radiation?

A

Naturally occurring radiation that we encounter in our everyday lives due to cosmic radiation and radioactive materials in rocks, soil and the air

42
Q

What are some sources of background radiation?

A
  • Radon gas
  • Medical uses
  • Ground and Buildings
  • Food and drink
  • Cosmic rays
43
Q

What type of radiation is used for medical tracers?

A

Gamma radiation

44
Q

Why is the radiation type chosen for medical tracers gamma radiation?

A
  • Low ionising ability - means it is unlikely to cause any major harm to internal organs as it passes out of the body
  • Infinite range - can be detected from outside the body so we know where block are in the body
45
Q

What does a decay curve show?

A

How the mass/number of the initial radioactive isotope changes with time (as the isotope decays into the nucleus of a different element)

46
Q

Definition of half-life of a radioactive isotope

A

The half life of a radioactive isotope is the time taken for the mass of the isotope to decrease to half the initial mass.

The half life of a radioactive isotope is the time taken for the number of radioactive nuclei of the isotope to decrease to half the initial number

The half life of a radioactive isotope is the time taken for the activity of the radioactive sample to reach half its initial activity

47
Q

What is the shape of a decay curve?

A

Exponential

48
Q

How would you describe the process of decay?

A
  • Random
  • Unpredictable
49
Q

Definition of activity, A, of a radioactive isotope?

A

The activity, A, of a radioactive isotope is the number of nuclei of the isotope that disintegrate per second.

-> The rate of change of the number of nuclei of the isotope

50
Q

Unit of activity, A

A

Becquerel, Bq

51
Q

What is the equation for the power of a source of activity, A, that emits particles (or photons) of the same energy, E?

A

P = AE

P - the energy transfer per second

52
Q

For a given radioactive isotope does the probability of a particular nucleus undergoing radioactive decay differ between nuclei?

A

No - every nucleus of a radioactive isotope has an equal probability of undergoing radioactive decay

53
Q

For a large number of nuclei of a radioactive isotope, what is the only factor that affects the number of nuclei that disintegrate in a given time interval?

A

The total number of nuclei

54
Q

What two values are proportional to the number of nuclei that disintegrate in a given time period?

A
  1. The number of nuclei remaining
  2. The duration of the time period
55
Q

What is the equation for the rate of disintegration of a radioactive isotope?

A

dN/dt = -(lambda)N

Where:
N - the number of nuclei remaining
lambda - decay constant
dN - the number of nuclei that disintegrate

56
Q

Why is the minus sign necessary for the equation of the rate of disintegration of a radioactive isotope?

A

As the number of nuclei that disintegrate is a decrease

57
Q

What is the equation for the activity of N atoms of a radioactive isotope?

A

A = (lambda)N

58
Q

What is the exponential equation that shows how the number of nuclei of a radioactive isotope change with time?

A

N = N0 x e^(-lambda x t)

Where:
N - number of nuclei remaining at time t
N0 - Initial number of nuclei in the source
lambda - decay constant

physics a - level (24 decks)

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