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AQA A Level Physics > Nuclear Physics - Rutherford Scattering and Radiation > Flashcards

Nuclear Physics - Rutherford Scattering and Radiation Flashcards

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1
Q

What did Rutherford do and why

A

He passed beams of alpha particles through a thin sheet of gold foil to investigate :

The different angles of deflection of the alpha particles
The number of alpha particles that were deflected at each angle

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2
Q

Apparatus for Rutherford scattering experiment

A

Source of alpha particles in a lead container
Thin sheet of gold foil
Moveable detector
Evacuated chamber

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3
Q

Purpose of the lead container in Rutherford’s experiment

A

Alpha particles are emitted in all directions
This was to produces a collimated beam of alpha particles
This is bcs alpha particles are absorbed by lead, so a long narrow hole at the front allowed a concentrated beam of alpha particles to escape and be directed as needed

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4
Q

Purpose of the thin sheet of gold foil

A

Target material needed to be very thin as a thicker foil would stop the alpha particles completely.
Gold was chosen due to its malleability so it would be easy to hammer into thin sheets

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5
Q

Purpose of the evacuated chamber in Rutherford’s experiment

A

Alpha particles are highly ionising and so it would ensure alpha particles did not collide with any particles on their way to the foil target

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6
Q

Observations from Rutherford’s experiment

A

The majority of alpha particles passed straight through the foil
Some alpha particles deflected through small angles <10 degrees
Only a small number of alpha particles deflected straight back at angles of >90

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7
Q

What does the majority of alpha particles passing through undeflected suggest

A

The atom is mostly empty space

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8
Q

What does some alpha particles deflecting through small angles suggest

A

There is a positive nucleus at the centre as 2 positive charges repel

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9
Q

What does a small number of alpha particles deflecting straight back at angles > 90 suggest

A

The nucleus is extremely small and is where most of the mass and charge of the atom are concentrated.

This led to the conclusion that atoms consist of small, dense +charged nuclei surrounded by negatively charged electrons

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10
Q

How do isotopes become more stable

A

The nucleus emits particles or radiation by the process of radioactive decay

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11
Q

What are the 3 main types of radioactive particles

A

Alphas
Beta
Gamma

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12
Q

Characteristics of alpha particles

A

The most ionising radiation as it has the highest charge
Do the most damage to cells
Least penetrating
Have a range of 3-7cm in air

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13
Q

When are beta particles emitted

A

B- = When a nuclei has too many neutrons
B+ = When a nuclei has too many protons

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14
Q

Characteristics of beta particles

A

Moderately ionising
Moderately penetrating
Range of 20cm-3m in air

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15
Q

When is gamma radiation emitted

A

When nuclei need to lose some energy

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16
Q

Characteristics of gamma radiation

A

Least ionising radiation as it has no charge
Most penetrating
Has an infinite range and follows inverse square law

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17
Q

What happens when any type of radiation collides with an atom

A

It can can knock out electrons and ionise the atom

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18
Q

What happens when a charged particle enters a electric field/magnetic

A

It is deflected

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19
Q

What happens to the radioactive particles when they enter an electric field

A

Alpha particles - deflected to negative plate
Beta particles - deflected to positive plate
Gamma radiation - Not deflected, travels straight through

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20
Q

What does the amount of deflection of a particle depend on

A

The speed of the particle
The mass of the particle
The charge on the particle

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21
Q

What happens to gamma radiation (happens to light as well) when it leaves a source

A

It begins to spread out uniformly as a sphere according to an inverse square law

22
Q

Inverse square law

A

Intensity of gamma radiation = constant of proportionality / (distance from source)^2

23
Q

How can the inverse square law be written for radiation at 2 different points

A

Intensity at x1 / Intensity at x2 = (X2 / X1)^2

24
Q

What does the inverse square law apply for and why

A

ONLY GAMMA radiation because it is not absorbed by matter easily, whereas alpha and beta are quickly absorbed before they can spread out

25
Q

Background radiation

A

The ionising radiation present in the environment

26
Q

What are the sources of background radiation

A

Radon gas
Rocks and building materials
Food
Cosmic rays

27
Q

How can you identify types of radiation from a source via a simple experiment

A

Use a geiger muller tube and counter to find the background count when the source is not present.
Place the source close to the GM tube and measure the count rate
Place a sheet of paper between the source and tube and measure count rate again.
If count rate decreases significantly, source is emitting alpha radiation
Repeat above steps using aluminium foil and several inches of lead.

28
Q

What are all three types of radiation used for

A

Monitoring the thickness of certain materials while they are being produced.

29
Q

Which materials do each radiation monitor the thickness of

A

Beta - aluminium foil
Alpha - paper
Gamma - steel sheets

30
Q

How is beta radiation used in the production of aluminium foil

A

Beta source is placed on one side of the material, while a detector is placed on the other.
If material too thick, less radiation passes through the foil so reading on detector decreases.
The rollers move closer together.
The opposite if the material is too thin.

31
Q

Describe the experimental verification of the inverse square law

A

Measure the count rate of a gamma source at different distance, measured using tape measure, from the GM tube.
Make sure to adjust for the background radiation.
Plot a graph of the count against 1/x^2
This forms a straight line

32
Q

How do you account for background radiation

A

Take readings with no radioactive source present and then subtract from readings with the source present.

33
Q

How to increase accuracy of count rates

A

Repeat readings and take averages
Taking readings over a long period of time.

34
Q

Equation for inverse square law (original)

A

intensity of gamma radiation = k / distance from source ^2

35
Q

Equation for inverse square law (derived)

A

intensity at x1 / intensity at x2 = ( x2 / x1) ^2

intensity is also called count rate sometimes

36
Q

Artificial sources of background radiation

A

Nuclear medicine - X-rays, CT scans
Nuclear waste / accidents

37
Q

What does the damage done by exposure to radiation / dose equivalent depend on

A

The amount of energy absorbed per kg of a body
The type of radiation absorbed

38
Q

How can you minimise the received radiation dose of a sample

A

Use short-lived isotopes
Use smaller samples of radioactive material

39
Q

What are the precautions to reduce the risk of harm when using radioactive sources

A

Keep sources shielded when not in use e.g. in lead lined box
Wear protective clothing to prevent contamination
Limit exposure time
Handle radioactive materials with long tongs
Monitor exposure of workers

40
Q

Precautions for patient using radiation therapy

A

Should be protected with lead to cover parts of body which do not need to be exposed
Calculate exact dose carefully
Dose should be directed very accurately at cancerous tissue

41
Q

Precautions for radiographer when doing radiation therapy

A

Handle source remotely with tongs/machine
Should be protected by a screen
Source should be immediately stored in lead case once dose given

42
Q

What are radioisotopes used for in medicine

A

Tracers to monitor the processes occurring in different parts of the body

43
Q

Why are radioactive tracers with short half life preferred

A

Shorter the half-life, the faster the isotope decays
Initially activity is very high so only a small sample is needed
Isotopes with shorter half life pose much lower risk to patient
Medical test does not last long so half life of a few hours is enough

44
Q

Explain why the isotope of 99-Tc is often chosen as a suitable source of radiation for use in medical diagnosis

A

It only emits gamma rays
May be detected outside the body
Weaker ioniser and causes little damage
Short enough half-life and will not remain active in body after use
Long enough half-life to remain active during diagnosis
May be prepared on site

45
Q

Which type of radiation is used in sterilising medical equipment and why

A

Gamma because:

It its the most penetrating
Penetrating enough to irradiate all sides of instruments
Instruments can be sterilised without removing packaging

46
Q

Why does using gamma radiation to sterilise equipment not cause the equipment to become radioactive

A

To become radioactive, the nuclei have to be affected
Ionising radiation only affects the outer electrons, NOT nucleus
radioactive material kept securely sealed away from packaged equipment

47
Q

A room is contaminated with dust containing americium which is an α−emitter. Explain the most hazardous aspect of the presence of this dust to an unprotected human entering the room.

A

Dust may be ingested into the body / breathed in
This causes cells to be killed/damaged by ionisation

48
Q

Why does gamma radiation obey an inverse square law but not alpha or beta

A

Gamma not absorbed
Spreads uniformly from a point source symmetrically
Area over which it spreads is proportional to radius squared
Alpha and beta are absorbed in addition to spreading out

49
Q

Main interaction when an alpha particle is scattered by a gold nucleus

A

electromagnetic repulsion between alpha particles and nuclei

50
Q

A small number of particles are scattered through 190 degrees. Explain what this suggests about the structure of atoms in the metal

A

Most of the mass is contained in its nucleus
Nucleus contains a positive charge
Charge is concentrated at nucleus

51
Q

Why is it necessary to remove air from the chamber in a rutherford scattering experiment

A

To prevent absorption/collision of the alpha particle by the air molecules

52
Q

Why should the gold foil be very thin

A

The alpha particles must not be absorbed by the foil

AQA A Level Physics (15 decks)

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