Nuclear Physics - Alpha/Beta/Gamma Radiation

Question 1

What did Rutherford do and why

Answer 1

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

Question 2

Apparatus for Rutherford scattering experiment

Answer 2

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

Question 3

Purpose of the lead container in Rutherford’s experiment

Answer 3

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

Question 4

Purpose of the thin sheet of gold foil

Answer 4

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

Question 5

Purpose of the evacuated chamber in Rutherford’s experiment

Answer 5

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

Question 6

Observations from Rutherford’s experiment

Answer 6

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

Question 7

What does the majority of alpha particles passing through undeflected suggest

Answer 7

The atom is mostly empty space

Question 8

What does some alpha particles deflecting through small angles suggest

Answer 8

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

Question 9

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

Answer 9

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

Question 10

How do isotopes become more stable

Answer 10

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

Question 11

What are the 3 main types of radioactive particles

Answer 11

Alphas
Beta
Gamma

Question 12

Characteristics of alpha particles

Answer 12

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

Question 13

When are beta particles emitted

Answer 13

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

Question 14

Characteristics of beta particles

Answer 14

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

Question 15

When is gamma radiation emitted

Answer 15

When nuclei need to lose some energy

Question 16

Characteristics of gamma radiation

Answer 16

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

Question 17

What happens when any type of radiation collides with an atom

Answer 17

It can can knock out electrons and ionise the atom

Question 18

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

Answer 18

It is deflected

Question 19

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

Answer 19

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

Question 20

What does the amount of deflection of a particle depend on

Answer 20

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

Question 21

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

Answer 21

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

Question 22

Inverse square law

Answer 22

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

Question 23

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

Answer 23

Intensity at x1 / Intensity at x2 = (initial distance / subsequent distance)^2

Question 24

What does the inverse square law apply for and why

Answer 24

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

Question 25

Background radiation

Answer 25

The ionising radiation present in the environment

Question 26

What are the sources of background radiation

Answer 26

Radon gas
Rocks and building materials
Food
Cosmic rays

Question 27

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

Answer 27

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.

Question 28

What are all three types of radiation used for

Answer 28

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

Question 29

Which materials do each radiation monitor the thickness of

Answer 29

Beta - aluminium foil
Alpha - paper
Gamma - steel sheets

Question 30

How is beta radiation used in the production of aluminium foil

Answer 30

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.

Question 31

Describe the experimental verification of the inverse square law

Answer 31

Measure the count rate of a gamma source at different distance 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

Question 32

How do you account for background radiation

Answer 32

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

Question 33

How to increase accuracy of count rates

Answer 33

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