2.6 Radioactivity

Question 1

What do radioactive substances emit?

Answer 1

Radiation

Question 2

What did J.J Thomson come up with?

Answer 2

The plum pudding model for the discovery of the nucleus

Question 3

Describe the plum pudding model?

Answer 3

A sphere of positive charge with small negative charges throughout

Question 4

What experiment did Ernest Rutherford conduct with Geiger and Marsden?

Answer 4

They fired alpha particles at thin gold foil (only a fee atoms thick)

Question 5

What observations did Rutherford find in his experiment?

Answer 5

Most of the Alpha particles went straight through
Some of the Alpha particles were deflected through large angles
Very few of the Alpha particles were deflected straight back

Question 6

What did Rutherford conclude from his experiment?

Answer 6

The plum pudding model is wrong

The nucleus is very small compared to the rest of the atom containing most of the mass and all of the positive charge

Question 7

Why did some of the Alpha particles deflect?

Answer 7

They were too close to the nucleus and repelled because the particles and the nucleus are both positively charged

Question 8

What is the charge of Alpha?

Answer 8

Positive

+2

Question 9

What is the mass of Alpha?

Answer 9

4

Question 10

What is the ionisation of Alpha like?

Answer 10

Strong

Question 11

What is an Alpha particle made of?

Answer 11

2 protons
2 neutrons
Which is a helium nucleus

Question 12

How is the penetration of Alpha?

Answer 12

Bad

Stopped by paper and a few cm of air

Question 13

What is the charge of Beta?

Answer 13

-1

Question 14

What is the mass of Beta?

Answer 14

Negligible

Question 15

What is the ionisation of Beta like?

Answer 15

Average

Question 16

What is a Beta particle?

Answer 16

An electron

Question 17

How is the penetration of Beta?

Answer 17

Average

Stopped by Aluminium and a few metres of air

Question 18

What is the charge of Gamma?

Answer 18

0

Question 19

What is the mass of Gamma?

Answer 19

0

Question 20

What is the ionisation of Gamma like?

Answer 20

Weak

Question 21

What is a gamma wave?

Answer 21

A Transverse electromagnetic wave

Question 22

What is the penetration of Gamma like?

Answer 22

Very good

Stopped by lead and concrete

Question 23

What happens to gamma in a magnetic field?

Answer 23

It is undeflected

Question 24

What happens to Alpha in a magnetic field?

Answer 24

Slightly deflected

Opposite to Beta

Question 25

What happens to Beta in a magnetic field?

Answer 25

Larger deflection

Opposite to Alpha

Question 26

Why do alpha and beta particles go in opposite directions in a magnetic field?

Answer 26

They have opposite charges?

Question 27

Why is alpha deflected less than beta in a magnetic field?

Answer 27

Alpha has a larger mass

Question 28

What happens to the new product in Alpha decay?

Answer 28

Mass number goes down by 4

Proton number goes down by 2

Question 29

What happens to the new product in Beta decay?

Answer 29

Mass number stays the same

Proton number goes up 1

Question 30

How can a beta particle be emitted if there are no electrons in the nucleus?

Answer 30

A neutron is turned into a proton and an electron

Therefore the electron can be emitted as a beta particle

Question 31

How is the mass number the same in Beta decay?

Answer 31

The loss of a neutron but the gain of a proton balances out to the original number

Question 32

What are the origins of background radiation?

Answer 32

Cosmic radiation from space
Nuclear weapon testing 
Nuclear accidents (power stations)
Food (banana)
Sun

Question 33

What categories can origins of background radiation be put into?

Answer 33

Natural

Manmade

Question 34

What is half life?

Answer 34

The time it takes for the number of radioactive nuclei in a sample or count rate to decrease by 50%

Question 35

How do we measure radioactivity?

Answer 35

By measuring the count rate

Question 36

How does radioactive decay occur?

Answer 36

It is random

You can’t do anything to make a radioactive substance decay

Question 37

Does the time taken for half life change?

Answer 37

No
The half life is fixed
Each time it halves it takes the same amount of time

Question 38

When you are given a graph about half life what must you do?

Answer 38

Draw on the lines to show the decay rates halving

Question 39

What is an example of radioactivity being used with Alpha particles?

Answer 39

Smoke alarms

Question 40

How do alpha particles help in smoke alarms?

Answer 40

Alpha particles are sent into a gap in the circuit
They ionise with the air allowing current to conduct
In a fire smoke absorbs the ions preventing current
This sounds the alarm

Question 41

What is an example of radioactivity being used with Beta particles?

Answer 41

Paper thickness control

Question 42

How do Beta particles help in paper thickness control?

Answer 42

Beta particles are passed through the paper with a sensor on the other side
If a lot of particles pass through the paper is too thin (rollers expand)
If too few particles pass through the paper is too thick (rollers contract)

Question 43

What is an example of radioactivity being used with gamma particles?

Answer 43

Leak detection in pipes

Radiotherapy

Question 44

How do Gamma particles help in leak detection in pipes?

Answer 44

A radioactive isotope is injected into the pipe
On the ground a Geiger counter will detect areas of high radioactivity
This is where the leaks are

Question 45

How do Gamma particles help in radiotherapy?

Answer 45

A controlled beam of gamma rays is used to kill cancer cells

It needs to be directed perfectly to avoid healthy cells

Question 46

What is an example of radioactivity being used with gamma particles or beta particles?

Answer 46

Radioactive tracers

Question 47

How do Beta or Gamma particles help in radioactive tracers?

Answer 47

A source is injected or swallowed by a patient
The progress of the tracer is monitored outside the body
Use a substance with a very short half life so the patient isn’t exposed for long