Radioactivity

Question 1

The bigger (top) number is

Answer 1

mass number (neutrons and protons)

Question 2

The smaller (bottom) number is

Answer 2

atomic number (protons)

Question 3

An isotope is

Answer 3

it has the same number of protons/same atomic number, but has a different number of neutrons/different mass number. Two atoms with the same atomic number but different mass numbers are isotopes

Question 4

alpha (α) particles, beta (β−) particles, and gamma (γ) rays are

Answer 4

ionising radiations emitted from unstable nuclei in a random process

Question 5

ionisation is

Answer 5

when an atom loses or gains an electron, causing it to become an ion (an atom which is positively or negatively charged).

Question 6

Alpha - ionising power, range in air and penetrating ability

Answer 6

Strong ionising power
a couple of cm range
stopped by paper

Question 7

Beta - ionising power, range in air and penetrating ability

Answer 7

Moderate ionising power
about 1m range
stopped by 5mm of aluminium

Question 8

Gamma - ionising power, range in air and penetrating ability

Answer 8

Very weak ionising power
at least 1km range
stopped by 10cm of lead

Question 9

Nature of alpha radiation

Answer 9

Helium nucleus

2 protons , 2 neutrons

Question 10

Nature of beta radiation

Answer 10

Fast moving electron

Question 11

Nature of gamma radiation

Answer 11

Electromagnetic waves

Question 12

investigate the penetration powers of different types of radiation using either radioactive sources or simulations

Answer 12

Detect using a Geiger Müller Tube.

Try the three different materials in order, paper then aluminium then lead.

Count rate will significantly decrease if radiation is stopped.

Question 13

Alpha decay - effects on nucleus

Answer 13

· 2 protons and 2 neutrons are lost.

· Mass number decreases by 4

· Atomic number decreases by 2

Question 14

Beta decay - effects on nucleus

Answer 14

• 1 neutron is converted to an electron (lost from the atom) and proton

· Mass number is unchanged

· Atomic number increases by 1

Question 15

Gamma decay - effects on nucleus

Answer 15

· Energy is lost from an atom in the form of an electromagnetic wave

· Mass number is unchanged

· Atomic number is unchanged

Question 16

Sources of background (ionising) radiation

Answer 16

radon in air
Granit in rocks
Cosmic rays
Medical equipment
Food and drink

Question 17

The activity of a radioactive source

Answer 17

Decreases over a period of time and is measured in becquerels.

Question 18

What is the half life

Answer 18

The half-life is the time taken for the radioactivity of a specific isotope to fall to half its original value

Question 19

Contamination

Answer 19

Occurs when material that contains radioactive atoms is deposited on materials, skin, clothing, or any place where it is not desired.

Question 20

Irradiation

Answer 20

The process by which an object is exposed to radiation.

Question 21

Dangers of ionising radiations

Answer 21

• radiation can cause mutations in living organisms

- radiation can damage cells and tissue

Question 22

What is nuclear fission

Answer 22

The process where heavy atoms are split into smaller, lighter atoms. This releases energy

Question 23

What is nuclear fusion

Answer 23

The process where lighter atoms are forced to join together to make heavier atoms. This releases energy.

Question 24

What is radioactive decay

Answer 24

Within the core of the Earth, radioactive isotopes of elements such as uranium, thorium and potassium provide a large proportion of the heat within the Earth through radioactive decay.

Question 25

Fission of Uranium

Answer 25

A slow moving neutron is absorbed by a uranium 235 nucleus.
The resulting uranium 236 nucleus is unstable.
It splits to form two smaller daughter nuclei, three neutrons and gamma radiation.

Question 26

How a nucleus of Uranium can be split

Answer 26

collision with a neutron

this process releases energy as kinetic energy of the fission products

Question 27

how a chain reaction can be set up if the neutrons produced by one fission strike other U-235 nuclei

Answer 27

The three neutrons produced by the fission may hit other nuclei of uranium 235, causing the process to repeat.
For a chain reaction to occur, there is a minimum mass of uranium 235 required. This is known as the critical mass.

Question 28

Role of the moderator

Answer 28

The purpose of the moderator is to absorb some of the kinetic energy of the neutrons to slow them down.
This is because slow neutrons are more easily absorbed by uranium 235 nuclei.

Question 29

Role of control rods

Answer 29

The purpose of the control rods is to absorb neutrons and completely remove them from the fission process.
Helps adjust the rate of nuclear fission in the reactor.

Question 30

Role of shielding

Answer 30

Reactor vessel is made of steel and surrounded by a concrete layer about 5 meters thick.
This prevents any radiation escaping, even neutrons.

Question 31

What is the difference between nuclear fission and fusion

Answer 31

Fission – Larger nuclei are split into smaller nuclei.

Fusion – Two smaller nuclei collide and combine to form a larger nucleus.

Question 32

Describe nuclear fusion

Answer 32

the creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy

Question 33

Nuclear fusion is the energy source of

Answer 33

Nuclear fusion is the source of energy for our sun and all stars.
In the case of the sun, it is typically hydrogen undergoing fusion to create helium.

Question 34

Why does nuclear fusion not happen at low temperatures and pressures (due to electrostatic repulsion between protons)

Answer 34

For nuclear fusion to occur, very high temperatures are required to overcome the repulsive force between the positively charged nuclei of each isotope.
High pressures are also needed to increase the chance of fusion between the nuclei.