P7. Radioactivity

Question 1

Give an approximation for the radius of an atom

Answer 1

1 x 10-¹⁰ metres

Question 2

What are the three subatomic constituents of an atom?

Answer 2

1. Proton
2. Neutron
3. Electron

Question 3

Where is the most of the mass of an atom concentrated?

Answer 3

In the nuleus

Question 4

Approximately what proportion of the total radius of an atom is the radius of the nucleus?

Answer 4

1/10000

Question 5

Describe the arrangement of protons, neutrons and electrons in an atom

Answer 5

The protons and neutrons are found in the atom’s nucleus
The electrons are found in discrete energy levels around the nucleus

Question 6

What type of charge does the nucleus of an atom have? Why?

Answer 6

Positive charge
The nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge

Question 7

Give two ways that an atom’s electron arrangement can be changed

Answer 7

1. Absorbing electromagnetic radiation
2. Emitting electromagnetic radiation

Question 8

Explain how an atom’s electron arrangement changes when it absorb EM radiation

Answer 8

Electrons move further away from the nucleus
They move to a higher energy level

Question 9

Explain how an atom’s electron arrangement changes when it emits EM radiation.

Answer 9

Electrons move closer to the nucleus
They move to a lower energy level

Question 10

How does the ratio of electrons to protons in an atom result in the atom having of no overall charge?

Answer 10

The number of protons is equal to the number of electrons
Protons and electrons have equal and opposite charges, so charges cancel

Question 11

What do all forms of the same element have in common?

Answer 11

They all have the same number of protons

Question 12

What is the name given to the number of protons in an atom?

Answer 12

Atomic Number

Question 13

What is an atom’s mass number?

Answer 13

The total number of protons and neutrons in the atom

Question 14

What is an isotope of an atom?

Answer 14

An atom of an element that has a different number of neutrons, but the same number of protons

Question 15

How do atoms turn into positive ions?

Answer 15

They lose one or more of their outer electrons
Electrons are negatively charged, so the resultant charge of the atom is positive

Question 16

What may lead to a significant model being changed or replaced?

Answer 16

The discovery of a new experimental evidence which doesn’t agree with the existing theory

Question 17

How did the plum-pudding model describe the atom?

Answer 17

A ball of positive charge, with negatively charged electrons distributed evenly through

Question 18

Prior to the discovery of the electron, what was believed about the atom?

Answer 18

The atom was believed to be indivisible

Question 19

Which experiment led to the plum-pudding model being discarded?

Answer 19

Rutherford’s alpha-scattering experiment

Question 20

What is the name given to the currently accepted model of the atom?

Answer 20

The Bohr Nuclear Model

Question 21

State the conclusions of the Alpha-Scattering experiment.

Answer 21

Most of the mass of the atom is concentrated at the centre in the nucleus
The nucleus is positively charged

Question 22

What reinforces a scientific theory?

Answer 22

When experimental results agree with the hypothesised theoretical calculations and theories

Question 23

What did James Chadwick’s experiments on the atom prove?

Answer 23

The existence of neutrons

Question 24

Why do unstable nuclei give out radiation?

Answer 24

Unstable nuclei undergo decay to become more stable
As they release radiation their stability increases

Question 25

What is the name of the process in which an unstable nucleus gives out radiation to become more stable?

Answer 25

Radioactive decay

Question 26

Define the activity of an unstable nucleus

Answer 26

Activity is the rate of decay of a source of unstable nuclei

Question 27

What is the unit of radioactive activity?

Answer 27

Becquerel (Bq)

Question 28

What is a count-rate?

Answer 28

The number of radioactive decays per second for a radioactive source

Question 29

Give an example of a detector that may be used to measure count-rate

Answer 29

Geiger-Muller Tube

Question 30

State four types of nuclear radiation

Answer 30

1. Alpha particles 2. Beta particles 3. Gamma rays 4. Neutrons

Question 31

What are the constituents of an alpha particle?

Answer 31

Two protons and two neutrons It is the same as a helium nucleus

Question 32

What is the range of an alpha particle through air?

Answer 32

A few centimetres (normally in the range of 2-10cm)

Question 33

What will stop beta radiation from passing through a point?

Answer 33

A thin sheet of aluminium Several metres of air

Question 34

What will stop gamma radiation from passing through a point?

Answer 34

Several centimetres of lead A few metres of concrete

Question 35

Which type of radiation is most ionising?

Answer 35

Alpha radiation

Question 36

Which type of radiation is least ionising?

Answer 36

Gamma radiation

Question 37

State any changes to mass or charge that occur due to the emission of a gamma ray

Answer 37

Both mass and charge remain unchanged

Question 38

Describe the nature of radioactive decay

Answer 38

Random Which nuclei decays and when is determined only by chance It is impossible to predict which nuclei will decay and when

Question 39

Define the half-life of a radioactive isotope

Answer 39

The time it takes for the number of unstable nuclei in a substance to halve The time it takes for the count rate from a sample to fall to half its initial level

Question 40

What is radioactive contamination?

Answer 40

The presence of unwanted radioactive nuclei on other materials

Question 41

What is irradiation?

Answer 41

The process of exposing a material to nuclear radiation The material does not become radioactive

Question 42

Why is important for the results of studies on the effects of radiation to be published and shared with other scientists?

Answer 42

To allow the findings to be independently checked This is known as peer review

Question 43

How should background radiation be dealt with in calculations?

Answer 43

The background count should be subtracted from any readings before calculations are attempted

Question 44

How many millisieverts equal 1 sievert?

Answer 44

1000 millisieverts = 1 sievert

Question 45

Why might the radiation dosage that different people experience differ?

Answer 45

Some occupations involve working with radiation Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing

Question 46

What factor determines how dangerous a particular radioactive isotope is?

Answer 46

The half-life of the isotope

Question 47

Why are isotopes with long half-lives particularly harmful?

Answer 47

They remain radioactive for much longer periods of time They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long

Question 48

What is nuclear fission?

Answer 48

The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons)

Question 49

Give an example of a fissionable isotope?

Answer 49

Uranium - 235

Question 50

What usually needs to happen to induce fission?

Answer 50

The unstable nuclei must absorb a neutron Spontaneous fission (where no neutron absorption occurs) is rare

Question 51

Alongside two smaller nuclei, what else is emitted in a fission reaction?

Answer 51

Two or three neutrons Gamma rays Energy

Question 52

What form of energy do all fission products have?

Answer 52

Kinetic energy

Question 53

What takes place during a chain reaction in a nuclear reactor?

Answer 53

An unstable nucleus absorbs a neutron The nucleus undergoes fission and releases 2 or 3 further neutrons These induce more fission, which results in a chain reaction

Question 54

What is the consequence of an uncontrolled chain reaction?

Answer 54

The rate of fission event becomes too high and results in the production of too much energy This can lead to a nuclear explosion

Question 55

What are the three main components of the core a nuclear reactor?

Answer 55

1. Fuel rods 2. Control rods 3. Moderator

Question 56

What is the role of the moderator in a nuclear reactor?

Answer 56

To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission

Question 57

How is the chain reaction in a fission reactor kept under control?

Answer 57

Control rods are positioned in between the fuel rods The rate of fission is controlled by moving these rods up and down The lower the rods are inserted, the slower the rate of fission

Question 58

What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?

Answer 58

Fissile Nuclei

Question 59

What is nuclear fusion?

Answer 59

The joining of two light nuclei to produce a heavier nuclei and release energy

Question 60

Which releases more energy, nuclear fission or nuclear fusion

Answer 60

Nuclear fusion

Question 61

Explain the difficulty of generating energy through nuclear fusion

Answer 61

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them

Question 62

Explain why nuclear fusion is currently not a viable way to produce energy on Earth

Answer 62

With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss