P7: Radioactivity

Question 1

What are the 3 subatomic constituents of an atom?

Answer 1

Proton
Neutron
Electron

Question 2

Where is most the mass of an atom concentrated?

Answer 2

In the nucleus

Question 3

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

Answer 3

1/10,000

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

Give 2 ways that an atom’s electron arrangement can be changed?

Answer 6

Absorbing electromagnetic radiation

Emitting electromagnetic radiation

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

They all have the same number of protons

Question 11

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

Answer 11

Atomic number

Question 12

What is an atom’s mass number?

Answer 12

The total number of protons and neutrons in the atom

Question 13

What is an isotope of an atom?

Answer 13

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

Question 14

How do atoms turn into positive ions?

Answer 14

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

Question 15

What may lead to a scientific model being charged or replaced?

Answer 15

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

Question 16

How did the plum-pudding model describe the atom?

Answer 16

A ball of positive charge, with negatively charged electros distributed evenly throughout it

Question 17

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

Answer 17

The atom was believed to be invisible

Question 18

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

Answer 18

Rutherford’s alpha-scattering experiment

Question 19

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

Answer 19

The Bohr nuclear model

Question 20

State the conclusions of the Alpha-Scattering experiment?

Answer 20

Most of the mass of the atom is concentrated at the centre in the nucleus

The nucleus is positively charged

Question 21

What reinforces a scientific theory?

Answer 21

When experimental results agree with the hypothesised theoretical calculations and theories

Question 22

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

Answer 22

The existence of neutrons

Question 23

Why do unstable nuclei give out radiation?

Answer 23

Unstabel nuclei undergo decay to become more stable
As they released radiation their stability increases

Question 24

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

Answer 24

Radioactive decay

Question 25

Define the activity of an unstable uncleus?

Answer 25

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

Question 26

What is the unit of radioactive activity?

Answer 26

Becquerel (Bq)

Question 27

What is count-rate?

Answer 27

The number of radioactive decays per second for a radioactive source

Question 28

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

Answer 28

Geiger-Muller tube

Question 29

State 4 types of nuclear radiation?

Answer 29

Alpha particles Beta particles Gamma rays Neutrons

Question 30

What are the constituents of an alpha particle?

Answer 30

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

Question 31

What is the range of an alpha particle through air?

Answer 31

A few centimetres (normally 2-10cm)

Question 32

What are the constituents of a beta particle?

Answer 32

Fast moving electron

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

What type of radiation is most ionising?

Answer 35

Alpha radiation

Question 36

What 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

Describe 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 unwnated 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

Give 4 sources of background radiation?

Answer 42

Rocks Cosmic rays from space Nuclear weapon testing Nuclear accidents

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

What is the unit used to measure radiation dosage?

Answer 44

Sieverts (Sv)

Question 45

How many millisieverts equal 1 sievert?

Answer 45

1000 millisieverts = 1 sievert

Question 46

Why might the radiation that different people experience differ?

Answer 46

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

Question 47

What factor determines how dangerous a particular radioactive isotope is?

Answer 47

The half-life of the isotope

Question 48

Why are isotopes with long half-lives particularly harmful?

Answer 48

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 49

State 2 uses of nuclear radiation in the field of medicine?

Answer 49

Examining of internal organs Controlling and destroying unwanted tissue

Question 50

How is radiation used in sterillisation?

Answer 50

Gamma emitters are used to kill bacteria/parasites on equipment

Question 51

Explain the process of radiotherapy?

Answer 51

Gamma emitters direct gamma rays at the cancerous cells The cancerous cells absorb the radiation and are killed

Question 52

What is nuclear fission?

Answer 52

The splitting of large, unstable nuclei from smaller more stable nuclei

Question 53

Give an example of a fissionable isotope?

Answer 53

Uranium - 235

Question 54

What usually needs to happen to induce fission?

Answer 54

The unstable nuclei must absorb a neutron Sponataneous fission

Question 55

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

Answer 55

Two or three neutrons Gamma rays Energy

Question 56

What form of energy do all fission products have?

Answer 56

Kinetic energy

Question 57

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

Answer 57

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 58

What is the the consequence of an uncontrolled chain reaction?

Answer 58

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

Question 59

What are the three main compounds of the core nuclaer reactor?

Answer 59

Fuel rods Control rods Moderator

Question 60

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

Answer 60

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

Question 61

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

Answer 61

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

Question 62

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

Answer 62

Fissile nuclei

Question 63

What is nuclear fusion?

Answer 63

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

Question 64

Name 2 isotopes of hydrogen which are commonly used in nuclear fusion?

Answer 64

Deuterium and Tritium

Question 65

Which releases more energy, fission or fusion?

Answer 65

Nuclear fusion