Nuclear physics

Question 1

Nuclear decay is said to be random and spontaneous. What is meant by random?

Answer 1

Random: you cannot identify which nucleus will decay next/ when an individual nucleus will decay

Question 2

Nuclear decay is said to be random and spontaneous. What is meant by spontaneous?

Answer 2

Spontaneous: decay cannot be influenced by any external factors

Question 3

What is meant by ionising radiation?

Answer 3

Ionising radiation removes electrons from atoms/ molecules

Question 4

What is an alpha particle, its mass and its charge?

Answer 4

Helium nucleus
Mass 4u
Charge +2

Question 5

What is the ionising ability, speed and penetration power of alpha particles?

Answer 5

Strong ionising ability
Slow
Not very penetrating- absorbed/ stopped by paper or a few cms of air

Question 6

When a nucleus is unstable, it will break down to become more stable. Explain why an alpha particle is emitted and what happens to the proton number and nucleon number?

Answer 6

Too many nucleons in total / nucleus too heavy

The proton number decreases by 2 and the nucleon number decreases by 4

Question 7

Why aren’t alpha particles very penetrating?

Answer 7

Alpha particles are strongly positive so can easily pull electrons off atoms/ are strongly ionising
When an alpha particle ionises an atom it transfers some of its energy to the atom
Alpha particles quickly ionise lots of atoms and lose all their energy quickly so can’t travel very far/ have a low penetrating power

Question 8

What is a beta-minus particle, its mass and its charge?

Answer 8

Electron, negligible mass, -1

Question 9

What is a beta-plus particle, its mass and its charge?

Answer 9

Positron, negligible mass, +1

Question 10

State ionising ability, speed and penetration power of beta-minus particles.

Answer 10

Weak/ moderate ionising ability
Fast
Moderately penetrating- absorbed/ stopped a few mm of aluminium

Question 11

When a nucleus is unstable, it will break down to become more stable. Explain why a beta- minus particles is emitted, what happens when it is emitted and what happens to the proton number and nucleon number.

Answer 11

Emitted due to nucleus being neutron-rich/ has too many neutrons

One of the neutrons in the nucleus decays into a proton and ejects a beta-minus particle/ electron and an electron antineutrino

Proton number increases by one and nucleon number stays the same

Question 12

Explain why a beta-plus particle is emitted, what happens when it is emitted and what happens to the proton number and the nucleon number.

Answer 12

Emitted due to the nucleus having two few neutrons

One of the protons in the nucleus changes into a neutron and releases a beta-plus particle/ positron and an electron neutrino

Proton number decreases by one and nucleon number stays the same

Question 13

Explain why beta-minus particles are more penetrating than alpha particles.

Answer 13

Beta-minus particles are moderately ionising because they travel at high speed

They are less ionising than alpha particles because they have a lower mass

This means they lose less energy so can travel further and are more penetrating

Question 14

State why beta-plus particles have virtually zero range.

Answer 14

After being produced they are almost immediately annihilated by an electron

Question 15

State what gamma radiation is, its mass and its charge.

Answer 15

Short-wavelength, high frequency electromagnetic wave/ photon.
0
0

Question 16

State ionising ability, speed and penetration power of gamma radiation.

Answer 16

Very weak ionising ability
Speed of light
Very penetrating- absorbed/ stopped by many cm of lead/ several m of concrete

Question 17

When a nucleus is unstable, it will break down to become more stable. Explain why a gamma ray is emitted and how gamma emission affects the nuclear equation.

Answer 17

Nucleus is excited/ has excess energy

This energy is lost by emitting a gamma ray

Nuclear equation is unchanged because there is no change to the nuclear constituents- the nucleus just loses excess energy

Question 18

Explain why gamma radiation is very penetrating.

Answer 18

Gamma radiation isn’t/ is very weakly ionising

Because it has no charge or mass/ it is photons of light

This means it loses barely any energy when travelling so can travel very far and is very penetrating

Question 19

State why and how readings from a Geiger counter must be corrected when you take readings from a radioactive source.

Answer 19

Because you have to subtract the background count rate from each reading to get the actual radiation count for the source.

Measure the background radiation in absence of the source

Question 20

State the 3 things conserved in nuclear equations and the 2 things conserved in nuclear reactions.

Answer 20

Nuclear equations: charge, nucleon number and electron lepton number

Nuclear reactions: energy and momentum

Question 21

State the other type of radiation and why it would not be detected by a film badge that relies on ionisation.

Answer 21

Neutron emission

Uncharged particles are not ionising so would not be detected

Question 22

State what is meant by the activity of a radioactive source.

Answer 22

Rate of decay of unstable nuclei/ the number of nuclei that decay per second/ per unit of time

Question 23

Explain why it is necessary to repeat the radioactive count when taking readings.

Answer 23

So you can take an average as nuclear decay is random so fixed count for a period will vary

Question 24

State why external exposure to gamma radiation is dangerous.

Answer 24

Gamma rays will pass through skin because they are very penetrating

Gamma rays can damage healthy cells/ DNA

Question 25

Suggest how a beta-minus source should be stored and handled so it poses minimal health risk.

Answer 25

Store in lead lined box Handle with long tongs/ don't handle directly/ point away from people

Question 26

State what is meant by the decay constant.

Answer 26

The probability that a given nucleus will decay each second.

Question 27

State what is meant by the half-life of an isotope.

Answer 27

The average time it takes for the number of undecayed/ unstable nuclei to halve

Question 28

What is safest: a long/ short half life and a big/small decay constant?

Answer 28

Long half-life Small decay constant- less activity

Question 29

Explain what is meant by a radioactive atom.

Answer 29

A radioactive atom has an unstable nucleus, which emits alpha, beta or gamma radiation.

Question 30

Suggest why it is safer to use a radioactive isotope with a short half life for a gamma trace in medicine.

Answer 30

Isotope decays quickly/ doesn't produce radiation for long. Patient doesn't remain radioactive for long so is not a risk to others for long like children and pregnant women.

Question 31

State what is meant by nuclear binding energy.

Answer 31

Energy equivalent to the mass deficit When nucleons bind together to form an atomic nucleus/ when an atomic nucleus separates into all its constituent nucleons

Question 32

Describe nuclear fusion and state what happens to total mass, energy released and binding energy per nucleon.

Answer 32

Nuclear fusion is when nucleons join together Total mass decreases Energy is released Binding energy per nucleon increases

Question 33

What does a high binding energy tell us about the amount of energy needed to remove nucleons from the nucleus and the nucleus' stability?

Answer 33

The higher the binding energy: The more energy is needed to remove nucleons from the nucleus. The more stable the nucleus

Question 34

State the most stable element according to the graph and give a reason why.

Answer 34

Iron because it has the highest binding energy

Question 35

Describe nuclear fission in terms of splitting.

Answer 35

Nuclear fission is splitting a heavy nucleus Into 2 smaller nuclei( and sometimes several neutrons)

Question 36

During nuclear fission, what happens to total mass, energy released, binding energy per nucleon and why in terms of nucleon numbers.

Answer 36

Total mass decreases Energy is released Binding energy increases Because the nucleon numbers of the 2 new nuclei are smaller than the original nucleus

Question 37

Fission can be induced or is spontaneous. Fission happens when a heavy nucleus is what?

Answer 37

Unstable

Question 38

State the 2 conditions for nuclear fusion. Explain why the kinetic energy of nuclei has to be so high for them to fuse in terms of forces and charge.

Answer 38

High density of matter Very high temperature High kinetic energy from high temperature needed because all nuclei are positively charged So there will be an exponential force of repulsion between them According to Coulomb's law Nuclei can only fuse if they overcome this electrostatic force and get close enough for the strong force/ interaction to act and hold them together High density of matter

Question 39

At very high temperatures, atoms don't exist. Electrons are stripped away leaving positively charged nuclei and free electrons. State the name of this resulting mixture.

Answer 39

Plasma

Question 40

State 2 advantages of nuclear power

Answer 40

No carbon dioxide released For a particular amount of energy produced, a small amount of fuel is needed compared to fossil fuels Lots of uranium left unlike fossil fuels

Question 41

State 2 disadvantages of nuclear power

Answer 41

Most mined uranium is not U-235 so has to be processed Radioactive waste produced Uranium is not sustainable so will run out one day

Question 42

State a problem with trying to do nuclear fusion on Earth referring to one of the conditions for fusion.

Answer 42

Confinement problems Due to plasma created from very high temperatures

Question 43

3 advantages of nuclear fusion over nuclear fission for generating power.

Answer 43

More energy released per unit mass for fusion Fusion has fewer radioactive products- fission products cause disposal issues Fission relies on a relatively limited resource whereas fusion fuel ( hydrogen) is virtually limitless.

Question 44

Describe how nuclear fission produces power.

Answer 44

Low energy neutron absorbed by heavy U-235 nucleus Nucleus becomes unstable And splits into two daughter nuclei and 2 or 3 neutrons So can go on to be absorbed by other nuclei causing more fission and creating a chain reaction Control rods absorb some of the neutrons thus slowing down chain reaction and limiting fission

Question 45

State the shape of fuel for greatest chance of self-sustaining reaction (bomb) and give a reason why in terms of surface area per unit mass

Answer 45

Sphere Smallest surface area per unit mass possible so neutrons less likely to escape so more are available to create lots of fissions

Question 46

State the shape of fuel for smallest chance of self-sustaining reaction (bomb) and give a reason why in terms of surface area per unit mass.

Answer 46

Pellets/ thin sheet/ fine wire Largest surface area per unit mass possible so neutrons likely to escape instead of creating more fissions