Nuclear Radiation

Question 1

Define Background Radiation

Answer 1

Low levels of radiation from environmental sources, always present around us.

Question 2

What are the types of nuclear radiation?

Answer 2

Alpha α, Beta β, Gamma γ

Question 3

What is the composition of an Alpha particle?

Answer 3

Two protons and two neutrons (same as helium). It has +2e charge so is highly ionising so it loses kinetic energy and is easily absorbed. Blocked by paper.

Question 4

What is the composition of an Beta particle?

Answer 4

Electron. Blocked by sheet of aluminium.

Question 5

What is the composition of an Gamma particle?

Answer 5

High energy, high frequency, em radiation. Photons with no charge and no mass, so rarely interact with particles in path - least ionising. Energy can be reduced by several cm of lead.

Question 6

Define Decay Contant, λ

Answer 6

The probability per second, a given nucleus will decay.
A = -λN
A - Activity
N - Number of nuclei in sample

Question 7

What does the minus indicate?

A = -λN

Answer 7

Number of nuclei in sample decreases with time.

Question 8

Define Activity

Answer 8

A = -λN = dN/dt

The number of radioactive decays in unit time

Question 9

Define Half Life

Answer 9

The time taken for half of the atoms of a nuclide within a sample to decay.
λ = ln 2 / t½

Question 10

Define Mass defect

Answer 10

The difference between measured mass of a nucleus and sum total of masses of its constituent nucleons.

Question 11

Define Nuclear Binding Energy

Answer 11

The energy used to hold the nucleus together converted from the mass deficit. E=mc^2

Question 12

Which isotope has the highest binding energy per nucleon?

Answer 12

Iron-56 at 8.8Mev per nucleon.

Question 13

What does binding energy per number - mass number graph show?

Answer 13

Small nuclides combine to make larger nuclei up to Fe-56 with a greater binding energy per nucleon - nuclear fusion. Larger nuclei can break up into smaller pieces which have a greater binding energy per nucleon than original nucleus - fission.

Question 14

Explain process of Nuclear Fusion releasing energy

Answer 14

Small nuclei fuse together to produce a larger nucleus. Mass of fused nucleus is less than total mass of initial nuclei. Binding energy increases so energy is released.

Question 15

Explain process of Nuclear Fission.

Answer 15

.

Question 16

Define Radioactive Isotope

Answer 16

Has an unstable nucleus which decays and emits radiation

Question 17

Radioactive decay is a random process. Explain what this means.

Answer 17

We can’t know when an individual nucleus will decay

We can’t know which nucleus will decay next. Each nucleus has a fixed probability of decay.

Question 18

Explain the conditions necessary for fusion

Answer 18

High temperature to overcome electrostatic repulsion. High pressure to maintain high collision rate.

Question 19

Massive stars can only produce elements up to iron (Fe) in their cores by fusion. Explain why.

Answer 19

Iron-56 is the peak of the graph. If nuclei were to be formed nucleon number would be greater than 56, so binding energy per nucleon decrease. This would require net input of energy so does not occur.

Question 20

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

Answer 20

Spontaneous: decay cannot be influenced by any external factors

Question 21

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

Answer 21

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

Question 22

What is meant by ionising radiation?

Answer 22

Ionising radiation removes electrons from atoms/ molecules

Question 23

State the most stable element and give a reason why.

Answer 23

Iron-56 has the maximum value of binding energy per nucleon

Question 24

State what is meant by isotopes.

Answer 24

same number of

protons but different numbers of neutrons

Question 25

State the conditions for fusion and hence explain why it has proved difficult to maintain a sustainable reaction in a practical fusion reactor.

Answer 25

Very high temperatures, o overcome electrostatic repulsion. Nuclei come close enough to fuse for strong (nuclear) force to act. Very high densities needed this gives a sufficient collision rate. Very high temperatures lead to confinement problems

Question 26

State two advantages fusion power might have over fission power.

Answer 26

Hydrogen fuel for fusion is unlimited whereas fission relies upon uranium a relatively limited resource. Fusion results in few radioactive products, but radioactive products produced in fission present significant disposal problems. For a given mass of fuel, the energy released by fusion is greater than the energy released by fission.

Question 27

State what red shift means and discuss the conclusions that can be drawn from the observation that radiation from all distant galaxies is red shifted.

Answer 27

Radiation is received with a stretched wavelength | compared to that emitted. This indicates that distant galaxies are receding. Hence the universe is expanding.

Question 28

A student measures the potential difference across the combination with a high resistance voltmeter. Explain why the resistance of the combination is hardly changed by the addition of the voltmeter.

Answer 28

Voltmeter is connected in parallel. Voltmeter draws | little/no current. 1/RV is very small.

Question 29

Nuclear power stations currently use the process of fission to release energy. Outline the process of fission.

Answer 29

A heavy nucleus absorbs a neutron. The nucleus becomes unstable and splits into two fragments. Neutrons are also emitted which cause a change reaction.

Question 30

State what is meant by nuclear fission and explain why energy is released during the fission of a nucleus such as uranium.

Answer 30

Fission is the splitting of a large nucleus into smaller nucleons. The mass of fragments is less than the mass of the original nucleus. E=mc^2: Binding energy per nucleon is greater in fragments than in original nucleus.

Question 31

Discuss the potential advantages of nuclear fusion, compared with nuclear fission, as a means of supplying our power demands.

Answer 31

- Hydrogen fuel is virtually unlimited. - Fission relies upon uranium which is a limited resource. - Fusion results in no radioactive products. -Radioactive products produced in fission present disposal problems. - For a given mass of fuel, energy released by fusion is greater than energy released by fission.