Radiation

Question 1

Half life

Answer 1

Time for activity to half

Question 2

What happens to a neutron that is incident on the moderator.

Answer 2

A neutron loses energy when it collides with the hydrogen particles causing it to slow down

Question 3

What happens to a neutron that is incident on a control rod

Answer 3

It is absorbed to control the reaction

Question 4

Describe the process of fission

Answer 4

Neutron absorbed and uranium-236 is formed. This causes the nucleus to split into small, daughter nuclei releasing several fast-moving neutrons.

Question 5

The most dangerous source of waste in a nuclear power plant.

Answer 5

Products from the fission of uranium-235 and spent fuel rods

Question 6

How is waste treated in a nuclear power plant

Answer 6

Waste is placed in cooling ponds. High level waste is vitrified and placed in concrete containers to be stored deep underground. This should all be done close to the plant.

Question 7

Problems faced dealing with radioactive waste and potential solutions

Answer 7

The waste will be highly radioactive (for thousands of years) so must be placed in a geographically stable area.
Transporting waste is a risk to public so extra strong casing should be used or keep close to plant.
Waste should be remotely handled to avoid human contact.

Question 8

Spontaneous reaction

Answer 8

Where no energy is supplied

Question 9

Binding Energy

Answer 9

The amount of energy needed to separate the nucleus into its constituent protons and neutrons

Question 10

Mass Defect

Answer 10

The difference between the mass of separated nucleons and the mass of the nucleus

Question 11

Drawing a binding energy against mass number graph

Answer 11

Curve with a steep rise

A maximum between 8 and 10 MeV at between 50 and 60 nucleons

Question 12

When can fusion occur?

Answer 12

When two smaller nuclei combine together to form a larger nucleus. The product nucleus (A < 50) has more binding energy per nucleus than the smaller nucleus. Fusion starts with two small nuclei on the left and moves to the right upwards towards the peak.

Question 13

When can fission occur?

Answer 13

When larger nuclei split into two smaller, approximately equal fragments when bombarded by neutrons with the releases of two or three further neutrons and energy. If fission occurs, the smaller nuclei (A > 50) has more binding energy per nucleon than the original nucleus. Fission starts with a large nucleus on the right and moves to the left upwards towards the peak, The fragments are more stable than the original nucleus.

Question 14

Critical Mass

Answer 14

The mass of material which will just allow a chain reaction to occur

Question 15

When can a chain reaction occur?

Answer 15

If the rate of loss of neutrons is lower than the rate of production of neutrons.

Question 16

How and why does the mass of a nucleus differ from the mass of its protons and neutrons when separated?

Answer 16

The mass of the nucleus is less because of the (binding) energy added to separate the nucleons.

Question 17

Why does fusion require such high temperatures?

Answer 17

Nuclei need to be close together for the Strong Nuclear Force to be involved. But the electrostatic forces of repulsion try to prevent this from taking place. If the temperature is high then the nuclei have a high enough kinetic energy to overcome the repulsion.

Question 18

Rutherfords experiment conditions

Answer 18

Alpha particles need to have the same speed
Evacuated container
Alpha source with long half life

Question 19

Observations of Rutherford’s experiment

Answer 19

1 in 2000 alpha particles deflected

1 in 10000 deflected with at an angle more than 90 degrees

Question 20

Conclusions of rutherfords experiment

Answer 20

Mass is concentrated towards the centre of the atom (nucleus)
The nucleus is positively charged

Question 21

Energy of radiation

Answer 21

Alpha and gamma are constant, beta varies

Question 22

When is gamma emitted

Answer 22

If a nucleus has excess energy after emitting an alpha or beta minus particle

Question 23

Why do alpha emitters occur beyond z = 60

Answer 23

Too large to be stable because the strong nuclear force between the nucleons is unable to overcome the electrostatic force of repulsion between protons.

Question 24

Why are beta minus emitters to the left of the stability belt?

Answer 24

They are neutron-rich. An electron is emitted from the nucleus along with an antineutrino. When a nucleus ejects a beta minus particle, one of the neutrons is changed into a proton.

Question 25

Why are beta plus emitters to the right of the stability belt?

Answer 25

They are proton-rich, a proton changes into a neutron.

Question 26

Thermal neutron

Answer 26

A slow moving neutron in thermal equilibrium with the moderator