Radioactivity And Nuclear Energy

Question 1

Explain background radiation. Give an example.

Answer 1

Radiation that is always present with no specific source. Uranium in granite rock decays to radon gas.

Question 2

When can you measure background radiation?

Answer 2

When all other sources of radiation emit 0 counts.

Question 3

Explain half-life.

Answer 3

Time taken for half of the nuclei in any given sample to decay.

Question 4

Formula for half life. Formula for decay constant. Unit of half life?

Answer 4

Half Life = ln2 / decay constant (lambda)
Decay constant (lambda) = ln2 / half life

Half life is measured in seconds

Question 5

What is the formula for the rate of decay? What is the unit for rate of decay?

Answer 5

dN/dt = -(decay constant)(N)

N = number of atoms
Unit is Becquerel (Bq)

Question 6

Name an instrument used to detect radioactivity.

Answer 6

Geiger Muller Tube

Question 7

Define the unit Becquerel. What is the unit?

Answer 7

1 Becquerel is defined as the activity of a quantity of radioactive material in one nucleus. Measured in disintegration per second. (Counts per second)

Question 8

Name two common sources of background radiation.

Answer 8

Nuclear pollution
Radon gas in rocks

Question 9

Describe how the Bohr model explains line emission spectrum.

Answer 9

Electron falling from one energy level to another produces light of a definite frequency.

Question 10

Formula for Chadwick’s discovery of the neutron.

Answer 10

9Be4 + 4He2 = 12C6 + 1n0

Question 11

Setup and Observations and conclusions of Rutherford experiment.

Answer 11

Setup: Alpha source produces particles which are used to bombard gold foil in a vacuum.
Observed: -Most particles went straight through.
-Some particles were slightly deflected.
-A few went almost straight back.
Conclusions:
-Mostly empty space with positive nucleus

Question 12

Define radioactivity

Answer 12

Spontaneous disintegration of a nucleus with emission of one or more types of radiation.

Question 13

Define isotopes.

Answer 13

Atoms of the same element which have the same number of protons but different number of neutrons.

Question 14

Why is radon gas considered dangerous? How can the build up of radon be reduced?

Answer 14

Radioactive. Ventilation.

Question 15

What is a line emission spectra?

Answer 15

Specific frequencies emitted by a material when electrons fall to lower energy levels.

Question 16

How do you convert to and from a.m.u?

Answer 16

Divide by unified atomic unit to put into a.m.u.
Multiply by unified atomic unit to put out of a.m.u.

Question 17

Explain excited state.

Answer 17

When energy is supplied electrons move to higher energy levels (excited state). But it is an unstable state and electrons fall back down emitting a (photon) light of definite frequency equal to the change in the energy levels.

Question 18

Define fission.

Answer 18

The breaking up of a large nucleus into small nuclei with the release of energy and neutrons.

Question 19

How many of the neutrons emitted in a fission reaction must, on average cause a further fission so that the reaction is self-sustaining and safe? Explain your answer.

Answer 19

1.
If greater than one uncontrolled.
If less than one chain-reaction will end.

Question 20

What is the function of the moderator in a thermal nuclear reactor?

Answer 20

Usually graphite or heavy water. Slows down neutrons to a speed suitable for further fission.

Question 21

List three quantities that are conserved in a nuclear reaction. Why would they not be conserved?

Answer 21

Momentum, charge, mass-energy
Neutrinos

Question 22

What is the principle of operation for a Geiger Muller Tube?

Answer 22

Ionisation

Question 23

Uses of fission.

Answer 23

Generates energy

Question 24

Describe a Geiger-Muller Tube.

Answer 24

A metal cylinder acts as a cathode and a thin wire along the centre acts as an anode.
A thin mica end-window allows radiation to enter the tube.
Voltage applied depends on density and pressure of the gas.
The gas in the tube is usually argon but bromine gas acts as a quenching agent.

Question 25

Explain how the number of particles entering the tube is measured.

Answer 25

Negative ions are rapidly accelerated towards the wire anode causing further ionisation. Avalanche effect causes measurable current on the external circuit.

Question 26

Explain purpose of quenching.

Answer 26

When the positive ions hit the cathode prevents electrons from being emitted from the cathode.

Question 27

Purpose of Scalar and Ratemeter in GM tube.

Answer 27

Scalar-Gives total number of particles that entered the tube.
Ratemeter-Gives a reading in counts per second.

Question 28

Explain chain reaction with relation to fission.

Answer 28

One fission reaction which causes another fission reaction and so on.

Question 29

Uses of radioisotopes.

Answer 29

Food irradiation
Medical Therapy
Radiocarbon dating

Question 30

Define Nuclear Fusion.

Answer 30

Combining two small nuclei to form a larger nucleus with a loss in mass and a release in energy.

Question 31

Problems with Fusion.

Answer 31

-Joining positive charges requires massive amounts of energy
-Joining together requires high speeds so massive temperatures
-Controlling such high temperatures has not yet been achieved.

Question 32

Advantages of Fusion.

Answer 32

Very little radioactive waste to dispose of.
Required fuel deuterium easily extracted from water.
Produces more energy than other sources

Question 33

What is enriched uranium?

Answer 33

Uranium with a higher percentage of uranium-235 and less natural uranium.

Question 34

What is the function of fuel rods in a thermal nuclear reaction?

Answer 34

Natural or enriched uranium fuel

Question 35

What is the function of control rods in a thermal nuclear reactor?

Answer 35

Made of boron or cadmium. Absorb emitted neutrons, stopping fission. Regulate energy output.

Question 36

What is the function of the coolant in a thermal nuclear reactor?

Answer 36

Temperature rises within the reactor and coolant carries the heat to the heat exchange unit. Usually is CO2 gas under high pressure.

Question 37

What is the function of the heat exchange unit in the thermal nuclear reactor?

Answer 37

Heat carried by coolant boils water. Steam turns turbine which produces electricity.

Question 38

What is the function of shielding in a thermal nuclear reactor?

Answer 38

Thick concrete safety shield gives protection from neutrons and gamma rays to the outside world.

Question 39

What is the environmental and health impact of a thermal nuclear reactor?

Answer 39

Uranium has to be mined exposing miners to carcinogenic radon gas.
Accident at a nuclear reactor releases radioactive chemicals into the atmosphere.
Nuclear fuel rods have to be carefully stored as they are very radioactive.

Question 40

Define ionisation.

Answer 40

Removing or adding electrons to an atom.

Question 41

Is nuclear fission a spontaneous or non-spontaneous process?

Answer 41

Non-spontaneous;
A neutron is required to initiate