P6.2 - Uses And Hazards

Question 1

What is contamination?

Answer 1

Having a radioactive material inside the body or on the skin.

Question 2

What is irradiation?

Answer 2

Being exposed to radiation from an external source, which has the potential to travel into the body.

Question 3

How can doctors use radioactive material to help diagnose disease?

Answer 3

Doctors inject you with a radiactive isotope that is absorbed by the organs of the body.

The isotope is detected by a gamma camera which makes images of the organs, which helps doctors to diagnose disease.

Question 4

Why do radiographers choose the isotope being inserted into the body to help diagnose disease very carefully?

Answer 4

If the half-life of the isotope is too short, then the tracer will decay before they can use the gamma camera.

If the half-life is too long, then the tracer will continue to emit radiation for a long time and increase the risk of cancer.

Question 5

How can materials that emit gamma radiation be used to treat cancer?

Answer 5

Doctors use a gamma knife (a moveable source of gamma radiation), to focus the gamma rays onto a cancer tumour.

The radiation can damage the cancer cells to restrict their growth, or kill them.

The source is moved around to reduce the radiation dose that the healthy tissue receives, while still aiming it at the tumour which receives a large dose.

Question 6

Why do unstable nuclei have too much energy?

Answer 6

Unstable nuclei have too much energy, due to an imbalance between the protons to neutrons.

Question 7

What happens to small unstable nuclei?

Answer 7

If small nuclei are unstable, nuclei will undergo radioactive decay.

Question 8

What happens to large unstable nuclei?

Answer 8

If large nuclei are unstable, nuclei will undergo nuclear fission.

Question 9

What is nuclear fission?

Answer 9

Nuclear fission is the splitting of a large parent nucleus into two smaller nuclei, with the release of energy and neutrons”.

Question 10

How is fission induced in a nuclear reactor?

Answer 10

In a nuclear reactor, fission is induced when a Uranium-235 nucleus is hit with a neutron.

Question 11

What are the properties of the two daughter nuclei produced in fission events?

Answer 11

• Different elements whose proton number adds up to the proton number of Uranium (92).
• The mass numbers combined is less than 236, with the difference being accounted for by the release of neutrons.
• The two smaller nuclei (daughter nuclei) are themselves unstable, and become stable by undergoing radioactive decay.

Question 12

What are the properties of “Nuclear Waste”?

Answer 12

• Very dangerous.
• Very long half-life.
• Man made source of background radiation.
• Must be buried and guarded.

Question 13

Define a chain reaction?

Answer 13

A process in which neutrons released during a fission event, go on to produce further fission events.

Question 14

Described a controlled chain reaction and where it takes place?

Answer 14

• Takes place in a nuclear power station.
• Only one neutron from each fission event is able to produce another fission event.
• Control rods in power plant absorb surplus neutrons and energy is generated at a steady rate.

Question 15

Describe an uncontrolled chain reaction and where it takes place?

Answer 15

• Takes place in a nuclear bomb.
• Every neutron from each fission event goes on to produce further fission events.
• Energy is released at an exponential rate.

Question 16

What are fissionable isotopes?

Answer 16

Fissionable isotopes of an element are those that can be made unstable, but they themselves are stable.

Question 17

Why is Uranium-238 non-fissionable?

Answer 17

• Not all heavy nuclei can be made unstable by adding neutrons.
• Uranium-239 is therefore stable.

Question 18

What must happen to uranium before it can be used in a nuclear power plant?

Answer 18

• Uranium must be enriched before it can be used in a nuclear power plant.
• Natural uranium from the ground is 99% non-fissionable U-238 and 1% fissionable U-235.
• Enriched uranium is 97% non fissionable U-238 and 3% fissionable U-235.

Question 19

What is nuclear fusion?

Answer 19

The joining of two small nuclei to form a larger nucleus, releasing energy.

Question 20

How does nuclear fusion occur in stars?

Answer 20

Occurs in stars when two very light nuclei (isotopes of Hydrogen) are forced together at high speeds, to form a heavier helium nucleus.

Question 21

What is the equation for nuclear fusion?

Answer 21

2 Mass Number, 1 Atomic Number Of Hydrogen + 3 Mass Number, 1 Atomic Number Of Hydrogen -> 4 Mass Number, 2 Atomic Number Of Helium + 1 neutron

Question 22

What are the advantages of nuclear fusion compared to nuclear fission?

Answer 22

• No radioactive waste produced, unlike fission which produces very long half-life radioactive waste.
• The fuel required for fusion is readily available water, unlike in fission where Uranium in non-renewable.
• Nuclear fission a lot more (around 4x) as much energy than fission.

Question 23

What are the disadvantages of nuclear fusion?

Answer 23

• Building fusion reactors is very difficult/ not viable.
• Currently, more much heat energy required to make nuclei to overcome their repulsive forces and fuse than is released from the fusion reaction.
• Therefore fusion is not a viable process of energy production.
• There needs a more cleverer method of fusing nuclei.

Question 24

Why can nuclear fusion occur in stars?

Answer 24

Stars are able to carry out fusion easily as they have very high temperatures and very high pressures.

Question 25

Where does the energy come from in nuclear fusion?

Answer 25

• There is a difference in mass (not number!) between the nucleons in the hydrogen nuclei and the helium nucleus they form.
• The helium nucleus has less mass than the sum of the masses of the hydrogen nuclei.
• The “missing mass” is transferred into energy, by Einstein’s mass-energy equivalence equation.
• A tiny difference in mass results in large release of energy.

Question 26

What is Einstein’s Mass-Energy Equivalence Equation?

Answer 26

E=mcc

• Change in energy
• Change in mass
• Sped of light (300,000,000m/s)

Question 27

Suggest how elements more massive that iron were made from giant exploding stars called supernovae.

Answer 27

• Fe is the most stable nucleus of all elements.
• In order to fuse together nuclei to form a nucleus larger than Fe, requires a lot of energy as a result.
• Stars do not have enough heat energy and pressure to fuse together elements larger than Fe.
• Supernovae produce very large amounts of energy, enough to fuse together nuclei to form elements larger than Fe.