P2.5 Nuclear Fission anf Fusion

Question 1

What is the atomic number/proton number?

Answer 1

The number of protons in the nucleus. The bottom number.

Question 2

What is the mass number or nucleons number?

Answer 2

The number of nucleons. The top number.

Question 3

What is an isotope?

Answer 3

Atoms of an element with the same number of protons and electrons but a different number of neutrons.

Question 4

What are the charges of the subatomic particles?

Answer 4

Neutron- no charge
Proton- positive
Electron-negative

Question 5

What is an ion?

Answer 5

An atom with a charge.

Question 6

What is ionising radiation?

Answer 6

Radiation that has enough energy to cause atoms to lose electrons and become ions.

Question 7

How does a radioactive substance become stable?

Answer 7

Radioactive substances have unstable nuclei. The nucleus decays to become stable by emitting ionising radiation.

Question 8

What are the three forms of ionising radiation?

Answer 8

Alpha, beta and gamma

Question 9

Describe the properties of alpha radiation.

Answer 9

Alpha particles contain to protons and two neutrons, like the nucleus of a helium atom. They have no electrons and have a positive charge of +2. They are emitted from the nucleus at high speeds. They lose energy quickly and are not very penetrating, so are stopped by a few millimetres of paper.

Question 10

What are the properties of beta particles?

Answer 10

Beta particles are electrons. They are much less ionising then alpha particles and have more penetrating power. They can be stopped by a few millimetres of aluminium or lead.

Question 11

What are the properties of gamma rays?

Answer 11

Gamma rays are high frequency electromagnetic rays. They travel at the speed of light and have no charge. They a re much less ionising then beta so can penetrate nearly everything and are only partially stopped by a few centimetres of lead and are absorbed by many metres of concrete.

Question 12

What three nuclear reactions release energy?

Answer 12

Decay
Fission
Fusion

Question 13

Describe the fission of uranium-235

Answer 13

When a neutron collides with uranium-235 it splits into two daughter nuclei, releasing energy and two or more neutrons.

Question 14

How would you control nuclear fission?

Answer 14

The chain reaction can be controlled by making sure that only one of the neutrons goes on to react with another uranium nucleus, meaning that the reaction is controlled. To do this control rods, which contain materials which absorb neutrons are placed into the reactor to absorb the neutrons. The neutrons are also slowed down using a moderator so that they will collide with uranium.

Question 15

How is electricity generated in a reactor?

Answer 15

The fission reaction provides thermal energy, which is then transferred to a coolant, usually water at high pressure. This super heated water is pumped to the heat exchanger where it is used to produce steam. The steam drives a turbine, turning a generator. The generator transfers kinetic energy to electrical energy.

Question 16

What is the problem with nuclear fission?

Answer 16

The products, krypton and barium are radioactive.

Question 17

Describe fusion.

Answer 17

Fusion occurs when small nuclei combine to form large ones. Fusion happens in the sun p, where hydrogen nuclei combine to for, helium (deuterium and tritium). Fusion reacts produce huge amounts of energy and doesn’t produce radioactive products. However the materials used to contain fusion do become radioactive.

Question 18

Why has cold fusion not been accepted by the scientific community?

Answer 18

New scientific theories have to be validated by the scientific community. A report has to be peer reviewed and other scientists need to be able to carry out the same experiment and get the same results. The results of cold fusion are too sporadic to be accepted.

Question 19

Why can’t we perform fusion on earth?

Answer 19

Nuclear fusion requires a lot of energy because the nuclei of two positive hydrogen isotopes need to be fused, which normally repel each other (electrostatic repulsion). In order to overcome this the nuclei need to be moving very very fast. This means that the temperature of the reactor needs to be very high to produce enough energy because the eart doesn’t have the same strong gravitational field as the sun which creates very high density atoms, which are more likely to collide. So ten temperature of the fusion reaction would have to be about 150 million degrees, ten time her tha the sun

Question 20

What are the subatomic particles found in the nucleus called?

Answer 20

Nucleons (protons and neutrons)