(SP6) Radioactivity

Question 1

Rutherford’s experiment -

Answer 1

most of the alpha particles past through the gold foil, bu a few bounced back. The plum pudding model could not explain this result.

Rutherford suggested that protons are in the nucleus and electrons move around it.

Question 2

Using which equipment the radioactivity can be measured and how does it work?

Answer 2

Geiger-Muller tube (GM tube)

Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow.

Question 3

Nature of radiation

Answer 3

The nucleus of a radioactive substance is unstable, which means it can easily decay. When decay occurs, radiation is emitted which causes the nucleus to lose energy and become more stable. It’s a random process

Question 4

Alpha radiation =

Answer 4

Helium 4; 2

Question 5

Beta radiation -

Answer 5

electron 0;1

Question 6

Gamma ray -

Answer 6

no particles, a wave of energy

Question 7

Positron -

Answer 7

positive electron 0; +1

Question 8

Neutron -

Answer 8

n 1; 0

Question 9

The activity of any radioactive substance -

Answer 9

the number of nuclear decays per second and is measured in becquerels (Bq). 1 becquerel - 1 nuclear decay per second

Question 10

The half-life -

Answer 10

the time taken for half the unstable nuclei in a sample of a radioactive isotope to decay

Question 11

Dangers of radiactivity -

Answer 11

A large amount of ionising radiation can cause tissue damage such as reddened skin (radiation burns)

Small amounts of ionising over long periods of time can damage DNA inside a cell and cause mutations

Question 12

Handling radioactive source

Answer 12

• tongs
• minimize explosure
• store in lead-line containers
• do not point sources at people

Question 13

Nuclear accidents -

Answer 13

people may become irradiated or contaminated

Question 14

Using radioactivity

Answer 14

• Killing microorganisms (irradiated with gamma rays)
• tracers (water contains a gamma source, using geiger-muller tube follow the pipe, higher levels of radiation => leak)
• Checking thickness of paper - industry
• Smoke alarms - americium-241 source gives a constant stream of alpha particles. Alpha particles ionise the air inbetween plates and the current is created. Smoke slows down ions which makes the current fall, the detector senses the amount of current.

Question 15

Nuclear fission -

Answer 15

Uranium-235 absorbs a neutron immediately splits into two smaller daughter nuclei, releasing two or more neutrons.

Question 16

Nuclear reactors -

Answer 16

Fuel is made into fuel rods. As fission reaction occurs neutrons leave the fuel rods at high speed and are slowed down by the moderator to increase the chance that they will be absorbed by another uranium-235 nucleus. Control rods are made of elements that absorb neutrons, they control the reaction.

Question 17

Generating electricity

Answer 17

Reactor core => hot coolant => steam => turbines => generator

Question 18

Nuclear fusion -

Answer 18

Hydrogen nuclei combine to form helium, release energy inside the Sun and other stars