Radiation

Question 1

What was the plum pudding model of an atom?

Answer 1

When Thomson, in 1897, discovered electrons could be removed from atoms, showing they have structure, he came up with the idea that matter was made up of positive spheres (atoms) with electrons stuck in them

Question 2

What are the similarities of the plum pudding model to the modern day model of an atom?

Answer 2

• Have positive and negative charges
• Have electrons
• Spherical

Question 3

What are the differences of the plum pudding model to the modern day model of an atom?

Answer 3

• No nucleus
• No neutrons
• Electrons in middle, not round outside
• No empty space
• Positively charged sphere, not nucleus

Question 4

What was the Rutherford scattering experiment?

Answer 4

Alpha particles (2 protons and 2 neutrons) were fired at thin gold foil to try and prove or disprove the plum pudding model

Question 5

What three things were discovered during the Rutherford scattering experiment?

Answer 5

• Most particles passed straight through, showing there is mainly empty space
• Very few particles were deflected straight back, showing the atom has a positive nucleus as the positive alpha particles were repelled
• This also showed that the concentrated mass in the nucleus is very small compared to the size of the atom, but contains most of the mass

Question 6

What are two properties of radioactive substances?

Answer 6

• Radioactive substances give out radiation from the nuclei no matter what is done to them
• Radioactivity is entirely random, and unaffected by physical conditions such as temperature

Question 7

What are isotopes?

Answer 7

Atoms with the same number of protons but a different number of neutrons

Question 8

How many elements have isotopes?

Answer 8

Most elements have different isotopes, but there are usually only one or two stable ones

Question 9

What happens to the isotopes which are less stable?

Answer 9

The others tend to decay into other elements and give out radiation

Question 10

What are the three types of radiation?

Answer 10

Alpha (α), Beta (β), Gamma (γ)

Question 11

What are alpha particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?

Answer 11

• Made from: two protons and two neutrons that have been kicked out of a nucleus
• Charge: +2
• Mass: 4
• Speed: slow
• Stopped by: a sheet of paper
• Ionising: strong, bash into atoms and knock off electrons
• Penetrating: low

Question 12

What are beta particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?

Answer 12

• Made from: a fast moving electron
• Charge: -1
• Mass: 1/2000
• Speed: quite fast
• Stopped by: few mm of aluminium
• Ionising: moderate, bash into atoms and knock off electrons
• Penetrating: medium

Question 13

What are gamma particles made from, what is their charge, mass and speed, what are they stopped by and how powerful are they at ionising and penetrating?

Answer 13

• Made from: very short electromagnetic waves
• Charge: 0
• Mass: 0
• Speed: speed of light
• Stopped by: few cm of lead
• Ionising: weak, tend to pass through rather than collide
• Penetrating: high

Question 14

What is background radiation?

Answer 14

Radiation that is present at all times

Question 15

What are some natural causes of background radiation?

Answer 15

-Cosmic rays
-Rocks and soil - give off radon
-Living things (plants absorb
radioactive materials from the soil and pass them up the food chain)

Question 16

What are some artificial causes of background radiation?

Answer 16

• Waste from nuclear power stations
• Nuclear weapons testing
• Medical x-rays

Question 17

What are some uses of radiation?

Answer 17

Smoke detector -Weak α radiation is put between 2 electrodes, causing ionisation and enabling a current to flow. In a fire, smoke absorbs the radiation, stopping current and sounding the alarm
Medical tracers -Certain isotopes are ingested and progress around the body is measured. All isotopes must be γ or β so radiation passes out of the body and have a short ½ life so radiation disappears
Radiotherapy -High doses of γ radiation is directed at cancer cells to kill them without damaging too many normal cells
Sterilisation of food and surgical equipment -High doses of γ rays kill all living cells, including microbes. The isotope has a long ½ life so doesn’t need to be replaced often

Question 18

What is nuclear fission?

Answer 18

• Splitting up of a large atomic nucleus
• Energy released heats water, which turns into steam and drives a turbine, creating electricity
• A slow moving neutron is absorbed by uranium or plutonium nucleus, making it unstable and causing it to split. When it splits, 2 or 3 more neutrons are released to carry on the reaction

Question 19

What are the pros and cons of nuclear fission?

Answer 19

Pros -Cheap fuel, give out lots of energy

Cons -Difficult waste disposal, high cost of power plant and decommissioning

Question 20

What is nuclear fusion?

Answer 20

• Joining together of small atomic nuclei

- Energy in stars comes from fusion and lots of energy is released

Question 21

What are the pros and cons of nuclear fusion?

Answer 21

Pros -Little radioactive waste, lots of fuel around

Cons -Only happens at very high temperatures (10,000,000°c), needs strong magnetic field to store it