P11. Atoms & Radioactivity

Question 1

Nuclear fission

Answer 1

The process of splitting a nucleus into 2 lighter nuclei

Question 2

Nuclear fusion

Answer 2

The process in which 2 small/light nuclei combine to form a larger/heavier nucleus

Question 3

Half-life

Answer 3

The time taken for half the nuclei present in any given radioactive sample to decay

Question 4

Conclusions of Ernest Rutherford’s gold foil experiment

Answer 4

1. Atom is mostly empty space

2. Most of the atom’s mass is concentrated in a tiny nucleus at the centre

Question 5

Features of alpha emission

Answer 5

1. Identical to the nucleus of helium-4
2. Positive charge of +2
3. Large mass
4. Strong(est) ionising effect
5. Least penetrating
   - stopped by a thick sheet of paper, skin, few cm of air
6. Deflected by magnetic & electric fields

Question 6

Features of beta emission

Answer 6

1. An electron
2. Negative charge of -1
3. Small mass
4. Weak ionising effect
5. More penetrating than alpha emission
   - stopped by a few mm of aluminium/metal
6. Deflected by magnetic & electric fields

Question 7

Features of gamma emission

Answer 7

1. Electromagnetic waves
2. No charge
3. No mass
4. Least ionising of nuclear radiations
5. Most penetrating
   - never completely stopped, though lead & thick concrete will reduce intensity
6. NOT deflected by magnetic & electric fields