1
Q

Define activity.

A

Number of decays per second.

2
Q

Define decay constant.

A

The probability of a nucleon decaying per unit time.

3
Q

Describe the spontaneous and random nature

of radioactive decay of unstable nuclei.

A

It is spontaneous because it happens with no external influence - it cannot be induced. It is random because we cannot predict which nucleon will decay next.

4
Q

Describe the nature, penetration and range of

alpha-particles.

A

Strongly ionising, slow, absorbed by paper or a few cm of air, have a charge of +2 and a relative mass of 4.

5
Q

Describe the nature, penetration and range of

beta-particles

A

Weakly ionising, fast, absorbed by about 3mm of aluminium, have a charge of -1, a negligible mass and are equivalent to an electron.

6
Q

Describe the nature, penetration and range of gamma-rays.

A

Very weakly ionising, speed of light, absorbed by many cm of lead, or several m of concrete. No charge or mass.

7
Q

How do we calculate the activity of a sample?

A

Decay constant x number of nuclei.

8
Q

Define half-life.

A

The average time it takes for number of undecayed atoms to halve.

9
Q

How do we calculate the decay constant?

A

ln2/half-life

10
Q

State the similarities and differences between the discharge of a capacitor and the decay of a radioactive substance.

A

They both have the same decay equations, where the letters represent the amount of charge and number of nuclei remaining. We use both of these equations in the same way. 1/decay constant is the equivalent to the time constant (CR), and the half-life of both of them is equivalent to ln2 multiplied by these values.

11
Q

Describe the uses of radioactive isotopes in smoke alarms.

A

Smoke alarms contain a weak alpha-particle emitter close to two electrodes. The radiation ionises the air, and a current flows between the electrodes. In the event of a fire, the smoke absorbs the radiation, breaking the current and sounding the alarm.

12
Q

Describe the technique of carbon dating.

A

Living organisms absorb the radioactive isotope carbon-14. When they die, the activity of the carbon-14 falls. We can compare the activity in a substance to a similar, living substance to see how long ago the organism died.