Radioactivity

Question 1

Alpha radiation

Answer 1

Each alpha particle is a helium nucleus - 2 protons and 2 neutrons. Charge = +2e
Alpha particles have a large mass and charge so they interact with surrounding particles. They are strongly ionising and have a very short range.
They are stopped by paper

Question 2

Beta radiation

Answer 2

Consists of fast moving electrons or positrons
Have a smaller mass and charge so they are less ionising and have a shorter range in air. It takes 1-3mm of aluminium to stop them

Question 3

Gamma radiation

Answer 3

High energy photons with wavelength <10^-13 m. They travel at the speed of light so carry no charge
Low ionisation and large range
Takes a few centimeters of lead to stop

Question 4

Parent nucleus

Answer 4

Nucleus before decay

Question 5

Daughter nucleus

Answer 5

New nucleus after decay

Question 6

Random

Answer 6

We cannot predict when a particular nucleus will decay or which will decay next.
Each nucleus in a sample has the same chance of decaying per unit time

Question 7

Spontaneous

Answer 7

Decay of nuclei is not affected by presence of other nuclei in the sample or other factors such as pressure

Question 8

Half-life

Answer 8

The time it takes for half the number of active nuclei in the sample to decay
t1/2

Question 9

Activity

Answer 9

The rate at which nuclei decay
1 Becquerel is 1 decay per second

Question 10

Decay constant

Answer 10

Probability of decay of an individual nucleus per unit time
A = decay constant x N

Question 11

Decay constant equation derrivation

Answer 11

ΔN ∝ NΔt
ΔN/Δt ∝ -N
A∝ -N
A=λN

Question 12

Nuclei decay equation

Answer 12

N=N0e^−λt
Where N0 is the number of undecayed nuclei at t-0
λ = ln(2)/half life

A=A0e^−λt

Question 13

Carbon dating

Answer 13

Uses the ratio of Carbon-14 to Carbon-12 to tell how long an organism has been dead, as Carbon-14 decays over time.
Ratio is constant in a living organism but no new carbon is taken in after death