P6

Isotopes: variants of an element with the same number of protons but different number of neutrons.

To find the neutron number :
mass number- proton number = neutron number

Examples of isotopes:
C-12 C-13 C-14
H H-2 H-3 (hydrogen, deuterium, tritirium)

α²⁺

Alpha particle (identical to a helium atom)

β

Beta particle (high energy electron)

γ

Gamma wave (high energy photons in bursts of high frequency electromagnetic waves)

A half-life is the amount of time it takes for an isotope to half its radioactivity.

Draw a half life table to figure out the answer to exam questions.

Example:

An isotope has a half life of 6 hours. What percentage will be left after 24 hours?

HALF LIVES 0 1 2 3 4

TIME (hours) 0 6 12 18 24

Percentage 100 50 25 12.5 6.25

After 24 hours, the percentage of radioactivity left is 6.25%

Most- least ionising: Most- least penetrative:

Alpha Gamma
Beta Beta
Gamma Alpha

Alpha:
Stopped by paper or a few centimetres of air.

Beta:
Stopped by thin sheet of aluminium.

Gamma:
Stopped by thick lead or a few metres of concrete.

Background radiation comes from all around us and there is barely a risk of damage. The amount of background variation varies over the globe, for example in Cornwall there is more background radiation due to the granite rocks.

Sources of background radiation:

• cosmic rays
• rocks and soil
• radon gas
• food and drink

Human sources that emit ionising radiation:

• nuclear tests
• radiative waste
• medical practices/ tracers