## AQA GCSE Half Life Calculations

**Half Life Calculations**

This formula can be used for some of the count rate calculations

**Sample question**

A radioactive isotope has an initial count rate of 60000Bq, with a half life of 4 minutes. Calculate the count rate after 12 minutes

12 minutes/4 minutes = 3 half lives

Count rate = 60000/(2^{3})

Count rate = 7500

**Net decline**

In physics:

**Net decline is **the ratio of the number of isotopes present in a sample now to the initial number of isotopes present.

**Sample Question**

A sample of a radioactive isotope has 4 x 10

^{18}atoms present. After two half lives there are 1 x 10

^{18}atoms present. Calculate the net decline

It can also be defined in terms of count rate:

Net decline is the ratio of the count rate in a sample now to the initial count rate.

**Sample Question**

The initial count rate of a radioactive isotope is 120,000Bq. Calculate the net decline after 3 half lives

The count rate will halve after each half life. So, after 3 half lives we need to halve the 120,000Bq three times

120,000/2 = 60,000Bq

60,000Bq/2 = 30,000Bq

30,000Bq/2 = 15,000Bq

So, after 3 half lives, the count rate is 15,000Bq

**Practice Questions**

1. Polonium-210 has a half life of 140 days. If an original sample of Polonium-210 has an activity of 500Bq what will its activity be after 560 days.

2. A radioactive isotope undergoes a series of half lives. At the start there are 8 x 10^{36} atoms of the isotope present. At a point later in time there are 1 x 10^{36} atoms remaining. Calculate the net decline.

3. If the initial count rate is 200,000Bq. Calculate the net decline after 4 half lives

Absorption and Emission of EM Radiation

JJ Thomson and Plum pudding model

Ernest Rutherford and the Nuclear Model

Niels Bohr changing the Nuclear Model

Discovering the Proton and Neutron

Measuring radiation from radioactivity

Radiation types and properties

Random nature of radioactive decay

Radioactive contamination or irradiation

Hazards of contamination and irradiation

Studies on the effects of radiation on humans

Different half lives of radioactive isotopes

Nuclear Fission Chain Reaction

Writing nuclear fission equations