Radiation is produced from unstable isotopes of atoms becoming more stable. There are three types of radiation released – alpha, beta and gamma.
For example 14 12
C C are examples of isotopes of carbon
Carbon-14 is unstable and will produce radiation to become a stable isotope.
Beta particles are bent a long way and to the positive electrode – thus they are very light and negative
Alpha particles are bent a little and to the negative electrode – thus they are slightly heavier and positive
Gamma particles do not have a charge as they are not deflected.
Alpha (α)particles have a mass of 4 and an atomic number of 2 ie 4
ie a helium nucleus
Beta (β) particles have a mass of 0 and an atomic number of -1 ie 0
Different radiations have different penetrating powers. Alpha can be stopped by a hand or a sheet of paper. Beta needs a layer of aluminium to stop it and gamma needs several cm of lead to stop it passing through.
Note that the mass numbers and the atomic numbers must add so that they are the same on both sides of the equation.
Loss of an alpha particle reduces the mass by 4 and the atomic number by 2.
Loss of a beta particle does not affect the mass and increases the atomic number by 1.
The half life of an isotope is the time taken for half of it to decay. For example one half life could be represented by:
1000 counts --------- 500 counts
or 20 g --------- 10g
or 100 % --------- 50%
or simply 1 --------- 0.5
The half life of an isotope could be in years, minutes, seconds etc
The half life of an isotope is not affected by the starting mass ie 1g has the same half life as 10g
The half life of an isotope is not affected by the state, (s),(l) or(g),that it is in.
The half life of an isotope is not affected by whether it is a compound or an element eg
The half life of an isotope is not affected by temperature or pressure.
The half life of Titanium-44 is 63 years. If you start with 100g of titanium-44:
63 years 63 years 63 years
100g ---------- 50g ------------ 25g ----------- 12.25g
Then in 3 half lives ie 189 years there will be 12.25g left. ie 87.75g would have turned into another isotope (not just disappeared)
Uses of radioisotopes.
Americium-241 is used in smoke detectors
Cobalt-60 is used to irradiate food to make it last longer
Iodine-131 is used to treat thyroid cancer
Using radioisotopes near humans requires alpha or beta radiation and a short half life (so it gets used up)
Use of isotopes to date materials.
Living things have a constant proportion of radioactive carbon-14.As it decays it is replaced.
When they die they can no longer take in carbon-14.
The carbon-14 continues to decay with a half life of 5700 years.
Thus if a piece of wood has a quarter of the carbon-14 it would have as a living tree:
5700 years 5700 years
1 ---------- 0.5 ------------ 0.25
The tree died 11400 years ago
These notes are for the Scottish National Chemistry course taught in fourth year in most Scottish schools.
The notes available here are concise notes. They are NOT to be considered as material to learn from - they are for revision.
The notes are arranged under the following topics
National 3 Unit 1
National 4 and 5 Unit 1 Rates of Reaction
National 4 and 5 Unit 2 Fuels and Homologous Series
National 4 and 5 Unit 3 Metals