Radioactivity. Henri Becquerel In 1896, Becquerel observed that uranium compounds emitted a...

Radioactivity

Henri Becquerel

In 1896, Becquerel observed that uranium compounds emitted a penetrating radiation that passedthrough paper and affected photographic film, effectivelydeveloping it

Becquerel found that mysterious rays from uranium discharged a charged electroscope

Rutherford showed that this radiation ionised gases and produced an electric current

Pierre and Marie Curie separated radium and polonium from uranium ores – these elements are more radioactive

than uranium i.e. they emit more radiation

Ra: 0.00003%Po: 0.0000000005%

The ‘activity’ of radioactive substances is not affected by temperature or chemical changes. It is

a property of the nucleus only

, and radiation

Types of radiation

Symbol Name Identity

alpha He nucleus (particle)

beta electrons (e -) (particle)

gamma electromagnetic waves (radiation)

radiation

radiation

T ½ = 5.3 years

radiation

T ½ = 1600 yearsEmission of an particle:-• reduces the atomic number by 2 and • the mass number by 4

particles

radiation

T ½ = 0.02 seconds

Emission of a particle:-• increases the atomic number by 1 but • does not change the mass number

Deflection of radiation

Penetration of radiation

Band of stability

Half lives

Half lives

Half lives

Half lives

Half lives

Carbon -14

emission

emission is:-• emission of an electron together with• an increase in 1 in the atomic number i.e. an increase in the number of protons in the nucleus• but no overall increase in the mass number

The only way an electron can be emitted and the number of protons increaseis by decay of a neutron

Another example of emission

atomic number increases by 1

Another example of emission

atomic number increases by 1

Balancing nuclear equations

Rutherford – Soddy rules

The sum of the mass numbers and charges in a nuclear equation

must be the same before and after the radioactive decay

238U radioactive decay

238U radioactive decay series

ALL radioactive decay series ultimately end in lead (206Pb) which is stable

IsotopesAll elements have isotopes –

there is no element where there is only one type of atoms

Hydrogen has three isotopes

Isotope Abundance1H 99.985%2H 0.015%3H radioactive T ½ = 12.3 years

Hydrogen is the only element where the isotopes can have different symbols

1H 2D (deuterium) 3T (tritium)

IsotopesAll elements have isotopes –

there is no element where there is only one type of atoms

Potassium has 17 known isotopes – three of which are found naturally

Isotope Abundance39K 93.26%40K 0.012%41K 6.73%

Mass spectrum of K

Uses of radiation

Medicine – radiotherapy

Industry – thickness measurements

Science – use of tracers