radioactivity. henri becquerel in 1896, becquerel observed that uranium compounds emitted a...
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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