Radioactivity

Henri Becquerel In 1896, Becquerel observed that uranium compounds emitted a penetrating radiation that passed through paper and affected photographic film, effectively developing 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: % Po: %

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 SymbolNameIdentity  alpha He nucleus (particle)  beta electrons (e - ) (particle)  gamma electromagnetic waves (radiation)

 radiation

T ½ = 5.3 years

 radiation T ½ = 1600 years Emission 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

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 increase is 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

238 U radioactive decay

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

Isotopes All elements have isotopes – there is no element where there is only one type of atoms Hydrogen has three isotopes IsotopeAbundance 1H1H99.985% 2H2H0.015% 3H3Hradioactive T ½ = 12.3 years Hydrogen is the only element where the isotopes can have different symbols 1 H 2 D (deuterium) 3 T (tritium)

Isotopes All 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 IsotopeAbundance 39 K93.26% 40 K0.012% 41 K6.73%

Mass spectrum of K

Uses of radiation Medicine – radiotherapy Industry – thickness measurements Science – use of tracers