g a b α,  and  RADIATION gamma alpha beta e- Marie Curie Antoine-Henri Becquerel (1852 – 1908) Marie Curie g gamma a alpha b beta e- α,  and  RADIATION © JP

1896: Becquerel accidentally discovered that uranyl crystals emitted invisible radiation when they exposed an enclosed photographic plate uranyl salt Photographic film Becquerel’s Notes © JP

Marie Curie discovered that thorium, (Z=90) was a radioactive element 1867-1934 90 thorium Marie Curie discovered that thorium, (Z=90) was a radioactive element 1898: Marie and Pierre Curie discovered polonium (Z=84) and radium (Z = 88), two new radioactive elements radium 88 as paint 84 polonium © JP

Photo film to detect radiation 1901 Ernest Rutherford found three types of radiation were emitted from a radium source, by separating the beam with a magnetic field Photo film to detect radiation Magnetic field acting inwards α alpha + ve  beta - ve  gamma no charge Lead collimating slit radium source Lead box © JP

nucleon number chemical symbol proton number ( = number of protons + neutrons ) chemical symbol proton number © JP

Alpha particles are helium nuclei Typical speed 0.1c; energy 5 MeV Beta particles are high speed electrons Typical speed 0.99c Gamma rays are energetic photons speed = c ; λ = 10-11 – 10-13 m © JP e-

Radioactive atoms have: too many neutrons or too many protons or are just too big An atom becomes radioactive if its neutron/proton ratio is outside the “band of stability” All elements with N > 83 (>Bi) are naturally radioactive An unstable nucleus can emit radioactive particles in order to reach stability: – Beta Particle Production – Alpha Particle Production – Gamma Ray Emission © JP

Line of stable nuclides – stable nuclides lie on or very close to this line proton number Z Neutron number N = A-Z N=Z 40 20 60 80 100 120 The stability line follows N = Z line up to Z = 16 Unstable nuclei lie either side of the stability line; the exact position determines the mode of decay. © JP

Alpha decay only occurs for Z > 83 proton number Z Neutron number N = A-Z N=Z 40 20 60 80 100 120 stability line α © JP

- emission - proton number Z Neutron number N = A-Z N=Z 40 20 60 80 100 120 stability line - © JP

+ emission, or electron capture proton number Z Neutron number N = A-Z N=Z 40 20 60 80 100 120 stability line + or electron capture © JP

Alpha decay energy + ? e.g. © JP

Beta (-) decay A neutron in the nucleus turns into a proton, an electron and an antineutrino. The nucleus now has one more proton than it started with. + + During a beta + plus decay, a proton in an atom's nucleus turns into a neutron, a positron and a neutrino. © JP

U 238 DECAY CHAIN ALPHA BETA © JP

U 238 DECAY CHAIN with emissions and half lives U-238 alpha 4.5 billion years Th-234 beta 24 days Pa-234 beta 1.2 minutes U-234 alpha 250 000 years Th-230 alpha 80 000 years Ra-226 alpha 1600 years Rn-222 alpha 3.8 days Po-218 alpha 3 minutes Pb-214 beta 27 minutes Bi-214 beta 20 minutes Po-214 alpha 0.0002 seconds Pb-210 beta 20 years Bi-210 beta 2.6 million years Po-210 alpha 140 days Pb-206 STABLE © JP

several cm of lead paper sheet 2mm of Aluminium     © JP

RANGE OF PARTICLES IN AIR ALPHA RADIATION HAS A RANGE OF A FEW CM IN AIR: BECAUSE THE PARTICLES ARE CHARGED AND RELATIVELY MASSIVE, THEY INTERACT WITH AIR MOLECULES, PRODUCING UP TO 200 000 ION PAIRS PER CM OF TRAVEL BETA RADIATION BETA PARTICLES HAVE A RANGE OF A FEW METRES IN AIR GAMMA RADIATION HAS UNLIMITED RANGE IN AIR NEUTRON RADIATION BEHAVES SIMILAR TO GAMMA © JP