2. © JP 1  alpha e-e-  beta  gamma Marie Curie Antoine-Henri Becquerel (1852 – 1908) α,  and  RADIATION

3. © JP 2 1896: Becquerel accidentally discovered that uranyl crystals emitted invisible radiation when they exposed an enclosed photographic plate uranyl salt Photographic film Becquerel’s Notes

4. © JP 3 1898: Marie and Pierre Curie discovered polonium (Z=84) and radium (Z = 88), two new radioactive elements Marie Curie discovered that thorium, (Z=90) was a radioactive element 90 thorium radium 88 as paint 1867-1934 84 polonium

5. © JP 4 radium source Lead box Lead collimating slit Magnetic field acting inwards 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 α alpha + ve  beta - ve  gamma no charge

6. © JP 5 chemical symbol proton number nucleon number ( = number of protons + neutrons )

7. © JP 6 Alpha particles are helium nuclei Beta particles are high speed electrons Typical speed 0.1c; energy 5 MeV e-e- Typical speed 0.99c Gamma rays are energetic photons speed = c ; λ = 10 -11 – 10 -13 m

8. © JP 7 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 Radioactive atoms have: too many neutrons or too many protons or are just too big

9. © JP 8 proton number Z Neutron number N = A-Z N=Z 40206080100 40 60 80 120 20 100 Line of stable nuclides – stable nuclides lie on or very close to this line 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.

10. © JP 9 proton number Z Neutron number N = A-Z N=Z 40206080100 40 60 80 120 20 100 stability line Alpha decay only occurs for Z > 83 α

11. © JP 10 proton number Z Neutron number N = A-Z N=Z 40206080100 40 60 80 120 20 100 stability line  - emission --

12. © JP 11 proton number Z Neutron number N = A-Z N=Z 40206080100 40 60 80 120 20 100 stability line  + emission, or electron capture  + or electron capture

13. © JP 12 Alpha decay + ? energy e.g.

14. © JP 13 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.

15. © JP 14 U 238 DECAY CHAIN ALPHABETA

16. © JP 15 U-238alpha4.5 billion years Th-234beta24 days Pa-234beta1.2 minutes U-234alpha250 000 years Th-230alpha80 000 years Ra-226alpha1600 years Rn-222alpha3.8 days Po-218alpha3 minutes Pb-214beta27 minutes Bi-214beta20 minutes Po-214alpha0.0002 seconds Pb-210beta20 years Bi-210beta2.6 million years Po-210 alpha140 days Pb-206STABLE U 238 DECAY CHAIN with emissions and half lives

17. © JP 16  e-e-    paper sheet 2mm of Aluminium several cm of lead

18. © JP 17 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