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

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Presentation transcript:

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

© JP : Becquerel accidentally discovered that uranyl crystals emitted invisible radiation which hit even an enclosed photographic plate uranyl salt Photographic film Becquerel’s Notes

© JP : 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 polonium

© 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 radiation beam with a magnetic field. α alpha + ve  beta - ve  gamma no charge

© JP 5 Alpha particles are helium nuclei. Beta particles come from the nucleus and are high speed electrons. How do electrons come from the nucleus? Typical speed 0.1c.They have a 2+ charge. e-e- Typical speed 0.9c They have a 1- charge. Gamma rays are high frequency, high energy electromagnetic radiation. speed = c. They have no charge.

© JP 6 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

© JP 7 ALPHA DECAY + ? energy e.g.

© JP 8 BETA DECAY A neutron in the nucleus turns into a proton, an electron, an antineutrino and energy. The nucleus now has one more proton than it started with During a beta + decay, a proton in an atom's nucleus turns into a neutron, a positron, a neutrino and energy.

© JP 9 U 238 DECAY CHAIN ALPHABETA

© JP 10 U-238alpha4.5 billion years Th-234beta24 days Pa-234beta1.2 minutes U-234alpha years Th-230alpha years Ra-226alpha1600 years Rn-222alpha3.8 days Po-218alpha3 minutes Pb-214beta27 minutes Bi-214beta20 minutes Po-214alpha seconds Pb-210beta20 years Bi-210beta2.6 million years Po-210 alpha140 days Pb-206STABLE U 238 DECAY CHAIN with emissions and half lives

© JP 11  e-e-    paper sheet 2mm of Aluminium several cm of lead

© JP 12 RANGE OF PARTICLES IN AIR ALPHA RADIATION Travels a few centimetres in air because they pick up electrons as they pass through air becoming helium atoms. This makes ions from the air particles (ionisation). They are stopped by a sheet of paper and are no danger to humans unless inhaled or ingested – then cancer or genetic defects. BETA RADIATION Because they travel faster, they do not pick up electrons (ionise the air) as much as alpha particles and so travel further. They travel about 1m in air, 1cm into body tissue and are stopped be a sheet of metal a few millimetres thick. Not dangerous unless the source is inside the body. GAMMA RADIATION Has an unlimited range in air. It is always given off by a radioactive substance and is very harmful – kills living tissue (cancer). It will penetrate 30cm into steel or several centimetres into lead.

© JP 13 Bubble Chambers Because the decay products have different charges and speeds, their paths in magnetic fields vary. This means we can tell them apart.