1. 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
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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
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3. Marie Curie discovered that thorium, (Z=90) was a radioactive element
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
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4. 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
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5. nucleon number chemical symbol proton number
( = number of protons + neutrons )
chemical symbol
proton number
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6. 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 = – m
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7. 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
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8. 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.
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9. 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
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10. - emission - proton number Z Neutron number N = A-Z N=Z 40 20 60 80
100
120
stability line -
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11. + 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
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12. Alpha decay
energy ?
e.g.
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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.
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14. U 238 DECAY CHAIN
ALPHA
BETA
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15. 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 years
Th-230 alpha years
Ra-226 alpha 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 seconds
Pb-210 beta 20 years
Bi-210 beta 2.6 million years
Po alpha 140 days
Pb-206 STABLE
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16. several cm of lead paper sheet 2mm of Aluminium   
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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 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
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