Radioactivity
description
Transcript of Radioactivity
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Radioactivity
Prepared by: Timothy John D. Matoy
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RADIOACTIVITYProcess of loosing energy to
reach a stable state.
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Radioactivity and Radioactive Decay
The nuclei of some nuclides are not stable
They disintegrate or undergo nuclear transformation spontaneously and in random process called radioactivity
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Henri Becquerel (1852-1908) Discover the radioactivity in
1896 He noted that a piece of
mineral containing uranium when placed over an exposed photographic plate just as if it has been exposed to light.
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Marie Curie (1867-1924) Pierre and Marie
Curie discovered that polonium and radium also emit radiation.
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Artificial Radioactivity Radioactivity produced by man
Irene Curie-Joliot produce the first radioactive product when they bombarded aluminum with alpha particles from polonium source to study the emitted neutrons and positrons.
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Radioactive elements emitted into 3 types of radiation
Alpha Particles Beta Particles Gamma Rays
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Alpha Particles Fast moving helium nuclei; positive
electrical charge
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Beta Particles
Negative electrical charged electrons.
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Electrons, Positrons Very light; in tissue do not travel in straight
lines but are deflected by coulombic repulsions from atomic orbital electrons
Lose an average 50% of their energy in interaction
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Gamma Rays Electromagnetic waves of very short
wavelength and travelling within the speed of light.
No charge at all.
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Protons Generated by cyclotron beams Because they are heavier than
electrons, travel mainly in straight line by boring a path through atomic clouds
Medium Z materials used for shielding
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Half-Life(t½) the time in which a radioactive
substance will lose half of its activity through disintegration. Physical Half-life Biological Half-life Effective Half-Life
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Physical Half-Life the average time required for the
decay of half the atoms in a given amount of a radioactive substance.
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Biologic Half-Life the time in which a living tissue,
organ, or individual eliminates, through biologic processes, half of a given amount of a substance that has been introduced into it.
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Effective Half-Life the half-life of a radioactive isotope in
a biologic organism, resulting from the combination of radioactive decay and biologic elimination.
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Types of Decay Alpha Decay Beta Negative Decay Beta Positive Decay Gamma Ray Emission Electron Capture
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ALPHA DECAY
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ALPHA DECAY
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BETA DECAY
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BETA DECAY Beta minus
Electron antineutrino Interacts with neutron
Beta plus Electron Neutrino Interacts with protons
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GAMMA RAY EMISSION
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ELECTRON CAPTURE
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ELECTRON CAPTURE
Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron (changing a nuclear proton to a neutron) and simultaneously emits a neutrino.
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Radioactive Decay Law Elster and Geitel observed that
the strength of a pure radioactive substance decrease exponentially.
Radioactivity was found to be a property of the individual atoms, not of a substance as a whole.
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Unit of Radioactivity Curie (Ci) Becquerel (Bq) 1 Bq = 1 disintegration per second 1 Ci = 3.7x1010 Bq
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Exponential decay law expressed in the following equation:
N = N0e-λt or A = A0e-λt
Where: A = present activity A0 = original activity
λ = disintegration constant/ decay constant t = elapsed time
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The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
Sample Problem
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Practice Problem A Cesium-138 radioactive source
has a half life of 30 years. If the initial activity is 10.25 Ci. What will be the present activity after 30 years?
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Practice Problem A certain radioactive source has a
present activity of 2.1626 mCi after 47.5 days. If the initial activity is 15 mCi. Find the decay constant?
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Activity Fraction the fraction of the activity that is remaining
after a given amount of time.
AF = 2 –n
Where n = time/ half life
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The half life for radioactive radon gas is 3.83 days, what will be the its activity fraction after 5 day?
Sample Problem
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Practice Problem A Cesium-138 radioactive source
has a half life of 30 years. If the initial activity is 10.25 Ci. What will be its activity fraction after 55 years?
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With the activity fraction, we can write a single equation to solve for the final activity if we are given the initial activity
Nf = (AF) Ni
Where Nf = final activity,
Ni = initial activity
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The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
Sample Problem
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Practice Problem A Cesium-138 radioactive source
has a half life of 30 years. If the initial activity is 10.25 Ci. What will be the present activity?
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Radioactive Decay LawActivity Remaining = original activity (0.5)n
Where n – number of half-lives
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The half life for radioactive radon gas is 3.83 days, what will be the present activity of the radon gas after 5 days if the initial activity is 30 mCi?
Sample Problem
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Practice Problem A Cesium-138 radioactive source
has a half life of 30 years. If the initial activity is 10.25 Ci. What will be the activity after 30 years?
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PRACTICE PROBLEM
A certain radioactive source has an initial activity of 10.25 Ci. After 30 years only 5.125 Ci of activity remains. What is its half-life?
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Practice problem
Technetium 99m with a half-life of 6 hours was left in the laboratory at 6 o’clock in the morning. If the original activity is 100 mCi, when do the radioactive substance will have a 6.25% of its original value? What will be its activity at that time?