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Radioactivity. Prepared by: Timothy John D. Matoy. RADIOACTIVITY. Process of loosing energy to reach a stable state. Radioactivity and Radioactive Decay. The nuclei of some nuclides are not stable - PowerPoint PPT Presentation
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Radioactivity
Prepared by: Timothy John D. Matoy
RADIOACTIVITYProcess of loosing energy to
reach a stable state.
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
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.
Marie Curie (1867-1924) Pierre and Marie
Curie discovered that polonium and radium also emit radiation.
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.
Radioactive elements emitted into 3 types of radiation
Alpha Particles Beta Particles Gamma Rays
Alpha Particles Fast moving helium nuclei; positive
electrical charge
Beta Particles
Negative electrical charged electrons.
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
Gamma Rays Electromagnetic waves of very short
wavelength and travelling within the speed of light.
No charge at all.
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
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
Physical Half-Life the average time required for the
decay of half the atoms in a given amount of a radioactive substance.
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.
Effective Half-Life the half-life of a radioactive isotope in
a biologic organism, resulting from the combination of radioactive decay and biologic elimination.
Types of Decay Alpha Decay Beta Negative Decay Beta Positive Decay Gamma Ray Emission Electron Capture
ALPHA DECAY
ALPHA DECAY
BETA DECAY
BETA DECAY Beta minus
Electron antineutrino Interacts with neutron
Beta plus Electron Neutrino Interacts with protons
GAMMA RAY EMISSION
ELECTRON CAPTURE
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.
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.
Unit of Radioactivity Curie (Ci) Becquerel (Bq) 1 Bq = 1 disintegration per second 1 Ci = 3.7x1010 Bq
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
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
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?
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?
Activity Fraction the fraction of the activity that is remaining
after a given amount of time.
AF = 2 –n
Where n = time/ half life
The half life for radioactive radon gas is 3.83 days, what will be the its activity fraction after 5 day?
Sample Problem
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?
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
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
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?
Radioactive Decay LawActivity Remaining = original activity (0.5)n
Where n – number of half-lives
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
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?
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?
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?
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