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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

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radioactivity

Radioactivity

Prepared by: Timothy John D. Matoy

radioactivity1
RADIOACTIVITY
  • Process of loosing energy to reach a stable state.
radioactivity and radioactive decay
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
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
Marie Curie (1867-1924)
  • Pierre and Marie Curie discovered that polonium and radium also emit radiation.
artificial radioactivity
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
Radioactive elements emitted into 3 types of radiation
  • Alpha Particles
  • Beta Particles
  • Gamma Rays
alpha particles
Alpha Particles
  • Fast moving helium nuclei; positive electrical charge
beta particles
Beta Particles
  • Negative electrical charged electrons.
electrons positrons
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
Gamma Rays
  • Electromagnetic waves of very short wavelength and travelling within the speed of light.
  • No charge at all.
protons
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 t
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
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
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
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
Types of Decay
  • Alpha Decay
  • Beta Negative Decay
  • Beta Positive Decay
  • Gamma Ray Emission
  • Electron Capture
beta decay1
BETA DECAY
  • Beta minus
    • Electron antineutrino
    • Interacts with neutron
  • Beta plus
    • Electron Neutrino
    • Interacts with protons
electron capture1
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
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
Unit of Radioactivity
  • Curie (Ci)
  • Becquerel (Bq)
  • 1 Bq = 1 disintegration per second
  • 1 Ci = 3.7x1010Bq
exponential decay law expressed in the following equation
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
sample problem
Sample Problem
  • 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?
practice 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 problem1
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
Activity Fraction
  • the fraction of the activity that is remaining after a given amount of time.
  • AF = 2 –n
  • Where n = time/ half life
sample problem1
Sample Problem
  • The half life for radioactive radon gas is 3.83 days, what will be the its activity fraction after 5 day?
practice problem2
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?
slide34
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

sample problem2
Sample Problem
  • 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?
practice problem3
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 law1
Radioactive Decay Law

Activity Remaining = original activity (0.5)n

  • Where n – number of half-lives
sample problem3
Sample Problem
  • 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?
practice problem4
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 problem5
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 problem6
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?