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Radiation Energy and matter that comes from the nucleus of an atom . Ch05 © Nick DeMello, PhD. 2007-2016 version 1.6
Radiation
Energy and matter that comes from the nucleus of an atom.
Ch05
© Nick DeMello, PhD. 2007-2016
version 1.6
Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Discovery of Radioactivity
‣ Antoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals also gave off X-rays.
‣ Phosphorescence is the long-lived emission of light by atoms or molecules that sometimes occurs after they absorb light.
‣ X-rays are detected by their ability to penetrate matter and expose a photographic plate.
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Antoine Becquerel
Discovery of Radioactivity
‣ Becquerel discovered that certain minerals were constantly producing energy rays that could penetrate matter.
‣ Becquerel determined that ‣ all the minerals that produced these rays
contained uranium, and
‣ the rays were produced even though the mineral was not exposed to outside energy.
‣ He called them uranic rays because they were emitted from minerals that contained uranium.
‣ Like X-rays
‣ Not related to phosphorescence
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Antoine Becquerel
Marie Curie Discovered Radioactive Elements
‣ Marie Curie determined the rays were emitted from specific elements.
‣ She also discovered new elements by detecting their rays. ‣ Radium named for its green phosphorescence
‣ Polonium named for her homeland Poland
‣ Because these rays were no longer just a property of uranium, she renamed it radioactivity.
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Marie Curie
Properties of Radioactive Rays
‣ Radioactivity is the release of tiny, high-energy particles or energy from an atom.
‣ Nuclear Radioactivity is release from the nucleus of an atom.
‣ Radioactive rays can ionize matter. ‣ Cause uncharged matter to become charged
‣ That is how a Geiger counter and electroscope function.
‣ Radioactive rays have high energy.
‣ Radioactive rays can penetrate matter.
‣ Radioactive rays cause phosphorescent chemicals to glow. ‣ That how a scintillation counter works.
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Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Radiation & Radioactivity
‣ Ernest Rutherford discovered three forms of emissions that come from radioactive elements. ‣ Gamma rays have no charge and and have no mass.
‣ Beta particles have a negative charge, beta radiation like cathode rays, are a stream of electrons.
‣ Alpha particles have a positive charge and as much mass as a helium atom. (four times the mass of a hydrogen atom)
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Mass Charge
α particles A Helium atom positive
β particles Electrons negative
γ rays none none
Rutherford
++++++++++++
--------------α
γβ
Radiation & Radioactivity
‣ Ernest Rutherford discovered three forms of emissions that come from radioactive elements. ‣ Gamma rays have no charge and and have no mass.
‣ Beta particles have a negative charge, beta radiation like cathode rays, are a stream of electrons.
‣ Alpha particles have a positive charge and as much mass as a helium atom. (four times the mass of a hydrogen atom)
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Mass Charge
α particles A Helium atom positive
β particles Electrons negative
γ rays none none
Rutherford
αβ γ
0.01 mm 1 mm 100 mm
Pieces of Lead
Radioisotopes
‣ It’s about mass.
‣ Only certain isotopes of a given element are radioactive.
‣ Carbon-14 is radioactive, Carbon-12 is not.
‣ Hydrogen-3 is radioactive, Hydrogen-1 is not.
‣ Silicon-27 (27Si) is radioactive, Silicon-28 (28Si) is not.
‣ All the isotopes of Polonium are radioactive (208Po, 209Po, 210Po).
‣ None of the isotopes of copper are radioactive.
‣ Radioisotopes are those isotopes of an element that are radioactive.
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Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Nuclear Reactions
‣ Chemical reactions involve changes in the electronic structure of the atom. ‣ Atoms gain, lose, or share electrons.
‣ No change in the nuclei occurs.
‣ Gold will always be gold in a chemical reaction.
‣ Nuclear reactions involve changes in the structure of the nucleus. ‣ When the number of protons in the nucleus changes.
‣ The atom becomes a different element.
‣ In a nuclear reaction, Lead can become Gold.
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Nuclear Reactions
‣ We describe nuclear processes with nuclear equations. ‣ Atomic numbers and mass numbers are conserved.
‣ The sum of the atomic numbers on both sides must be equal.
‣ The sum of the mass numbers on both sides must be equal.
‣ You cannot create or destroy matter.
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Nuclear Decay
‣ Radioisotopes are not stable. They will degrade, or decay, to form stable isotopes.
‣ There are two primary ways a nucleus changes. ‣ Alpha decay
‣ Loss of an alpha particle.
‣ Beta decay ‣ A neutron breaking into a proton and
electron.
‣ Some nuclear events will also release a proton from the nucleus. This proton (or packet of energy) is called gamma radiation.
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Alpha Decay
‣ Occurs when an unstable nucleus emits a particle composed of two protons and two neutrons
‣ Most ionizing, but least penetrating of the types of radioactivity
‣ Loss of an alpha particle means ‣ the atomic number decreases by 2, and
‣ the mass number decreases by 4.
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Beta Decay
‣ Occurs when an unstable nucleus emits an electron, turning a neutron into a proton.
‣ About 10 times more penetrating than α, but only about half the ionizing ability
‣ When an atom loses a β particle (an electron) its ‣ atomic number increases by 1, and
‣ the mass number remains the same.
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Gamma Emission
‣ Gamma (γ) rays are high energy photons of light.
‣ No loss of particles from the nucleus
‣ No change in the composition of the nucleus ‣ Same atomic number and mass number
‣ Least ionizing, but most penetrating
‣ Generally occurs after the nucleus undergoes some other type of decay and the remaining particles rearrange
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Nuclear Decay
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Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Rate of Radioactive Decay
‣ The rate of change in the amount of radioactivity is constant, and is different for each radioactive “isotope.”
‣ Change in radioactivity measured with Geiger counter
‣ Counts per minute
‣ Each radionuclide had a particular length of time it required to lose half its radioactivity—a constant half-life.
‣ We know that processes with a constant half-life follow first order kinetic rate laws.
‣ The rate of radioactive change was not affected by temperature.
‣ In other words, radioactivity is not a chemical reaction!
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Half-Lives of Various Nuclides
‣ We measure the rate of nuclear decay by half lives.
‣ A half live is how long it takes an isotope to decay to half it’s current mass. ‣ Some half lives are very long (thousands of
years).
‣ Some are very short (fractions of a second).
‣ Rates of nuclear decay are very precise.
‣ They are so precise, so precise we use them as our standard for time.
‣ The decay of Cs isotopes is the definition of a second.
‣ The decay of C isotopes is how we “carbon” date fossils.
‣ The decay of U isotopes is how we determined the age of the earth is between 4.0 and 4.5 billion years old.
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Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Fission and Fusion Reactions
‣ Fission ‣ The large nucleus splits into two smaller nuclei.
‣ Fusion
‣ Small nuclei can be accelerated to smash together to make a larger nucleus.
‣ Both fission and fusion release enormous amounts of energy.
‣ Fusion releases more energy per gram than fission.
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Fission and Fusion Reactions
‣ Fusion ‣ Small nuclei can be accelerated to smash together to make a larger nucleus.
‣ All life on earth is fueled by the nuclear fusion going on in our sun.
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Fission and Fusion Reactions
‣ Fission ‣ The large nucleus splits into two smaller nuclei.
‣ Fission (other than alpha decay) is rare in nature.
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Nuclear Chain Reactions
‣ Fission reactions can create a chain reaction. ‣ Where one fission reaction initiates two more.
‣ Which initiate too more, and so on…
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Radiation
‣ The Discovery of Radioactivity ‣ Phosphorescence
‣ Radioactive history ‣ Antoine Becquerel
‣ Marie Curie
‣ Ernest Rutherford
‣ Properties of Radiation
‣ Classes of Radioactivity ‣ Alpha Radiation
‣ Beta Radiation
‣ Gamma Radiation
‣ Nuclear Reactions ‣ Nuclear Decay
‣ Half Life
‣ Nuclear Fusion
‣ Nuclear Fission
Ch05
Questions?
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1. Chemistry Defined — the science of matter.
2. Measurement — the edge of knowledge.
3. Matter & Energy — differences in substances.
4. Atoms & the Elements — flavors of the atom.
6. Compounds & Molecules — complex particles.
7. Reactivity & Stoichiometry — transmutation & “how much”.
8. Chemistry in the Gas State — chemistry taught man to fly.
9. Solutions — electrolytes & concentration.
10. Acids & Bases — moving raw protons.
5. Radioactivity — radiation & nuclear reactions.
Exam #1
Exam #2
Exam #3
Final Exam
The final is cumulative!
This semester we will discuss…
