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Unit 1.3 Nuclear Chemistry. 1.3-1 Types of Radioactivity. Learning Objectives. By the end of this section you will be able to: Observe nuclear changes and explain how they change an element. Express alpha and beta decay in nuclear equations. Model the half life of an isotope.

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Unit 1.3 Nuclear Chemistry

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Unit 1.3Nuclear Chemistry

1.3-1 Types of Radioactivity


Learning Objectives

  • By the end of this section you will be able to:

    • Observe nuclear changes and explain how they change an element.

    • Express alpha and beta decay in nuclear equations.

    • Model the half life of an isotope.

    • Explain how half life is used to date materials.


Important Terms

  • Radioactivity

  • Alpha Particle

  • Beta Particle

  • Alpha Decay

  • Beta Decay

  • Gamma Decay

  • Half life

  • Radioactive Dating

  • Radioactive Decay


Discovery of Radioactivity

  • Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus.


Nuclear Reactions

  • Nuclear reactions involve the protons and neutrons found in the nucleus

  • During nuclear reactions a nucleus can gain or lose protons and neutrons.


Nuclear Reactions

  • Remember that the number of protons determines the identity of an element.

    • Changing the number of protons changed the element into another element.

    • During nuclear reactions atoms of one element are changed into atoms of another element


Nuclear Notation

  • Different isotopes of atoms can be represented using nuclear notation.


Review of Nuclear Notation

  • In your notebook write the following isotopes in nuclear notation.

    • Hydrogen-1

    • Hydrogen-2

    • Hydrogen-3


Radiation causes Radioactive Decay

  • Radioactive decay is the release of radiation by radioactive isotopes.

  • Not all radioactive isotopes decay in the same way.

    • Different types of decay change the nucleus in different ways.

      • The three types of decay are:

        • Alpha

        • Beta

        • Gamma decay


Radioactive ALPHA Decay

  • Alpha decay is the release of alpha particles (2 protons and 2 neutrons).

    • Alpha particles are helium nuclei consisting of two protons and two neutrons.

    • Alpha particles are represented as or α.


Radioactive ALPHA Decay

  • Alpha particles, which are large in size, collide with objects around them.

    • Do not penetrate very deeply

    • Are easily stopped by a thin layer of material.


Radioactive ALPHA Decay

  • Alpha decay causes the decaying nucleus to lose 2 protons and 2 neutrons.

  • This means:

    • the mass # decreases by 4 (2P and 2N)

    • The atomic # decreases by 2

    • Examples

  • ParentDaughter alpha particle


Equation for Radioactive ALPHA Decay

  • The parent element turns into a daughter element with a mass number 4 less and an atomic number 2 less than the parent!

  • Does this reaction demonstrate the law of conservation of matter?

    • How can we check it? Explain


ALPHA Emission

Two protons and neutrons are lost

The protons and neutrons leave as an alpha particle.

+ Energy!


Radioactive Alpha Decay

  • Write the equation for alpha decay for the following particle in your notebook.

    • Thorium-230


Radioactive BETA Decay

  • Beta decay is the release of beta particles from a decaying nucleus.

  • A beta particle is a high energy electron with a 1- charge.

    • Beta particles are written as β- or

    • Beta particles pass more easily through matter than alpha particles and require sheets of metal, blocks of wood or specialized clothing to be stopped.


Radioactive BETA Decay

  • The electron released during beta decay is not one of the original electronsthat existed outside the nucleus.

  • The beta particle (electron) is produced by the change of a neutron into a proton and an electron.

    Mass# is same!

    • Parent Daughter Beta

      (add P+) (sub e-)


Equation for Radioactive BETA Decay

  • The parent nucleus turns into a daughter with an atomic number 1 greater.

  • The mass number stays the same.


BETA Emission

  • A neutron becomes a proton (which stays in the nucleus) and electron (which is ejected from the atom).

  • ADD A PROTON and LOSE an ELECTRON

+ ENERGY


Radioactive BETA Decay

  • Write the equations for beta decay for the following particles.

    • Magnesuim-27

    • Sulfur-35


Radioactive Gamma Decay

  • Gamma decay is the release of gamma rays from a nucleus.

    • A gamma ray is a high energy form of electromagnetic radiation with out a change in mass or charge.


Radioactive GAMMA Decay

  • Gamma rays have high penetrating ability and are very dangerous to living cells.

  • To stop gamma rays thick blocks of lead or concrete are needed.


Radioactive GAMMA Decay

  • During gamma decayonly energy is released!

    • Gamma decay does not generally occur alone, it occurs with other modes of decay. (alpha or beta)


Equation for Radioactive GAMMA Decay with Beta or Alpha Decay

  • When gamma decay is expressed in an equation it is expressed as γ.

    • Electron from beta decay is captured to cause gamma particle to emit.

    • The following equation shows both gamma and alpha decay occurring.


GAMMA Emission with Beta decay

Beta emission

Co-60  Ni-60 + Beta e-  Ni-60 + gamma photon (particle of radiation)

(excited state)


Quiz!!

PLEASE DO NOT WRITE THE QUESTIONS!

Each correctly answered question is worth 1 point!

  • What are the three types of decay?

  • Explain what occurs to the element in each type of decay, be specific.

    • A.

      B.

      C.

  • Which type of decay is least harmful to living cells.

  • Which is most harmful?

  • If Uranium-238 alpha decays, what would the decay equation be?


Answers to quiz questions

  • Alpha, beta and gamma

  • Alpha- gives off alpha particle which is 2 protons and 2 neutrons. It reduces the atomic number by 2 and the mass by 4 so becomes a new element

    Beta- a neutron becomes a proton and an electron and gives off the electron, it adds 1 to the atomic number but leaves the mass number the same so a new element is formed

    Gamma- just a gamma ray, pure electromagnetic radiation (energy)

    3. Alpha

    4.Gamma

    5 238 U -> 234 Th + 4 He

    92 90 2


Nuclear Equations: What type of decay is Represented? Fill in the blanks


Nuclear Equations: try these!


Radioactive Decay

  • Radiation can be detected with Geiger counters and scintillation counters.

    • Geiger counters detect ionizing radiation.

    • Scintillation counters register the intensity of radiation by detecting light.


Rate of Radioactive Decay

  • It is impossible to predict when a specific nucleus in a sample of radioactive material will undergo decay.

  • The rate of overall decay is constant so that it is possible to predict when a given fraction of a sample will have decayed.


Half-Life

  • Half-life is a term used to describe the time it takes for half of a given amount of a radioactive isotope to decay.

    • Half-life varies greatly depending on the isotope


Half-life: How long is it?


Half-Life and Radioisotope Dating

  • Radioactive decay has provided scientists with a technique for determining the age of fossils, geological formations and human artifacts.

    • Four isotopes are commonly used for dating objects

      • Carbon-14

      • Uranium-238

      • Rubidium-87

      • Potassium-40


Half-Life and Radioisotope Dating;C-14

  • Carbon-14 Dating

    • All organisms take in carbon during their lifetime.

    • When organisms die they stop taking in carbon.

      • Most carbon that organisms take in is stable (Carbon-12 or Carbon-13).

      • About one atom in a million is Carbon-14.

        • While the organism is alive the amount of Carbon-14 in its tissues remains constant.

        • After the organism dies no more Carbon-14 is taken in and the amount begins to decline at a predictable pace. (half-life of C-14=5730 years)


Half-Life of Carbon-14


Half-Life and Radioisotope Dating

  • The half-life of Carbon-14 is 5730 years.

    • Objects greater than 60,000 years old cannot be dated using this method because the amount of Carbon-14 that remains is too small to be detected.

      • Objects greater than 60,000 years old are dated using:

        • Uranium-238 (t½ = 4.5 billion years)

        • Rubidium-87 (t½ = 48 billion years)

        • Potassium-40 (t½ = 1.25 billion years)


Radioactive Decay Series: U-238


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