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Nuclear transformations

Nuclear transformations. Nuclear transformations. Nuclear transformations : reactions that occur in the nucleus of an atom. Nuclear transformation change the number of protons and neutrons , that is the nature of the element . Some are exothermic (release a huge amount of energy).

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Nuclear transformations

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  1. Nuclear transformations

  2. Nuclear transformations Nuclear transformations: reactions that occur in the nucleus of an atom. Nuclear transformation change the number of protons and neutrons, that is the nature of the element. Some are exothermic (release a huge amount of energy). Nuclear transformations are used for the generation of electricity.

  3. Nuclear transformations Nuclear stability: state of the nucleus in which the nuclear force is bigger than the electrical repulsion force between protons. • Number of neutrons directly related to stability of the nucleus. (see Fig. 4.25 on page 125) • Nuclear force decreases as the size of the nucleus increases.

  4. Nuclear transformations Radioactivity: • Naturally occurring nuclear transformation. • An unstable atom spontaneously transforms into a more stable or several more stable atoms. • It transforms while releasing energy in the form of radiation.

  5. Nuclear transformations Radioactivity(ionizing radiation) • Alpha (α) particles • Beta (β) particles • Gamma (γ) rays (See fig 4.26 on page 127 for more details)

  6. Nuclear transformations Radioactivity(ionizing radiation) Alpha (α) particles • Positive particles (deflected towards negative pole of electrical field) • Made of two protons and two neutrons • Relatively large and heavy • Can be stopped with a sheet of paper

  7. Nuclear transformations Radioactivity(ionizing radiation) Beta (β) particles • Negative particles (deflected towards positive pole of electrical field) • Made of an electron (or a positron if a positive beta particle) • Lighter than alpha particles • More penetrating power than alpha particles • Can be stopped with a sheet of foil 3 mm minimum

  8. Nuclear transformations Radioactivity(ionizing radiation) Gamma (γ) rays • Neutral (no deflected by an electrical field) • Made of only energy • Greatest penetrating power of the three radiations • Can be stopped with a very dense material (lead or high density concrete)

  9. Nuclear transformations Advantages of Radioactivity (ionizing radiation) • Improve quality of materials. • Increase shelf life of fresh products (food). • In medicine to treat cancer, or to obtain images of organs. Disadvantages of Radioactivity (ionizing radiation) • Can be harmful to living organisms. • Alters DNA cells leading to cancer development.

  10. Nuclear transformations Radioactivity • Random and spontaneous process. • Impossible to predict which atoms will decay. • Impossible to predict when they will decay. What is possible to predict is the half life of a sample of atoms. Half-life: time required for half of the nuclei in a sample of radioactive material to decay. (See Fig. 4.28 on page 128 for half-life of C14) (See Fig. 4.29 on page 129 for half-life values)

  11. Nuclear transformations How does half-life works? _Take carbon-14 in figure 4.28. _Half-life is 5770 years Meaning, if you have two grams of carbon-14: • After 5770 years you would still have one gram. • After 5770 more years (11540 years) you would still have half a gram. • After 5770 more years (17310 years) you would have a quarter of a gram. • After 5770 more years (23080 years) you would still have an eighth of a gram. • After 5770 more years (28850 years) you would still have a sixteenth of a gram. • And so on…until is completely gone. The longer the half-life of an element or isotope, the longer it takes to completely eliminate it from the environment!

  12. Nuclear transformations Nuclear fission (humans): nuclear reaction where the nucleus of an atom is split to form two or more lighter atomic nuclei. (See Fig. 4.30 on page 130 for U-235 nuclear fission)

  13. Nuclear transformations Nuclear fission: • 3 neutrons produced that can react with as many U-235 nuclei to continue the chain reaction (atomic bomb). • Slowing the neutrons produced, is the way to control these reactions. • Then nuclear fission can be used to generate electricity. • Some of the waste of nuclear reactors is used in medicine, the rest is buried!

  14. Nuclear transformations Nuclear fusion (stars): nuclear reaction in which two small atomic nuclei join together to form one heavier nucleus. (See Fig. 4.31 on page 131 for U-235 nuclear fission)

  15. Nuclear transformations Nuclear fusion: • This type of reaction can only be started and maintained at temperatures of million degrees Celsius. • Few applications (H bomb is one of the few, in it nuclear fission is used to start nuclear fusion). • More energy efficient than nuclear fission. • Produces less radioactive waste.

  16. Assessment: Questions 24 – 28 on page 134 Textbook

  17. Homework: Questions 1 – 4 on page 70 Workbook

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