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3-4: Changes in the Nucleus

3-4: Changes in the Nucleus. Nuclear reaction:. A reaction in which the composition of an atom’s nucleus is changed. What makes an atom’s nucleus stable?. Strong nuclear force An attractive force that overcomes the electric repulsion between protons, due to the presence of the neutrons

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3-4: Changes in the Nucleus

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  1. 3-4: Changes in the Nucleus

  2. Nuclear reaction: • A reaction in which the composition of an atom’s nucleus is changed

  3. What makes an atom’s nucleus stable? • Strong nuclear force • An attractive force that overcomes the electric repulsion between protons, due to the presence of the neutrons • The neutrons help “glue” the nucleus together

  4. How many neutrons do you need to make a nucleus stable? • Elements 1-20: need approximately equal numbers of protons and neutrons • Elements 21-83: need increasingly more neutrons to hold the protons together • Elements 84 and up: no stable combination, all are radioactive

  5. How many neutrons do you need to make a nucleus stable? • Too many neutrons can make an atom unstable (emits beta radiation) • Isotopes that are much heavier or much lighter than the most common isotope are usually radioactive

  6. Types of Radioactive Decay

  7. Alpha decay • From the alpha particle (made of 2 protons and 2 neutrons) • Charge of +2 • Travels only a few centimeters • Stopped by paper or clothing • Not a particular hazard unless it enters the body

  8. Beta decay • From the beta particle (a stream of high speed electrons) • A neutron changes into a proton and an electron • The proton stays in the nucleus, the electron is emitted • Charge is -1 • Can penetrate solid object a few mm • Can pass through clothing and damage skin • Stopped by heavy clothing

  9. Gamma decay • From gamma particle (similar to X-rays, does not consist of particles) • Charge of zero • Accompanies gamma and beta radiation • Penetrates deeply into solid material and human tissue • Must be shielded by lead or concrete

  10. Radioactive decay: • When an atom emits alpha, beta, or gamma radiation

  11. Nuclear decay problems • Write the nuclear equation for the alpha decay of radium-226

  12. Nuclear decay problems • Write the nuclear equation for the beta decay of iodine-131

  13. Nuclear decay problems • Write the nuclear equation for the alpha decay of uranium-238

  14. Nuclear decay problems • Write the nuclear equation for the beta decay of sodium-24

  15. Nuclear decay problems • Write the nuclear equation for the alpha decay of gold-185

  16. Other nuclear reactions • Nuclear fusion • The combining of two atoms in one • Uses: occurs in the sun, hydrogen bombs • Nuclear fission • The splitting of one atom into two or more • Uses: atomic bombs, nuclear power plants

  17. Mass and energy • Remember E=mc2? • In any nuclear reaction, a small amount of matter is turned into a large amount of energy. • Example: • E=mc2? • E=1 g (3.0x108m/s)2 • E=9.0x1016units

  18. Four fundamental forces • Strong nuclear force: attractive force that the neutrons provide • Weak nuclear force: occurs in radioactive decay • Gravity: attractive force that exists between all objects, based on mass and distance • Electromagnetic: holds atoms and molecules together

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