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Atomic Nucleus and Radioactivity

Atomic Nucleus and Radioactivity. Chapter 39 (1 st half). 39.1 Atomic Nucleus. It would take 30,000 carbon nuclei to stretch across a single carbon atom. The nucleus is so VERY VERY tiny compared to the rest of the atom. It’s like a cookie crumb on the 50 yard line of a NFL football stadium.

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Atomic Nucleus and Radioactivity

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  1. Atomic Nucleus and Radioactivity Chapter 39 (1st half)

  2. 39.1 Atomic Nucleus • It would take 30,000 carbon nuclei to stretch across a single carbon atom. • The nucleus is so VERY VERY tiny compared to the rest of the atom. • It’s like a cookie crumb on the 50 yard line of a NFL football stadium.

  3. 39.1 Atomic Nucleus cont. • The nucleus contains nucleons, which when positive are protons, and when neutral, neutrons. • Neutrons and protons have roughly the same mass. • Electrons are so very very light compared to nucleons, so the mass of an atom is really only based on the nucleus.

  4. 39.1 Atomic Nucleus cont. • The number of protons equal the number of electrons in an atom (unless it is an ion). • The protons keep the electrons moving around the nucleus (positive charge attracts negative charge). • The neutrons do not have to equal the protons or electrons, and as such, they act a little like a nuclear cement holding the nucleus together. • The force holding protons and neutrons together is called the strong force.

  5. 39.1 Atomic Nucleus cont. • The strong force is only strong enough to hold things together at very small distances. • When the number of protons increases in a nucleus, then the number of neutrons needed to hold the nucleus together must get larger too. • At small atomic numbers, the number of neutrons may be equal or slightly more than the number of protons, but at higher atomic numbers, the number of neutrons must be A LOT more than the protons.

  6. 39.2 Radioactive Decay • The neutron is unstable. • A lone neutron will spontaneously decay into a proton plus an electron (and also an antineutrino, a tiny particle that will not be discussed). • Out of a bunch of lone neutrons, about half of them will decay in 11 minutes. • Particles that decay like this are said to be radioactive.

  7. 39.2 Radioactive Decay cont. • Particles only decay when their combined products weigh less than what they started out as. • The mass of a neutron is greater than a decayed neutron (a proton, electron and antineutrino), so there is less mass after decay.

  8. 39.2 Radioactive Decay cont. • All the elements heavier than Bismuth (atomic number 83) decay in one way or another. • There are three types of radioactive decay: Alpha, Beta, and Gamma.

  9. 39.2 and 39.3 Radioactive Decay cont. • Alpha rays are streams of particles that are made of two protons and two neutrons, and are identical to the nuclei of a helium atom. • These particles are called alpha particles. • They can be stopped by a few sheets of thin paper or a sheet of heavy paper. • They quickly grab some random loose electrons in the air and become harmless Helium atoms.

  10. 39.2 and 39.3 Radioactive Decay cont. • A beta ray is a stream of electrons. • An electron is ejected from the nucleus when a neutron is transformed into a proton. • Beta particles go through paper, but are stopped by several sheets of aluminum foil. • They lose energy by collisions with other atomic electrons.

  11. 39.2 and 39.3 Radioactive Decay cont. • Gamma rays are mass-less energy. They are like photons of light, but of much higher frequency and energy. • Visible light is given off when electrons jump from one orbit to another of lower energy, and gamma rays are emitted when nucleons do a similar sort of thing inside the nucleus. • Gamma rays require lead or other heavy shielding to stop them.

  12. 39.4 Radioactive Isotopes • An isotope is an atom that has the same number of protons as another atom of the same element, but it has a different amount of neutrons. • Example: Carbon-14 is an isotope of regular carbon, Carbon-12. • All elements have isotopes. • Some isotopes are radioactive. ALL isotopes of elements above atomic number 83 are radioactive.

  13. Assignment: • Questions 1, 3, 5, 6, 7, 9, 27, 29, 30…….. on page 627. • Google search: What type of radiation is used to treat cancer? Gamma, Beta, Alpha or other? Do they pick certain kinds of radiation based on the type of cancer they are treating? Explain what you find out and list the website you used.

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