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GNEP

GNEP. Alan J Hays Genoa Central High School Arkansas. Before you can intellectually discuss nuclear energy, one must understand nuclear physics. Challenges to discussing Nuclear Physics. Homer Simpson The “stigma” of “physics” too difficult, therefore is to be avoided at all costs

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GNEP

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  1. GNEP Alan J Hays Genoa Central High School Arkansas

  2. Before you can intellectually discuss nuclear energy, one must understand nuclear physics.

  3. Challenges to discussing Nuclear Physics • Homer Simpson • The “stigma” of “physics” too difficult, therefore is to be avoided at all costs • Society issues too difficult, therefore is to be avoided at all costs • Religious issues young earthers and other controversies, therefore is to be avoided at all costs • Mathematics is language of physics, therefore is too difficult, therefore is to be avoided at all costs

  4. Misconceptions • All radioactive elements are extremely dangerous to living things. • There is no way to protect oneself from radioactivity. • There are very few naturally occurring radioactive elements. • Radioactive elements only occur in nuclear power plants and nuclear weapons.

  5. It’s all Earth Science to me! Most all of the earth’s rock material contains uranium. Ratio of U-238 to U-235  0.7% U-238 →Pb T1/2 4.5 bil yrs. U-235 T1/2  700 million yrs. @t = 0 yrs [U-238] = [U-235] Ratio of T1/2U-238 to T1/2U-235  7  Age of earth  8 U-235 half-lifes  5.6 bil yrs

  6. Lab Sequence • What’s hot and what’s not • Background radiation • Radiation and Distance • Shielding and absorption • Half-Life

  7. What’s Hot and What’s Not • A discovery lab • Students are given a brief on GM tube use • Given a bag of miscellaneous materials. • Observations

  8. Background Radiation • Count the “ticks” for a specified time • From a class get 20 – 30 recordings • Sample data: counts per 30 seconds. Background radiation: 40 cps

  9. Radiation and Distance • Familiar “inverse square law” • Sample data: Background Radiation = 58cpm

  10. Radiation and Distance • Graphing y = 144651x-2.0132 The exponent of x -2; data function very closely follows the inverse square law

  11. Shielding • Beta source • Data:

  12. Absorption • Beta source and aluminum shielding • Sample data y = 16545e-47.1x

  13. Absorption • Gamma source and lead shielding • Sample Data y = -4967x + 3744

  14. Half-Life • Ba-137m Isogenerator Cs-137 Parent nuclide; half-life(t1/2)  30yrs This decays to a metastable form(excited state) of barium(Ba-137m). Ba-137m decays to Ba-137(ground state) by gamma emission. t1/2 2.5min. • Freshness of samples is critical to good data

  15. Half-Life • Sample data: Time vs Counts y = -6.39ln(x) + 15.2

  16. Half-life • Mathematical modeling: N = # of nuclei present at time t. N0 = # of nuclei present at t = 0.  = decay constant (it’s constant!) Linear!

  17. Half-life • Linear graph • Slope =  • = - 0.2852 Ln(N) vs time y = -0.2852x + 2.9821

  18. Physics Mantras • Don’t memorize; understand • To know physics is to do physics • A single good observation is worth a century of bad philosophy • Process is more important than results • You only arrive at the right answer after making all possible mistakes. • A theory is accepted only when the last of its opponents dies off. • Pollyannas who believe anything is possible should be subjected to a course in thermodynamics.

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