Download Nuclear Physics: Nuclear Binding Energy and Radioactivity and more Study notes Physics in PDF only on Docsity! Physics 102: Lecture 27, Slide 1 Nuclear Binding, Radioactivity • Today’s Lecture will cover 29.1-4 Physics 102: Lecture 27 •Make sure your grade book entries are correct •Honors projects are due! Physics 102: Lecture 27, Slide 2 Hydrogen atom: Binding energy =13.6eV Binding energy of deuteron = or 2.2Mev! That’s around 200,000 times bigger! 2.2 ×106 eV Simplest Nucleus: Deuteron=neutron+proton neutron proton Very strong force Coulomb force electron proton Strong Nuclear Force (of electron to nucleus) Physics 102: Lecture 27, Slide 5 Binding Energy Einstein’s famous equation E = m c2 Proton: mc2 = 938.3MeV Neutron: mc2= 939.5MeV Deuteron: mc2 =1875.6MeV Adding these, get 1877.8MeV Difference is Binding energy, 2.2MeV Physics 102: Lecture 27, Slide 6 Iron (Fe) is most binding energy/nucleon. Lighter have too few nucleons, heavier have too many. B IN D IN G E N E R G Y in M e V /n u c le o n 92 238U 10 Binding Energy Plot Fusion = Combining small atoms into large Fission = Breaking large atoms into small Physics 102: Lecture 27, Slide 7 Which element has the highest binding energy/nucleon? Preflight 27.3 • Neon (Z=10) • Iron (Z=26) • Iodine (Z=53) Physics 102: Lecture 27, Slide 10 92 238U→ 90 234 Th + αα: example 2 4He = αrecall β: example Decay Rules 1) Nucleon Number is conserved. 2) Atomic Number (charge) is conserved. 3) Energy and momentum are conserved. γ: example γ00 * +→ PP AZ A Z 1) 238 = 234 + 4 Nucleon number conserved 2) 92 = 90 + 2 Charge conserved − −+→ e 0 1 1 1 1 0 pn Needed to conserve energy and momentum. ν00+ Physics 102: Lecture 27, Slide 11 A nucleus undergoes α decay. Which of the following is FALSE? 1. Nucleon number decreases by 4 2. Neutron number decreases by 2 3. Charge on nucleus increases by 2 Preflight 27.6 Physics 102: Lecture 27, Slide 12 β−The nucleus undergoes decay. 90 234 Th Which of the following is true? 1. The number of protons in the daughter nucleus increases by one. 2. The number of neutrons in the daughter nucleus increases by one. Preflight 27.7 Physics 102: Lecture 27, Slide 15 ACT: Radioactivity ∆N ∆t = −λN No. of nuclei present decay constant Decays per second, or “activity” Start with 16 14C atoms. After 6000 years, there are only 8 left. How many will be left after another 6000 years? 1) 0 2) 4 3) 8 Physics 102: Lecture 27, Slide 16 time N(t ) =N0e −λt =N0 ⋅2 − t T1/2 Decay Function Physics 102: Lecture 27, Slide 17 Preflight 27.9 The half-life for beta-decay of 14C is ~6,000 years. You test a fossil and find that only 25% of its 14C is un-decayed. How old is the fossil? 3,000 years 6,000 years 12,000 years Physics 102: Lecture 27, Slide 20 Carbon Dating We just determined that living organisms should have a decay rate of about 0.23 decays/ gram of carbon. The bones of an ice man are found to have a decay rate of 0.115 decays/gram. We can estimate he died about 6000 years ago. Physics 102: Lecture 27, Slide 21 ACT: Binding Energy Which system “weighs” more? 1) Two balls attached by a relaxed spring. 2) Two balls attached by a stretched spring. 3) They have the same weight. Physics 102: Lecture 27, Slide 22 Strong Nuclear Force • Acts on Protons and Neutrons • Strong enough to overcome Coulomb repulsion • Acts over very short distances Two atoms don’t feel force
