Nuclear Stability and Decay: Understanding Half-Life and Radioactive Nuclides
Explore the concepts of nuclear stability, decay reactions, and half-life in this physics lesson. Learn how to write nuclear equations, predict types of radiation, and calculate binding energy. Discover the fascinating world of nuclear physics.
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Physics 4 March 14, 2019 Get out #6-13 for Hmk check Do Now: Get cart P3 Challenge What is the half-life of a nuclide if a 30.0 mg reduces to 28.5 mg after 2.00 weeks? (Mass weighed at the same time of day . 9 am Monday routine maintenance routine in a radiation lab.)
Objectives/Agenda/Assignment Agenda: Objective: 7.2 Nuclear Stability Nuclear equations for decay reactions Assignment: Binding energy and nuclear stability p294 #16, 17, 23 and Handout 7.2 Nuclear Stability Time to work with Table of Nuclides
Writing Nuclear equations for decays An alpha decay loses a helium nucleus ? daughter nucleus which can be determined by conservation of nucleon number A and charge Z. ?H He e . The other product is called a Ex: 238? 2 238? 2 4He + Z 4He + 90 A??238 = 4 + A A = 234 92 = 2 +Z Z = 90 = Thorium Th 92 92 234?? An beta decay loses an electron 1 more proton and one less neutron. Nucleon number does not change. There is also an anti-neutrino 0 Ex: 27 60?? 1 0e ..from the nucleus . Net result is there is one 0 emitted at the same time. 60?? 1 0e + Z 0e + 28 A?? + 0 60?? + 0 0 A = 60 Z -1 = 27 Z = 28 = Nickel Ni 0 27
Predicting type of radiation Based on its mass number you can predict what kind of radioactive decay a nuclide will experience. If Z > 83, alpha decay. If A > atomic mass, then it is neutron rich and will have beta decay If A < atomic mass then it is neutron poor and will have positron decay or electron capture If A is very near the atomic mass, it is likely stable. Can predict stable if both the number of neutrons (N) and the number of protons (Z) is even. 157/264 stable nuclides fit this description. Only 4/264 are odd, odd.
Mass Defect and Binding Energy The mass of a nucleus is always less than the combined masses of its nucleons. The lost mass, or mass defect, is released as energy. = Zmp + (A-Z)mn Mnucleus Mnucleus = Atomic Mass Zme Amount of energy produced from the mass defect is E = mc2. This energy is the nuclear binding energy: the energy required to break a nuclei into individual nucleons. Binding energy is usually expressed using mega eV (MeV) per nucleon. 1.66 x 10-27 kg = 1 amu = 931.5 x 106 eV = 931.5 MeV = 1.49 x 10-10 J
Calculating binding energy Iron-56 is an extremely stable nuclide. Compute the binding energy per nucleon in MeV for 56Fe. (mass of proton = 1.007276 amu; mass of neutron = 1.008665 amu; mass of electron = 0.000549 amu)
Binding Energy and nuclear stability Graph of Binding Energy per Nucleon (divide binding energy by mass number) Ni-62 is most stable The energy released in a decay comes from the energy required to bind a nucleus together.
Exit slip and homework Exit Slip Nitrogen-14 has a mass of 14.003074 u. What is the binding energy of a Nitrogen-14 nucleus in J? (Atomic number= 7) What s due? (homework for a homework check next class) p294 #16,17, 23 and Binding Energy Worksheet #1-5 What s next? (What to read to prepare for the next class) Read 7.2 p
