Introduction to Nuclidesthe big bang.ppt

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1、Nuclides,1,Introduction to Nuclides the big bang,The big bang theory www.uwaterloo.ca/cchieh/cact/nuctek/universe.html Einstein-Wheeler: “Matter tells space how to curve, and space tells matter how to move.“ 1927 Lemaitre: The universe began with an explosion based on red shift.Hubble observed the r

2、ed shift proportional to distance of stars from us. 1964 Penzias and Wilson discovered the cosmic microwave background (CMB) radiation, as due to remnants of big bang.,Depending on the outcome of the observations, the big bang theories will be abandoned, revised or extended to accommodate additional

3、 observartions.,What is in the universe? How did the universe begin? Where did materials come from? Can material and energy really inter-convert into each other?,Nuclides,2,Nuclides,3,The Big Bang View,All energy (and matter) in the universe concentrates in a region smaller than a marble 12 billions

4、 years ago. It started to expand and cool to a billion K. Elementary particles roamed free in a sea of energy. Further expansion caused a drop in temperature and confined quarks in neutrons and protons. Galaxies began to form.,Galaxy clusters,Nuclides,4,Hubbles Observation,One method for gauging dis

5、tance is to observe the apparent brightness of a galaxy.,The red shift shows that the universe is constantly expanding,Nuclides,5,Cosmologic Matters,Radiation: massless or nearly massless, photons (light) and neutrinos. Baryonic matter (Nuclides): composed primarily of protons, neutrons and electron

6、s; has essentially no pressure of cosmological importance. Dark matter: exotic non-baryonic matter that interacts only weakly with ordinary matter; This form of matter also has no cosmologically significant pressure. Dark energy: a bizarre form of matter, or perhaps a property of the vacuum itself;

7、characterized by a large, negative pressure; a form of matter that can cause the expansion of the universe to accelerate,Nuclides,6,What is the history of the universe?,Nuclides,7,Nuclides composite particles of nucleons,Protons and neutrons are bound together into nuclei. Atoms contain a complement

8、 of electrons. A nuclide is a type of atoms whose nuclei have a specific numbers of protons and neutrons. Nucleons (protons and neutrons) are convenient units to consider nuclear changes, although the standard model considers quarks as basic components. Like particles, nuclides are energy states, wi

9、th amounts properties. Some basic principles are seen for stability of nuclide.,A nuclide AEZ A-mass number Z-atomic number eg. 238U92,Nuclides,8,Stable Nuclides,Stable nuclides remain the same for an indefinite period. Some characteristics of stable nuclides: Atomic number Z 83, but no stable isoto

10、pes for Z = 43 and 61. There are 81 elements with 280 stable nuclides. Usually there are more neutrons than protons in the nuclei. Nuclides with magic number of protons or neutrons are very stable. Pairing of nucleons (spin coupling) contributes to nuclide stability. Is abundance of a nuclide relate

11、d to its stability?,Nuclides,9,Stable Nuclides number of neutrons and protons,Find N / Z for 4He2 = 1 16O8 = 40Ar18 = 91Zn40 = 144Nd60 = 186Re75 = 209Bi83 =,N = # of neutrons,Z = # of protons,Nuclides,10,Stable Nuclides N/Z of some light nuclides,Z 14 Si Si Si 13 Al 12 Mg Mg Mg . 11 Na 10 Ne Ne Ne9

12、F . 8 N,Nuclides,11,Stable Nuclides N/Z of nuclides,40 Zr . . . . . . . . + . . . XXX X X 39 Y X 38 Sr X XXX 37 Rb X X 36 Kr X X XX X 35 Br . . . . . + . . X X 34 Se XXXX X X 33 As X 32 Ge X XXX X . 31 Ga X X 30 Zn . . . + . X XXX X . 29 Cu X X 28 Ni X XXX X . . 27 Co X 26 Fe X XXX . . 25 Mn + X 24

13、Cr X XXX . . 23 v XX 22 Ti XXXXX . . . 21 Sc X 20 Ca X X 2 2 3 4 5 01234567890123456789012345678901,N / A ratio increases as A increases More stable isotopes for even Z than odd Z More stable isotones for even N than odd N More stable isotopes and isotones for magic Z and N,Nuclides,12,Stable Nuclid

14、es natural occurring heavy nuclides,Natural Occurring Isotopes of Heavy Elements (abundance)76 Os 184 (0.018), 186 (1.59), 187 (1.64), 188 (13.3), 189 (16.1), 190 (26.4), 192 (41.0) 77 Ir 191 (38.5), 193 (61.5) 78 Pt 190 (0.0127), 192 (0.78), 194 (32.9), 195 (33.8), 196 (25.2), 198 (7.19) 79 Au 197

15、(100) 80 Hg 196 (0.146), 198 (10.02), 199 (16.84), 200(23.13), 201(13.22), 202(29.8), 204(6.85) 81 Tl 203 (29.5), 205 (70.5) 82 Pb 204 (1.4), 206 (25.1), 207 (21.7), 208 (52.3) 83 Bi 209 (100) 90 Th 232 (100% half life 1.4x1010 y) 92 U 235 (0.720, half life 7.04x108 y), 238 (99.276, half life 4.5x10

16、9 y),Nuclides,13,Stable Nuclides pairing of nucleons,Effect of Paring NucleonsZ N # of stable stable nuclideseven even 166even odd 57odd even 53odd odd *4total 280*They are: 2D1, 6Li3, 10B5, & 14N7,Two protons or neutrons occupy a quantum state, due to their spin. Pairing nucleons stabilises nuclide

17、s, leading to a large number of stable nuclides with even Z and N. No stable isotopes for Z = 43 or 61. No stable isotones with N = 19, 31, 35, 39, 61, 89 More stable isotopes for even Z than odd Z and for even N than odd N Elements with even Z are more abundant than those with odd Z of comparable m

18、ass.,Nuclides,14,Stable Nuclides magic numbers of nucleons,Magic numbers are 2, 8, 20, 28, 50, 82, and 126. Double-magic number nuclides: 4He2, 16O8, 40Ca20, 48Ca20, & 208Pb82. 4He2 as alpha particles, abundant in the universe, 16O8 abundant on Earth. Six stable isotopes of Ca20, 5 stable isotopes o

19、f Ni28, high for their masses. Large number of stable isotopes and isotones with Z & N = 50 and 82. The heavies stable nuclide 209Bi83 has 126 neutrons. O8, Ca20, Ni28, Sn50 and Pb82 have relative high abundance.,Nuclides,15,Stable Nuclides abundances of elements,Even Z elements are more abundant th

20、an odd Z ones of comparable mass.,Nuclides,16,Stable and Radioactive Nuclides mass and stability of nuclides,Mass and energy are equivalent, E = m c2. Relative mass is the key for stability of nuclides. Energy drives changes. If a system can lower its energy, it will. Unstable nuclides undergo decay

21、 or fission, releasing energy stabilises the system. Discuss the stability of carbon isotopes.,Half life 9C 127. ms 10C 19.3 s 11C 20.3 m 12C stable 13C stable 14C 5730. y 15C 2.45 s 16C 0.75 s,Nuclides,17,Stable and Radioactive Nuclides binding energy,The binding energy (BE) of a nuclide is the ene

22、rgy released when the atom is synthesized from the appropriate numbers of hydrogen atoms and neutrons. Z H + N n = AEZ + BE or Z mH + N mn = mE + BE where mH, mn, and mE are masses of H, n, and AEZ respectively. Eg BE = Z mH + N mn - mE BE (3He) = (2*1.007825 + 1.008665 - 3.01603) 931.481 MeV = 7.72

23、 MeV BE (4He) = (2*1.007825 + 2*1.008665 - 4.00260) 931.481 MeV = 28.30 MeV,Nuclides,18,Stable and Radioactive Nuclides average binding energy,The binding energy and average binding energy of some nuclides Nuclide BE BE / A MeV MeV / nucleon 3He2 7.72 2.57 4He2 28.3 7.08 16O8 127.6 7.98 56Fe26 492.3

24、 8.79 54Fe26 471.76 8.74 208Pb82 1636.44 7.87 238U92 1801.7 7.57,BE A,A,Nuclides,19,The Average Binding Energy Curve,Nuclides,20,Stable and Radioactive Nuclides mass excess (ME),The difference between the mass of a nuclide and its mass number, A, is the mass excess (ME), ME = mass - A.,Masses (amu)

25、of some entities H 1.00782503 18O 17.99916 2D 2.014102 54Fe 54.938296 3H 3.016049 56Fe 55.934939 4He 4.002603 206Pb 205.975872 12C 12.000000 209Bi 208.9804 14C 14.003242 235U 235.043924 16O 15.994915 238U 238.055040,What are the MEs for the nuclides listed here? Which is the standard? Which have neg

26、ative MEs?,Nuclides,21,Stable and Radioactive Nuclides mass excess (ME) and average -BE,Comparison of mass excess and average binding energy (amu) Nuclide Mass ME -BE average BEH 1.007825 0.007825 0 0 n 1.008665 0.008665 0 0 3He 3.01603 0.01603 -0.00276 0.00828 4He 4.00260 0.00260 -0.0076 0.0304 12C

27、 12.000000 0 -0.00825 0.09894 16O 15.994915 -0.005085 -0.00857 0.1369 40Ca 39.96259 -0.03741 -0.00917 0.3669 54Fe 53.939612 -0.060388 -0.00938 0.5065 56Fe 55.934939 -0.065061 -0.00944 0.52851 208Pb82 207.976627 -0.023373 -0.00845 1.757 238U92 238.050784 0.050784 -0.00813 1.934,Nuclides,22,Stable and

28、 Radioactive Nuclides fission and fusion energy and ME,Nuclides,23,Stable and Radioactive Nuclides application of mass excess (ME),Like masses, the ME can be used to calculate energy of decay, because the same scale is used for both. eg: MEs of 40Sc21 and 40Ca20 are -20.527 and -34.847 MeV respectiv

29、ely. Estimate the energy of decay for 40Sc21 40Ca20 + b+ or 40Sc21 + e 40Ca20 solution: Edecay = -20.527 - (-34.847) = 14.32 MeV Edecay includes 1.02 MeV for the positron-electron pair for b+ decay.,Nuclides,24,Stable and Radioactive Nuclides ME of isobars,In49 Sn50 Sb51 Te52 I-53 Xe54 Cs55 Ba56 -0.

30、0896 -0.0943 -0.0958 -0.0967 -0.0944 -0.0915 -0.0870 -0.0808,Mass excesses (amu) of isobars with mass number 123:,Z,ME,Nuclides,25,Stable and Radioactive Nuclides BE of isobars,Plots of BE an ME are very similar, and either one can be used to show the decay of isobars. Only 57Fe26 is stable for isob

31、ars of mass 57.Mass .BE .amu .amuCr24 56.9434 0.53031 Mn25 56.9383 0.53462 Fe26 56.9354 0.53667 Co27 56.9363 0.53493 Ni28 56.3980 0.53240,Nuclides,26,Stable and Radioactive Nuclides problem types,Evaluate the BE of a nuclide tell nuclide with zero BE evaluate ME of a nuclide tell nuclide with zero M

32、E evaluate decay energy estimate decay mode predict the stable isobar(s) estimate max kinetic energy of beta or positrons in beta decay,Mass and BE of mass 57 isobars .Mass .BE .amu .amuCr24 56.9434 0.53031 Mn25 56.9383 0.53462 Fe26 56.9354 0.53667 Co27 56.9363 0.53493 Ni28 56.3980 0.53240,Nuclides,

33、27,Stable and Radioactive Nuclides ME of isobars continue,Pairing of nucleons plays a role for stability of isobars with even mass numbers. There are even-even and odd-odd type of nuclides in isobars of even mass numbers,Nuclides,28,Stable and Radioactive Nuclides a semi-empirical equation for BE,BE(A,Z) = 14.1A - 13A2/3 - - + Ea,Proportional to A,Decrease due to surface tension,Instability due to p,Instability due to neutron to proton ratio,Pairing of nucleon,Nuclides,29,Nuclides summary,The big bang Factors for stable nuclides mass and stability,