1 Elements and Isotopes A = Mass / nucleon number A = number of protons + neutrons A = Z + N Z = Atomic / Proton number, nuclear charge Element = set of atoms, same Z Nuclide = set of atoms, same A and Z Isotopes = set of nuclides of an element Isobars = nuclides, same A, different Z (14C-14N; 3H-3He) Isotons = nuclides, same number of neutrons, N = A – Z Isomers = same nuclides, different content of energy Frederick Soddy (1877-1956) NP in Chem. 1921 2 Isotopes Isotopes set of nuclides of an element 2600 nuclides (stable and radioactive) 340 nuclides found in Nature 270 stable and 70 radioactive, other artificial Monoisotopic elements: 9Be, 19F, 23Na, 27Al, 31P, 59Co, 127I, 197Au Polyisotopické elements : 1H, 2H (D), 3H (T) 10B, 11B Sn has the highest number of stable isotopes – 10 112, 114, 115, 116, 117, 118, 119, 120, 122, 124Sn 3 Stability of Nuclei Stability with respect to radioactive decay is given by the number of protons and neutrons - Zone of stability Light nuclides are stable for Z ~ N Only 1H and 3He have more p than n. 2H, 4He, 6Li, 10B, 12C, 14N, 16O, 20Ne, 24Mg, 28Si, 32S, 36Ar and 40Ca Have the same number of p and n All other nuclides have more n than p N > Z Mattauch Rule: Of two isobars that differ by 1 in Z, one is radioactive. 40Ar 40Ca ΔZ = 2 40Ar 40K 40Ca ΔZ = 1 40K is radioactive. 4 Stability of Nuclei Numberofneutrons,N Number of protons, Z 5 Stability of Nuclei In some elements, radioactive isotopes exist in Nature with a long half life 40K, 0.012%, 1.3 1010 years Elements with Z ≤ 83 (Bi) have at least 1 stable isotope Z = 43 (Tc), 61 (Pm) do not exist in Nature Artificial radioactive isotopes prepared by nuclear reactions Nuclides with Z ≥ 84 (Po) are all unstable with respect to radioactive decay = radioactive elements 6 Magic Numbers Aston’s Rule: Elements with even Z have more isotopes, elements with odd Z have no more than 2 isotopes, one of then unstable, elements with odd number of nucleons (A) have only one stable isotope (19F, 23Na, 27Al, 31P). Only 2H, 6Li, 10B,14N, 40K, 50V, 138La, 176Lu have odd number of both p and n. 4oddodd 50evenodd 57oddeven 168eveneven Number of stable isotopes NZ 7 Magic Numbers Magic Numbers = 2, 8, 20, 28, 50, 82 and 126 Elements with Z = magic number have a large number of stable isotopes; when an isotope is radioactive, it has a long half life Sn Z = 50, 10 stable isotopes Nuclides 4He, 16O, 40Ca, 48Ca and 208Pb have magic number of both p and n = very stable nuclides 8 Island of Stability Number of protons, Z Number of neutrons, N Pb208 82 9 Mass of Electron and Nucleons 1.0086651.675 10−27n 1.0072761.673 10−27p 0.00054869.11 10−31e m / um / kgSymbol 1 amu = 1.6606 10−27 kg 10 Mass Defect Nucleus mass is always smaller than the sum of masses of nucleons Mj < Z mp + (A−Z) mn Mass loss Δm < 0 [Δm in amu units] Binding energy of nucleus Eb = − Δm c2 Eb = − 931.5 Δm [MeV] NP in Physics 1921 11 Binding Energies of Nuclei, Eb Nuclide Eb, MeV 2H 2.226 4He 28.296 14N 104.659 16O 127.619 40Ca 342.052 58Fe 509.945 206Pb 1622.340 238U 1822.693 12 Binding Energy per One Nucleon, Eb(n) Nuclide Eb(n), MeV Ev, MeV 2H 1.113 2.226 4He 7.074 28.296 14N 7.476 104.659 16O 7.976 127.619 19F 7.779 147.801 40Ca 8.551 342.052 55Mn 8.765 482.070 58Fe 8.792 509.945 62Ni 8.795 545.259 206Pb 7.875 1622.340 238U 7.658 1822.693 Eb(n) = Eb / A Energy for removing of one nucleon 13 Binding Energy per Nucleon, Eb(n) 4He 12C 16O 14 Binding Energy per Nucleon Even A and even Z 15 Elements in the Universe 16 Binding Energies of Nucleus and Chemical Bond Binding Energy per Nucleon for 58Fe 8.792 MeV Bond Energy for C-H 411 kJ mol−1 = 4.25 eV Nuclear binding energies are 106 times bigger than chemical bond energies. 1 eV (molecule)−1 = 96.485 kJ mol−1 17 Discovery of Radioactivity Antoine Henri Becquerel (1852-1908) Uranium, Thorium NP in Physics 1903 M. C. NP in Chemistry 1911 Radium, Polonium Marie Curie (1867-1934) Pierre Curie (1859-1906) Discovery of radioactivity 1896 NP in Physics 1903 18 Radioactivity Radioactivity = transformation of some nuclei to other nuclei with emission of small particles and energy (exo) Radioactivity = spontaneous process, products have a lower energy content and are more stable than the original nuclei If a nucleus possesses too little/much of neutrons → Geiger counter 19 Geiger Counter Hans Geiger (1882-1945) particle Ionization = current 20 Measurement of Radioactivity Radioactivity 1 Bq (becquerel) = 1 decay per 1 s (40K in human body 4 kBq) 1 Ci (curie) = 3.7 1010 Bq Radiaton Dose 1 Gy (gray) = absorption of 1 J in 1 kg of tissue 1 Gy = 100 rad Effective Dose 1 Sv (sievert) = 1 Gy × Q factor 1 Sv = 100 rem 3 Sv = LD 50/30 dose from cosmic radiation and natural background radiation in ČR = 2 mSv/year 21 Nuclear Reactions Rutherford – deflection of radioactive rays in electric and magnetic fields Alpha = positive charge Beta = negative charge Gama = neutral Formation of a new nuclide Shift rules – changes in Z and N Radioactive substance 22 Alpha Radiation Heavy nuclei Alpha particle speed = 10% c Low penetration, several cm in air, stopped by a sheet of paper Very harmful to cells in case of inhalation HePoRn 4 2 218 84 222 86 +→ 23 Alpha Radiation A shift of two elements to the left in periodic table A Z N1 A − 4 Z − 2 N2 24 Alpha Radiation Radium-226 Curium-240 Uranium-232 Gold-185 Thorium-230 Americium-241 (smoke detectors) Polonium-210 A Z N1 A − 4 Z − 2 N2 25 Beta Radiation Nuclei with excess of neutrons, lack of protons Beta particles are electrons (but not from e cloud !!!) Decay of neutrons e speed = 90% c Penetration of several m in air Stopped by 1cm of Al foil eNC 0 1 14 7 14 6 −+→ epn 0 1 1 1 1 0 −+→ 26 Beta Radiation A Z N1 A Z +1 N2 A shift of one element to the right in periodic table 27 Beta RadiationKrypton-87 Zinc-71 Silicon-32 Cobalt-60 Magnesium-27 Sodium-24 Iron-59 Phosphor-32 A Z N1 A Z +1 N2 28 Gamma Radiation Nuclei with excess of energy Electromagnetic radiations with very short wavelength High energy, MeV Speed of light Deep penetration, 500 m in air m99Tc → 99Tc + γ 29 Tracers Gyorgy Hevesy 1913 NP 1943 m99Tc → 99Tc + γ 30 Positron Emission Nuclei with excess of protons, lack of neutrons Positron (antiparticle) recombines in 10 −10 s Very small penetration Anihilation 1e + −1e → γ A Z − 1 N2N1 A Z eBC 0 1 11 5 11 6 ++→enp 0 1 1 0 1 1 +→ A shift of one element to the left in periodic table 31 Positron Emission Rubidium-81 Germanium-66 Praseodymium-140 Neon-18 Oxygen-15 Nitrogen-13 Copper-59 A Z N1 A Z − 1 N2 32 Electron Capture An electron from atom’s electron cloud is captured by nucleus, e transforms p to n, e from outer shell drops to the hole and emits gamma Nuclei with Z > 83 cannot stabilize by beta emission, positron emission, or electron capture A Z − 1 N2N1 A Z AreK 40 18 0 1 40 19 →+− nep 1 0 0 1 1 1 →+− A shift of one element to the left in periodic table 33 Electron Capture nep 1 0 0 1 1 1 →+− Rubidium-83 Vanadium-48 Gallium-67 Beryllium-7 Calcium-41 Cobalt-57 Selenium-72 A Z N1 A Z − 1 N2 34 Beta emission Alpha emission Positron emission, electron capture 35 Nuclear Disintegration Series Thorium 232Th - 208Pb A = 4n Neptunium (artificial) 241Pu - 209Bi A = 4n+1 Uranium 238U - 206Pb A = 4n+2 Actinuranium 235U - 207Pb A = 4n+3 36 Spontaneous Fission A heavy nucleus disintegrates to 2-3 fragments and one or more neutrons 37 Nuclear Fusion and Fission Nuclear Fission Nuclear Fusion 38 Nuclear Fusion and Fission Fusion Fission 39 Nuclear Synthesis in the Universe Big Bang 1n → 1H + e− Sun (temperature = 2 ×106 K inside, energy form PP or CN cycle) PP cycle 1H + 1H → 2H + e+ + ν + 0.42 MeV 1H + 2H → 3He + γ + 5.49 MeV 3He + 3He → 4He + 2 1H + 12.86 MeV 3He + 1H → 4He + e+ e+ + e− → γ + 1.02 MeV 40 PP cycle CN cycle 41 Nuclear Synthesis in the Universe Sun → red giant → white dwarf 3He + 4He → 7Be + γ + 1.59 MeV 4He + 4He → 8Be 7Be + p → 8B + γ + 13 MeV 8B → 8Be + γ + e+ + 10.78 MeV 8Be + 4He → 12C 12C + 4He → 16O 42 Nuclear Synthesis in the Universe Heavy stars 12C → Ne, Mg 16O → Si, S Si → 58Fe Fe nuclei are the most stable, what next? Supernova explosion high neutron fluxes Fe + n → Au → Pb → U 43 Thermonuclear Reactions 2H + 2H → 3He + n + 3.3 MeV 2H + 2H → 3H + p + 4.0 MeV 3H + 2H → 4He + n + 17.6 MeV ITER Cadarache, France National Ignition Facility, USA 44 Transmutations 1919, Rutherford, 1st artifical synthesis of an element 14N(α, p)17O OHNHe 17 8 1 1 14 7 4 2 +→+ 45 Transmutations OHNHe 17 8 1 1 14 7 4 2 +→+ Rutherford 46 Wilson Cloud Chamber Gas (air, He, Ar,...) and vapors of water or ethanol in a chamber, piston for volume change Expansion, cooling, supersaturated vapor, particles ionize gas atoms, condensation – trail Charles Wilson (1869-1959) NP in Physics 1923 47 Cyclotron Ernest O. Lawrence (1901-1958) NP in Physics 1939 1929 Accelerator of positive ions (H+, D+, ...) Pass thru potential step, alternating pos/neg charging of Dees, Circular movement in magnetic field, energies up to 100 MeV Hollow electrodes Dees 48 Large Hadron Collider Linear Accelerator (protons and ions) Proton Synchrotron Super Proton Synchrotron 27 km LHC tunnel Protons with energies 7 TeV 49 Nuclear Fission 1932 John D. Cockcroft (1897-1967) and Ernest T. S. Walton (1903-1995) Cascade accelerator, protons 800 keV The 1st splitting of a stable nucleus by an accelerated particle 1951 joint NP in Physics HeHeLiH 4 2 4 2 7 3 1 1 +→+ 50 Discovery of a Neutron James Chadwick (1891-1974) NP in Physics 1935 neutron = particle with zero charge, spin ½ m = 1.67470 10−27 kg 1932 nCBeHe 1 0 12 6 9 4 4 2 +→+ 51 Transmutations Cyclotron Bombardment with neutrons nPuUHe 1 0 239 94 238 92 4 2 3+→+ ConCo 60 27 1 0 59 27 →+ 52 Artificial Radioactivity Frederic and Irene Joliot-Curie (1900-1958) (1897-1956) 1933 nPAlHe 1 0 30 15 27 13 4 2 +→+ eSiP 0 1 30 14 30 15 ++→ 53 Nuclear Fission Otto Hahn (1879-1968) NP in Physics 1944 235U, 0.71% Slow neutrons 190 MeV 54 Chain Reaction 55 Nuclear Reactor Enrico Fermi (1901-1954) NP in Physics 1938 1942 Chicago 1st Fission reaction of 235U 56 Controlled Fission Reaction of 235U Moderator = slowing of neutrons – graphite Cd absorbs neutrons – captures n 57 Transuranium Elements Untill 1940 heaviest natural element Z = 92 (U) Z ≥ 93 (Np) transuranium, only artificial 1940 the 1st artificial = 239 93Np Bombardment with neutrons 238U + n → 239U → 239Np + e 239 94Pu Adress of Glenn Seaborg Sg, Lr, Bk, Cf, Am Glenn T. Seaborg (1912- 1999) Edwin M. McMillan (1907- 1991) Joint NP in Chemistry 1951 Sg 58 Synthesis of Transuranium Elements Joint Institut of Nuclear Research, Dubna, Russia GSI (Gesellschaft fur Schwerionenforschung), Germany LBL (Lawrence Berkeley Lab), USA Bombardment with positive ions 4He, 12C, 15N, 18O, ... Synthesized transuranium elems to Z = 118 208 82Pb + 62 28Ni → 269 110Ds + 1n t½ = 270 ms 208 82Pb + 64 28Ni → 271 110Ds + 1n 209 83Bi + 54 24Cr → 262 108Bh + 1n 59 Synthesis of Transuranium Elements GSI (Gesellschaft fur Schwerionenforschung), Germany Bombardment with positive ions 4He, 12C, 15N, 18O, ... 70Zn Synthesized transuranium elems to Z = 118 249 97Bk + 48 20Ca→ 293 117X + 3 1n The last named element 208 82Pb + 70 30Zn→ 278 112Cn → 277 112Cn + 1n 60 Kinetics of Radioactive Decay −dN/dt = k N dN/N = −k dt Integrate t = 0 N = N0 ln(N/N0) = −k t N/N0 = exp(−k t) N = N0 exp(−k t) N t 61 Half-life, t½ t = t½ N = N0/2 ln(N/N0) = −k t ln(1/2) = −k t½ t½ = ln(2) / k k = ln(2) / t½ ln(N/N0) = −t ln(2) / t½ 62 Half-life, t½ 63 Carbon Dating 14C 14C continually produced in high atmosphere 14 7N + 1 on (cosmic radiation) → 14 6C + p+ Decays by beta emission with half-life of 5730 y 14 6C → 14 7N + 0 −1e In atmosphere and living plants (CO2, photosynthesis), established equilibrium concentration of 14C. After death of organism, concentration of 14C decreases. 14C/ 12C established by mass spectrometry Willard Libby (1908-1980) NP in Chemistry 1960