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Radiochemistry CHE 711 / FS 2017

Radiochemistry CHE 711 / FS 2017. Roger Alberto, Henrik Braband. Department of Chemistry , University of Zürich. Inhaltsverzeichnis. Historisches The atomic nucleus - General features - Nuclear stability , Modes of decay - Nuclear forces - Nuclear states

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Radiochemistry CHE 711 / FS 2017

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  1. Radiochemistry CHE 711 / FS 2017 Roger Alberto, Henrik Braband Department of Chemistry, University of Zürich

  2. Inhaltsverzeichnis • Historisches • The atomicnucleus • - General features • - Nuclearstability,Modes ofdecay • - Nuclearforces • - Nuclearstates • UnstableNuclides • - Chart of isotopes • - Laws ofdecay • - Typesofdecay • - -Zerfall • - - decay/+ decay/e capture • - -radiation / Isomerictransitions • - Internal conversion IC / Auger Electrons • - Other decays

  3. Inhaltsverzeichnis 4. RadioaktiveZerfallsgesetze - Natural decayseries - Parent-daughterrelationships, -transient andsecularequilibria - Radionuclide Generators 5. Interaction ofIonizing Radiation with Matter - Ionizationwithelectrons - Bremsstrahlung - Photoeffect - Comptoneffect - Pair formation 6. Biological Action ofIonizing Radiation - Dose / Doserate - Shielding / Calculations - Dose calculations

  4. Inhaltsverzeichnis 7. ProductionofRadioisotopes - by Neutron capture (n,x) - NeutronActivationAnalysis (NAA) - by Proton capture (p+,x) - othernuclearreactions - SzilardChalmersreactions 8. ApplicationofRadionuclides in Radiopharmacy - Whatisradiopharmacy - Tools ofradiopharmacy: radiationandradionuclides - PET and SPECT - Generators andradiopharmaceuticals 9. Synthesisof Elements - Synthesis ofthechemicalelements: Nucleosynthesis - Synthesis oftransactinides / super heavy elements

  5. 1. Historical Background Atomic theory Leukipp (about 450 b.C.): creates the expression „atomos“ Demokrit (ca 460 – 400 b. C.): Atomic theory “Nur der Meinung nach gibt es süss, bitter, warm, kalt, Farbe, in Wahrheit gibt esAtome und leeren Raum” “Atoms and Void“

  6. Historical Background Epikur (341 – 271 b.C): summarizedDemokrit‘stheses (letterto Herodot) “Ausserdemsind die kompaktenAtomkörperchen, auswelchen die Stoff- zusammensetzungenentstehen und in welchesiesichauflösen, unerfasslich in Bezug auf die VerschiedenheitihrerFormen......” “Die Atomebewegensichfortwährend,......die einenschwebendabeiweit auseinan der, die anderenführeneineSchwingung am Ort aus, wennsie etwa in einerStoffverbindungverflochten und eingeschlossensind.....” J.C. Magien (1590 – 1679): Revival of Demokrit Oft beobachtet, dasseinWeihrauchkorndurchVerbrennen das 8x108-fache seines Volumen (von Erbsengrösse auf Zimmergrösse) gleichmässigmitDufterfüllt. EinerbsengrossesVolumenkönntemechanisch in ca. 103nochsichtbareTeilchengeteiltwerden, jedesdieserTeilchenbestehtsichernochausmindestens 106Atomen.BeigleichmässigerVerteilung muss das Weihrauchkornaus 8x108x103x106 8x1017Atomenbestehen.

  7. Historical Background W.C. Röntgen (1896): X-rays “MM. les Drs.Oudin et Barthélemycommuniquentunephotographie des os de la main, obtenue à l’aide des “X-Strahlen” de M. le professeurRöntgen.” c. r. 122, 1896, 150, séance du lundi 20 janvier 1896 A.H. Becquerel (1852 - 1908): Uranium rays “...l’origine de cesexpériencesavaitétél’idée de recherchersi les corps phosphor- escents, après avoirétéexcités par la lumière, émettaient des rayonspénétrants.” In contrast to Röntgen‘s X-rays, the report of Becquerel did not find any interest and Becquerel stopped publishing anything for a long time!

  8. Historical Background A.H. Becquerel (1852 - 1908): Uranium rays Within 3 months, Becquerel found that K2SO4UO2SO4, a phosphorescing substance (t1/2 = 0.01 s) emits invisible, strongly penetrating radiation “On doitdoncconclure de cesexpériencesque la substance phophorescente en question émet des radiations qui traversent le papier opaque à la lumière et réduisent les selsd’argent.” “On peutvérifiertrèssimplementque les radiations émises par cette substance, quandelleestexposée au soleilou à la lumière diffuse du jour, traversent, non seulement des feuilles de papier noir, mais encore divers métaux....”

  9. Historical Background A.H. Becquerel (1852 - 1908): Uranium rays ... and then that sunlight is not necessary at all ! “J’insisteraiparticulièrementsur le fait suivant, qui me paraît tout à fait important et en dehors des phénomènesquel’onpouvaits’attendre à observer: Les mêmeslamelles cristallines...mais à l’abri de l’excitation des radiations incidentes et maintenues à l’obscuritéproduisent encore les mêmes impressions photographiques.... Quelques-unesavaientétépréparées le mercredi 26 et le jeudi 27 février et, comme cesjours-là, le soleil ne s’estmontréqued’unemanièreintermittante, j’avais conservé les expériences.... dans le tiroir d’un meuble, en laissant en place les lamel- les du seld’uranium. Le solei ne s’étantmontré de nouveau les jourssuivants, j’ai développé les plaques photographiques le ler mars, en m’attendant à trouver des images trèsfaibles. Les silhouettes apparurent, au contraire, avec unegrande intensité.“

  10. Historical Background A.H. Becquerel (1852 - 1908): Uranium rays In contrast to Röntgen‘s experiment‘s, reproduction of Becquerel‘s was rare. “Hence the writer ventures to give to the new phenomenon thus independently observed by M. Becquerel and by himself the name of hyperphosphorescence. A hyperphosphorescent body is one which, after due stimulus, exhibits a persistent emission of invisible rays not included in the hitherto recognized spectrum.” “1. Die Angaben Becquerels bezüglich der physikalischen Eigenschaften der dunkeln, von Uransalzen ausgehenden Strahlen fanden wir, soweit wir sie prüften, duchweg bestätigt. 2. Die Energiequelle der diese Strahlen entstamen ist noch vollständig dunkel. Mo- natelanges Aufbewahren des Salzes unter Lichtabschluss vermindert die Strahlungs- intensität nicht merklich.” S. P. Thompson, On hyperphosphorescence, Phil. Mag. (5) 42, 1896, 128-135 J. Elster, H. Geitel, Versuche über die Hyperphosphoreszenz 10. Jahresber. Ver. Naturw. Braunschweig 10, 1897, 157

  11. Historical Background The first new elements 1898 Polonium 4n+2 Po-210 138.38 d “Nous croyons donc que la substance que nous avons retirée de la pechblende contient un métal se confirme, nous proposons de ’appeler polonium, du nom du payd’origine du l’un de nous.” Radium 4n+2 Ra-226 1600 y “On réalise ainsi une source de lumière, à vrai dire très faible, mais qui fonctionnne sans source dénergie. Il y a là une contradiction, tout au moins apparente, avec le principe de Carnot.” Accumulation of radium from pitchblend was very tedious, unknown problems emerged • radioactivity of fresh samples increases steadily • nearby compounds start becoming radioactive

  12. Historical Background F. Giesel (1852 – 1927): Excellent experimentalist • fresh solid radium compounds increase in activity, solution activity decreases • formation of coloured centers in crystals after irradiation • physiological action of radiation “Ich habe 0.27g Radium-Baryum-Bromid in doppelter Celluloidkapsel 2 Stunden auf die Innenfläche des Armes gelegt. Anfangs war nur eine schwache Rötung vorhanden; nach 2-3 Wochen stellte sich starke Entzündung mit Pigmentierung und schliesslich ....Abstossung der Oberhaut ein, worauf bald Heilung erfolgte.” “Als bequeme Kontrolle der fortschreitenden Reinigung benutzt man die Färbung der Bunsenflamme.”

  13. Historical Background Actinium 4n+3 Ac-227 21.77 y Debierne finds a newactivity (1899), chemicallyrelatedtolanthanum Gieselconfirmsfinding 1902 (itproducesemanation) andcalledit „Emanium“ Debierne wins, hence, thename „Actinium“ remains Emanation and induced radioactivity Emanation: Rn-222 4n+2 3.825 d U-238 Rn-219 4n+3 3.96 s U-235 Rn-220 4n 55.6 s Th-222

  14. Historical Background The nature of emanation remains mysterious: Owens and Rutherford (1899): “It was very early observed that the radiation from thorium oxide was not constant, but varied in a most carpicious manner. This was the more peculiar as the sulphate and the nitrate were fairly constant. All the compounds of uranium give out a radiation which remains remarkably constant..... The sensitiveness of thorium oxide to slight currents of air is very remarkable and made it difficult to work with... A large number of experiments of various kinds have been tried, but so far, no clue has been obtained as to why this action should be so manifest in thorium oxide......” Giesel (1903): “Legt man ein Filter mit einigen Centigrammen der Substanz auf den Schirm, so verbreitet sich die Emanation auf grössere Strecken desselben und erzeugt ein durch den leisesten Luftstrom hin- und herwogendes Phosphorescenzlicht.” “Ein Gas scheint die Emanation jedenfalls nicht zu sein, wenigstens wurde unter Wasser keine Gasentwicklung von der Substanz bemerkt. E. Rutherford, R. B. Owens, Thorium and uranium radiation, Trans. Roy. Soc. Canada (3) 2, 1899, 9-12 F. Giesel Über Radium und radioaktive StoffeBer. 35, 1902, 3608

  15. The massdifference m = mn – (mp + me) 1 a.u. = 12C = 1.66054·10-27 kg 1 a.u.  931.748 MeV (1MeV = 1.602·10-13 J) - is exactly the same what is found for n  p+ + e- + ( ) (t½ = 10.4 min) 2. The atomicnucleus neutrons: mn = 1.0086647 a.u. protons: mp = 1.007276 a.u. (electron): me = 5.485799 ·10-4 a.u. Atomic nucleus consists of: - corresponds to 0.78 MeV of stabilisation energy

  16. neutronsandprotons Baryons electronsandneutrinos  Leptons The atomic nucleus: General features + and - Mesons are responsible for the attractive forces between p and n or n and p respectively. - / + Meson: 0.15 a.u.  273 em t½ = 2 · 10-8 s O Meson: 0.145 a.u. t½ = 10-16 s -Mesonen have been detected in cosmic radiation. - exchange forces explain, why neutrons have a magnetic moment.

  17. The atomic nucleus: General features http://commons.wikimedia.org/wiki/File:%C3%9Cbersicht_einiger_Hadronen.svg

  18. The atomic nucleus: General features The structure of the nucleus is almost a sphere. range of radii: 3 ·10-15 - 16 · 10-15 m (3 fm – 16 fm) Original determination by Rutherford with -particle scattering experiments

  19. empirical relation: R = ro (9.1 fm für A = 222) • with A = number of nucleous and ro = 1.4 fm (radius of nucleons) The atomic nucleus: General features atomic radius Newer definition through the extremly short range nuclear forces - The potential energy of a p+ approaching the nucleus increases strongly. - At a certain distance (radii of nuclei) nuclear forces start and Epot decreases.

  20. The atomic nucleus: General features Atomic density The density of the nucleus is about 1.5 · 1017 kg/m3 Compare mass of earth: 5.972 · 1024 kg Charge distribution: R.L. Hofstadter: elastic scattering with high energy electrons for A > 16 charge density constant over a certain range.

  21. The atomic nucleus: General features Charge distribution The mass and charge distribution are constant Layer of decreasing density (dn  2.5 fm) follows Fermi statistics For nuclear reactions, a charged nucleon needs to reach that distance to overcome the Coulomb potential.

  22. Epot = = 29.5 MeV (r = 9.1 fm) (226Ra, 9Be) C-12 226Ra = 4.8 MeV Epot(Be) = = 4.25 MeV first neutron sources !! The atomic nucleus: General features Potential wall The wall potential can be calculated from Ec if the radius is known. • The wall is 14.7 MeV for a proton • natural -particles don‘t have such high energies but nuclear reactions with lighter elements are possible

  23. Considering 2 p+ with d  3fm and EC =  EPP  0.5 MeV The atomic nucleus: General features Nucleon-nucleon interactions follows within a nucleus also the Coulomb potential (which is little in comparison to mean binding energy of  8 MeV) increases with increasing atomic number. nuclear forces go to saturation but Coulomb forces increases  Instability of heavy nuclei.

  24. The atomic nucleus: General features Comparison of the 4 principal forces in nature interaction mediating particle force constant strong Gluon 1 electromagnetic Photon 10-2 weak Boson 10-5 gravitation Graviton 10-40 further fundamental particles (a)Electricchargeandquantumnumbersareoppositetothoseofthecorrespondingparticles.

  25. The atomic nucleus: General features Binding energies The nucleon-nucleon interaction shown previously resembles the Morse potential for chemical bonds The mean binding energy is about constant nucleon interacts with essentially one partner

  26. The atomic nucleus: General features Binding energies Empirical calculation of binding energy E = mc2, 1 u  931.5 MeV MZ,N= Z·M(1H) + N·M(n) - M with M =  the higher EB, the more stable the nucleus

  27. 7.01822  4.0026 + 3.017012 doesn‘twork  doeswork 8.0053 > 2 x 4.0026 The atomic nucleus: General features Binding energies fission of 238U to 2 equal nucleii of same mass should deliver about 200 · 1 MeV = 200 MeV which is the amount experimentally found Exact masses are known from high resolution MS Stability of a nucleus in respect of a decay can be predicted (as in chemistry)

  28. EB = total bindingenergyof all nucleous EV = Volume energy = aV·AaV = 15.8 MeV EC = mutual repulsion = -aC· aC = 0.71 MeV EF = surfaceenergy = -aF· aF = 17.8 MeV ES = symmetryenergy = -aS· aS = 23.7 MeV + 33.6 MeVee EG = considersee / oonucleii = aG/A-3/4 aG = 0 MeVoe / eo - 33.6 MeVoo The atomic nucleus: General features Binding energies Semiempirical calculation of binding energy Bohr compared the nucleus with a incompressibel drop of liquid the larger the drop the less stable it is Bethe-Weizsäcker: EB = EV + EC + EF + ES + EG

  29. The atomic nucleus: General features Binding energies The B-W Formula allows calculation of all BE for A  15 within 1%  very usefull for unknown nuclides example: calculated experimental 97.947 97.943 51.959 51.956 235U + 1n  236U: binding energy of neutron 6.81 MeV 236U „  237U: „ 5.51 MeV 237U „  238U: „ 6.56 MeV 238U „  239U: „ 5.31 MeV

  30. MZA – M =  (z – z0)2 with  The atomic nucleus: General features Binding energies The high potential of the B-W Formula can be seen from EB within nuclides with equal A (Isobares) if A is kept constant: which yields a parabolic curve (for oe/eo) the larger A, the flater the potential pot the more stable nuclides

  31. For even mass numbers we receive two parabolas, separated by The atomic nucleus: General features Binding energies This explains: - why ee nuclides are particularly stable - and why oo are not. Statistic of stable nuclides: Z N A type numbers e e e ee 162 e o o eo 55 o e o oe 50 o o e oo 5

  32. The atomic nucleus: General features Binding energies • The most stable nuclides are close to the maximum EB • Rule of Mattauch • Nuclids with odd mass number have only one stable nuclide The others along the slope are - or + unstable

  33. The atomic nucleus: General features Binding energies More complex situation with even A (ee and oo nuclides) depending on the shape of the parabolas, more than one stable nuclide is possible • RuleofMattauch • Nuclidswitheven mass numberfrequentlyhavetwoorthreestable • Isotopes whichatomicnumbers must beseparatedby 2.

  34. 0.01% natural abundance t1/2 = 1.28·109y (stable) (stable) The atomic nucleus: General features Binding energies Inspection of isotope chart confirms the rules and explains... ... why43Tc hasnostablenuclides ... why61Pm hasnostablenuclides andwhyoonuclidesmaydecay witheither-or +.

  35. The atomic nucleus: General features Binding energies Inspecting the valley of stability it looks like a smooth landscape pm. - The stability of a nuclide depends on the sum of Z and N and their relative ratio - most stable nuclides are found for Z = 26 or 28

  36. The atomic nucleus: General features The valley of b-stability

  37. The atomic nucleus: General features The valley of b-stability Z N=Z Electron capture • Dark blue line: • valley of b-stability • extra neutrons b- emission A=N+Z Table of Nuclides: http://www2.bnl.gov/ton/

  38. The atomic nucleus: General features The valleyofb-stability Source: http://ie.lbl.gov/toi

  39. The atomic nucleus: General features The valleyofb-stability

  40. The atomic nucleus: General features The valley of b-stability

  41. The atomic nucleus: General features The valley of b-stability

  42. The atomic nucleus: General features The valley of b-stability

  43. The atomic nucleus: General features The valleyofb-stability

  44. The atomic nucleus: General features The valley of b-stability

  45. The atomic nucleus: General features The valley of b-stability

  46. The atomic nucleus: General features The valley of b-stability closer look shows that the energy landscape is rather bumpy with local minima along Z / N = 2, 8, 20, 28, 50, 82, 126 and theoretically predicted Z = 114 N = 184 These numbers are called „magic numbers“

  47. The atomic nucleus: General features • Elements with magic Z have many stable Isotopes (Sn = 10 Isotopes) • Elements with magic N have many stable Isotones • so called „double magic“ nuclides are particularly stable and abundant (Pb – 208, Ca – 40) • unstable double magic nuclides have a relatively long t½ compared to their neighbours

  48. The atomic nucleus: General features The observation of particularly stable numbers can be explained with a shell model (similar to electrons). Filled shells are more stable than partly filled ones.

  49. 3. UnstableNuclides If an atomic nucleus is along the wall of the Epot parabola, it can energetically relax to a lower state according to E = Mc2 = [MA-(MB-MX)]c2 - an activation barrier has to be surmounted or crossed by quantum mechanical tunelling - it is sort of activation energy comparable to chemical first order kinetics

  50. Unstable nuclides: the nuclide chart More detailed view at the chart of the nuclides The chart of the nuclides lists all known nuclei together with most important decay data (energy, decay type, daughter nuclide, etc.)

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