The electromagnetic radiation. Environmental Toxicology, Master Sc. in Industrial Biotechnology

Transcription

1 The electromagnetic radiation

2 The electromagnetic radiation c = c = light speed in vacuum = 2.99 x 10 8 m/s Picture taken from

3 The electromagnetic spectrum

4 The electromagnetic spectrum Picture taken from

5 The electromagnetic spectrum Picture taken from

6 Ionizing radiations: gamma rays see part on radioactivity in this lecture

7 Ionizing radiations: X-rays

8 Ionizing radiations: X-rays

9 The discovery of X-rays 8. Novembre 1895 Wilhelm Conrad Röntgen "eine neue Art von Strahlen una nuova tipologia di radiazione Premio Nobel, 1901 Röntgenstrahlung = raggi X Ann. Phys. Chem. 64 (1898) 1-11

10 The discovery of X-rays: Röntgenstrahlung The first Nobel Prize in Physics 1901 was awarded to Wilhelm Conrad Röntgen "in recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him". Wilhelm Conrad Röntgen Born: 27 March 1845, Lennep (now Remscheid), Prussia (now Germany) Died: 10 February 1923, Munich, Germany Affiliation at the time of the award: Munich University, Munich, Germany

11 generation Ionizing radiations of X-rays Photoelectric effect (Albert Einstein, 1905) h h E kin K L M

12 generation Ionizing radiations of X-rays

13 generation Ionizing radiations of X-rays

14 generation of X-rays vacuum tube, Pb wall (opaque to X-rays), cooling system, Be window (transparent to X-rays) electrons emission from an incandescent tungsten wire (the cathode) electrons are accelerated towards the anode by a voltage of kv emission of two X-rays radiation typologies: Bremsstrahlung and characteristic X-ray radiation

15 generation of X-rays used for diagnostic, analytics Bremsstrahlung

16 Radioactivity

17

18 how people perceive the radioactivity?

19 What radioactivity really does/is used for

20 Radioactivity deals with: Technology Chemistry & Physics Environment Medicine Politics

21 the structure of the atoms NUCLIDE A species of atom, characterized by its mass number, atomic number and nuclear energy state, provided that the mean life in that state is long enough to be observable. Source: IUPAC Goldbook Electron (e - ) mass: kg charge: C Proton (p + ) mass: kg charge: C Neutron (n) mass: kg charge: none

22 Nuclide symbolism: Nuclide: a specific atom characterized by its nuclear properties (i.e. the number of neutrons and protons and the energy state of its nucleus). Atomic number (Z): the number of protons in the nucleus of an atom of a given element (and, therefore, the number of electrons normally surrounding the nucleus of the neutral element). Mass number (A): the number of nucleons (protons and neutrons) constituting the nucleus of a given element.

23 Nuclide symbolism: Mass number Element symbol Atomic number

24 Isotopes: atoms having the same number of protons (atomic number Z) but different number of neutrons (mass number A). Some isotopes are radioactive (so-called radioisotopes or radionuclides applications in medicine).

25 Nuclear properties: involving the nucleus If spontaneous: radioactivity Mass of 1 H = m e + m p Mass of all other atoms < Σ m e + m p + m n Mass defect: measure of the binding energy of protons and neutrons (energy released related to mass by Einstein equation) DE =Dmc 2 mass defect as a measure of BE

26 DE =Dmc 2 mass defect as a measure of BE c = * 10 8 m/s, 1 u = * kg 7 Li: 7 nucleons (3 protons + 4 neutrons) Mass of the electron= *10 nuclear binding energy -31 kg Mass of the proton = *10-27 kg Mass of the neutron = *10-27 kg Effective mass of 7 Li = * * kg = *10-26 kg Calculated mass as S(m p +m n +m e ) = (3* *10-31 ) +(3* *10-27 )+(4* *10-27 ) = *10-26 kg Dm = *10-26 kg *10-26 kg = *10-26 kg DE = Dm*c 2 = ( *10-26 kg) * (2.998 * 10 8 m/s) 2 = 6.29*10-12 J/nucleus (J = kg m 2 /s 2 ) Binding energy per mole: = 6.29*10-12 J/nucleus * 6.022*10 23 = 3.79*10 12 J/mole = 3.79*10 9 kj/mole For comparison: combustion of butane -2.9*10 3 kj/mole Energy per nucleon: 6.29*10-12 J/nucleus/7 = 8.98*10-13 J/nucleon = energy released per nucleon upon formation from its fundamental particles = 8.98*10-13 J/nucleon = 5.6 MeV Most stable nucleus 56 Fe (bulk of Earth core) 1 ev = 1.60*10-19 C*V= 1.60*10-19 J

27 Average nuclear binding energy curve (stability) 56 Fe most stable 62 Ni, 58 Fe, 56 Fe, 60 Ni ca MeV/nucleon, at ca. A = 60 (the iron group). For lighter atoms the energy increases rapidly with A with stability peaks for 4 He, 12 C and 16 O (all even A and Z); these lighter isotopes can release high amounts of energy by combining each other (fusion).

28 Magic number nuclides Some particularly stable and common isotopes have magic numbers of protons and/or neutrons: 2, 8, 20, 28, 50, 82 and 126.

29 Nuclei stability curve all nuclei with Z > 83 (Bi) can exist only as radioactive isotopes; Z = N elements corresponding to Z = 43 (Tc) and Z = 61 (Pm) do not exist in the stability band; distribution of naturally occurring stable isotopes: Z and N even: 157 Z even, N odd: 52 Z odd, N even: 50 Z and N odd: 4

30 Radioactivity : Is the spontaneous emission of electromagnetic radiation either directly from unstable atomic nuclei or as a consequence of a nuclear reaction (fission). These phenomena lead to formation of other chemical species and/or charged particles (a emission) and/or energy (e.g. g emission) Nuclear isomers: nuclides having the same number of neutrons and protons but existing in different energy states and undergoing different radioactive decays; the excited state exists for a measurable interval of time and nuclides in such a state are defined as metastable.

31 Radioactivity: formation of other species as a source of energy - nuclear fission: a heavy nucleus is divided (e.g. through action of thermal neutrons) into two nuclei, whose sum + mass on the neutron equals that of original nucleus + formed neutrons - nuclear fusion: two light nuclei are combined to give one heavier nucleus

32 Radioactivity: formation of other species decay of U 238 through alfa-emission

33

34 118 known elements (IUPAC, well-characterized stable isotopes over 60 natural radioisotopes over 1,000 artificial radioisotopes All possible radioisotopes created during the evolution of the Universe (aged ca billion years), but only isotopes whose overall radioactive decay is longer than the age of the Earth ( y) are present.

35 radioactive elements

36 Radioactive decays:

37 Radioactive decays Radioactive decay Nuclear equation Particle/radiation emitted 1) alfa emission 2) beta emission 3) positron emission 4) K electron capture x-rays 5) gamma emission g-rays

38 1. Radioactive decays: a decay two protons and two neutrons escaping g

39 1. Radioactive decays: a decay typical of radioisotopes with Z > 82 (Pb) and A > 200 too many protons, electrostatic repulsion much higher than attractive strong nuclear forces; a particles are very fast (5-7% c) high kinetic energy (3-9 MeV); interact strongly with matter strongly ionizing radiation (bonds breaking, electrons release); weakly penetrating (max 10 cm in the air, stopped by a paper sheet).

40 2. Radioactive decays: b decay (neutron into proton) g

41 2. Radioactive decays: b decay Too high (A-Z)/Z ratio by b - decay only Z increases so the (A-Z)/Z ratio diminishes; b - particles have modest kinetic energy ( MeV); less ionizing than a particles (but can induce lots of secondary ionization processes caused by their primary direct interaction with matter); more penetrating than a particles (stopped by a few mm aluminum foil).

42 3. Radioactive decays: positron decay (proton into neutron) g

43 3. Radioactive decays: positron decay Too low (A-Z)/Z ratio by b + decay only Z diminishes so the (A-Z)/Z ratio increases; typical of artificial radionuclides; b + particles have medium kinetic energy; less ionizing than a particles (but can induce lots of secondary ionization processes caused by their primary direct interaction with matter); more penetrating than a particles (stopped by a few mm aluminum foil).

44 4. Radioactive decays: K electron capture decay Process in which a nuclide absorbs an inner (K shell) atomic electron changing a nuclear proton to a neutron and simultaneously emitting a neutrino. Various photon emissions follow the electron cascade, in order to allow the energy of the atom to fall to the ground state of the new nuclide.

45 4. Radioactive decays: K electron capture decay Too low (A-Z)/Z ratio by K electron capture decay only Z diminishes so the (A-Z)/Z ratio increases; typical of artificial radionuclides; b + and K capture decays are competitive and usually operate together; the second is characterized by emission of X-rays.

46 5. Radioactive decays: g decay (often related to a and b decays) A ZX A ZX* g-rays

47 5. Radioactive decays: g decay High frequency electromagnetic radiation (> Hz, higher than X-rays); Well defined (discrete) energy values depending on the radionuclide nature ( MeV); interact very weakly with matter (secondary ionization processes caused by their primary direct interaction with matter); highly penetrating (may cross some cm of lead).

48 Radioactive decays: a= 6-16*10-13 J penetration of few cm b= *10-13 J Al to block them g > Hz Pb to block them

49 Radiation penetration depth

50 Half life radioactive decay The half-life (t 1/2 ) is the time it takes for one half of a parent radionuclide to decay to its daughter isotope. is the radioactive decay constant and depends on the radionuclide.

51 Half life radioactive decay Time t needed for a number N of nuclides to become N/2. First order kinetics -dn/dt = kn N/N 0 = e -kt t 1/2 = ln2/k = /k (from 10-4 sec ( 214 Po) to 4.4*10 9 years ( 238 U) It is a casual event not dependent from the number of nuclides

52 Half-life radioactive decay: Parent radionuclide Half-life Decay mode 5,715 y b y b - (89.3%) / b + EC (10.7%) y b y a y a y a 1,599 y a 5.27 y b d b s a

53 Half life radioactive decay: stability of nuclides Stable > 4 My ,000 y 1 d 103 y minutes 1 d < minutes

54 Decays Among the natural radionuclides with Z > 83, only three have t 1/2 longer or, at least, comparable to the age of the Earth ( y) and, thus, are still present (primordial origin). All the other natural radioactive isotopes have shorter t 1/2 and result from the radioactive decay of one of these primordial progenitor. All the decays involve a and b - emissions. The same radionuclide can simultaneously undergo different nuclear processes.

55 Half life radioactive decay 14 C : up to years (t1/2 = 5730 years) 238 U: up to 4 billions years: geological dating

56 14 C-dating

57 Radioactive series Usually, the radioactive decay of an unstable isotope generates another radionuclide which, in its turn, undergoes a subsequent decay to another nuclide, and so on until a stable isotope forms. Starting from a given parent radionuclide, all the subsequent daughter isotopes formed constitute a radioactive series. All isotopes with Z > 83 (Bi) are radioactive and, among them, the naturally occurring radionuclides belong to well-defined families (series).

58 Radioactive series

59 Radioactive decay series of/2004/1050/uranium.htm

60 Radioactive series U-235 radioactive series

61 Uranium in abandoned mines Environ Sci Pollut Res (2013) 20: DOI /s Uranium decay series

62 Radioactive series U-238 radioactive series (all steps have different rates)

63 Depleted Uranium (DU) Depleted uranium is a by-product of enrichment of natural uranium to make nuclear fuel. It is less radioactive than naturally occurring uranium as it contains less of the fissionable material U-235. Uranium is an extremely dense metal, 1.7 times as dense as lead, and this lends itself to uses where a large mass in a small volume is advantageous. These include armour-piercing shells and bombs. DU-containing ammunition was used in both Gulf Wars, in 1991 and 2003, and in Serbia and Kosovo.

64 Radioactive series Th-232

65 Radioactive series Np-237 radioactive series Np-237 has half-life of two million years. Thus, all primordial neptunium should have decayed by now. Therefore the presence of Np- 237 is strictly connected with the human activity

66 Radioactivity measurements Units Bequerel (Bq) 1 disintegration/second (SI) Curie (Ci) = 3.7 x Bq =37 GBq (SI units) Geiger counter

67 Radioactivity measurements 90% Ar and 10% EtOH vapours, p tot 0.1 atm Voltage 1000 V