HSC Chemistry Module 1- Production of Materials

1. HSC ChemistryModule 1- Production of Materials Nuclear Chemistry

2. NOTE Remove the word “chemical” from dot point 5.2.6 Should read.....explain their use in terms of their properties

3. OUTCOMES • explain the stability of the nucleus • write equations for nuclear decay processes • describe how transuranic elements and commercial radioisotopes are produced • identify processes and instruments used to detect radioactivity • describe some industrial and medical applications of nuclear chemistry • analyse benefits and problems associated with the use of radioactive isotopes

4. Radiation • energy traveling through space • invisible except for light • transmitted as waves OR as energetic particles • detected by changes caused in substances around it

5. Radioactivity • the spontaneous and uncontrollable decay of an atomic nucleus resulting in the emission of this radiation • a natural process throughout the Universe and part of the inherent properties of many elements

6. The Nucleus The mass of an atom is concentrated in a tiny nucleus >> nuclear electrostatic force force protons - neutronselectrons - nucleus force required to hold positively charged protons together is enormous

7. Identifying the nucleus anuclideis a particular species of nucleus mass number A = Z + N N = number of neutrons Z = number of protons nucleonsare protons and neutrons

8. Stability of the nucleus • depends on the ratio of protons to neutrons • radioisotopes are radioactive because they have unstable nuclei

9. Band of stability • along the black band isotopes are stable • above and below isotopes are unstable • all isotopes above Z=83 (Bi) are radioactive

10. Stability of the nucleus • nuclei whose n/p ratios lie outside the stable region undergo spontaneous radioactive decay by emitting one or more particles and/or electromagnetic radiation • atomic number > 83 • most forms of radioactive decay cause a change in the atomic number producing a new element aTRANSMUTATION

11. Nuclei above the band of stability • have too high a n/p ratio • decay to DECREASE the ratio • most commonly by beta emission

12. Beta decay (b) unstable nuclide is proton deficient high energy electron emitted ( particle) transforms a neutron to a proton resultant nuclide: Athe same - Z increases by 1

13. Nuclei below the band of stability • have too low a n/p ratio • increase this ratio usually by positron emission or electron capture (k-capture) • a positron has the mass of an electron but a positive charge – forms when a proton is converted to a neutron

14. Positron emission unstable nuclide is proton rich high energy positron emitted transforms a proton to a neutron resultant nuclide: Athe same - Z decreases by 1

15. Electron capture/K-capture an electron from the first shell (K shell) is captured by the nucleus and combines with a proton to form a neutron resultant nuclide: Athe same - Z decreases by 1

16. Nuclei with Z > 83Alpha decay When Z > 83 an  particle (4He2+) may be emitted A decreases by 4  particle emitted Z decreases by 2

17. Gamma Radiation (g) • high-energy electromagnetic radiation • has no mass and no charge • usually accompanies the emission of aand b particles when the product nucleus must lose excess energyto become stable • alone cannot cause a transmutation

18. Complete the equation below ? ? ?

19. How much radiation is safe?

20. 5.2.2 describe how transuranic elements are produced 5.2.3 describe how commercial radioisotopes are produced

21. Synthesis of radioisotopes • Particle Accelerators • target nuclei are bombarded with high energy particles like protons in cyclotrons to induce nuclear reactions • produce neutron deficient radioisotopes

22. Positron emission tomography • important diagnostic technique • uses positron emitters • e.g. 11C (t½20.3 min) or 15O (t½124 s) • incorporated into a molecule like glucose and injected into the body • can study blood flow, glucose metabolism by monitoring the positron emission • must be generated on-site as short t1/2

23. Synthesis of radioisotopes • Nuclear Reactors • source of neutrons from the fission of the fuel e.g. U-235 • radioisotopes may be products of fission of U-235 e.g. Mo-99, Cs-137 • produces neutron rich radioisotopes

24. Nuclear fission When 235U is bombarded with neutrons the nuclei split into smaller nuclei, release some neutrons and energy Another way of producing Mo-99 g Tc-99m

25. Synthesis of new elements • Nuclear Reactors • neutron bombardment of U-238 produced the first transuranic element Np-239

26. Synthesis of new elements Particle Accelerators • high energy projectile ions are fired at target nuclei Ununbium 112 now Copernicium • Discovered on 9th Feb 1996 at GSI in Darmstadt, Germany. • produced by firing accelerated zinc nuclei at lead nuclei • Very short ½ life: 240 microseconds • Undergoes alpha decay

27. Uses of Radioisotopes There are 3 main uses of ionising radiation in medicine: • Treatment • Diagnosis • Sterilisation

28. Radiotherapy TreatmentIrradiation Using High Energy Gamma Rays • Gamma rays are emitted from a Cobalt-60 source • The cobalt source is kept within a thick, heavy metal container. • This container has a slit in it to allow a narrow beam of gamma rays to emerge.

29. Radiation TherapyBrachytherapy A radiation source is placed inside or next to the area requiring treatment. Can be used to treat the following cancers: • Uterus • Cervix • Prostate • Intraocular • Skin • Thyroid • Bone “Seeds" - small radioactive rods implanted directly into the tumour. e.g. prostate cancer

30. Brachytherapy

31. Sterilisation • Radiation not only kills cells, it can also kill germs or bacteria. • Medicalinstruments (e.g. syringes) are prepacked and then irradiated using an intense gamma ray source. • This kills any germs or bacteria but does not damage the syringe, nor make it radioactive.

32. Technetium-99m • most significant radioisotope used in medicaldiagnosis • t1/2 = 6 h – long enough to get a good scan, but decays quickly to reduce exposure of patient • decays by release of gamma rays • chemically versatile as it can be bound to a variety of compounds to target many areas of the body • can be economically produced in large quantities • used to image – brain, thyroid, lungs, liver, spleen, kidney, gall bladder, skeleton, bone marrow, heart

33. Technetium-99m • decay product of Mo-99 which has a t1/2 = 66h • Mo-99 produced in nuclear reactor at Lucas Heights in Sydney and transported around country

34. Industrial radioisotope Cesium-137 • half-life of 30 years • decays by emission of a beta particle and gamma rays to Ba-137m • one of the most common used in industry • thickness gauges – sheet metal, paper, plastic film • levelling gauges to detect liquid flow in pipes and tanks • densitometer to check roads • one of the products of the fission of uranium when U-235 absorbs neutrons in a nuclear reactor

35. 5.2.4 Identify instruments and processes that can be used to detect radiation • Ionisation • removal of an electron from an atom to form a positive ion • Excitation • moving an electron to a higher energy level • emits photon of light when returns to ground state

36. Excitation

37. Instruments to detect radiation • Ionisation • Photographic film (Radiation badge) • Geiger-Muller tube (Geiger counter) • Cloud chamber • Excitation and ionisation • Scintillation counter (gamma camera)

38. Cloud Chamber http://www.yteach.com/page.php/resources/view_all?id=affect_radiation_live_organism_scintillation_counter_Geiger_Muller_Wilson_cloud_absorbed_dose_equivalent_source_t_page_2&from=search

39. Nuclear fission • when uncontrolled enormous amounts of energy released • chain reaction • atomic bomb • when controlled a rich source of power • nuclear power reactors • radioactive waste • likelihood of catastrophic accidents

40. Nuclear Fission Animated Controlled and Uncontrolled Fission

41. Nuclear fusion • union of two light nuclei to form a heavier nucleus • produces much more energy than nuclear fission and should be a rich source of “clean” power

42. Nuclear Fusion Animation

43. Half-life t1/2 • a radioisotope decays at a fixed fractional rate • in each second a constant fraction of the total amount present decays • t1/2 is the time for half of the atoms of a radioisotope to decay • the half-life for a given radioisotope is always the same • the longer the half-life the more stable the radioisotope

44. Half-life

45. A radioactive decay curve 0.5 g of Pb-207 0.75 g of Pb-207 1 g of U-235 0.875 g of Pb-207 0.5 g of U-235 0.25 g of U-235 0.125 g of U-235 713 million years 713 million years 713 million years

46. Measuring radiation • Film badges • radiation darkens the photographic emulsion • degree of darkening  quantity of radiation • Scintillation counter • crystal of NaCl “doped” with Tl+ ions • pulse of light emitted on absorbing  particles or  rays • photomultiplier tube detects and counts the pulses • Geiger counter • cylindrical tube containing argon and ethanol vapour • tube is –ve electrode, wire down middle +ve electrode • measures current caused by electrons and positive ions produced by high energy radiation (better for )