Radioac'vity and Radioac've Decay. Isotopes too!

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1 Radioac'vity and Radioac've Decay Isotopes too!

2 Warmup If you ve got 1.62 x atoms of Carbon, what is that weight in grams? What assump'ons about atomic mass are you making in your calcula'on? Write out the symbol for Carbon- 14. Convert one of the neutrons into a proton and re- write the symbol. In general, how would your first answer change? (do not actually calculate)

3 10.17 MSFWBAT MSFWBAT Dis'nguish between the different types of radioac've par'cles Explain how conserva'on of mass, energy, and charge are applied in alpha and beta decay calcula'ons

4 10.17 MSFWBAT Explain how some isotopes are made of unstable nuclei Differen'ate between nuclear fission and fusion

5 Radioac've Decay Radioac've decay involves the stochas'c transforma'on of one element into another. In nuclear decay, the nuclei of radioac've atoms decay spontaneously to form other nuclei, a process that always results in a loss of energy and oven involves the release of one or more small par'cles. Some elements are naturally radioac've. Some isotopes are normally non- radioac've elements are naturally radioac've

6 Background the EM spectrum

7 The law of conserva'on of Thou shalt not create or destroy There is a loophole in the law, it is that energy and mass are are equivalent and one can be converted into the other

8 Another law (or two) In all energy exchanges, if no energy leaves or enters the system, the final poten'al energy state of the system must be less than the ini'al energy state This is called entropy Energy is lost in every transfer all things want to lose energy Lowest energy state (ground state) is what nature strives to achieve why does a heated pot of water become room temperature? This law has no loopholes. It is absolute.

9 Essen'ally, all the Hydrogen and a lot of the Helium in the universe was created all at once in the Big Bang Stars are the result of the energy released from H atoms colliding with each other and genera'ng new He nuclei The big bang

10 Nuclear Fusion As stars age, the supply of Hydrogen begins to run out, so they begin to fuse He into Be He + He Be + energy Be + He C + energy C + He O + energy In general, produc'on of all elements proceeds this way up to Fe/Ni Fusion of elements heavier than this is no longer energy releasing, so it does not happen in stars

11 It happens in supernovae The energy released in the explosion of massive stars is enough to put together the heavier elements

12 But it s a liale more complicated

13 Other observa'ons The lighter elements weigh less than the sum of their parts The heavier elements weigh more than the sum of their parts??

14 What E means

15 Summary: fusion and fission Nuclear fusion releases energy but only fusion of light element nuclei are energy releasing Nuclear fission releases energy but only fission of heavy nuclei are energy releasing

16 Slow release of energy Heavy isotopes or unstable nuclei release energy at a steady rate, usually not all at once Not all atoms of a par'cular unstable element release at once, but on average, the release of energy from a par'cular molar mass of a sample may be measured over 'me This measure over 'me gives us (in Bequerel) the ac'vity of a radionuclei

17 Concept check Why in general are some elements radioac've?

18 10.18 warmup Why would an atom of Carbon be lighter than the sum mass of its protons, neutrons, and electrons? What equa'on explains this discrepancy?

19 MSFWBAT Explain the rela'onship between the number of neutrons, protons and the stability of nuclei Explain why nuclear reac'ons occur and know how to balance a nuclear equa'on (material is chapter 21 in your text) HW for Wednesday: ques'ons 1-4 p 684 (3 has three parts so there are six ques'ons)

20 Nuclear binding energy The energy released when a nucleus is formed from nucleons Recall: what is mass defect? What might mass excess mean? The binding energy per nucleon is the binding energy of the nucleus divided by the number of nucleons it contains

21 Binding energy per nucleon Binding energy energy released when a nucleus is formed This is equivalent to energy required to break apart then nucleus Why is Lithium less common than Helium?

22 Incidentally Hint: flip the one on right upside down!

23 Proton- proton interac'on repels at short distances BUT at very short ranges the STRONG nuclear force: proton- proton is aarac've What happens to this interac'on as atomic # increases? As elements get heavier, more neutrons required Beyond 83 (Bi), repulsive force is too great Band of stability

24 Nuclear shell model Nucleons exist in energy levels A certain number of nucleons (protons OR neutrons) completes a shell (2, 8, 20, 28, 50, 82, 126) These are referred to as magic numbers Non magic number nuclei are less stable (have lower binding energies means easier to break apart to release excess E) Through nuclear reac'ons, atoms with unstable nuclei aaempt to become stable by jemsoning excess mass/energy

25 Warmup: Why does the sun shine?

26 MSFWBAT Balance a nuclear equa'on Explain how the process of decay can change an isotope s atomic and mass numbers

27 Concept check: why is lithium rare?

28 Concept check Why are some elements more rare/abundant than others? What does stability mean? What is the rela'onship between entropy and stability? What do magic numbers and the neutron:proton ra'o have to do with stability?

29 For fun The mass defect of He can be calculated to amu. How much energy is this equivalent to? Convert amu to Kg (energy units are expressed in Kg): x Kg per amu Plug this mass into E=mc 2 Speed of light = 3.00 x 10 8 m/s) How much energy is released by 1.0 moles He?

30 Ways to become stable Alpha emission Beta emission Positron emission Electron capture Gamma emission

31 Alpha Par'cle Mass of 4 amu (2 protons and 2 neutrons) 2 protons

32 Alpha emission Deflects toward (- ) poles Two protons and two neutrons (an He nuclei) Only done by heaviest nuclei where stability can only be achieved by decreasing number of neutrons AND protons Ex: decay of U- 238 What is the general formula?

33 Beta Par'cle A beta particle has negligible mass A beta particle is a stream of high speed electrons

34 Beta emission Par'cle deflects towards posi've poles Done because neutron/proton ra'o is too large Neutron is converted into a proton and an electron Why must an electron be produced? What is the energy of that electron? Ex: decay of C- 14 What is the general formula?

35 Positron emission Done by nuclides below the band of stability; the neutron/proton ra'o is too small A proton is converted into a neutron by emimng a positron an an'- electron A positron is a equal to an electron in all aspects except for being posi'vely charged When a positron leaving the nucleus meets an electron (inevitable!) they annihilate each other producing 2 γ Ex: decay of C- 11

36 Electron capture Another way for nuclides to raise a neutron/ proton ra'o that is too small An inner orbital electron is captured and combined with a proton forming a neutron The energy of the electron is released as an x- ray (remember the Bohr model) Ex: decay of Al- 26

37 Gamma Ray Gamma rays have no charge or mass and are similar to X rays.

38 Gamma emission Usually produced shortly aver (as in s aver) an unstable nuclei has decayed via α- decay The resul'ng nucleus is meta- stable and in an excited state The release of the γ photon reduces the energy of the nucleus (cooling it off!) Will mass change? Why or why not?

39 Warmup Predict the products of the following nuclear reac'ons (show fully balanced reac'ons) A. electron emission by C- 14 B. Positron emission by B- 8 C. electron capture by I- 125 D. alpha emission by Rn- 210

40 MSFWBAT Prac'ce prac'ce prac'ce problems in order to understand energy, mass, and radio- decay Feel rainbows and puppy- dogs happy about balancing nuclear reac'ons Go home for the weekend and tell your parents you know what E=mc 2 actually means and how to use it!

41 Today - No lecture prac'ce ~ calcula'ons of mass defect ~ radio decay prac'ce problems COLLABORATE and SHARE this is important in science but use your 'me effec'vely! Wrap up for today: show me one completed sheet and one half- completed sheet you finish remainder for HW test Wednesday

42 Selected problems See pages , 7, 11, 18, 27, 40, 44, 46, 47, 50/51, 52 Don t necessarily sit down and plow these all at once, do a few a at 'me. Take a break, then come back and do a couple more... Regular prac'ce for short periods is bewer than a single long drill and kill

43 Par'cle problems Given a source of par'cles on the lev, and the two charged plates, predict the path of each of the par'cles + ==< -

44 Warmup: Why are there elements? 2. Why are some elements radioac've? 3. As atomic number increases, what happens to atomic mass? Must this always be true? 4. Look at the periodic table at the following element pairs: Argon and Potassium Nickel and Cobalt Tellerium and Iodine Does you answer to #3 change?

46 MSFWBAT Given sufficient informa'on, determine how much of a radioac've sample will remain aver a period of 'me

47 Review and Extend: Differences between alpha, beta and gamma radia'on? Charge Mass Penetra'ng Power

49 Half life calcula'on The 'me it takes for half of a radioisotope to decay N = N o (½) t/t N = the remaining amount N o = the ini'al amount t = the elapsed 'me T = the dura'on of the half- life

50 examples If half- life of C- 14 is 5730, how much Carbon remains from a 10.0g sample aver 5730 years? years? 3 half lives? 6 half lives? years? years?

51 Genera'on of C- 14 If C- 14 always decays to Nitrogen, and the half- life is only 5730 years, where does C- 14 come from?

52 Carbon- da'ng

53 Radioac've candy! Lab

54 Wrap The half life of C- 14 is 5730 years. Based on this, would it be possible to use the ra'o of N- 14 to C- 14 to determine the age of a dinosaur fossil? Again with C- 14, would it be useful to determine the age of a neolithic human sealement in modern day Britain? Are your answers for each ques'on different? Why/why not?

55 Decay series

56 Nuclear fusion and fission Fusion is combina'on of nuclides into a new and heavier nucleus Happens in stars, such as our sun H + H He + energy Fission is breaking apart (through decay) of an unstable heavy nucleus into smaller nuclei (and par'cles)

57 Italian disccovery: Enrico Fermi was bombarding Uranium nuclei with neutrons, believed he had synthesized a trans- Uranic element, but could not verify it Discovery

58 Next Lise Meitner worked out that the transuranics were merely radioisotopes of known elements This proved that nuclei could be shaaered

59 The natural conclusion Because of the mass excess of heavy isotopes Einstein s conclusion that mass and energy are equivalent Fermi and Meitner s demonstra'on of the fission of Uranium came the realiza'on that the energy holding a nucleus together could be released if the nucleus itself was shaaered

60 Neutron release drives nuclear fission In a nuclear reac'on, the heavy nuclei is struck by a slow neutron The neutron is absorbed, which renders the nuclei unstable The nuclei disintegrates into two new nuclei Three neutrons are released (they are fast neutrons ) The binding energy of the nucleus is released

61 Chain reac'ons Because more neutrons are released than began the process, each neutron is capable of impac'ng another nucleus and inducing fission in that nucleus The reac'on then is self- sustaining, a chain reac'on This released a spectacular amount of energy (binding energy + conversion of a por'on of mass into energy)

62 fission

63 Driving the reac'on Cri'cal mass the minimum amount of fissile material needed to provide the number of neutrons needed to sustain the reac'on If each nuclei releases >1 neutron the reac'on will accelerate out of control If each nuclei release 1 neutron the reac'on is controlled If each nuclei releases <1 neutron, the reac'on will slow down and stop

64 The Manhaaan Project

65 Nuclear energy

Alta Chemistry CHAPTER 25. Nuclear Chemistry: Radiation, Radioactivity & its Applications

Alta Chemistry CHAPTER 25. Nuclear Chemistry: Radiation, Radioactivity & its Applications CHAPTER 25 Nuclear Chemistry: Radiation, Radioactivity & its Applications Nuclear Chemistry Nuclear Chemistry deals with changes in the nucleus The nucleus of an atom contains Protons Positively Charged