Nuclear Physics

1. Nuclear Physics The Manhattan Project brings the world into the Nuclear Age. Test bomb code named “the gadget” 1st nuclear test explosion New Mexico, 1945

2. Key Physicists working on the Manhattan Project Robert Oppenheimer Edward Teller “father of the H-bomb” Enrico Fermi Niels Bohr Leó Szilárd 1st conceived of a “chain reaction” Klaus Fuchs David Bohm

3. What goes on Energy is released when electrons find lower energy states, often when shared between atoms Chemical reaction Nuclear reaction The nuclei certain atoms are more stable than others. When an unstable nucleus changes to one that is stable, some energy is released.

4. Some things to figure out How to represent a nuclear reaction like in a chemical equation How to predict a product (find the missing player) What holds the nucleus together Where does the energy come from 1st a bit of review from chemistry…..

5. Representing the parts making up a specific atom Protons + neutron Net Charge if there is one Mass # Symbol atomic # # protons depend only on the element

6. Symbols • Find the • Atomic number • Mass Number • number of protons • number of neutrons • number of electrons 9 19 19 9 F 10 9 9

7. Symbols • if a neutral atom has an atomic number of 34 and a mass number of 78 what is the • number of protons • number of neutrons • number of electrons • Complete symbol 34 78 Se 44 34 34

8. 6 Neutron/6 Protons 8 Neutron/6 Protons Carbon-12 Carbon-14 These are called isotopes. Same element different masses. Which particle does one atom have more of? 14 12 C C 6 6

9. IONS? 56 2+ Fe 26 How many of each… 26 # Protons = 30 # neutrons = 24 # electrons =

10. Next, Its fairly obvious what holds the electrons to the atom. An attraction to the positive nucleus! But what holds the nucleus together, but before we answer lets revisit some atomic geography…

11. Marble dropped here is volume of nucleus Football field, “Volume” occupied by electrons

12. The electrons can spread out a lot more to reduce mutual repulsions and are pulled inward by the nucleus

13. The same amount of positive charge is concentrated in the center. The protons repel each other and are pulled outward by the electrons!

14. The protons and neutrons are so concentrated. A nucleus the size of a golf ball would have a mass of about… 4,100,000,000,000 kg It could never exist due to instabilities that come with the number of protons and neutrons put together.

15. The glue that holds it together is the neutron. I knew they had to be there for a reason!

16. 4 “Fundamental Forces” Gravity Electricity/magnetism Strong Weak The neutrons invoke the strong force to glue the nucleus together. Hence the name of the sub-sub atomic particle responsible

17. The strong force holding the nucleus together is a stronger force than the electric force trying to break it apart. (huh that makes sense) BUT! The strong force WEAKENS with distance much more quickly that the electric force. So as atoms get BIGGER, the force holding it together doesn’t extend as far as the repulsive force trying to break it apart. There does happen to be a happy size around Iron & Nickel where nuclei are the most stable. (for a given amount of neutrons, many will enter few will win, not valid in california)

18. Large heavy unstable nuclei will tend to break apart into smaller nuclei. This is source of nuclear energy. Often in the process, atomic “shrapnel” is produced that we refer to as radiation. 226 222 4 He Ra Ra + 2 88 86 But balancing the books is not that hard. # of protons initial = final Initial mass # = Final mass number

19. 226 222 4 He Ra Ra + 2 88 86 This is a piece of shrapnel COMMONLY produced. So common is it called an alpha particle and called alpha decay or alpha radiation. Sometimes it is given the symbol… 4 a Don’t let it freak you out, just balance the books. 2

20. Another example, whose the missing player. And I am just making up random examples here not likely reactions 24 7 17 Na O + Li 11 8 3

21. Neutrons are symbolized to make the books work out. Makes sense. Why wouldn’t this be Nitrogen 26 1 25 Na Na + n 11 11 0

22. Now a “little bit” of energy can be released from the reactions if a lot of them happen. How does this play out? Einstein had predicted that a little bit of mass could be converted to a whole lot of energy aka E = mc2. He considered himself a pacifist and would take no part in any war-time activity. However, a short guy with a little mustache who was trying to take over the world (among other atrocious deeds) did cause him to write a letter to President Roosevelt that we should work on developing a nuclear weapon. The Nazis scientists were coming to the same realizations as us. They were making the same discoveries we were, also with gifted scientists. However, there was not the PUSH to make it work there as it was here. Not to mention a small band of countries trying to take over the rest of the world has it resources rather strapped.

23. So here’s the deal (more or less / but it still depends on a happy proton to neutron ratio which I am not going into) atoms will release energy if an event happens that they can get closer to the sweet spot (Fe/Ni). Light atoms fuse together to form heavier ones given huge speeds to start the impact. called FUSION Some heavy atoms break apart spontaneously or given the slightest push. Called FISSION

24. If we look at the mass “isolated” proton and neutrons they are listed below mp = 1.6726x10-27 kg mn = 1.6749x10-27 kg

25. The kilogram is a bit of a clumsy unit to use for a sub-atomic particle. So we typically deal with them using amu (aka atomic mass units) also abbreviate as “u” 1 “u” is defined as 1/12 the mass of a 12C atom. 1 u = 1.6605x10-27 kg

26. If we look at the mass “isolated” proton and neutrons they are listed below mp = 1.6726x10-27 kg mn = 1.6749x10-27 kg mp = 1.00728 u Where 1 u = 1.6605x10-27 kg mn = 1.00867 u

27. When I take these isolated protons and neutrons and put them together, the nucleus has LESS mass than the parts I started with! Huh? Where does the mass go? It is converted into ENERGY! according to e = mc2

28. The difference in mass between the separate protons/neutrons and the measured mass of the nucleus is known as the mass defect. mass defect = S (individual p+ and no masses)- (measured mass of nucleus)

29. The energy released in the process is called the binding energy EB = (mass defect) c2 binding energy The source of all binding energy is the strong force.

30. How much binding energy would be produced if a mass defect of 1 u (amu) was seen 1 u = 1.6605x10-27 kg E = mc2 E = (1.6605x10-27 kg)(2.9979x108 m/s)2 E = 1.4924x10-10 J

31. Converting to eV 1.4924x10-10 J 1 eV = 1.6022x10-19 J 1 9.31x108 eV 931 MeV

32. A handy thing to have written 1 u = 931 MeV The binding energy per amu mass deficit

33. 4 A helium nucleus has mass of 4.002602 amu He 2 mp = 1.00728 u mn = 1.00867 u What is the: mass deficit, binding energy binding energy per nucleon

34. 2.01560u 2 protons 2 x 1.00728 u = 2.01734 u 2 neutrons 2 x 1.00867 u = 4.03190 u total mass of protons and neutrons Mass Deficit = 4.03190 u - 4.002602 u Mass Deficit = 0.029298 u

35. Mass Deficit = 0.029298 u Binding energy = 0.029298 u 931 MeV 1 u = 27.3 MeV Next, how many nucleons in an alpha particle

36. 2 neutrons and 2 protons so 4 27.3 MeV = 6.82 MeV / nucleon 4 nucleons

37. The greater the binding energy, the more energy that was lost in its formation and the more stable it is. Just like nitroglycerine will degrade into very stable molecules like N2, H2O, CO2 and release a lot of energy? Can I take the products of the explosion and turn them back into nitroglycerine Yes, but I will have to supply energy. It will not happen spontaneously!

38. The most stable atoms are in the Iron / Nickel size energy released getting by bigger energy released getting by breaking apart

39. a lot of energy is released when 2 hydrogen nuclei fuse together into a helium nucleus

40. Energy is absorbed by the atoms when increasing beyond the approximate mass of an Iron nucleus. The nucleons gain mass

41. Reactants Products + ENERGY Remember in nuclear reactions mass is converted to energy. Since the reaction above released energy, the product pieces must have less mass than the reactants.

42. The difference in masses of the reactants and products is used to calculate the disintegration energy according to E = mc2 Dm = (mass of products – mass of reactants ) E =(Dm)c2 Disintegration Energy

43. If the products end up with less mass then energy was ___________ Released Exothermic happens spontaneously

44. If the products end up with less mass then energy was ___________ Released Exothermic happens spontaneously If the products end up with MORE mass then energy was absorbed. Endothermic do NOT happen spontaneously

45. In the following reaction, what is the disintegration energy in MeV? Would the reaction be spontaneous or not? 4 17 1 14 He O + H N + 2 8 1 7 The mass of the alpha particle is 4.0015 u. The Nitrogen nucleus is 13.9992 u. The oxygen nucleus is 16.9947 u

46. In the following reaction, what is the disintegration energy in MeV per nucleon? Would the reaction be spontaneous or not? It is just an isolated proton! mp = 1.00728 u 4 17 1 14 He O + H N + 2 8 1 7 4.0015 u 13.9992 u 16.9947 u What about the last particle?

47. + = 18.0007 u Will the reaction be spontaneous or not? 4 17 1 14 He O + H N + 2 8 1 7 4.0015 u 13.9992 u 16.9947 u 1.00728 u + =18.00198 u NO

48. + = 18.0007 u In the following reaction, what is the disintegration energy in MeV per nucleon? 4 17 1 14 He O + H N + 2 8 1 7 4.0015 u 13.9992 u 16.9947 u 1.00728 u + =18.00198 u Dm = 18.00198 u - 18.0007 u = 0.001280 u

49. 4 17 1 14 He O + H N + 2 8 1 7 Convert to MeV 931 MeV Dm = 0.001280 u 1 u 1.12 MeV