Nuclear Chemistry

1. Nuclear Chemistry Jump to alpha decay a.k.a. “PHC 25 Section Assessment Answers” Init 9/16/2008 by Daniel R. Barnes

3. First, let’s clear something up.

4. a b g Nuclear radiation does not make super-heroes.

5. Nuclear radiation makes hospital patients and asylum inmates.

8. http://inmotion.magnumphotos.com/essay/chernobyl If you want to see more of that, here’s a nice, disturbing link to a photoessay w/spoken narration about the aftermath of the Chernobyl nuclear reactor accident. It’s in two parts. The link takes you to the introduction, but make sure you watch/listen to the main photoessay as well. Required viewing materials: box of kleenex.

9. https://www.youtube.com/watch?v=u7QYJKnagas Here’s a YouTube video that shows a geiger counter being used. You probably don’t need to watch it past the one minute mark.

10. If an atom’s nucleus has the right balance of protons and neutrons, it can last pretty much forever. e = mc2 However, if the atom has too many or too few neutrons, the nucleus will be unstable. At some random, unpredictable moment, the nucleus will “decay”, spitting out a piece of itself.

11. The three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. g a b alpha particle beta particle gamma particle g - 0 e 2+ 4 He -1 2 high energy, high frequency photon high speed helium nucleus high speed electron

12. 238 U 92 Alpha Decay Uranium-238 undergoes alpha decay to become thorium-234. a e = mc2 The nucleus’ mass number . . . . . . goes down by four. The nucleus’ atomic number . . . . . . goes down by two. a 234 Th + He 4 2 90

13. Jump to fission Beta Decay Carbon-14 undergoes beta decay to become nitrogen-14. b e = mc2 The nucleus’ mass number . . . . . . stays the same. The nucleus’ atomic number . . . . . . goes up by one. b 14 C 14 N + e 0 6 7 -1

14. g Gamma radiation is the most penetrating. Alpha radiation penetrates 0.05 mm into the human body. Beta radiation penetrates 4 mm into the human body. Gamma radiation shoots right through the human body. In fact, gamma radiation not only shoots right through skin, flesh, and bone, but also through substantial amounts of lead, concrete, or whatever. Gamma rays are very hard to stop. Even air can stop gamma rays, though, if you have enough air. The 50-mile-thick (or so) layer of air that surrounds our planet shields us nicely from gamma rays that come from outer space.

15. g Gamma radiation is the most penetrating. Alpha particles may be the largest radiated particle that we’re studying here, but they stop the quickest. This seems odd, considering that it’s easier to stop a baseball than it is to stop a freight train. Alpha particles lose their energy rapidly by ionizing other atoms . . .

16. Alpha particles are a form of "ionizing radiation". Skip ionizing radiation, please. Here’s an ordinary carbon atom minding its own business. Perhaps it’s part of a keratin protein molecule in your epidermis. It’s got the usual six electrons oribiting its nucleus. 6 positive protons 6 negative electrons  neutral atom

17. Alpha particles are a form of "ionizing radiation". I’m gonna go mess up a DNA molecule! Look out, little carbon atom! Here comes an alpha particle! Aw, gee! That psycho alpha particle just knocked one of your electrons out of orbit! I’m CHARGED already! Look at me! I’m an ION! 6 positive protons 5 negative electrons  +1 ION! 6 positive protons 6 negative electrons  neutral atom No! Please don’t! You’ll be charged with causing cancer!

18. Alpha particles are a form of "ionizing radiation". Notice something about the alpha particle’s motion . . . It takes energy to ionize an atom. Knocking electrons out of orbit is hard work. . . . It slows down after it knocks the electron out of orbit. It loses lots of speed by ionizing the atoms it bumps into, so it doesn’t go very far. 6 positive protons 5 negative electrons  +1 ION! 6 positive protons 6 negative electrons  neutral atom

19. Alpha particles are a form of "ionizing radiation". Beta particles are a form of ionizing radiation, also. Gamma rays ionize atoms, too. Alpha, beta, and gamma particles all lose energy when they ionize an atom. The thing about beta and gamma particles seems to be that they don’t bump into electrons as easily as those huge alphas do, so they get to penetrate deeper into matter before they bump into an electron, lose their energy, and stop. I think.

20. The neutron-to-proton ratio determines what kind of decay a radioisotope will undergo. If an isotope has too many neutrons, it will probably undergo beta decay, in which one of its excess neutrons turns into a proton as it spits out a beta particle (an electron). The opposite of this, electron capture, is when a nucleus with too many protons captures an electron, turning one of its excess protons into a neutron. Also, if a nucleus is simply too big (atomic number > 83), the nucleus will be radioactive. Such large, unstable nuclei are often alpha emitters, but some are also beta emitters.

21. WARNING • The following simulation of radioactive decay focusing on the issue of half-life is somewhat oversimpilfied.

22. 234 234 234 234 234 234 234 234 234 234 234 234 234 234 234 234 Th Th Th Th Th Th Th Th Th Th Th Th Th Th Th Th 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 238 238 238 238 238 238 238 238 238 238 238 238 238 238 238 238 U U U U U U U U U U U U U U U U 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 92 0 years 4.5 billion years 9 billion years 13.5 billion years 18 billion years ? years

23. Decay Curve for a Radioactive Isotope 1/2 = 50% of the original amount Remaining radioisotope / % of original amont 1/4 = 25% 1/256 = 0.390625% 1/128 = 0.78125% 1/8 = 12.5% 1/16 = 6.25% 1/64 = 1.5625% 1/32 = 3.125% 0 1 2 3 4 5 6 7 8 Half-lives gone by

24. Decay Curve for a Radioactive Isotope Remaining radioisotope / % of original amont Amount approaches zero but never reaches zero 0 1 2 3 4 5 6 7 8 Half-lives gone by

25. Kr-91 Kr-91 Kr-91 Kr-91 Ba-142 Ba-142 Ba-142 Ba-142 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-235 U-236 U-236 U-236 U-236 Nuclear Fission

29. “The atom bomb dropped on Hiroshima contained 64 kg of uranium, of which 0.7 kg underwent nuclear fission, and of this mass only 0.6 g was transformed into energy.” The energy released by nuclear reactions is much larger, per gram of explosive material, than the energy relased by chemical explosions. Jump to fission vs fusion c2 = 34,500,000,000 mi2/s2 c = 186,000 mi/s The 1.5 pounds of uranium that split that day yielded the same explosive energy as 15,000 tons of TNT. e = mc2 1.5 pounds of uranium = 30,000,000 pounds of TNT.

31. Kr-91 Ba-142 U-235 U-235 U-236 Without a moderator . . . TOO FAST! . . . fission can not continue

32. Kr-91 Kr-91 Ba-142 Ba-142 U-235 U-235 U-236 U-236 But with a moderator . . . Nice throw! Nice and slow! MODERATOR . . . the chain reaction can continue.

33. Fusion Boosting Later models of the atom bomb used the heat and pressure from fission to cause deuterium and tritium to fuse. The fusion of these forms of “heavy hydrogen” into helium released energy, but not much compared to what the fissioning uranium or plutonium did. However, the neutrons released by the fusion of heavy hydrogen did help cause more of the fissile material to split, greatly increasing the efficiency and power of the fission chain reaction. Although uranium-238 can not sustain a fission chain reaction, it can be made to split, exothermically, if you shoot neutrons at it. Atom bombs always contained lots of 238U in addition to the main 235U fissile material.

34. Kr-91 Ba-142 U-235 U-236 Fusion Fission Gluing atoms together "Splitting the atom"

35. Protons close enough to join and form one nucleus will repel each other with extreme force. Fusion Protons don’t like other protons. Positives don’t like positives. The closer two charged particles get, the stronger the force between them. To get protons to get close enough to fuse together, you need to overpower this electrostatic repulsion. Remember how small a nucleus is compared to the atom as a whole? Extreme heat and/or extreme pressure, both of which are found in the centers of stars, can make fusion happen. Gluing atoms together In a nucleus, protons are VERY close together.

36. The strong force has a strength of zero until protons get VERY close together, and then it gets VERY strong, very suddenly. Fusion If protons are smashed together by exterme heat and/or pressure, they will get close enough for something magical to happen . . . The strong force is so powerful, that it overpowers the electrostatic repulsion the protons feel for each other . . . The “strong force” turns on. (The “strong force” is sometimes called the “strong nuclear force”.) Gluing atoms together . . . and it “glues” them together.

37. He Kr-91 Ba-142 H H H H U-235 U-236 Fusion Fission Gluing atoms together "Splitting the atom"

38. FISSION FUSION split glue Big atom splits in two Little atoms join together Atoms change element Has been happening naturally for billions of years – a LOT Almost never occurs naturally Nuclear bombs High particle speed helps reaction Neutrons must not go too fast e = mc2 Negative yield electricity . . . Profitable electricity

39. Chemical Reactions Nuclear Reactions Atoms do NOT change element. Atoms DO change element. Electrons are the main actors The nucleus is the main actor. Electromagnetic forces  lower energies Nuclear forces  higher energies Immeasurably small mass changes Small but measurable mass changes Bonds are broken, bonds are made Some endo, some exo Matter changes properties

40. The End All pages after this are graphical scrapheaps. Just get out of here now.

41. TRASH PAGE Kr-91 Kr-91 Ba-142 Ba-142 U-235 U-235 U-235 U-236 U-236 NO TRESPASSING! KEEP OUT! GO AWAY! JUNKYARD FOR GRAPHIC ORPHANS NOTHING TOSEE HERE! SHOVE OFF! CONDEMNED Why not crawl off into a corner and get a life or something?

42. TRASH PAGE • JUNKYARD FOR GRAPHIC ORPHANS

44. Nuclear Chemistry HYPERINDEX Click a button. Go to a place!™ Title Page Alpha decay animation Nuclear fission animation Chernobyl kids Beta decay animation Fission & fusion animations Half-life animation