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Welcome to Nuclear Chem It’s a bizarre-o world, where things are one thing, then they change into another. Leave your normalcy in the hall! Welcome to.

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Presentation on theme: "Welcome to Nuclear Chem It’s a bizarre-o world, where things are one thing, then they change into another. Leave your normalcy in the hall! Welcome to."— Presentation transcript:

1 Welcome to Nuclear Chem It’s a bizarre-o world, where things are one thing, then they change into another. Leave your normalcy in the hall! Welcome to crazy!

2 Pull out tables N and O now (like now without the “W”) Table N lists all of the radioisotopes that you need worry about in our class. Radioisotopes are radioactive, they are unstable isotopes (or atoms) with a p + to n° ratio that is out of synch with normal. They exist naturally, or they can be formed. As you recall, isotopes are chemically identical atoms with different numbers of neutrons, and therefore different masses. These are unstable isotopes, they literally cannot stay together the way they are, so they EMIT radioactivity (or radiation).

3 Radiation, in our class, comes in 6 forms, all listed neatly in table O. These unstable atoms (radioisotopes) literally spit out parts of themselves, to change the ratio of p + : n° in their nucleus, in an attempt to get stable. Doing this changes them from one kind of an atom to another, which is called transmutation. It can just happen naturally (natural transmutation), or people can cause it (artificial transmutation)

4 The unstable nuclei are the interesting ones. They are unstable because the ratio of n° : p + is outside the so called “band of stability”. Small atoms have about a 1:1 ratio of n° : p +. Larger atoms have n° : p + ratios up to 1.5 n°: 1p +1 All nuclei with ratios outside this band are unstable, and that’s what we’ll look at. Band of Stable n° : p + ratios

5 Transmutation Is one of the weirdest things that you’ll learn. Atoms “wake up” one day as some unstable atom and on that day, for no obvious reason that this is their day, they will emit radiation (some of their nucleus) and become something else, a different kind of atom. That’s like if you go to bed tonight and wake up normally, but just after lunch (or before) you turn into a dog. A dog named Redox, or something else, like a fish maybe. That’s how weird it is.

6 ALL ATOMS ARE ISOTOPES. Most are STABLE, because their neutron:proton ratio falls within “normal” range and the atoms just are. They don’t emit radiation. When an isotope is unstable, it’s a radioisotope. One day, for no apparent reason, it will decide to emit radiation to change its nucleus to become more stable, the radiation comes in six forms we’ll learn about. All of the radiation forms are dangerous to living things. There is NO safe dose, all radiation is bad for your health. Radiation can cause cancer, or with a big enough dose, kill you in a few days, or even hours. Radiation sickness is when you get a big dose, which might or might not kill you. Until you do die, you’ll wish you were already gone. If you don’t die, you will likely end up with a variety of cancers, often affecting your glands or blood.

7 Controlled forms of radiation are actually used for medical treatment, but let’s not get into that right now. All radiation is bad for living things all of the time. In our class radiation comes in these forms (table O) Alpha particles Beta particles Gamma radiation (energy, not particles) Protons Neutrons Positrons (which are really cool and super-duper odd)

8 Let’s stop thinking too much and start doing some stuff, let’s look hard at table N. The first radioisotope is called gold-198 The 198 is the atomic mass of this isotope. It has 198 amu or 198 total protons plus neutrons in the nucleus. It’s on this Table N list because that is an unstable ratio. What is that ratio you might ask (I was hoping someone would ask right now) 198 Au 198 79 Au This is really… this 198 p + plus n° Of those 198 total, 79 are protons

9 198 79 Au Table N says that this stuff will undergo β– decay, or beta decay. That means it emits a beta particle as radiation to adjust the proton – neutron ratio in the nucleus to get stable. Table O shows us the symbols. It’s a chemical reaction but with simple math to figure everything out. A beta particle of radiation + what ever then heck it turns into. Radiation emission causes transmutation 198 79 Au + 0 e

10 198 79 Au 0 + 198 80 Hg Radioactive gold atoms will emit beta particles and transmute into mercury-198 This has many names: 1.Radioactive decay 2.Spontaneous radioactive decay 3.Beta decay 4.Natural transmutation 5.Beta radiation emission e

11 Let’s do the next to radioisotopes, carbon 14, and then calcium 37. Carbon is also going to emit a beta particle, but watch out for that calcium, when it emits a positron particle of radiation, the math adds up differently. 14 C 0 + e 37 Ca 0 +1 + e

12 14 6 C 0 + e 37 20 Ca 0 +1 + e 14 7 N 37 19 K Carbon 14 is unstable so it naturally transmutes into nitrogen 14 and a beta particle. The radioactive carbon 14 emitted a beta particle to get more stable, and transmuted into a stable isotope of nitrogen, N-14. Radioactive Ca-37 emitted a positron from it’s nucleus and transmuted into K-37. The calcium 37 under went natural radioactive decay (positron decay) to become more stable, transmuting into K-37.

13 Both cobalt-60 and cesium-137 undergo beta decay. The Iron-53 transmutes by emitting radiation called positron particles. Do the decay reactions now. (tables N and O without the “W”) 60 Co 137 Cs 53 Fe

14 Both cobalt-60 and cesium-137 undergo beta decay. The Iron-53 transmutes by emitting radiation called positron particles. Do the decay reactions now. (tables N and O without the “W”) 60 27 Co 137 55 Cs 53 26 Fe 0 + e 137 56 Ba 0 + e 60 28 Ni 0 +1 + e 53 25 Mn Cobalt 60 transmutes into nickel 60 by emitting a beta particle Cs-137 undergoes natural beta decay and transmutes into barium 137 Iron-53 emits positron radiation and transmutes into a manganese isotope: Mn-53

15 Just for the record, a beta particle is sort of built like an electron, but is not an electron. It has no mass in our class, and it’s got a -1 charge like an electron, but it’s from inside a nucleus, so we call it a beta particle. Here’s the strangeness. It’s formed when a neutron which has no net charge emits a particle of no mass with a negative charge, leaving the neutron with the same mass as before, but without any negative charge (so now it’s positive). One neutron emits one beta particle, and the neutron is now a proton. No change in atomic mass, but a change in the number of protons in the nucleus.

16 A positron is emitted from the nucleus as radiation by some isotopes. Positrons have a positive charge and no mass (like an opposite electron). Protons emit their “postive charge by spitting out this positron, leaving that proton without charge. Here the Proton becomes a neutron! There’s no change in atomic mass, but a change in the proton to neutron ratio.

17 Alpha particles are much bigger, mass of 4 amu, containing 2 protons plus 2 neutrons. It’s got the same form as a helium nucleus, but it’s not helium, it’s an alpha particle. Remember the Gold Foil experiment, Rutherford shot alpha particles at the gold to see what these positively charged (+2) particles would do when they got to the gold atoms. 220 Fr What does this francium-220 do?? Look over table N.

18 220 87 Fr 4242 He + 216 85 At Francium 220 undergoes natural transmutation by emitting an alpha particle, and becoming astatine 216 Do the next alpha particle emitting radioisotope, which is plutonium-239 239 Pu 4242 He

19 239 94 Pu 4242 He + 235 92 U For classwork/homework, finish up the rest of table N as neatly as you can. Skip lines between each isotope, count carefully, peace love and nuclear chemistry. PS: for every time I hear the word NUKE-u-LAR, I deduct one point from your nuclear celebration score. The word is not NUKE-u-LAR, and if you pronounce it like that, you are not being cute, or speaking with an accent, you just sound like you don’t really know what you’re talking about and I will find it hard to cope. I’m serious! I will undergo some weird personal transmutation into a fish or something worse. What could be worse?

20 OB: nuclear chem class #2 practice decay reactions, the half life of radioisotopes A half life is the amount of time it takes for one half of a given radioisotope to transmute. Which half? Which atoms will actually decay is a total mystery. But, statistically, half will transmute in a given half life.

21 First, let’s practice the decay reactions for these isotopes… 14 6 C 198 79 Au 131 53 I 239 94 238 92 37 20 Pu U Ca

22 First, let’s practice the decay reactions for these isotopes… 14 7 N 198 79 Au 131 53 I 239 94 238 92 37 20 Pu U Ca 198 80 Hg 14 6 C 131 54 Xe 235 92 U 234 90 Th 37 19 K + + + + + + 0 -1 e e e 4242 He 4242 0 +1 e Gold-198 undergoes beta decay and transmutes to mercury-198 Carbon-14 transmutes to N-14 by beta decay. Iodine-131 becomes Xe-131 by beta decay. Pu-239 transmutes into U-235 by alpha decay. Alpha decay occurs and uranium-238 becomes thorium-234. Calcium-37 undergoes positron decay and forms into potassium-37.

23 HALF LIFE: the amount of time it takes for one half of a radioisotope to decay into a daughter isotope. The details of why this occurs or how this occurs, or even when any particular isotope will decay is unknown. What is known very well is the amount of time it takes for these isotopes to decay. Statistics are easy compared to looking at individual atoms. Some half lives of isotopes are very, very long, in the millions of years. Some isotopes have half lives measured in milliseconds (thousandths of a second). Many half lives are listed in table N, let’s look now…

24 The half life of radioactive gold-198 is 2.69 days. This means that if you have 150.0 grams of Au-198, in 2.695 days you will have just 75.00 grams of this isotope, and 75.00 grams of what ever it is that it transmuted into (Hg-198) In 2.695 more days, you will have just 37.50 grams of the radioactive gold, and 37.50 more grams of the mercury. After yet another 2.695 days, you’ll have only 18.75 grams of your gold. Each half life passes and another half of the radioactive isotope decays away.

25 The beta decay of gold-198 Mass Half Lives 150.0 g 0 75.00 g 1 37.50 g 2 18.75 g 3 In our class the half lives will always be whole numbers, we will not measure these in partial half lives. The math is easy in high school. Total time passed: 2.695 days 5.390 days 8.085 days

26 What’s the half life in time? What’s the decay mode? K-37 I-131 Ra-226 Uranium 238

27 What are the half lives of these radioisotopes? What is their decay mode? K-371.23 secondspositron I-1318.021 daysbeta Ra-2261599 yearsalpha Uranium 238 4,470,000,000 years alpha

28 You accumulate 22.0 grams of the radioisotope carbon-14. How long before you have only 2.75 grams? Every single half life problem demands that you draw a timeline. Every single one, even this one. 22.0 g NOW

29 22.0 g NOW You accumulate 22.0 grams of the radioisotope carbon-14. How long before you have only 2.75 grams? 1 half life 11.0 g 2 half lives 5.50 g 3 half lives 2.75 g It takes the length of time of three half lives for 22.0 g of Carbon-14 to transmute into just 2.75 grams. Since each half life of this radioisotope is 5715 years, 5715 years X 3 = 17,145 years It will take 17,145 years for this to happen.

30 The doctor wants to inject you with some radioactive Iodine-131 to measure your thyroid uptake. She injects you with 2.00 grams. How long until you have just 0.03125 g left in you? (disregard the significant figures here) 2.00 g NOW Start your timeline, and watch the calculator buttons. Go slowly.

31 The doctor wants to inject you with some radioactive Iodine-131 to measure your thyroid uptake. She injects you with 2.00 grams. How long until you have just 0.03125 g left in you? (disregard the significant figures here) 2.00 g START 1.00 g0.500 g0.250 g 0.125 g0.0625 g0.03125 g 123456 It will take 6 half lives for this 2.00 g radioactive iodine to transmute away so that only 0.03125 g remains. Each half life is 8.07 days, so… 6 X 8.021 days = about 48.126 days, about 1 ½ months.

32 You put 400.0 grams of Fe-53 in your pocket at noon. At what time you have 12.5 grams of this iron left? What has the other 387.5 grams become? What decay mode did this undergo? 400.0 g NOW The easy stuff first, then the math… Iron-53 undergoes positron decay this way:

33 You put 400.0 grams of Fe-53 in your pocket at noon. At what time you have 12.5 grams of this iron left? What has the other 387.5 grams become? What decay mode did this undergo? 400.0 g NOW The easy stuff first, then the math… Iron-53 undergoes positron decay this way: 53 26 Fe 0 +1 e+ 53 25 Mn This is positron decay.

34 You put 400.0 grams of Fe-53 in your pocket at noon. At what time you have 12.5 grams of this iron left? What has the other 387.5 grams become? What decay mode did this undergo? 400.0 g 0 half lives 200.0 g100.0 g50.0 g25.0 g12.5 g 1 2 3 4 5 5 half lives must pass for this to happen. Each half life of Iron-53 is 8.51 minutes. 8.51 minutes X 5 = 42.6 minutes

35 24. If a scientist purifies 1.0 gram of radium-226, how many years must pass before only 0.50 gram of the original radium-226 sample remains unchanged? 25. Based on Reference Table N, what fraction of a radioactive Sr-90 sample would remain unchanged after 58.2 years? 1. ½ 2. ¼ 3. 1/8 4. 1/16

36 24. If a scientist purifies 1.0 gram of radium-226, how many years must pass before only 0.50 gram of the original radium-226 sample remains unchanged? Only one half life must pass to transmute 1.0 grams into 0.5 grams, so just LOOK at table N: Radium 226 has a half life of 1599 years. 25. Based on Reference Table N, what fraction of a radioactive Sr-90 sample would remain unchanged after 58.2 years? 1. ½ 2. ¼ 3. 1/8 4. 1/16 START 29.1yr 58.2 years Whole Half Quarter

37 26. What is the half-life and decay mode of Rn-222? 1. 1.910 days and alpha decay 2. 1.910 days and beta decay 3. 3.823days and alpha decay 4. 3.823 days and beta decay 27. What is the half-life of sodium-25 if 1.00 gram of a 16.00-gram sample of sodium-25 remains unchanged after 237 seconds? 1. 47.4 s 2. 59.3 s 3. 79.0 s 4. 118 s

38 26. What is the half-life and decay mode of Rn-222? 1. 1.910 days and alpha decay 2. 1.910 days and beta decay 3. 3.823days and alpha decay 4. 3.823 days and beta decay LOOK at table N: 3.823 days, Alpha Radiation emitted, choice 3 27. What is the half-life of sodium-25 if 1.00 gram of a 16.00-gram sample of sodium-25 remains unchanged after 237 seconds? 1. 47.4 s 2. 59.3 s 3. 79.0 s 4. 118 s 16.00 g becomes 8.00 g, which becomes 4.00 g, which becomes 2.00 g, which becomes 1.00 g. That is 4 half lives. 237 seconds divided by 4 = 59.3 seconds (choice 2)

39 OB: nuclear chem class #3 Natural Radioactive Decay Modes, and Artificial Transmutations How does the Sun work, how does the chemistry inside a nuclear reactor work, and how do nuclear bombs make energy?

40 Let’s first look at an example of alpha decay… 238 92 U 234 90 Th+ 4242 He Radioactive (unstable) uranium-238 naturally undergoes alpha decay and transmutes into thorium-234. An alpha particle is emitted from the original nucleus, leaving a “daughter” nucleus of thorium. And then, beta decay… 3131 H 0 -1 e + 3232 He Radioactive hydrogen (tritium, mass of three) undergoes natural beta decay. A beta particle is emitted as radiation, and an isotope of helium is formed as the daughter nucleus.

41 Positron decay example… 19 10 Ne 0 +1 e+ 19 9 F The radioisotope neon-19 undergoes natural positron decay, transmuting into fluorine-19 while emitting a positron particle from the nucleus. Note, this starts with a single radioisotope, and then comes the arrow. Nothing makes this happen, it’s natural. It just happens. Nothing can speed this process up, nothing can slow it down. Nothing can change it either. It just happens. If you were to see a different style of radioactive decay reaction, one where the original radioisotope has a neutron added to it, that would be artificially induced, not natural. Artificial transmutation comes next. It’s easy to spot since there’s a + sign on the left of the arrow, and the simple math of adding the top numbers (mass) and the bottom numbers (protons) still works.

42 Artificial transmutation is caused by humans. It is a forced reaction, and does not occur naturally. It usually involves the release of massive amounts of energy inside a nuclear reactor or a nuclear bomb. The first artificial transmutation reactions were carried out by some of the “regular” characters in our class, notable Earnest Rutherford (gold foil), James Chadwick (discovered the neutron), and the husband and wife team of Marie and Pierre Curie. 1919: Rutherford “bombs” some nitrogen atoms with alpha particles. 14 7 N + 4242 He 17 8 O +H1 Nitrogen bombarded with alpha particles artificially transmutes into oxygen-17 and emits a proton

43 In 1932 Chadwick bombards beryllium-9 with alpha particles… 9494 Be + 4242 He 12 6 C + 1010 n Alpha particles are blasted into beryllium atoms, transmuting artificially into carbon-12 and emitting a neutron in the process. In 1934 the Curie’s bombard aluminum with alpha particles, they form the first artificially created radioisotope in the process. 27 13 Al + 4242 He 30 15 P + 1010 n Aluminum atoms are bombarded with alpha particles, causing the aluminum to artificially transmute into radioactive phosphorous while emitting a neutron. The radioactive phosphorous will undergo natural transmutation.

44 Those examples of artificial transmutation are relatively speaking minor concerning energy emitted. They were done in the lab, no explosions occurred. According to Albert Einstein, energy and matter are the same thing, just in different forms. His famous equation, E = mc 2 Stands for energy equals mass times the speed of light squared. He proved that in a nuclear reaction, some matter could be converted into a lot of energy. This was the basis for nuclear reactors and nuclear bombs. In chemistry, matter cannot be created or destroyed. In nuclear chemistry that is not the case.

45 The artificial transmutation of U-235 by neutron bombardment into barium, krypton, and three more neutrons. Very strangely, there is a small loss of mass, and that mass is converted into energy. In the “second” round, three more U-235 nuclei are bombarded with the three newly formed neutrons, and this process occurs three more times, with three times the loss of a small amount of mass. (and again and again, until lots of energy can be released). This is called FISSION (the splitting of an atom). The mass of the Kr and Ba looks the same as the neutron and original U-235, but it is in fact slightly less. This slight amount of missing mass, the MASS DEFECT, is converted into energy. Lots and lots of energy!

46 The fission of uranium-235 is called a chain reaction, because one neutron causes the release of three neutrons plus some energy. These three neutrons cause the release of nine more neutrons, and more energy. Those nine cause the release of 27 neutrons and more energy. Those 27 neutrons cause the release of 81 neutrons, etc. The reaction becomes bigger and bigger quickly, releasing more and more energy all the while. With enough (a critical mass) of radioactive uranium-235, so much energy could be released it could cause an enormous explosion. Those are giant sized ships from a navy, watching a nuclear test explosion from a “safe” distance.

47 Fission splits larger isotopes into smaller ones. The Sun does something different, it fuses smaller atoms of hydrogen into larger helium atoms. In doing so some mass is lost (mass defect) and even more enormous amounts of energy are released. The Sun has an unbelievable mass and with that comes huge gravity and pressures. The heat and pressure allow it to squash hydrogen atoms into helium at the center, and it takes more than 10,000 years for that heat to escape to the surface to radiate out into space.

48 The Sun squashes four hydrogen's into helium to release energy this way: 1 4 H 4242 He + 2 e + energy! 0 -1 Also given off in this reaction is gamma radiation and neutrinos, which are very small particles that you will learn about in advanced physics if you are lucky enough to go there. For fusion to occur, crazy high temperatures and pressures must be acting. Fission reactions SPLIT atoms apart, Fusion reactions squish atoms together.

49 Nuclear bombs are either fission bombs that split atoms of uranium-235 and release huge amounts of energy, Or, they can be fusion bombs (hydrogen bombs). To make a fusion, or hydrogen bomb you have to first set off a fission bomb around the core of hydrogen, so enough heat and pressure can be exerted onto this hydrogen, to make that secondary fusion reaction occur. It’s hard to believe but fission reactions can be “controlled”, as in nuclear power plants, and the energy released can be harnessed and used. A fusion reaction is so much bigger that nothing can contain that energy. Fusion reactions are fine for the Sun, or for horrifically powerful bombs, but so far, not useable for human energy needs. Primary fission bomb. Secondary Fusion bomb

50 Nuclear Chem Class #4 A short review problem; and then, How does a nuclear power plant make electricity? What happened in Japan after the tsunami?

51 You dig up an old wooden box from under your garage and find a metal box inside. Inside this metal box is a bottle marked 64.0 grams of strontium-90. When you mass this metal (under the care of a nuclear chemist), you find it only has mass of 0.500 grams. The rest of it is gone?! First, write the nuclear decay reaction for Sr-90. Was this a natural transmutation or an artificial one? What did the other 63.5 grams of this strontium become? How long ago did this box get buried in your dirt?

52 You dig up an old wooden box from under your garage and find a metal box inside. Inside this metal box is a bottle marked 64.0 grams of strontium-90. When you mass this metal (under the care of a nuclear chemist), you find it only has mass of 0.500 grams. The rest of it is gone?! First, write the nuclear decay reaction for Sr-90. Was this a natural transmutation or an artificial one? Natural, we didn’t do anything to assist this to happen. What did the other 63.5 grams of this strontium become? Yttrium-39. 90 38 Sr 0 -1 e + 90 39 Y

53 How old is the box assuming it really had 64.0 grams once, and you measured the left over correctly? (backwards to go back in time) Mass (g) Half lives 64.0 32.0 16.0 8.0 4.0 2.0 1.0 0.500 7 6 5 4 3 2 1 0 7 half lives X 28.1 years = 195 years ago! 2011 – 195 = 1816 (that was a very good year!)

54 How does a nuclear power plant make electricity? To make it sound really easy, the nuclear fission reaction which is the splitting of a big atom into smaller ones, that keeps going and keeps getting bigger and keeps giving off lots of heat makes water boil into steam. This steam is forced through pipes at high pressure, which is directed to turn a generator round and round. The movement of the generator (Iots of wire + magnets) makes an electric current. This electric current is sold to you by companies like NYSEG. They often have to transmit this current from the plants (far away), and they have to moderate it (too much power at once and you’ll melt all your wires). They also have to be sure it comes all the time and doesn’t stop. It’s tricky to be a power company.

55 There is the “inside” the containment dome part. And the outside the containment dome part. Don’t mix these up.

56 Inside the reactor vessel is where the fission reaction happens. Uranium 235 is bombed with neutrons and the chain reaction starts. The containment dome is (hopefully) strong enough to keep the radiation in, and everything else out.

57 This reaction should start a nuclear explosion, a chain reaction leads quickly to a massive energy release because of the small but measurable mass defect. Because of E=mc 2, this mass loss should cause a huge explosion, but it doesn’t. Inside the vessel are control rods, that control the reaction. They are able to be pushed in or out of the reactor. They absorb neutrons, which slows down or moderates the reaction. It keeps it hot, but not too hot. Often they are cadmium or silver or indium metals.

58 The water in the pink pipes gets super heated, and the heat transfers to the water in the blue steam generator. The steam it makes is pumped to the turbines which spin and make a current.

59 Hopefully this water in red stays in the pipes and never escapes. It’s touching the nuclear material and gets rather radioactive itself. All the radiation is supposed to stay inside the containment dome. The water in the turbine area cools down from steam back into water, to be reheated into steam again by more heat from the reactor. This water should stay un-radioactive if all goes well.

60 Cool water, from the really big lake, or from an ocean comes in here to help cool the water down. This water absorbs the excess heat from the turbine steam so it can be recycled. The environmental water is heated and then run through the cooling tower to disperse the heat as steam to the air. Lots more heat is pumped back to the ocean/lake nearby. STEAM

61 If all goes well, the only pollution put back into the environment is excess heat. Since fish don’t vote, and warm water makes fish grow bigger and faster, lots of people like this affect. Of course, sometimes big mistakes happen. In Japan, the tsunami knocked out the electricity to pump water through the reactor, and to push the control rods back in to the core. The back up water pumps also failed because the tsunami knocked out the general electric supply and backup electric supply. When that happened the core got hotter and hotter. And hotter and hotter still. And things start to melt down, which is bad.

62 And when the reactor core melts because it’s too hot, the radioactive materials escape to the air and water. This is as bad as anything you could imagine. It causes panic, it makes big areas uninhabitable for long periods of time, it’s invisible – you don’t start to die until it’s too late to save yourself, and it lasts for a very long time.

63 In the US, not one death can be attributed to nuclear power generation. So far it’s been a pretty good run of safety, except for Three Mile Island in Pennsylvania. There, in 1979, the reactor almost melted down, and we almost had our own Japan like problem. Luckily the control rods were somehow pushed back into the core in time to slow down the overheating. Years later, cameras showed that the core nearly melted down. Nearly means 2 things. First it means that we almost had a disaster of epic proportions. Or, it means that science is smart enough to protect us from any difficulties with nuclear power. This is where the ethics and the pros + cons of nuclear power come into play. How can you feel safe and how can you get safe, cheap electricity to run your world? ?

64 One other problem with nuclear plants is that even when they run perfectly safe for long periods of time, the waste products are dangerous. Some wastes are radioactive (emit dangerous radiation) for weeks, or months, or years. Some wastes like plutonium-239 can last millions of years. MILLIONS of years is really a long time to safely put this stuff. Where should we put it? How should we get it there? On a train through your town? What about a plane flying over your heads? Or by truck, no accidents are allowed. No terrorists can attack it and spread it out. No lost packages, or else.

65 Right now, the general plan is to store in underwater at nuclear plants, while we figure out what else to do with it. In Japan this did not work well, as the water boils away if it is not kept cool.

66 Nuclear Chem Class #5 X. Nuclear Chemistry – From NYS Curriculum X.1 Stability of isotopes is based on the ratio of neutrons and protons in its nucleus. Although most nuclei are stable, some are unstable and spontaneously decay, emitting radiation. X.2 Each radioactive isotope has a specific mode and rate of decay (half-life). X.3 A change in the nucleus of an atom that converts it from one element to another is called transmutation. This can occur naturally or can be induced by the bombardment of the nucleus by high-energy particles. X.4 Spontaneous decay can involve the release of alpha particles, beta particles, positrons and/or gamma radiation from the nucleus of an unstable isotope. These emissions differ in mass, charge, and ionizing power, and penetrating power. X.5 Nuclear reactions include natural and artificial transmutation, fission, and fusion. X.6 There are benefits and risks associated with fission and fusion reactions. X.7 Nuclear reactions can be represented by equations that include symbols which represent atomic nuclei (with the mass number and atomic number), subatomic particles (with mass number and charge), and/or emissions such as gamma radiation. X.8 Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of mass converted into energy. Nuclear changes convert matter into energy. X.9 Energy released during nuclear reactions is much greater than the energy released during chemical reactions. X.10 There are inherent risks associated with radioactivity and the use of radioactive isotopes. Risks can include biological exposure, long-term storage and disposal, and nuclear accidents. X.11 Radioactive isotopes have many beneficial uses. Radioactive isotopes are used in medicine and industrial chemistry, e.g., radioactive dating, tracing chemical and biological processes, industrial measurement, nuclear power, and detection and treatment of disease.

67 How does radioactive carbon dating work? On Earth there is a certain amount of radioactive carbon by percent. It’s measurable if you’re college level smart and you have some fancy tools. I can’t do it, but I am sure I could learn how. Many college students can do this, all over the world. There is a “normal” level of radioactive carbon in our environment, and it’s been stable a long time. The ratio of radioactive carbon to stable carbon is a constant. Although some is always transmuting, there is always more being made, by a variety of means, all involving the bombardment of carbon with high energy particles (from the Sun, from inside the Earth, etc. The ratio is known and measurable. If this ratio were to be different, that would be measurable too. This radioactive carbon is everywhere in small quantities. In plants and in the animals that eat the plants, and in animals that eat both plants and animals. Even though it’s always decaying, it’s also being replaced constantly too. There in lies the catch. High energy neutrons + Nitrogen C-14 + protons

68 If an animal eats regularly, and all animals do (except for one kind), they all have a constant ratio of radioactive to stable carbon. Only when they stop eating (when they die) does the ratio begin to change. It changes because the decaying doesn’t stop but the replacing does. Casually, the radioactive carbon is 1 part per trillion, or, 600 billion atoms per mole. (moles are really big). It has been more or less constant with some fluxuations that are explained by radioactive bomb testing, the industrial revolution adding so much carbon to the atmosphere, etc. Once animals die, this ratio changes. Since the ratio is not great to start (1 part per trillion), the measuring is only going to be accurate to about 60,000 – 80,000 years. After that there is so little C-14 left, that the measurements become very much less accurate. Using this method scientists can definitively determine the ages of biological materials that died up to about 80,000 years ago.

69 Saber tooth cats lived until about 11,000 years ago. Some lived millions of years ago. Some cats that died in the more recent era can be accurately dated with carbon dating. Dinosaurs died out too long ago to use carbon dating, but you can measure the other isotopes in the rocks that they have been found in to determine how old they are (many millions of years).

70 There are only 2 uses for nuclear radiation that are discussed in our class. 1. Use of Iodine-131 for the diagnosis of thyroid disorders. This radioactive isotope is injected into a person, then after a given period of time a special “picture” is taken, a radiograph, which measures the amount of radiation in someone’s throat (that’s where the thryoid gland is). Since it’s chemically identical, just different mass (that’s why it’s radioactive), the thryoid gland picks it up (or doesn’t) and doctors can assess your glandular activity. 2. Use of cobalt-60 to treat some cancers. This isotope produces excess beta radiation, which can be aimed as a sort of invisible beam of killer rays, which gets pointed at tumors inside people. The beta particles kill most all cells they pass though, but they also can kill some cancers. The plan is to zap the tumors precisely, and kill as few of the good cells at possible. Pain and sickness followed by (hopefully) smaller or no tumors.

71 Let’s practice three easy problems, and be done. Choose 2 table N isotopes that you have not worked out the decay reactions for, and do them. Describe the difference between natural and artificial transmutation. Give one example reaction for each as well. Describe the difference between fusion and fission. Where is one place that fusion can occur? What is a place that fission can occur? Finally, you win the boobie prize at a party, it’s 39.0 grams of Cs-137. How long until you have just one thirtysecond of that amount? (oooh, tricky, tricky!)


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