Nuclear Chemistry: Include It in Your Curriculum Charles H. Atwood Mercer University. Macon, GA 31207 R. K. Sheline Florida State University, Tallahassee, FL 32306 How manv hieh school or universitv chemistrv teachers include nuciear chemistry as a part oftheir rigorous introductory course? More than likely there are very few. Why is this valuable part of any science major's undergraduate education.left out? Is it because the teacher's knowledge of this area is weak, or because the teacher decides this subject is unimportant to students, or because the subiect is alwavs hidden in those last few chapters of the textbook? Now look at nuclear chemistry from the viewpoint of your studen-. Most of them are aware of the nucleartopics in the news from television or weekly news magazines. Recent articles have focused on Chernobvl. - . nuclear waste dumm. & .radon, star wars, and nuclear weapons treaties. Would some basic knowledee of nuclear chemistrv heln our students understand theseissues? More than likely it would. However, there are other considerations besides relevance that must be addressed when designing a course curriculum. First there is the usefulness to the students in their chosen profession. Ponder for a moment the multitude of ways that radiation, tracers, X-rays, and isotopes are used in fields such as biology, engineering, medicine, geology, and physics. Think about the variety of techniques that we chemists employ that involve radiation or nuclear chemistry. X-ray diffraction, mass spectroscopy, tracers, MBssbauer spectroscoov. ... and NMR.. iust to name a few. Clearlv our science students will need a basic understanding of nuclear phenomena for their chosen profession, whatever it might be. Historically there are good reasons for including nuclear chemistry a t an early stage in your course. We all know that Rutherford's explanation of alpha-particle scattering from metal foils as an atom containing a massive, positively charged core preceded Bohr's elucidation of the hydrogen atom spectrum. Also in most textbooks the chapter on atomic structure is just sprinkled with bits and pieces of nuclear information that are needed to clarify the discussion. Why' not stop at this point and explain the concepts of nuclear phenomena rather than have the students try to assemhle it from those bits and nieces? Later in the course a firm understanding of protons; neutrons, and isotopes will clarify the discussion of atomic weiehts for the students. Nuclear n henomena can also be used-as a basis for discussing thermodynamics and kinetics. Finally it would be nice if our students knew what the N in NMR stood for and what effect is being measured before this vital subject is dropped in their laps in organic. Let us look a t some of the topics that might be included in a nuclear chemistry section of your course. As the teacher, you will have to pick and choose from these topics to fit your course and students' needs. Time spent on the topic can range from a few days to as much as two weeks for a full discussion.
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Most sections on nuclear chemistry hegin with a discussion of radioactivitv and its effect uDon the decavine nucleus. Detailed discussions of a,p, a d 7 decay are gven by Seaborg ( I ) and Choppin and Rydberg (2).Other rarer forms
of radioactive decay are also known such as the emission of neutrons after 8- decay and proton or alpha-particle emission following of decay (3). More recently a very new and rare radioactive decay has been observed ( 4 , 5 ) .223Radecays bv the emission of a '4C fraement. Furthermore. several oiher fairly large fragments lice 20Ne are obseived t o decay from other nuclei in the vicinity of 223Ra.While these decays are very rare, their existence has some important implications reaardina the structure of these nuclei. We will discuss this poi& later. Commonly, students can retain and understand the mechanics of radioactivity hut are befuddled by what causes nuclei to decay. The reason is simply that unstable nuclei t best decav in an attemnt to attain stahilitv. This ~ o i n is illus&ated by lookkg at Figure 1,the &clear periodic chart. Each noint on this chart renresents a nucleus havine the proton (2) and neutron (M vhues as indicated by the graph. Heavy points are used for the naturally occurring nuclei, medium-weight points for nuclei with half-lives greater than 1year. Thus the darkest region corresponds to greatest stability. The nuclei that are more stable are shown as residing on a "peninsula" with the unstable nuclei in the "sea of instabiiity" that surrounds the .'peninsula". Note also that an "island of stability" is predicted where superheavy nuclei that are stable or nearly stable might exist (6).The unstable nuclei are trying to come ashore on the peninsula by decaying to those more stable nuclei. Furthermore, how a nucleus decays (whether by a,8-, p+ emission or one of the rarer decav " tvues) ". . is also determined to a large degree by this chart. For instance, a decay primariIv occurs in heaw nuclei that are bevond the limits of Droton Ability, i.e., hive Z > 83. These nuclei need to remove as much mass as possible in a given decay, and a decay effectively removes two protons and two neutrons in one step. 13decay occurs in nuclei that have too many neutrons to be
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NEUTRON NUMBER N
Fiaure I.The Deninsulaof known nuclei dotted as a functionof Braon number and neutron number Ciosad shells of protons end neutrons are plotted as horizontal and ven cal ilnss, reopsctlvsiy me hsi+ilves of Me planed n~clel are also represented in this graph (see text for details). The informationon the half-lives is accurate for ail the nuclei known as of the late 1970's. Half-lives far me superheavy elements are theoretical predictions. This diagram is known as Me nudear periodic Chart.
Volume 66 Number 5 May 1969
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stable (a neutron-rich nucleus). Because 8- decay can increase the number of protons while simultaneously decreasina the number of neutrons, neutron-rich nuclei can attain stability most efficiently via p- decay. Conversely, protonrich nuclei attain stability most effectively through p+ or electron-capture decay (a subset of p+ decay), which converts a proton into a neutron in one step. Gamma decav is sliehtlv different from the other t w e s of " decay because does not require that the nucleus b e - h a ble. What is reauired is that the nucleus be in an excited state. Gamma decay is analogous t o the emission of light or X-ravs from atoms in excited states. Atoms de-excite themselves through electron transitions to lower lying states and the emission of photons of electromagnetic radiation. Nuclei that are in excited states can also de-excite by either proton or neutron transitions to lower lying states and the emission of a ohoton of hiehlv enereetic electromaenetic radiation. a gamkaray. Nuclei can be excited by eithe;nuclear reactions that leave them in excited states or by radioactive decay processes that populate excited states of the daughter nucleus rather than the mound state. Radioactive decay is a statistical process that obeys firstorder rate laws. As such i t provides an excellent example of first-order processes for use later in your chemistry course. The discussion can include the concept of half-lives as well as the determination of the amount of nuclei remaining or the activity that results after a certain time period has passed. Details of these concepts are given by Choppin and Rydberg (2) and probahly also in your textbook. We are all aware that radiation interacts with matter. including human beings. In order to quantify the amount of radiation and its effects on human beines. we have developed many physical units for radiation anbits effects. Typical units of radioactive decav are the Curie (Ci) and the Becquerel (Bq) for activity. 0 i e Curie is equal to 3.7 X 101° disintearations per second, and a Becauerel is 1 disintegrasecond.- he unit dosage f o r k - and 7 radiation is tion the Rontgen (K).One Rbntgen corresponds to the deposition 01'93.3 x 10-7joules per gram of tissue. The unit of ahsorhed dosage of radiation is the rad. One rad corresponds to 1.00 X lo-' ioules oer " eramof ahsorhine material. Six hundred rads isalethal dose for mostpeople. f h e unit of radiation causing damaee to humans is the rem. One rem corres~ondsto a dosage of any type radiation that has in a human the effect of 1R. Six hundred rem is lethal to nearlv all humans. T o put some of these units into perspective for your students, these numbers miaht be useful. The Environmental I'rotection Agency has r&ommended that 222Rnlevels in the home not exceed 4 pCi/L of air (7). The radiation released a t Three Mile Island has been estimated a t roughly 20 Ci with no one person being exposed to more than 100 mrem (8). The Chernobyl release is estimated a t 50 to 100 MCi (9). The fire fighters and service personnel who were initially on the scene a t Chernobvl received more than 100 rem of radiation in their efforgto extinguish the fires (10). People who lived in the vicinity of Chemobyl received an average dosage of 43 rads (11). By comparison a typical dental X-ray delivers annroximatelv 0.5 mrem. and the average background radiati% in the united stateshas been meas;red a t 360 mrem per year (12). One of the nice things about radioactive decay is that the range of decay processes and time scales can provide so many examples for use in the classroom. For instance '4C dating of the Shroud of Turin, which was scheduled to begin in the summer of 1987, can be used. Seven different laboratories throughout the world will be given 5-10-mg pieces of the shroud, which they will date by either counting the 8particles from the I4C decay or directly counting the I4C nuclei in accelerator experiments (13).I t is hoped that these experiments will determine the approximate age of the shroud. The recent concern over Rn concentrations in the average American home can be discussed. Questions such as
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where does R n come from, what effect does Rn have on us, and how can someone decide if they have dangerous Rn levels in their home are possible topics. Recent articles have discussed these points in some detail (7, 14, 15). Another possibility is the debate over the siting of the high-level nuclear waste depository and the reason this depository is necessary. Information on this topic has been detailed by Hoffman and Choppin (16). A prohlem with two of the topics outlined above is that they tend to leave the student with the impression that nuclear chemistry is associated with negative subjects. There are, of course, very good uses for radioactivity and other nuclear related phenomena. Examples of these subjects are the use of radioisotopes in industrial applications such as determinine the wear i a t t e m s in machines. detecting had welds on coktruction sites, and the measurement of coating thicknesses (17,lS). The medical and pharmaceutical industries also employ nuclear techniques for a variety of reasons. Pacemakers can be powered by 238P~, gallstones can be detected without invasive exploratory surgery, and the doctor's newest diaenostic tool, the MRI scan. is nothina- but NMR in disguise (YE, 19,20). Finallv, a topic that is appropriate a t this stage of the course i s the effects of radi&onupon human beings. Obviously, Hiroshima and Chernobyl provide proof that large doses of radiation are fatal. Smaller doses of radiation must not be immediately fatal or we all would be dead from the natural background radiation we are subjected t o everyday from cosmic rays, radon, and the materials that are used in construction. In fact much larger doses than background are sometimes used for therapeutic purposes such as radiation therapy for cancer patients. However, the distinction between a nondamaging dosage of radiation and one that is damaging, when subjected t o i t for long periods of time, is difficult to make. Chemobyl provides an excellent example of this problem. We know fromaccidents and the bombing of Hiroshima and Nagasaki the radiation levels that are necessary to cause death and serious illness due to radiation syndrome. When those values are extrapolated down to the smaller radiation doses delivered to much of Russia and Eurooe from Chernobvl. . . then intemated over both the laree populationsof thearea and a time frame of 70 years, the roll sounds horrifying. The Russians initally estimated that in European Russia alone there might be an many an 45.000 new fatal cancers over 70 vearndue to the Chernobvl fallout (10). However, the estimated number has decreased since then and probablv will continue to fall. One of the most vexing in this argument is whether the extrapolation from the high radiation levels associated with accidents or bombings is applicable to the much smaller doses that millions of people received from Chernobyl. Radiobiologists have argued about this point since theChernobyl accident occurred. The studies that will be done on the populations of Europe and Hussiaoverthe next 50 to70 years might provideus with the data necessary to determine the cutoff point for what constitutes damaging low level radiation (21.22). Closed Shells in Nuclel One important aspect of nuclear structure that is generally not discussed in introductory courses is also shown in Figure 1. Just as we have closed shells of electrons with electron numbers 2, 10, 18, 36, 54, and 86 corresponding to the noble gases He, Ne, Ar, Kr, Xe, and Rn, so we also have closed shells in nuclei. In nuclei, however, both the neutrons and nrotons can attain closed shells. For nrotons. the closed sheis correspond t o 2,8,20,28,50,82, aGd the theoretically oredicted shell a t 114. renresentine the elements He. 0. Ca. ~ i Sn, , Pb, and the as-iet-undiscovered element 114.'~o; neutrons, closed shells are observed a t 2,8,20,28,50,82,126, and the theoretically predicted shell a t 184 neutrons. Commonly these numbers are referred to as "magic numbers". Just as for the closed shells of electrons, the closed shells of
is 94.9 kJImol. By comparison the energy for the process
Flgure 2. Swiatecki's (321allegory showing the peninsula of known nuclei and the possible island of superheavy nudei.
neutrons and protons are especially stahle. It is this stability that helps us to identify thenmagic numhers" for nuclei. The stability for closed shells of neutrons and protons is presented in the schematic drawing Figure 2 in terms of the topogranhv of the neninsula of known nuclei. Ridees run alone the "magic n u i b e r " lines, and doubly closed siells like 208gb ( Z = 82, N = 126) are labeled as "magic mountains". We know that in atoms the closed shells lead to the comoletion of periods of the neriodic table. Because we have closed shelis of both neutrons and protons, i t is more difficult to make a periodic table for nuclei. Perhaus for that reason the long peninsula of known nuclei together with the horizontaland vertical lines representing closed shells of protons and neutrons (as presented in Fig. 1) is usually called the nuclear periodic tahle. As in atoms, our understanding of the nuclear periodic tahle has led us into a rich new knowledge of nuclear information. For example, we know that the shapes of nuclei include spherical, prolate (American foothall-shaped), oblate (doorknob-shaped), and octupole (pear-shaped). An understanding of the nuclear periodic tahle allows us t o predict the regions where various shapes of nuclei are exnected. For example. nuclei close to theclosed shells in ~ i ~ u1rare e spherical,%ereas those that are far from closed shells are either ~ r o l a t eor oblate. Recent theoretical predictions have suggested that nuclei with mass numhers, or A values where A = Z N, equal to 220 to 230 should be octupole-deformed or pear-shaped (23). The discovery of the radioactive decay of 223Ravia the emission of a I4C fragment lends credence to the prediction of octupoleshaped nuclei. The small end of the pear shape could he a~nroximatelvthe size of aI4Cnucleus. I t is conceivable that t k pear-shaped nucleus decays by cleaving its small end and reaches a stahle nucleus P ' P h ) in one s t e rather ~ than several n and 0 decay steps.
+
Energy of Nuclear Processes Ever since Einstein developed the theory of relativity, scientists have realized that the nucleus contains a vast amount of potential energy. The struggle t o release this energy is an interesting story that many students will enjoy (24). Ultimately the efforts of Fermi, Frisch, Strassmann, Hahn, Meitner, and the Manhattan Project released this energy. Since that time humankind has attempted both to utilize and harness this nuclear enerw -" for its own .nurooses. . In an introductory class there are certain aspects of this topic that deserve discussion. The quantity that determines the conversion of mass to energy in the nucleus is called the mass defect. Details reeardine the calculation of mass defect values for nuclei are in Choppin and Rydherg (25). For classroom use it is good to know that nuclear processes are typically a million times or more energetic than chemical ones. For instance, the energy for the process CH,-C+4H.
(1)
is 2.73 X lo9 kJ/mol. Nuclear chemists normally use the energy units of millions of electron volts (MeV) rather than joules. The relevant conversion factor is that 1 MeV = 1.60210 X 10-l3 J. One other fact of importance is that 1 atomic mass unit (amu) is equivalent to 931.478 MeV. Thus if vou know that the mass defect of a 4He nucleus is 0.d3037652 amu, i t is easy to determine that this mass defect corresponds to 28.2951 MeV (0.03037652 X 931.478). In Figure 3 the mass defect per nucleon (mass defectlA) is plotted versus the mass number A across theentire nuclear periodic table. The high mass defect of 4He is obvious in the figure. Nuclear Reacilons One of the most interesting aspects of nuclear chemistry is the area of nuclear reactions or transmutations. Nuclear transmutations are reactions in which elements are transformed into new elements. fulfilline the ancient alchemists' dream. The details of reaction processes, balancing reactions, energetics, and acceleration of particles are given by Seahorg ( I ) and Choppin and Rydherg (26). We should also point out to our students that not all nuclear reactions occur in the laboratory. For instance, a natural fission reactor site has been discovered in the Oklo mine in Gabon that was active approximately 1.7 X lo9 years ago and might have continued its activity for -lo6 years (27). Ultimately all of the energy on Earth comes from the natural fusion reactor we call the Sun. Also, i t appears that the elements are the nroducts of the nuclear reactions that occur in stars via the brocess we call nucleosynthesis (28). Thus there are several examnles of natural nuclear reactions that will make this subject more interesting to the student. Nuclear reactions can also be used t o introduce the verv basics of thermodynamics. Just as chemists discuss the the;modynamic property AH, which describes whether a reaction will he endo- or exothermic, nuclear chemists have a similar quantity called the Q value. The Q value is defined as the mass of the products minus the mass of the reactants times the energy conversion factor 931.478 MeV per amu. For instance, if we want to know the Qvalue for the following reaction:
-
2H+SH-4He+n
(3)
The masses are 2H = 2.014102 amu, 3H = 3.016049 amu, 4He = 4.002603 amu, and n = 1.008665 m u . Thus the Q value is
+
+
Q = [(4.002603 1.008665) - (2.014102 3.016049)amul
X 931.478 Mevlamu Q = -17.589 MeV
(4)
which tells us that this is an exoergic reaction. Notice that this calculation is hasicallv the same one used to determine the AH of a reaction, hut masses are used rather than AHrO. This calculation will reenforce the thermodvnamic concepts that are introduced in your course. One note of caution is necessarv a t this point. Q values in many nuclear books are determined using the f&ula mass of the reactants minus the mass of the products. This is iust the reverse of the norm used in most chemistry texthobks and can cause serious confusion for your students if they are not aware of this fact. Fission and Fusion There are two nuclear reactions that humankind has used extensively for making weapons and for power production. These two reactions, fission and fusion, require some detailed discussion in the course. A good starting point for the discussion is provided by Figure 3. Note that the highest point on the graph is in the area of A = 56. Nuclei with A < 56 or A > 56 are unstable by comparison to nuclei near A = 56. Thus it should be possible t o make the heavier nuclei split Volume 66
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reactions among the light nuclei are extremely exoergic, particularly those that produce IHe nuclei. The reason for this can he seenfrom Figure 3. Notice that themass defect of IHe is fairlv close to that of the A = 56 reeion of this curve. So a fusion-reaction that produces 4He can release close t o the maximum amount of energy possible from a fusion reaction in only one step rather than the many steps necessary to release the maximum amount. Furthermore production of 4He through fusion has one more advantage: i t can he done with the least charged nuclei available, namely the H isotopes. In a fusion reaction the two nuclei that must collide are both positively charged. Overcoming themutualelertn~static repulsion presents a dit'licult challenge to the scientists who wish to desien a nuclear fusion device. T o attain enoueh kinetic energy fo; the nuclei to collide and fuse requires &at the nuclei have an internal temperature of -108 "C. Obviously temperatures of this magiitude are not easily ohtainahle. The designers of thermonuclear weapons chose t o use a fission bomb as the fuse to ignite the fusion reactions and make even more destructive~weaponsthan those used on Japan. The first of the fusion weapons was exploded on November 1,1952, a t Eniwetok Atoll. This event set off the second round of the nuclear arms race, which only recently has slowed down with the signing and ratification of the Intermediate Nuclear Forces Treaty (29). Just as electricitv is eenerated from a nuclear fission reactor, i t should be pksihre t o generate electricity from nuclear fusion reactions. We could use the enerev -- generated from the fusion reactions as an efficient heat source to generate steam that will drive steam turbines. However, desimina a fusion reactor is an even more formidable task than making a thermonuclear weapon because the lo8 "C temperatures must not only he hut also contained. ~t present there are no known physical materials that could possibly withthere are a t stand such en6rious temperatures. least three possihle pathways for generating these temperatures while a t the same time confining the hot nuclei and, it is hoped, producing enough fusion events to generate electricity. These three ways are magnetic confinement fusion, inertial confinement fusion, and muon-catalyzed fusion. Maenetic confinement fusion reauires the use of laree magnetic fields to produce a doughnut-shaped "magnek hottle"that confines the reactinenuclei. As the nuclei rotate around inside the magnetic field; there is some resistance to their rotation Gust as there is electrical resistance in a transformer) that causes the nuclei to heat up. This heating action alone is not enough to produce nuclear fusion; however, there are other ways to increase the temperature of the nuclei while confining them inside the bottle. Using this anoroach. the Tokamak Fusion Test Reactor a t Princeton ~ n i v e r s i tattained '~ a temperature of 2.3 X los K during the summer of 1986 (30).Further develooments are needed to maintain the nuclei a t this temperature while confining them t o a small volume and, i t is hoped, producing a selfsustaining, controlled fusion reaction. However, magnetic confinement fusion certainly looks promising as a future energy source. Inertial confinement fusion uses lasers or accelerated particle heams to force small pellets of a frozen mixture o i 2H and 3H to collapse upon themselves. During this collapse the nuclei attain temperatures and densitiesthat are roughly equal t o those found in stars. Under these conditions fusion can occur for a few microseconds until the enerw eenerated by the fusion causes the pellet to expand agaL;a'nd ceases thereaction.This techniaue has been used l ~ vthe Y w a laser system a t the Lawrence ~ i v e r m o r e~ a b o r a i o r yto produce temperatures that nearlv eaual those of the maenetic confinement fusion effort (%). Again more research Ls needed in this field hefore a viahle fusion reactor based on this design . can he built. ~
MASS NUMBER Figure 3. A plot of i k mass defect per nucleon versus the mass number across lhe entire nuclear periodic table. Soma of the nuclei with especially largemass defectsare pointedout in Me llght region. Arrows are shown for the fission and fusion processes indicating lhe dlrectlons that each of these two reactions takes.
into two lighter nuclei with masses closer to 56 (a process we call fission) and to make two light nuclei join or fuse into a single heavier nucleus with a mass closer to 56 (the fusion process). Both processes are indicated in Figure 3. Certain nuclei, called fissile nuclei, will easily fission when struck hy a slowly moving neutron. The two most commonly . either of these used fissile nuclei are 235Uand 2 3 9 P ~When nuclei fissions, i t can produce a variety of medium-mass nuclei, called fission products, that have a mass closer to A = 56 and some neutrons. For example, one of the possihle fission pathways for 235U is
235U +n
-
'"Cs
+ 93Rb+ 2n + 181 MeV
(5)
As indicated in eq 5, the Q value for this reaction is -181 MeV. The 181 MeV produced is for asingle fission event. If 1 g of 235Uwere to fission in this manner, i t could produce 7.43 X lo7 kJ. By comparison the combustion of 1 g of CHI produces 55.5 kJ. Fission events such as the one described ahove are the primary energy source for nuclear reactors and for the earliest nuclear bombs such as used a t Hiroshima. In order for fission reactions t o occur in significant enough amounts to generate electricity or an explosion, a series of fissions must occur in a certain amount of time. This process involves the capture of the excess neutrons from one fission event, or neutrons from the radioactive decay of the fission products, in a second 235U nucleus and is called a chain reaction. In order for the chain reactiou to sustain itself, a certain minimum amount of the fissioning material must he present. This amount is called the critical mass and for 235U is approximately 1 kg. In nuclear reactors the fissioning material is arranged in such a way that the reaction is relatively slow and a steady source of energy results. Nuclear weapons reauire that the fission reaction occur in a o ~ r o x i maiely 1p s a n d that the energy he dissipated in on; large burst. This is accomolished hvseoaratine the critical mass of the fissioning material into pikces that are rapidly assembled just before detonation or by squeezinga near-criticalmass of the fissionable material with chemical explosives until a critical density is achieved. A typical f&on reaction is given in eq 3. On the surface this reaction does not appear t o he especially exoergic; however. i t oroduces 8.49 X lo8 kJ oer mam of 2H or 3H. This is rou~hl;ll times more energetic on a weight-foilweight basis than the fission reaction discussed ahove. In general, fusion
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Muon-catalyzed fusion must he considered the infant in the controlled fusion reactor business. However, this method is also unique in that it might allow a fusion ieactor to he built that operates a t room temnerature rather than a t the enormous t6mperatures discussed up to now. This method takes advantaae of the fact that a nuclear particle called the muon ( p - ) is capable of binding a 2H nucleus to a 3H nucleus so tiahtlv that the conditions inside the molecule simulate those fo"nd in a white dwarf star. Under these conditions the fusion process can rapidly occur and release the muon to catalyze another fusion reaction. Notice that this reaction does not require the addition of external heat to force the nuclei t o fuse. Instead i t takes advantaee of the uniaue properties of the muon t o drive the fusion reaction a t ambient tenmeratures. Indeed this a ~ ~ r o a has c h been called cold nuclear-fusion. Promising r e s i l k from this research have only recently heen ohtained, and there arestill many years of work ahead before the practicality of muon-catalyzed fusion can he proven (31). One question that will occur t o your students is why are we interested in nuclear fusion reactors? After all. have the fission reactors not caused usenough trouble, andin particular what about the radiation and waste from fusion reactors? These questions certainly deserve informed answers. ~ Present day fission reactors require either 235Uor 2 3 9 Pas their fuel. The mineral deposits of 235U are not infinite and even now are hecoming somewhat depleted and harder to find. 2 3 9 P u is made as a byproduct of fission reactors and must he separated from the highly radioactive fission products in order to he used in a reactor. Both of these Drocesses are expensive and eventually all of these nonrenewable resources will he consumed. Add to that the fact that fission reactors generate large amounts of highly radioactive waste that must he stored for thousands of vears. and some of the t fusion reactors problems with fission are obvious. ~ n t e r e sin stems from a desire to alleviate these ~ r o h l e m sand provide ourselves with a long-term, reliable energy source. The fuel for fusion reactors is ordinary water, which contains sufficient amounts of 2H, in the form of heavy water, to power fusion reactors for generations t o come. I t has been estimated that a l-in.-thick sample of water taken from the entire surface of San Francisco Bay would supply enough fusion fuel to fulfill the United States's entire energy needs well into the 21st century. Indeed, the knownamounts of deuterium in the total water s u ~ ~ ofl vthe earth are enoueh to satisfy the present energy &eds of the earth for appoximately 1billion years. Secondly, the waste products from fusion reactors are not entirely free of radioactivity, hut the levels of radiation are sianificantlv less than for fission products. Furthermore, fusi& waste-products have relatively short half-lives, which makes their disposal a simpler problem
-
than is the case for fission products. If we can overcome the inherent deisgn problems of fusion reactors, they should provide us with a reliable and relatively safe energy source for centuries. Conclusion The fields of nuclear chemistry and physics have significantly increased humankind's understanding of the fundamental nature of matter. Thev have also benefited us in many areas of medicine, electronics, geology, archaeology, and industw. I t is important that our students he exposed to this valuabie area of knowledge. Equally important is the fact that our students realize that the word nuclear should not be solely associated with weapons or hazardous, radioactive waste. If we present them with the facts of both theguod and .-- had sides of the issues.. thev should be able to decide for themselves where the truth lies in the issues that confront our society.
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Llterature Clted 1. Seabox, G. T. J. Chem. Edur. 1985,62,392-398. 2. Chowin.G. R.:Rvdhem, J. Nuelear Chsrniatv ThroryondApplieoliom:Pe%amon:
Lett. 198453.759. 6. Seaborg, G. T. J. Chsm.Educ. 1985.62.463-467. . W.; Re-, 7. Ner0.A. V.: Sehwehr, M. B.;Nszarofl, W 997. Noteadded in prwt 8. Weinberg. A.M. Bull. At. Sci. 1986.43 (1). 57-60. 9. Ahemne. J. F. Seirnes 1987.236.675679.
K. L. Science 1986,234,992-
11. Galdmsn, M. Science 1987.238.622-623. 12. National Council on Radiation Protation and Measurement "Ioniring Radiation Exposure of the Population of the UnitedStstd"'ReporlNo. 93; 1987. 13. Hsubdtle, G. 193rd American Chcmid Society Meeting; Denver. CO, peraond com-
.~ . ..
15, sc;N& 1981.132 (71,105. 16. Hoffmann, D. C.; Choppio, G. R. J. Chem. Edur. l986,67,1059-1064. 17. Foldisk, G., Ed. Industrid Applications oiRodiaisotop~8;Elssviar:NecuYork, 1986. 16. C h m ~ i nG. . R.;Rydbm, J. Nuelaor Chemutry TheoryondApplicotiom;Perg-on: N& York, 1980; Chapters l4and 18. 19. Atwoad, C. H. CHEM MATTERS 1985,3(3), 6 7 . 20. Msur. J. L. Scianca 1987.238. -9. 21. O'Sullivan, 0. Chem. EM. News 1987.65 (23). 19. 22. Galdman. M. Science 1987.238.622-621. 23. Lesnder. G. A,; Sheline, R K. Nucl. Phys 1964,A414 375. 24. Rhodea, R. The Making offhe Atomic Bomb: Simon and Schuabr: New York, 1986. IS Chnnnin.G. R.: Rvdherz. J. Nuclear Chrmisfrv Theorvond Aoolicatiom: Pemaman: 27. Re125: ~ h s b t e r1 9 28. Selbin, J. J. Charn.Edue. 1973.50,306310. Selbin, J. J. Chem Edue. 1973.50.380"a" "",.
29. 30. 31. 32.
Congressioml Buortsrly LJS7, IDecwdw 12). 3025. Pea8e.R. S. Notura (London) 1986,324,512-513. Jonea, 8. E. Noturn (London) 1936,321,127-133. . J., peraonal communication. SwiatecLi, W
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