Nuclei

Contents

Binding Energy

		A nucleus is specified by its number of protons Z, number of neutrons N, and the mass number A = Z+N. The nucleons (protons and neutrons) in a nucleus are bound together -- their total energy is less than the total energy of the separated particles. The binding energy is the amount of energy given up when the nucleus is formed. Plotting the binding energy per nucleon versus the mass number A (Figure 14-01) shows that starting from Hydrogen, nuclei become more
Figure 14-01 Nuclear Binding Energy [view large image]	Figure 14-02 Proton/Neutron & Decay [view large image]	stable as there are more protons and neutrons, until Iron. After that, the trend reverses.

The curve of stable nuclei portrays in Figure 14-02 is the result of the balancing act between the various repulsive and attractive effects:


1. Electric force (repulsive) : There is the obvious electric repulsion between the protons each carrying a positive charge.
2. Uncertainty principle (repulsive) : According to this principle at short distance (equivalent to reduced uncertainty in position) the uncertainty in momentum becomes correspondingly large giving rise to higher kinetic energy and a tendency to disperse.
3. Exclusion principle (repulsive) : Since identical particles cannot be in same state, close proximity between similar particles also implies higher kinetic energy and a tendency to disperse.
4. Strong Interaction (attractive) : This is the short range nuclear force that operates on all the protons and neutrons. It is this force that holds the nucleus together.
5. Neutrons (attractive or repulsive) : Adding neutrons to the nucleus tends to minimize the repulsive effects. However, too many of them in there would favor the beta decay reaction, which turns neutron into proton and makes the nucleus unstable. Isotopes are elements with varying number of neutrons but same number of protons in the nucleus. If there are too many protons in the nucleus, there is no way to add neutrons to overcome the electric repulsion. This kind of elements would become unstable via alpha decay or other processes to reduce the number of positive charge.

Origin of Elements

Light elements (mainly hydrogen, helium and trace of deuterium, lithium) were generated in the first few minutes of the Big Bang, which was not able to produce more complex elements as the universe rapidly cooling off. Since then hydrogen and helium contribute by mass of respectively 70 and 28 per cent of all baryonic matter in the universe. Most of the remaining 2% of the elements up to iron and nickel are made in the interior of the stars. The resulting elements are thrust into space by booming stellar winds or when a star explodes as a supernova. Carbon, nitrogen and oxygen are the most abundant heavy elements. Oxygen is created by supernovae, while carbon is created in low-mass stars (red giants, planetary nebulae) and nitrogen is made by both processes mentioned above.

Figure 14-03 Element Abundance [view large image]

The Liquid-Drop and The Shell Models

		The liquid-drop model assumes that the constituents of the nucleus interact only with their nearest neighbors, and the density is constant inside the nucleus, like the molecules in the liquid. Using this analogy, a semiempirical formula has been developed to describe the binding energy as a function of the mass number A (shown by the solid curve in Figure 14-01). The result is not particularly accurate for the lower value of A. The expression is useful in discussing stability, radioactivity, and the fluctuations from the average behavior due to shell effects. The top diagram in Figure 14-04a shows two vibrational energy levels, which split into finer structures due to rotation.
Figure 14-04a Liquid Drop Model [view large image]	Figure 14-04b Fission [view large image]	Figure 14-04b shows the deformation of the liquid drop, which eventually separates into two pieces (caused by the electrostatic repulsion of the protons).

		There is extensive experimental evidence of the contrary hypothesis that the nucleons move in an effective potential well created by all the other nucleons. Since the nucleons are densely packed into a small region, it is expected that the chance of collision is very high. However, the interaction by collision is minimized by the Pauli exclusion principle, which forbids two fermions to occupy the same quantum state. If there are no nearby, unfilled quantum states that can be reached by the available energy for an interaction, then the interaction will not occur.
Figure 14-05a Nuclear Potential [view large image]	Figure 14-05b Nuclear Energy Levels [view large image]

• Enhanced abundance of those elements for which Z or N is a magic number.
• The stable elements at the end of the naturally occurring radioactive series all have a "magic number" of neutrons or protons.
• The neutron absorption cross-sections for isotopes where N = magic number are much lower than surrounding isotopes.
• The binding energy for the last neutron is a maximum for a magic neutron number and drops sharply for the next neutron added.
• Electric quadrupole moments (a measurement for deviation from spherical distribution) are near zero for magic number nuclei.
• The excitation energy from the ground nuclear state to the first excited state is greater for closed shells

		even if it happens to be located right in the middle of the island of stability. Figure 10-05d presents all the trans-uranium elements synthe-sized artificially. It shows the steady decrease in half-life with increasing atomic number (# of protons), then this sudden jump in the disputed claim. The color of the square represents the
Figure 14-05c Nuclear Island [large image]	Figure 14-05d Trans-uranium Elements [view large image]	chemical property of the element as indicated in the traditional periodic table (see also insert in the figure).

A more realistic nuclear (nucleon-nucleon) potential is the empirical curve shown in Figure 14-05e. As originally proposed by H. Yukawa, the longest range part of the strong internucleon force can be attributed to exchange of the mesons (pions). At shorter distances, exchanges of heavier mesons become important. However, the origin of the repulsive hard-core below 1 fermi (10-13cm) remains unclear until recently in 2007, when numerical results convincingly demonstrate that it is a consequence of QCD. The numerical computation is actually rather involved because of the virtual gluons and quark-antiquark pairs surrounding the three quarks (the components of the nucleon). The required computational power is only available now to reproduce the empirical potential from first principles. This potential represents the residual force derived from the more fundamental forces (as prescribed in QCD) between the constituent particles. The form of this potential is remarkably similar to the molecular

Figure 14-05e Nucleon-Nucleon Potential [view large image]

potential curve even though these residual forces originated from different sources - one from quantum chromodynamics, while the other from quantum electrodynamics.

Nuclear Decay

Unstable nuclei, called radioactive isotopes, will undergo nuclear decay to make it more stable. There are only certain types of nuclear decay which means that most isotopes can't jump directly from being unstable to being stable. It often takes several decays to eventually become a stable nucleus. When unstable nuclei decay, the reactions generally involve the emission of a particle and or energy. Half-lives are characteristic properties of the various unstable atomic nuclei and the particular way in which they decay. Alpha and beta decay are generally slower processes than gamma decay. Half-lives for beta decay range upward from 10^-2 sec and, for alpha decay, upward from about 10^-6 sec. Bismuth-209 has the longest half-life of 2x10¹⁹ years. Half-lives for gamma decay may be too short to measure (~ 10^-14 second), though a wide range of half-lives for gamma emission has been reported.

There are five types of nuclear decay:



Alpha Decay - The strong force, despite its strength, has a very short range; it can't even reach from one end of a fair-sized atomic nucleus to the other. If a proton is at the edge of a big nucleus, it can feel the pulling strong force only from the particles in the neighborhood, but there is an electromagnetic force, which tends to push it out, all the way from the other side of the nucleus. There is a sensitive balance between these two competing forces. The nucleus needs not to acquire extra energy to escape; the quantum mechanical effect called tunneling allows a certain probability of escape through a potential wall. Alpha decay, in which just a small chunk breaks off from the main nucleus, is a rather mild case of fission; in more dramatic examples, the nucleus can break more or less in half. The broken-off chunk most often is packed into a helium nucleus (alpha particle) because it is in a more stable form. Figure 14-06 shows the effect of tunneling

Figure 14-06 Alpha Decay [view large image]

through the Coulomb barrier; the nucleus has a small probability of escape to the outside depending on the height and width of the wall.

Beta Decay - The weak interaction is responsible for the instability of "free" neutrons, which decay according to the reaction: n p + e + electron-anti-neutrino with a lifetime about 15 minutes in a process known as beta decay. Neutrons in a nucleus are subject to the protection of the nuclear and the electromagnetic forces from the other nucleons, and they will remain stable provided there are not too many of them. If there are too many, such protection would not be sufficient for all of them to remain stable, and the nucleus would undergo beta decay. Figure 14-07

Figure 14-07 Beta Decay [view large image]

shows that in the beta decay process, the down quark turns into an up quark (thus changes the neutron to proton) by emitting a W- meson, which decays into an electron and an electron-anti-neutrino.

Gamma Decay - In gamma decay, a nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation. It happens usually after the transmutation of the nucleus; the end product has to re-arrange the occupancy of energy levels in order to arrive at a more stable state. The number of protons (and neutrons) in the nucleus does not change in this process, so the parent and daughter atoms are the same chemical element. In the gamma decay of a nucleus, the emitted photon and recoiling nucleus each have a well-defined energy after the decay. Figure 14-08 shows the adjustment of energy level by emitting gamma ray after Mg has transmuted into Al.

Figure 14-08 Gamma Decay [view large image]

• Positron Emission - Positron emission is a type of beta decay, referred to as "beta plus"(ß+ ) or inverse beta decay. In beta plus decay, a proton is converted to a neutron, a positron and a neutrino via the weak interaction. This spontaneous nuclear process releases an amount of energy equal to the energy equivalent of the rest mass that disappears in the process. The positron and neutrino are created in the nucleus at the moment of disintegration. The "endothermic reactions" receives the energy from the nuclear fission. That positron decay is a nuclear process is consistent with the fact that the decay of free protons by positron emission is not observed in nature. On the other hand, the beta decay of free neutrons is a familiar fact. The positron is made of anti-matter and does not last very long in the world of ordinary matter. As soon as the positron meets an ordinary electron the two particles annihilate and

the energy contained in their mass appears as two gamma-rays of 0.5 MeV each, flying off in opposite directions. Positron radioactivity is therefore always accompanied by the emission of gamma rays with an energy of about 0.5 MeV in addition to any other gamma-rays which might be emitted. Example isotopes, which emit positrons are C-11, N-13, O-15 and F-18. These isotopes are used in positron emission tomography (PET). Figure 14-09 shows the transmutation of C-11 into B-11 by positron emission.

Figure 14-09 Positron Emission [view large image]

• Electron Capture - Electron capture is a decay mode for nucleus that will occur when there are too many protons in the nucleus of an atom, and there isn't enough energy to emit a positron. In this case, one of the orbital electrons is captured by a proton in the nucleus, forming a neutron and a neutrino. Since the proton is essentially changed to a neutron, the

	number of neutrons increases by 1, the number of protons decreases by 1, and the atomic mass remains unchanged. By changing the number of protons, electron capture transforms the nucleus into a new element. Electron capture is also called K-capture since the captured electron usually comes from the atom's K-shell. Figure 14-10 shows another way of transmuting C-11 into B-11 by electron capture.
Figure 14-10 Electron Capture [view large image]

Type	Emission	Penetrating Power	Example
Alpha Decay	Helium nuclei	1, stopped by skin, very damaging due to ionization	92U238 90Th234 + 2He4 Applicable to nuclei with Z>83, see Figure 14-02
Beta Decay	Electron, high speed	100, penetrates human tissue to ~ 1 cm	53I131 54Xe131 + -1e0 Applicable to nuclei with high neutron-proton ratio
Gamma Decay	Photons, high energy	10000, highly penetrating but not very ionizing	92U238 90Th234 + 2He4 + 2 photon Energy lost from settling within the nucleus after transmutation
Positron Emission	Positron	100	6C11 5B11 + 1e0 Applicable to nuclei with a low neutron-proton ratio
Electron Capture	Electron, inner shell	~ Infinite for Neutrino	37Rb81 + -1e0 36Kr81 + neutrino Applicable to nuclei with a low neutron-proton ratio

Table 14-01 Types of Nuclear Decay

Fission

		more tightly than they were in the uranium nucleus, and that decrease in mass comes off in the form of energy according to the Einstein's equation E = mc2, where m is the loss of mass in the reaction. For elements lighter than iron it is the process of fusion that releases the binding energy. Figure 14-11b shows a bomb-grade U-235 cake at left, while the
Figure 14-11a Chain Reaction [view large image]	Figure 14-11b Uranium [view large image]	sample on the right is the natural uraninite (UO2) in black-brown crystals.

In one of the most remarkable phenomena in nature, a neutron can be captured by a uranium-235 nucleus, rendering it unstable toward nuclear fission. When a U-235 nucleus splits, it gives off energy ( ~ 166 Mev / nucleus) in the form of heat and Gamma radiation, which is the most powerful form of radioactivity and the most lethal. When this reaction occurs, the split nucleus will also give off two or three of its `spare' neutrons. These spare neutrons fly out to split other U-235 nuclei they come in contact with. In theory, it is necessary to split only one U-235 nucleus, and the neutrons from this will split other U-235 nuclei, which will split more...so on and so forth -- a chain reaction. (See Figure 14-11a.) This progression does not take place arithmetically, but geometrically. All of this will happen within a millionth of a second. The minimum amount to start a chain reaction as described above is known as Critical Mass. The actual mass needed to facilitate this chain reaction depends upon the purity of the material and whether it is tampered. The tamper is a thick casing made of natural uranium. It reflected neutrons back into the core and helped to hold it together for a fraction of a second. For pure U-235, the bare critical mass is 50 kg and the tampered critical mass is 15 kg (with a spherical tamper size of 11.5 cm diameter); it is 10 kg and 5 kg respectively for Pu-239 (with 8 cm tamper size).

Table 14-02 Fissionable Isotopes

		after a lunch recess. No photographers were present to witness the arrival of nuclear age. Figure 14-12a is the recreation of the occasion by an artist in 1957. Enrico Fermi (captain of the team of 42 scientists) is the half-bald individual standing next to Walter Zinn who is leaning with his elbow on the rail.
Figure 14-12a First Reactor [view large image]	Figure 14-12b Modern Nuclear Reactor [view large image]	A schematic diagram of a modern nuclear reactor running on the same principle is shown in Figure 14-12b.

In a breeder reactor, the fuel consists of 90% U-238 together with 10% Pu-239. There is no graphite to moderate the reaction by slowing down the neutrons hence it is sometimes referred to as fast breeder - meaning fast neutrons. The fast neutrons are absorbed by U-238, which is then transmuted into fissionable (fissile) plutonium. The great advantage of this type of reactor is that, rather than merely burning uranium to create energy, the naturally abundant U-238 is used in a cyclical process that simultaneously generates both fission energy and more nuclear fuel than there was in the first place. It is called breeder because it breeds fuel. Figure 14-12c shows a breeder reactor. It is rather similar to the conventional nuclear reactor except that there is an U-238 blanket to capture and reflect

Figure 14-12c Breeder Reactor [view large image]

the neutrons back to the core, and liquid sodium is used as coolant in extreme temperatures surrounding the reactor.

cular fire ball and mushroom cloud seconds after the detonation. Unknown to the scientists on the project, the real purpose of the bomb was to target Japan and to intimidate the Soviets according to General Groves, the equivalent of political commissar in the project. Some team members consider such intent to be the betrayal of the original aim of using it on Nazi Germany, which was believed to be

Figure 14-12d First Nuclear Explosion [view large image]

on the verge of making similar weapon. Anyway, the development came too late as Germany has already capitulated on May 8, 1945 before the Trinity test.

The North Korean nuclear test in 2006 seemed to fizzle out with very low yield. Probable causes of the misfiring:
• Non-symmetrical implosion - The implosion must be extremely symmetrical to be fully successful. Typically a combination of fast and slow conventional explosives surrounds a sphere of plutonium (the "core" or "pit"). Engineers must carefully machine all the pieces that make up this explosive shell into shapes that, when detonated simultaneously, produce a precisely spherical shock wave that compresses the plutonium to two to five times its normal density (the more compression, the greater the explosive yield). At the higher density, what was a subcritical mass of plutonium becomes supercritical, i.e., one in which a sustained chain reaction takes place, producing the blast.
• Wrong timing of the initiator - The initiator is a small device at the center of the core that emits a burst of neutrons to start the chain reaction reliably at a precise stage of the implosion. An initiator going off early or late or not at all would reduce the yield.

Impurity - The fuel rods of nuclear reactors produce the desired isotope, plutonium 239, but the longer it remains in the reactor, the more of it becomes plutonium 240. Plutonium 240 constantly emits tens of thousands of times more neutrons a second than plutonium 239. Although neutrons are the key particles in producing a nuclear chain reaction, an excess of them early in the implosion is a recipe for predetonation. Figure 14-12e shows the fuel rods from the Yongbyon nuclear reactor. They probably provided the plutonium 239 needed for the test.

Figure 14-12e NK Fuel Rods [view large image]

North Korea has conducted an underground nuclear test successfully on May 25, 2009.

Fusion

		Thermonuclear, or hydrogen bombs explode with enormous power via uncontrolled self-sustaining chain fusion reactions (Figure 14-13a). Deuterium and tritium form helium under extremely high temperature, providing the energy: D + T He + n + 17.6 Mev (See Figure 14-13b). In principle, a mixture of D and T heated to very high temperature and in high density will start a chain fusion
Figure 14-13a Thermalnuclear Explosion [view large image]	Figure 14-13b Fusion [view large image]	reaction, liberating an enormous amount of energy. But tritium is an unstable element; an ingenious method is to have it produced from lithium deuterate (Li6H2) in

the fission phase of the explosion -- thus one compound is used for both types of fuels ( D and T). In a thermonuclear bomb, the explosive process begins with the detonation of what is called the primary stage. This consists of a relatively small quantity of conventional explosives, its detonation brings together enough fissionable uranium or plutonium to create a fission chain reaction (sometimes magnified with a smaller fusion reaction), which in turn produces another fission explosion inside the temper in the secondary device and raises the temperature to several million degrees. When the temperature of the mixture reaches 10,000,000 oK, fusion reactions take place. The neutrons from the fusion reactions induced fission in the uranium-238 pieces (highly enriched with U-235) from the tamper and shield, which produced even more radiation and heat and the bomb exploded (See Figure 14-13c). Specialized type of small fusion bombs designed to release neutrons rather than causing further fission reactions are called neutron bombs. This is accomplished by removing the U-238 tamper. Neutrons kill people, leaving the hardware and buildings intact. It is a "clean" bomb. The theorized cobalt bomb is, on the contrary, a radioactively "dirty" bomb having a cobalt tamper. This tamper is made of cobalt-59, which is transmuted into cobalt-60 by neutrons released from the fusion reactions. Cobalt-60 has a half-life of 5.26 years and produces energetic (and thus penetrating) gamma rays. The half-life of Cobalt-60 is just long enough so that airborne particles will settle and coat the earth's surface before significant decay has occurred, thus making it impractical to hide in shelters. This is the

Figure 14-13c Nuclear Detonation [view large image]

"doomsday machine" since it is capable of wiping out life on earth. The whole point about an automated doomsday response to nuclear attack is to let all the world know about its existence, and to demonstrate the viability of the process perhaps in a small scale testing (to show that it's not a bluff). This is the ultimate meaning of deterrence.

Table 14-03 Yields of Nuclear Bomb/Explosion

course entirely classified. Because of the nuclear testing moratorium, researchers are trying to design new weapons without a test. It is known as RRW (Reliable Replacement Warhead). New design includes improving the plutonium pit, replacing the toxic materials with other heavier material (for the tamper to amplify the initial explosion), and substituting the volatile explosives (on the outer shell) with an insensitive type (Figures 14-13c). Such ideas have to pass the review of the generals, who have to change the software and hardware systems for delivering the bomb. RRW designers try to reassure the critics that the new warheads will be compatible with existing systems. Figure 14-14 shows the differences in the design of the old and new types.

Figure 14-14 H Bomb, Old and New [view large image]

A 2007 study shows that existing warheads will last for at least another 50 years making the new bomb seemingly less necessary. The US House of Representatives will vote on a bill that would eliminate funding for the RRW from the 2008 budget. But the RRW is not done yet. Other plans are working its way through Congress and the Senate.

Effects of Nuclear Explosions

Nuclear weapons are similar to those of more conventional types in so far as their destructive action is due mainly to blast or shock. On the other hand, there are several basic differences between nuclear and high-explosive weapons. In the first place, nuclear explosions can be many thousands (or millions) of times more powerful than the largest conventional detonations. Second, a fairly large proportion of the energy in a nuclear explosion is emitted in the form of light and heat, generally referred to as "thermal radiation". It is capable of causing skin burns and of starting fires at considerable distances. Third, the nuclear explosion is accompanied by highly penetrating and harmful invisible rays, called the "initial nuclear radiation". Finally, the substances remaining after a nuclear explosion are radioactive, emitting similar radiations over an extended period of time. This is know as the "residual nuclear radiation" or "residual radioactivity". Figure 14-15a shows the distribution of energy in a typical nuclear explosion. The detonation of nuclear weapon leads to the liberation of a

Figure 14-15a Distribution of Energy [view large image]

large amount of energy in a very small period of time within the casing. Tre-mendous pressures (over million times the ambient pressure) is produced in the form of shock wave. Damage is done at the shock front by the huge difference in air pressure as well as by the drag force (strong winds) trailing behind. The radiation energy are absorbed within a few feet

		As the shock wave travels in the air away from its source, the overpressure at the front steadily decreases, and the pressure behind the front falls off until it develops a "negative pressure", in which a partial vacuum is produced and the air is sucked in reversing the wind direction. Figure 14-15c illustrates the variation of overpressure with distance at successive times. Its effects on a light structure, a tree, and a small animal are indicated with a series of pictures corresponding to the
Figure 14-15b Mushroom Cloud [view large image]	Figure 14-15c Shock Wave [view large image]	various times. Speed of the shock front varies from about 1600 ft/sec initially to 1150 ft/sce (slightly faster than the sound speed of 1115 ft/sec) at later time.

and RNA is modified. There are consequently changes in the cells which may have significant detectable effects on the body as a whole. All radiations apparently induce the same general biological consequences, but neutrons are unusual in the respect that they can convert a N-14 atom in an amino acid into one of C-14. Such a change might inactivate an enzyme or affect a nucleic acid. Certain macroscopic phenomena are soon apparent in the living cell. Among these are breaking of the chromosomes. Figure 14-15d shows the

Figure 14-15d Biological Effects [view large image]

normal plant cell, with two groups of chromosomes (left), and changes (right) produced by X-rays. Frequently, the cells are unable to undergo mitosis, so that normal replacement occurring in the living organism is inhibited.

		the shock wave, and acute exposure to the high radiation. Beyond the immediate blast area, casualties are caused from the heat, radiation, and fires spawned from the heat wave. Figure 14-15f presents two views of Hiroshima before and after an atomic-bomb attack. It occurred in the morning (8:16 a.m.) of August 6, 1945. The bomb detonated at an altitude of 580 meters killing or wounding about half of its 350,000 inhabitants with long-term effects on
Figure 14-15e Effects of A-Bomb [view large image]	Figure 14-15f Hiroshima [view large image]	incalculable numbers among the survivors.

Some of the resulting health conditions include:


		Nausea, vomiting and diarrhea. Cataracts. Hair loss. Loss of blood cells. Infertility. Birth defects. Leukemia. Cancer. Figure 14-16a shows the symptoms of radiation sickness according to the dose received. The dose is defined in unit of rontgen (abbreviated to r), which produces 2.1 x 109 ion pairs in a volume of 1 cubic centimetre of air. It is equivalent to about 100
Figure 14-16a Radiation Sickness [view large image]	Figure 14-16b Sick Survivor [view large image]	ergs per gram of water or tissue irradiated. Although it seems to be a minute amout of energy when one considers that 42 million

ergs are required to raise the temperature of 1 gram of water by 1^oC. The remarkable property of ionizing radiation is that the small amout of energy represented by a few hundred rontgens can kill a person. For low level irradiation, the effect is similar to premature aging depending on doses and duration of exposure. Figure 14-16b shows the consequences from radiation exposure at the median level of 500 rad and the lower level of 100 rad.

Protection against nuclear attack:

Preplanned protection - A massive, reinforced, fireproof shelter structure is required at close distances to protect individuals against the severe immediate effects (blast, thermal, and initial nuclear radiation) of a nuclear explosion. Conventional buildings may also be designed to be blast and fire resistant. Thermal and fire hazard can be minimized by reduction of potential ignition points and by provision for isolation or rapid extinction of ignitions to prevent development of large fires. In those areas where early fallout is expected to be a hazard, shelters may be constructed and provision made for occupying them for considerable lengths of time. Knowledge of warning systems and evacuation procedures will also minimize confusion. Unprepared attack - In the event that shelters are not available, certain evasive actions may prove helpful at distances where the immediate effects are least severe. By instantly falling prone and covering exposed portions of the body or getting behind opaque objects, much of the thermal radiation may be avoided, especially in the case of large-yield weapons. Under no circumstances should an individual look in the direction of the fireball. Staying behind thick walls or lying in a deep ditch may help to avoid initial nuclear radiation. Moreover, persons should avoid areas which have frangible materials, such as window glass, plaster, etc., which may become

Figure 14-16c Nuclear Protection [view large image]

flying debris by the action of the blast.

• Aftermath - After the immediate effects of the nuclear explosion are over, certain acts are required to minimize the hazards of the early fallout and from the fires which may result from thermal radiation and secondary blast effects. First, if small fires can be quickly extinguished, extensive conflagrations may be prevented. This must be accomplished before the arrival of the fallout or in areas of low radioactivity levels. Some protection from the fallout may be secured in the basements of buildings or in a quickly constructed shelter, such as placing a sturdy table in a corner adjacent to an unexposed outer wall and covered with 10 to 12 inches of soil, sandbags, solid concrete block, etc., according to what is available. It is important to keep from coming into physical contact with the fallout particles, and to prevent contamination of food and water sources. Monitoring equipment should be used to determine areas which have safe radiation levels and decontamination efforts can proceed to recover necessary equipment, buildings, and areas.

Helium-3

	There are three main energy producing processes in the interior of the Sun. One of them is the proton-proton reaction as shown below:
Figure 14-17 He3-He3 Reaction [view large image]	The He3-He3 reaction (Figure 14-17) in the third step is by far the most frequent of the various alternatives under a central temperature of about 15x106 K.

Another possibility for He3 fusion is via the reaction with D2 (Figure 14-18): He3 + D2 H1 + He4 + 18.4 Mev The fusion reaction rate becomes significant at a temperature of about 10x106 K, and peak about 200x106 K. Researchers see He3 as the perfect fuel source: extremely potent, nonpolluting, with virtually no radioactive by-product. The trouble is, hardly any of it is found on Earth. But there is plenty of it on the Moon.

Figure 14-18 He3-D Reaction [view large image]

Recent reports indicate progress toward making helium-3 fusion. Inside a lab chamber, researchers have produced protons from a steady-state deuterium-helium3 plasma at a rate of 2.6 million reactions per second. That's fast enough to generate fusion power but not churn out electricity. The chamber, which is roughly the size of a basketball, relies on the electrostatic focusing of ions into a dense core by using a spherical grid called Inertial Electrostatic Confinement (IEC) fusion system. Figure 14-19 shows a schematic

Figure 14-19 IEC [view large image]

diagram and the actual construction of an IEC. This one is used for neutron generation.

Meanwhile, news in November 2005 reports that China will make a manned moon landing around 2017. The project includes setting up a moon-based astronomical telescope, measuring the thickness of the moon's soil and the amount of helium-3 on the moon. According to the Chinese announcement: "It will provide the most reliable report on helium-3 to mankind". The United States has unveiled a $104 billion plan in September, 2005 to return Americans to the moon by 2018. Figure 14-20 shows the renderings of a Moon Base by NASA-commissioned artists.

Figure 14-20 Moon Base [view large image]

References:

• Binding Energy -- http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html
• Nuclear Models -- http://csep1.phy.ornl.gov/guidry/Math-9-94html/models.html
• Nuclear Decay, Fission, Fusion -- http://www.lbl.gov/abc/Basic.html
• Nuclear Energy -- http://zebu.uoregon.edu/1999/ph161/l18.html
• Nuclear Reactor -- http://www.npp.hu/mukodes/lancreakcio-e.htm
• Hiroshima, Effect of A-Bomb -- http://www.pref.hiroshima.jp/hiroshima/bunka/htmleng/elegacy3.htm

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Index

Alpha decay Beta decay Binding energy Cobalt bomb Critical mass Doomsday machine Electron capture Fission Fusion Gamma decay Liquid drop model

Magic number Mass number Multiplicity Neutron bomb Nuclear decay Plutonium 239 Positron emission Radioactive series Shell model Uranium 235

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