Nuclear Weapons Nuclear Weapons Yes Yes Y Y A. A. No No B. - PDF document

Nuclear Weapons 1 Nuclear Weapons 2 Introductory Question Introductory Question Is it possible to have 100 tons of plutonium Is it possible to have 100 tons of plutonium � and not have it explode? and not have it explode? Nuclear Weapons Nuclear Weapons Yes Yes Y Y A. A. No No B. B. Nuclear Weapons 3 Observations about Nuclear Weapons 4 Observations about 3 Questions about 3 Questions about Nuclear Weapons Nuclear Weapons Nuclear Weapons Nuclear Weapons � They release enormous amounts of energy They release enormous amounts of energy � Where is nuclear energy stored in atoms? Where is nuclear energy stored in atoms? � They produce incredible temperatures They produce incredible temperatures � Why are some atomic nuclei unstable? Why are some atomic nuclei unstable? � They produce radioactive fallout They produce radioactive fallout � How does a nuclear chain reaction work? How does a nuclear chain reaction work? � They are relatively difficult to make They are relatively difficult to make � They use chain reactions They use chain reactions Nuclear Weapons 5 Nuclear Weapons 6 Question 1 Question 1 Atomic Nuclei Atomic Nuclei � Where is nuclear energy stored in atoms? Where is nuclear energy stored in atoms? � Atoms are usually electrically neutral Atoms are usually electrically neutral � � They must have as many + charges as They must have as many + charges as – – charges charges � Each electron must be matched by a + charge Each electron must be matched by a + charge � At the center of an atom is its nucleus A A At the center of an atom is its nucleus h h f f i i i i l l � Extremely small (1/100,000th of atom’s diameter) Extremely small (1/100,000th of atom’s diameter) � Contains most of the atom’s mass Contains most of the atom’s mass � Also contains most of the atom’s potential energy Also contains most of the atom’s potential energy � Evidence is related to: E=mc Evidence is related to: E=mc 2 2 1

Nuclear Weapons 7 Nuclear Weapons 8 Structure of Nucleus Structure of Nucleus Clicker Question Clicker Question � Nucleus contains two kinds of nucleons Nucleus contains two kinds of nucleons � If you snipped the nucleus of a very massive If you snipped the nucleus of a very massive atom in half, it would release energy stored in atom in half, it would release energy stored in � Protons are positively charged Protons are positively charged � Neutrons are electrically neutral Neutrons are electrically neutral � Two forces are active in a nucleus T Two forces are active in a nucleus T f f i i i i l l A. the electrostatic repulsion between protons. the electrostatic repulsion between protons. h h l l i i l i l i b b A. � Electrostatic repulsion between protons Electrostatic repulsion between protons B. the nuclear attraction between nucleons. the nuclear attraction between nucleons. B. � Nuclear force attraction between touching nucleons Nuclear force attraction between touching nucleons � At short distances, the nuclear force dominates At short distances, the nuclear force dominates � � At long distances, the electric force dominates At long distances, the electric force dominates � Nuclear Weapons 9 Nuclear Weapons 10 Question 2 Question 2 Nuclear Stability Nuclear Stability � Why are some atomic nuclei unstable? Why are some atomic nuclei unstable? � The nucleons in a nucleus are in equilibrium The nucleons in a nucleus are in equilibrium � To be classically stable, that equilibrium must be stable To be classically stable, that equilibrium must be stable � To be quantum To be quantum- -mechanically stable, that equilibrium mechanically stable, that equilibrium must also be the overall potential energy minimum must also be the overall potential energy minimum ust a so be t e ove a pote t a e e gy ust a so be t e ove a pote t a e e gy u u � Quantum mechanics and the Heisenberg uncertainty Quantum mechanics and the Heisenberg uncertainty principle allow the nucleons to “try out” arrangements principle allow the nucleons to “try out” arrangements that are quite different from their equilibrium positions that are quite different from their equilibrium positions � If they find a path to a new, lower If they find a path to a new, lower- -potential potential- -energy energy equilibrium, the nucleus may fall apart equilibrium, the nucleus may fall apart Nuclear Weapons 11 Nuclear Weapons 12 Radioactivity Radioactivity Question 3 Question 3 � Large nuclei have two possible problems: Large nuclei have two possible problems: � How does a nuclear chain reaction work? How does a nuclear chain reaction work? � Too many protons: too much electrostatic potential Too many protons: too much electrostatic potential � Too many neutrons: isolated neutrons are unstable Too many neutrons: isolated neutrons are unstable � Balance between protons and neutrons is tricky B l Balance between protons and neutrons is tricky B l b b d d i i i k i k � Large nuclei tend to fall apart spontaneously Large nuclei tend to fall apart spontaneously � These breakups are known as radioactive decay These breakups are known as radioactive decay � and can include a splitting process called fission and can include a splitting process called fission 2

Nuclear Weapons 13 Nuclear Weapons 14 Induced Fission Induced Fission Clicker Question Clicker Question � A large nucleus can break when struck hard A large nucleus can break when struck hard � Fissioning Fissioning nuclei may also release protons, but nuclei may also release protons, but those fission- those fission -produced protons don’t cause produced protons don’t cause � Collision knocks its nucleons Collision knocks its nucleons subsequent fissions because they subsequent fissions because they out of stable equilibrium out of stable equilibrium � Collision � Collision Collision altered nucleus Collision-altered nucleus altered nucleus altered nucleus may undergo induced fission may undergo induced fission A. don’t have enough mass to cause fissions. don’t have enough mass to cause fissions. A. � Since a neutron isn’t repelled Since a neutron isn’t repelled B. collide too softly with nuclei to cause fissions. collide too softly with nuclei to cause fissions. B. by nucleus, it makes an ideal by nucleus, it makes an ideal projectile for inducing fission projectile for inducing fission C. don’t have enough momentum to cause fissions. don’t have enough momentum to cause fissions. C. D. don’t collide with nuclei at all. don’t collide with nuclei at all. D. Nuclear Weapons 15 Nuclear Weapons 16 Chain Reaction Chain Reaction Requirement for a Bomb Requirement for a Bomb � Since neutrons can induce fission Since neutrons can induce fission � A fission bomb requires 4 things: A fission bomb requires 4 things: � � and induced fission releases neutrons, and induced fission releases neutrons, � An initial neutron source An initial neutron source � this cycle can repeat, this cycle can repeat, � a fissionable material (undergoes induced fission) a fissionable material (undergoes induced fission) a chain reaction! a chain reaction! a chain reaction! a chain reaction! � each fission must release additional neutrons each fission must release additional neutrons h fi i n m h fi i n m t r l t r l dditi n l n dditi n l n tr n tr n � � Each fission releases energy Each fission releases energy � material must use fissions efficiently (critical mass) material must use fissions efficiently (critical mass) � Many fissions release Many fissions release � 235 235 U and U and 239 239 Pu are both fissionable materials, Pu are both fissionable materials, prodigious amounts of energy prodigious amounts of energy but 235 235 U is rare and must be separated from U is rare and must be separated from 238 238 U � but � Sudden energy release Sudden energy release � and and 239 239 Pu is made by exposing Pu is made by exposing 238 238 U to neutrons. U to neutrons. produces immense explosion produces immense explosion Nuclear Weapons 17 Nuclear Weapons 18 The Gadget & Fat Man The Gadget & Fat Man Introductory Question (revisited) Introductory Question (revisited) � Each of these fission bombs started as a Each of these fission bombs started as a 239 239 Pu Pu Is it possible to have 100 tons of plutonium Is it possible to have 100 tons of plutonium � � sphere below critical mass (6 kg) sphere below critical mass (6 kg) and not have it explode? and not have it explode? � It was crushed explosively to supercritical mass It was crushed explosively to supercritical mass � and promptly underwent and promptly underwent d d l l d d Yes Y Yes Y A. A. an explosive chain reaction. an explosive chain reaction. No No B. B. 3