Where did the energy for this come from? The nucleus.

Unstable nuclei … the beginnings of nuclear medicine. Wilhelm Conrad Röntgen

E = mc 2 + energy VI.Fission and Fusion A. In nuclear reactions, the amount of mass and energy must be conserved. In energy-producing reactions: reactants: products: 1 or more  1 or more particles particles more mass less mass The total mass of the products is less. The “missing” mass is called the mass defect. It is converted into energy according to Einstein’s famous equation: m = mass in kilograms c = speed of light in a vacuum = 3 x 10 8 m/s

How were these things explained?

The energy appears as gamma radiation and as the kinetic energy of the product particles, as they move off at high speeds. The energy produced by nuclear reactions is far greater than that of ordinary chemical reactions. Ex. chemical: Burn 1 gram of methane: E = 55,600 J nuclear: Convert 1 gram of any matter into pure energy by E= mc 2 = (1 x10 -3 kg)(3 x 10 8 m/s) 2 = Gram for gram, the nuclear reaction releases over a billion times more energy. 9 x J

Electron powered as chemicals burn. Nucleus powered as nuclei lose mass burn.

B Fission begins with the capture of a neutron by a heavy element, making it unstable. It fissions ( splits ). The products are middle -weight nuclei, n’s + energy. Ex. A typical reaction is: before: after: mass: U-235 n Ba-142 Kr-91 n n n (1) charge: (0) = = U n Ba Kr n

Is charge conserved? Is mass conserved? YES: The # of nucleons (n and p) is __________________. NO:The nucleons in Ba and Kr are ________________!!! ___________mass! _________mass! The “missing” mass became ___________ ( E = mc 2 ) in the form of _______ of Ba, Kr, n and _________________. This energy can be used to heat water into steam in a ____________________ or 2/ ________________________ in an _______________________. Yes. Yes and no. the same smaller less more KE radiation to kill people energy power plant atomic bomb U n Ba Kr n

The neutron is easily absorbed because it is neutral. A moderator slows the neutrons to make capture easier. A chain reaction occurs when the neutrons produced in one reaction are used to start new reactions. ________________– used to ____________the reaction by ____________neutrons absorbing limit control rods n U-235 or Pu-239

Design of a nuclear reactor:

First atomic bomb test: “Trinity”July 16, 1945, at Alamogordo, New Mexico was set off by imploding a subcritical mass of plutonium. 20 kilotons of TNT Today:

First military use of atomic weapons: Hiroshima, Japan, August 6, 1945.

HiroshimaHiroshima Little Boy use U-235 It contained 64 kg of uranium, of which less than a kilogram underwent nuclear fission, and of this mass only 0.6 g was transformed into energy

Nagasaki – 3 days later Replica of Fat Man: Yield: 21 kilotons of TNT Method: implosion of Pu

Churchill = Fat Man Roosevelt = Thin Man  Little Boy after design change Stalin = The Butcher Knife

Indian Point: 1970 MW Nine Mile Point: 1756 MW 2 plants in Oswego New York Nuclear Power Plants:

James Fitzpatrick: 844 MW near Oswego R. E. Ginna: 498 MW on Lake Ontario east of Rochester

C. Fusion occurs when light nuclei combine to form heavier ones. However, extremely high temperatures and pressures are needed because the positive charges of the nuclei repel each other. Fusion only occurs in stars. Ex. A typical reaction: charge mass before: after: H-2 He-3 n = = H 1 2 H 1 2 He 2 3 n

less more Is charge conserved? Is mass conserved? YES: The number of nucleons (n and p) is the same. NO:The nucleons in He are smaller !!! Yes. Yes and no. The “missing” mass became energy ( E = mc 2 ) in the form of KE of He and n and radiation. ____________mass! _________mass! H 1 2 H 1 2 He 2 3 n

How can both fission and fusion release energy? Both result in less mass. Fission : Big nuclei can be fissioned to produce energy b/c the products have less mass.

Fusion : Notice: In both fission and fusion, iron (Fe) is the lowest point on the curve. Its nucleons are smallest. Small nuclei can be fusioned to produce energy b/c the products have less mass.

Number of fission reactors in the world: Number of fusion reactors in the world: 439 reactors in 31 countries 150 naval vessels 6% of world’s energy 15% of world's electricity In the US: 10% of fission energy is supplied by using old Soviet warheads.

Recognizing fission vs. fusion reactions: fission:fusion: BIG + n small nuclei BIGGER NUCLEI smaller nuclei The products of fusion are much less radioactive than the products of fission. Also, H is much more abundant than U. Moreover, fusion yields more energy per unit mass. This is why fusion power is more desirable than fission. Alas, currently we have no fusion plants but many hydrogen bombs. i  splits u  unites

First hydrogen bomb test The Soviet Tsar bomb: 57 megatons (largest ever) A hydrogen bomb uses fusion, the same process that powers the Sun. It is more powerful than a fission bomb.