Lecture13-16

This is called a global su2 symmetry spin also has an

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Unformatted text preview: s - 80.2 days for Iodine- 131 - 99.9% of it has decayed to a stable state.[108] 48 Doses •  Measured doses are fairly small. •  Briefly 0.01 sieverts per hour at main gate. •  long term: 0.00002 sieverts in nearest town. •  The real danger from reactor releases are elements that are absorbed by humans. •  Iodine 131 is a big problem for a few weeks. •  Iodine absorbed by body, with high concentra;on in thyroid gland •  clear evidence of increased thyroid cancer from Chernobyl •  Iodine tablets can nearly eliminate the problem. •  Cesium 137 (half life 30.2 y) most radioac;ve fallout •  90Sr (half life 29 y) goes into bones 49 Fusion u༇  Need to get hydrogen very hot to overcome Coulomb repulsion between protons. u༇  Works well at the center of the sun. u༇  Quite hard to make a fusion reactor on earth. o  We are trying o  It is not clear fusion reactors will be prac;cal. 50 The Sun u༇  The sun fuses hydrogen into helium giving off about 27 MeV. o  This energy heats up the sun; the heat slowly migrates to the surface and is radiated away mainly in visible light (that’s why its visible). o  Almost all the energy is radiated in EM waves u༇  The sun also will later fuse the Helium into Carbon… o  But the sun isn’t massive enough to make Iron. o  Its fate is to become a white dwarf (diamond?) u༇  More massive stars make iron o  And when they collapse into neutron stars and supernova, they make the heavier elements in the explosion. 51 Supernovae u༇  Humans have seen the bright A star of 10 solar masses or more finishes the fusion process and cools to a explosion of supernovae throughout history. white dwarf. o  White dwarf held up by electron Fermi pressure. With enough mass, the reac;on p +e→n+ν suddenly makes the electrons go away. u༇  The star goes into free fall un;l it hits the Fermi pressure of the neutrons. u༇  The shock wave blows off the outside of the star producing many heavy elements. u༇  o  Neutrino blast o  Neutron rich SN 1987a 52 Older Supernovae Cygnus 15000 years ago Crab nebula 1054 (visible in daylight for 23 days) 53 Equa;ons For Chapter 13 and 14 u༇  54 Nuclear Force Par;cles u༇  Based on the range of the nuclear force, Yukawa predicted a massive par;cle that mediates the strong interac;on (uncertainty principle calcula;on). u༇  Eventually the pion was found with about the right mass and proper;es. o  It is consistent with the force carrier. o  But the interac;on was s;ll complicated. u༇  Par;cles like the pion and proton were considered elementary par;cles for a long ;me. 55 More par;cles like proton and pion u༇  Hundreds more (unstable) par;cles were found. u༇  A symmetry consi...
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This note was uploaded on 02/24/2014 for the course PHYS 2D taught by Professor Hirsch during the Winter '08 term at UCSD.

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