Lecture+p - Ch 15.3 Recap Nuclear Chemistry Isotope...

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Isotope numbering X A Z Mass number Atomic number Element symbol = number of protons + neutrons = number of protons Ch 15.3 – Recap Nuclear Chemistry X A Z Y A - 4 Z - 2 + He 4 2 unstable atom more stable atom alpha particle Alpha Decay Beta Decay X A Z Y A Z + 1 + β 0 -1 unstable atom more stable atom beta particle
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Carbon Dating Cosmic rays can collide with the atmosphere to produce high energy neutrons. These can react with nitrogen atoms (7 protons 7 neutrons) to knock a proton out from it’s nucleus, replacing it with a neutron. The proton number is reduced by 1 (it is now 6), but the mass number remains the same (14). C-14, 14 C, is radioactive and decays with a half-life of 5730 years back to 14 N. The 14 C atoms are oxidized to CO 2 gas which can be exchanged between the atmosphere, hydrosphere and biosphere. As long as an organism is alive it will continually exchange carbon within its reservoir and remain in equilibrium as new 14 C is replenished. After the organism dies the 14 C clock is set as the ratio of 14 C/stable carbon ( 12 C and 13 C) decreases as 14 C decays to 14 N.
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Radioactive Decay Measurement of Radioactivity -- Radiocarbon ages can be determined for organic matter by simply counting β -emissions, as decays per minute (dpm) - - quanties of radiation are defined in Curies (Ci) which is 3.7 x 10 10 decays sec - 1 . a very big number! - - Biological exposures are measured in radiation absorbed dose (rad) or in roentgen equivalent man (rem) which equals the rads x radiations biological effect Ch 15.6 – Nuclear Chemistry “Background” radiation has an a decay activity of ~ 0.082 rem/yr, very weak. Other more potent sources are X-rays, nuclear testing, and other technological exposures.
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Ch 15 – Radioactive Decay Kinetics Practice problem #43b Radioactive elements follow first-order kinetics as they decay to stable isotopes. The decay of 14 C has a half-life of 5730 years. Using this information, answer the following questions. a)
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This note was uploaded on 11/04/2009 for the course CHEM Chem 1C taught by Professor Farmer during the Spring '09 term at UCL.

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Lecture+p - Ch 15.3 Recap Nuclear Chemistry Isotope...

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