NUCLEAR CHEMISTRY © Copyright R.J. Rusay Dr. Ron Rusay Chem 106 Spring 2004

NUCLEAR CHEMISTRY Nuclear Particles: Mass ChargeSymbol Mass ChargeSymbol PROTON 1 amu +1 H+, H, p NEUTRON 1 amu 0 n © Copyright R.J. Rusay

Nuclear Decay / Radioactivity  Unstable nuclei “decay” i.e. they lose particles which lead to other elements and isotopes.  The elements and isotopes produced may also be unstable and go through further decay. © Copyright R.J. Rusay   Nuclear decay: reactions conserve mass.

Nuclear Particles emitted from unstable nucleii  Emitted Particles: Mass Charge Symbol Mass Charge Symbol  alpha particle 4 amu +2  beta particle very small -1  gamma very very small 0  positron very small +1 © Copyright R.J. Rusay

Nuclear Penetrating Power © Copyright R.J. Rusay  alpha particle: low  beta particle: moderate  gamma: high  X-rays? Water

Dosimeters measure radiation absorbedDosimeters measure radiation absorbed Radiation effects are cumulative (Madame Curie)Radiation effects are cumulative (Madame Curie) rad = radiation absorbed dose ( 0.01 J/kg)rad = radiation absorbed dose ( 0.01 J/kg) rem= radiation equivalent for man (= rad x Q; Q=1 for X-rays,3 for neutrons, 10 for p+, 20 for  -particles)rem= radiation equivalent for man (= rad x Q; Q=1 for X-rays,3 for neutrons, 10 for p+, 20 for  -particles) Background radiation = 0.13 remBackground radiation = 0.13 rem Annual limit is set at 0.17 rem above backgroundAnnual limit is set at 0.17 rem above background

Alpha Decay–Heavy Elements  238 U  234 Th +  + e t 1/2 = 4.48 x 10 9 years t 1/2 = 4.48 x 10 9 years  210 Po  206 Pb +  + e t 1/2 = 138 days t 1/2 = 138 days  256 Rf  252 No +  + e t 1/2 = 7 ms t 1/2 = 7 ms For Cobalt 60 predict the alpha decay product:

Nuclear Decay Series  If the nuclei produced from radioactive decay are unstable, they continue to decay until a stable isotope results.  An example is Radium which produces Lead © Copyright R.J. Rusay

The 238 U Decay Series

Radiodating Methods © Copyright R.J. Rusay  Three isotopes are currently used: Carbon-14half life 5,730 yrs Potassium-40 half life 1.3 x 10 9 yrs Uranium-238 half life 4.47 x 10 9 yrs  The age of samples can be determined by measuring their disintegrations over time.

Decrease in Number of 14 C Nuclei Over Time

Radiocarbon Dating for Determining the Age of Artifacts An ancient wood sample has 6.25% of the 14 C of a reference sample. What is the age of the sample?

Nuclear Reactions  The mass of the visible universe is 73% H 2 and 25% He. The remaining 2%, “heavy” elements, have atomic masses >4.  The “heavy” elements are formed at very high temperatures (T>10 6 o C) by FUSION, i.e. nuclei combining to form new elements.  There is an upper limit to the production of heavy nuclei at A=92, Uranium.  Heavy nuclei split to lighter ones by FISSION © Copyright R.J. Rusay

NUCLEAR STABILITY Patterns of Radioactive Decay  Alpha decay (  –heavy isotopes  Beta decay (    –neutron rich isotopes  Positron emission (   )–proton rich isotopes  Electron capture–proton rich isotopes x-rays  Gamma-ray emission (   Spontaneous fission–very heavy isotopes © Copyright R.J. Rusay

NUCLEAR ENERGY  EINSTEIN’S EQUATION FOR THE CONVERSION OF MASS INTO ENERGY  E = mc 2  m = mass (kg)  c = Speed of light c = x 10 8 m/s

Mass  Energy Electron volt (ev) The energy an electron acquires when it moves through a potential difference of one volt: 1 ev = x J Binding energies are commonly expressed in units of megaelectron volts (Mev) 1 Mev = 10 6 ev = x J A particularly useful factor converts a given mass defect in atomic mass units to its energy equivalent in electron volts: 1 amu = x 10 6 ev = Mev

Nuclear Reactions  Fission and Fusion reactions are highly exothermic (1 Mev / nucleon).  This is 10 6 times larger than “chemical” reactions which are about 1 ev / atom.  Nuclear fission was first used in a chain reaction: © Copyright R.J. Rusay

Nuclear Reactions:  Fission and Fusion reactions are highly exothermic (1 Mev / nucleon).  This is 10 6 times larger than “chemical” reactions which are about 1 ev / atom. Fission: Fusion:

Nuclear Reactions  Nuclear fission was first used in a chain reaction:

Nuclear Reactions / Fission  The Fission Chain Reaction proceeds geometrically: 1 neutron -> 3 -> 9 -> 27 -> 81 etc.  1 Mole of U-235 (about 1/2 lb) produces 2 x kJ which is equivalent to the combustion of 800 tons of Coal!  Commercial nuclear reactors use fission to produce electricity....Fission bombs were used in the destruction of Hiroshima and Nagasaki, Japan, in August © Copyright R.J. Rusay

The Nuclear Dawn August 6, 1945

Nuclear Power Plant

Worldwide Nuclear Power Plants

Chernobyl, Ukraine April,1986 and April,2001

Nuclear Reactions / Fusion  Fusion has been described as the chemistry of the sun and stars.  It too has been used in weapons. It has not yet found a peaceful commercial application © Copyright R.J. Rusay  The application has great promise in producing relatively “clean” abundant energy through the combination of Hydrogen isotopes particularly from 2 H, deuterium and 3 H, tritium: (NIF/National Ignition Facility, LLNL)

National Ignition Facility Lawrence Livermore National Laboratory

© Copyright R.J. Rusay