Nuclear Reactions

Nuclear ReactionsThe Nucleus

Nuclide: a unique atom represented by the symbol:AXZZone of StabilityStability

Radioactive Decay: the probability that a nucleus will undergo decomposition to form a different nucleusIsotopes: Atoms that have identical atomic numbers but different mass number values (neutrons have changed)Important ObservationsAll nuclides with 84 or more protons are unstableLight nuclides (P to N ration =1) are stable For stable heavy nuclides P to N ratio is >1Special Stability: certain combinations confer special stability (even vs odd)Magic Numbers: certain combinations confer especially stable nucleus 2,8,20,28,50,82,126 (parallels behavior for stable electrons for chemical stability)

Decay

The atomic mass number (A) and atomic number (Z) must remain constant across the reaction!A: 238 = 234 +4

Z: 92 = 90 + 2Types of Decay

Alpha Decay () : A very common mode of decay for heavy nuclides. (helium nucleus)

Types of Decay

Beta Decay (-) : Most common, The mass number of the decaying remains constant, the net effect is the change of a neutron to a proton!

Types of DecayPositron Production (+) : Occurs for nuclides below the zone of stability, a particle with the same mass as an electron but opposite charge. The net effect is a change of a proton to a neutron.

Types of DecayGamma ray () : Release of a high energy photon, frequently accompanies other reactions

Types of DecayElectron Capture : process in which one of the inner orbital electrons is captured by the nucleus

Interesting, and why do we not just turn mercury into gold?Types of Decay

Summary of Decay reactionsDecay Series

Decay Series: a sequence of nuclear reactions that ultimately result in the formation of a stable isotope.Half-lifeHalf-life (t)Time required for half the atoms of a radioactive nuclide to decay.Shorter half-life = less stable.

Half-life

mf:final massmi:initial massn:# of half-lives15m = mass defectE = change in energyIf E = (exothermic), mass is lost from the system.

When a system gains or loses energy it also gains or loses a quantity of mass.E = mc2

Mass Defect7Nuclear TransformationsNuclear Transformation: the change of one element to another.

F issionsplitting a nucleus into two or more smaller nuclei1 g of 235U = 3 tons of coal

F issionChain reaction - self-propagating reactionCritical mass - mass required to sustain a chain reactionSubcritical: When the process dies outSupercritical: rapid escalation of reaction

F ission

Fusioncombining of two nuclei to form one nucleus of larger massthermonuclear reaction requires temp of 40,000,000 K to sustain1 g of fusion fuel = 20 tons of coaloccurs naturally in stars

Fission vs. Fusion235U is limiteddanger of meltdowntoxic wastethermal pollutionfuel is abundantno danger of meltdownno toxic wastenot yet sustainable

FISSIONFUSION