Chapter 4.4 and 25
Lawrence’s cyclotron: Articles/Archive/early-years.html Articles/Archive/early-years.html FermiLab CERN A.k.a. “Large hadron collider” (LHC) SuperCollider
CHEMICALNUCLEAR Bonds are broken or formed. Atoms are unchanged, but rearranged. Involve valence electrons. Associated with small energy changes. Reaction rate influenced by temp, pressure, concentration, catalysts. Nuclei emit particles and/or rays. Atoms are converted into atoms of another element. Involve protons, neutrons, and electrons. Associated with large energy changes. Reaction rate not normally affected by temp, pressure, catalysts.
Radiation – the rays and particles emitted by the radioactive material Radioactive atoms undergo significant changes in their identity Atoms of one element change to atoms of another element Reason? Nuclei are unstable Gain stability by losing energy
Radioisotopes – isotopes of the same atoms with unstable nuclei Undergo radioactive decay to become more stable Most common radiation types: Alpha Beta Gamma
Which atomic nuclei are radioactive? Neutrons – add attractive force within the nucleus Stability – related to balance between electrostatic and strong nuclear forces Neutron/proton ratio Low atomic numbers ~1:1 ratio High atomic numbers ~1.5:1 ratio Figure 25.8 p. 811
Too many neutrons to be stable (above band of stability): Beta decay Alpha decay Gamma decay Too few neutrons to be stable (below band of stability): Positron emission Electron capture
Types of Decay Notes on Board….
Radioisotopes have differing decay rates Half-life – time required for one-half of a radioisotope’s nuclei to decay into its products Example: Strontium-90 half-life (t) = 29 years Today g strontium 29 years from now – 5.0 g strontium
Equation: amount remaining = initial amount (1/2) n OR amount remaining = initial amount (1/2) t/T t = time elapsed T = duration of one half life *** must have same units of time Table 25.5 p. 818 Radioisotopes all have different half-lives