Radiocarbon dating a third radiocarbon revolution. Occasionally, radiocarbon dating techniques date an object of popular interest, for example the Shroud of Turin, a piece of linen cloth thought by some to bear an image of Jesus Christ after his crucifixion. Three separate laboratories dated samples of linen from the Shroud in 1988; the results pointed to 14th-century origins, raising doubts about the shroud's authenticity as an alleged 1st-century relic. Researchers have studied other radioactive isotopes created by cosmic rays to determine if they could also be used to assist in dating objects of archaeological interest; such isotopes include , , , ,
Kinetic isotope effect at which the substitution occurs. Interpretation of the leaving group kinetic isotope effects had been difficult at first due to significant contributions from temperature independent factors. Kinetic isotope effects at the α-carbon can be used to develop some understanding into the symmetry of the transition state in S2 reactions, although this kinetic isotope effect is less sensitive than what would be ideal, also due to contribution from non-vibrational factors. A secondary kinetic isotope effect is observed when no bond to the isotopically-labeled atom in the reactant is broken or formed. Secondary kinetic isotope effects tend to be much smaller than