Page 221 - Instant notes

G2
APPLICATIONS OF NUCLEAR
STRUCTURE

Key Notes
The isotopes of some elements are intrinsically unstable and will
spontaneously disintegrate. Radioactivity is the emission of sub-
atomic particles and/or electromagnetic radiation accompanying
these conversions (transmutations) from parent isotope to
daughter isotope. The three common forms of radioactive
emission are: α-particles (helium-4 nuclei); β-particles
(electrons); and γ-rays (very short-wave electromagnetic
radiation). The time taken for 50% of a radioactive sample to
decay is called the half-life. Radioactivity is measured in units of
bequerel and the absorbed dose in units of gray.
The kinetic isotope effect is the reduction in the rate of reaction
by the replacement of an atom in a molecule by a heavier isotope
(usually the replacement of hydrogen by deuterium). The effect is
caused by the lowering of the zero-point energy of the X-H bond
by the heavier atom which increases the activation energy
required to break the bond. Observation of an isotope effect
indicates that cleavage or formation of the bond forms part of the
rate determining step.
Both radioactive and stable isotopes can be used to tag specific
molecules to elucidate chemical reaction mechanisms. Molecules
containing radioactive markers can be identified by the radiation
emitted. Molecules enriched with a particular stable isotope are
commonly identified using mass spectrometry.
Related topic Nuclear structure (G1)

Radioactivity

The isotopes of a number of elements are naturally unstable and will lose mass and/or
energy in order to form a more stable state. The spontaneous decay of such radioisotopes
(or radionuclides) creates a different element (the daughter) from the starting element
(the parent). The conversion of one isotope into another is called transmutation.
Radioisotopes can also be prepared synthetically υia the deliberate bombardment of
stable nuclei with sub-atomic particles.
In all cases the mass or energy loss during radioactive decay can cause damage to the
environment through the formation of reactive ions or free radicals. The extent of damage
depends on the type of mass or energy emitted. In general, three types of ionizing