Untitled - Kelly Walsh High School

294 CHEMISTRY FOR THE UTTERLY CONFUSED
Gamma Emission
Gamma emission is the release of high-energy, short-wavelength photons,
which are similar to x-rays. The representation of this radiation is g. Gamma
emission commonly accompanies most other types of radioactive decay, but we
normally do not show it in the balanced nuclear equation since it has neither
appreciable mass nor charge.
Alpha, beta, and gamma emission are the most common types of natural decay
modes, but we do occasionally observe positron emission and electron capture.
Positron Emission
A positron is essentially an electron that has a positive charge instead of a neg-
0
ative one. It is represented as or 1 . Positron emission results from the conversion
of a proton to a neutron and a positron:
e
0
1b 1
1p l
We observe it in the decay of some radioactive isotopes, such as potassium-40:
40
19K l
Electron Capture
The four decay modes described above all involve emission or giving off a particle,
but electron capture is the capturing of an electron from the energy level
closest to the nucleus (1s) by a proton in the nucleus. This creates a neutron:
0
1e 1 1p However, this leaves a vacancy in the 1s energy level and an electron, from a
higher energy level, drops down to fill this vacancy. A cascading effect occurs as
the electrons shift downward releasing energy. This released energy falls in the
x-ray part of the electromagnetic spectrum. These x-rays give scientists a clue
that electron capture has taken place.
Polonium-204 undergoes electron capture:
204
0
84Po 1e 1
0n 0 1e 40
18Ar 0 1e l
204 l Bi x-rays
Notice that the atomic number has decreased by 1, but the mass number has
remained the same.
83
1
0n