The
chart below lists all of the decay
products of radon gas (radon-222) in
their order of appearance. They are
called the "radon progeny" (formerly
"radon daughters"). Each radioactive
element on the list gives off either
alpha radiation or beta radiation
-- and sometimes gamma radiation too
-- thereby transforming itself into
the next element on the list.
Lead-206, the last element on the
list, is not radioactive. It does not
decay, and therefore has no half-life.
When
radon gas is allowed to build up in an
enclosed space, such as a mine shaft
or basement, the radioactive hazard
increases enormously because of the
build-up of radon progeny. Conversely,
when radon gas migrates through the
atmosphere, the solid radon progeny
are deposited on the soil and water
below, entering into the food chain
and hence the bodies of birds,
animals, fish and insects.
NOTES ON THE
CHART
The vertical axis measures the MASS NUMBER,
while the horizontal axis measures the ATOMIC NUMBER.
DIAGONAL ARROWS indicate alpha decay
while HORIZONTAL ARROWS indicate beta
decay.
MeV =
MILLION ELECTRON-VOLTS.
It is a measure of the ENERGY of the
alpha radiation.
The more energetic it is, the more
damaging it is.
What
are the Mass Number
and the Atomic Number?
All the atoms of a given element are identical. Each
atom has a tiny core called a "nucleus", containing even smaller
particles called "protons" and "neutrons". The number
of protons in the nucleus is the "atomic number", while the
number of protons and neutrons together is the "mass number".
These numbers are characteristics of the particular element.
Elements having the same atomic number
are chemically indistinguishable, even
if the mass numbers are different.
They are called "isotopes". For
example, polonium-218, polonium-214,
and polonium-210 are three isotopes of
polonium. They have different mass
numbers -- as indicated by their names
-- but they share the same chemical
properties because they all have the
same atomic number, 84.
During
"alpha decay", the nucleus gives off
an alpha particle, which is made up of
two protons and two neutrons. Thus the
atomic number goes down by two and the
atomic number goes down by four.
During
"beta decay", one of the protons in
the nucleus spontaneously turns into a
neutron, giving off a high-velocity
electron in the process. Thus the
stomic number increases by one (as
there is now an extra proton) and the
mass number is unchanged. The escaping
electron is called a beta particle.
Notice: The atomic weight changes when an Alpha Particle escapes from the
nucleus. This is because the the alpha particle has a definite mass while the beta particle is pure energy and has no mass. It is the impact of the alpha particle on the lung tissue that constitutes the health risk associated with radon.
