X-rays and gamma rays:
These are electromagnetic waves of relatively
high energy and therefore having relatively high penetrability through
matter.
They may be emitted from a nucleus,
a gamma ray,
electron rearrangements outside of the nucleus,
Alpha particles:
or produced by
X-rays.
These are helium nuclei and are emitted from the
nucleus of radioactive atoms.
These particles have a low penetrability
and, when they are emitted from an atom inside the body,
they may produce
substantial local damage.
Beta particles:
These are low to high speed electrons given off by
a radioactive material.
Their penetrability in matter is between that of
alpha particles and X-ravs,
Half-Life
Tne rate of emission of a given type of particle from a sample of
radioactive material decreases with time.
when this decrease is rapid the
isotope is said to be siiort-lived and when it is long the isotope is said
to be long-lived,
The time for the rate of emission to reduce to one-half
of its initial value is called its half-life.
half-lives of from a small
fraction of a second to many thousands of years have been observed for different radionuclides.
Thus,
The half-life tor plutonium 239 is about 24,000 years.
after 24,000 years it will have emitted half of that remaining, and so
on.
It is as though we started out with $100 and after one half-life we have
$50,
after another half-life we are down to $25,
another one leaves $12.50,
and so on until nothing is left and the element has returned to its original
stable form,
and
Pu25%
is one of the longest-lived elements.
cesium 137 have half-lives of about 30 vears.
lives
of
1014608
a few months,
days,
minutes,
or
;
seconds.
Strontium 90
Other isotopes have half-