Advertisement
a few inches at most before coming to a stop. Therefore, alpha
particles cannot be detected without being in close contact with
the source, and even then only the alphas coming from the surface
of the source can be detected. Alphas generated within the source
are absorbed before reaching the surface. Due to short range,
alpha particles are not a serious health hazard unless they are
emitted from within the body when their high energy, in close
contact with sensitive living tissue, is an extreme hazard.
Fortunately, almost all alpha-emitting substances also emit
gamma rays, allowing for their detection.
Neutrons, having no net charge, do not interact with matter as
easily as other particles, and can drift through great thicknesses of
material without incident. A free neutron, drifting through space,
will decay in an average of 11.7 minutes, yielding a proton and an
electron (beta ray). The neutron can also combine with the nucleus
of an atom, if its path carries it close enough. When a neutron is
absorbed into a nucleus, it is saved from its ultimate fate (decay),
but may render the nucleus unstable. This absorption process is
used in medicine and industry, to create radioactive elements from
non-radioactive ones. Detecting neutrons is specialized and
beyond the scope of typical Geiger counters, but most possible
neutron sources also emit gamma and beta radiation, affording
detection of the source.
The highly energetic X-ray and gamma rays lose their energy as
they penetrate matter. X-rays have an energy of up to about
200,000 eV, compared to gamma radiation which can be as
energetic as several million eV. One million eV gamma radiation
can penetrate an inch of steel. Gamma and X-ray radiation are by
far the most penetrating of all common types, and are only
effectively absorbed by large amounts of heavy, dense material of
high atomic number, such as lead.
For other radiation basics, go to:
http://www.hps.org/publicinformation/ate/faqs/radiation.html
©2011 Industrial Test Systems, Inc. Rock Hill, SC
Rev. 03/24/11
11
Advertisement
