Some
common objets around us contains radioactive elements. In the
past this radioactivity was wanted , when peoples thought they
could take advantage of the radioactivity. We now know the disasters
of the radioactivity and nevertheless, the radioactivity is
still used within common objects. If the use of radioactive
elements is still underway it is mainly because people don't
realize yow radioactive some objects are. It is a mater a fact
that the radioactivity is impossible to percept with our sense
: no smell , invisible, no noise... However the international
standards (CIPR) and regulations limit, for people, the radioactivity
level at 1 millisievert per year above the natural background
(equivalent to an average of 11 micro Rem/h). Sometime it is
interpreted by national regulators as being 5 millisievert like
in France or more. The natural background is around 10 to 15
micro Rem/h in France (see Map). That's mean that the regulator
accept a level of about 4 millisievert above the background.
The
use or radiometers commonly call "GEIGER counters" give to people
the opportunity to detect radioactive object. Already fifty
types of such objects have been listed in Europe. The most well
known are describe in this document.
1.
WATCHES AND CLOCKS
About twenty years ago the needle of clock and watches were
luminescent (event the numbers). The material used for such
an effect was usually the Radium, sometime other radioactive
elements was used. The level measured can raise 600 *Rem/h in
front of the face. Of course, it is not recommended to wear
such watches.
2.
GAS LAMP HEAD SET
If
you have ever camp, you certainly have used a gas lamp! The
lamp headset is heated by the gas combustion and generates a
sweet light.
The
irradiation risk
Measured levels vary between 150 and 360 micro Rem/h at the
contact. Beyond 50 cm, the radiation is no longer perceptible.
You can protect from radiation by remaining at more than 50
cm of lamps. It is necessary to avoid to put muffs in a pocket!
Risks of contamination
They are far more important that risks of irradiation. It concerns
indeed muff that comprise Thorium 232. Besides direct effects
by radiation of these muffs, they present an other danger :
The Thorium is a very radiotoxic element, it suffices to inhale
some becquerels to reach the limit of the bearable risk; out
the distribution of radioactive micro particles when the muff
is carried to incandescence is not again known. there are also
risks during the manipulation of these muffs arrived in end
of life. Fibers leave very easily in dust and increases the
risk to breathe or to inhale radioactive particles. To manipulate
the old muffs it is recommended to use gloves and if possible
to avoid to breathe. .
3.
THE LIGHTNING CONDUCTORS
Fifty years after the discovery of the lightning conductor by
Benjamin Franklin in 1760, a Hungarian scientist has had the
idea to place a radioactive source near the sharp pin of lightning
conductors. It thought that the radioactivity was going to ionize
the air, to render it conductive around the lightning conductor's
pin and to allow thunderbolt to shoot there in priority. This
process, although very controversial as for its efficiency,
has been patented and commercialized in 1932. It is estimates
that in France only approximately 30 000 radioactive lightning
conductors are still on roofs. In the eighties, a decree forbids
the use of radioelements in the manufacture of lightning conductors,
leaving 4 years to manufacturers to adapt their process. Later
a new decree completes the first to forbid also the sale and
import.
Not
to confuse lightning conductor and parafoudre The radioactive
substance used for the parafoudres has not again been forbidden.
These machines are equipped with sources of tritium or promethium
147. These radio elements have significant short periods 12,3
and 2,6 years.
Risks
The radioelements used are very radiotoxic products with very
long period of radioactivity. Sources remain harmful during
years, perhaps for thousands of years. For example the period
of Americium 241 is 433 years. It is the necessary time for
the radioactivity to decreases half. For a source of 30 millions
of becquerels in 1987, it will be 15 millions in 2420; again
7,5 millions in 2863 then 3,7 millions in 3296 etc. The period
of the radium 226 is clearly longer : 16000 years. The rhythm
of decrease is therefore again slower. Sources used in lightning
conductors are therefore going to remain harmful for future
generations. It is necessary to proceed to their recovery and
stocking to limit the dispersion risks.
External
irradiation risks are very variable : weaker for Americium 241
that for the radium 226 witch counts among its descendants a
very radiating radio element: the bismuth 214. For a source
of 37 Mbq, at 10 cm the debit of dose is 100 000 mRem/h !! By
remaining an hour near the radioactive part of the lightning
conductor, you can receive the annual dose defined by the CIPR.
Some lightning conductors are equipped with radium sources whose
activity is up to 20 times superior. The annual dose can then
be received in less of 5 minutes!! In most of lightning conductors,
sources are apparent. They can easily damage and contaminate
their implantation site, as much that their coating is slim.
Most current Risks is, that, in case of building demolitions,
lightning conductor's sources contaminate the vicinity and rubbles.
4.
SMOKE DETECTORS
Most of public and industrial building have fire alarms generally
in ceiling. As the adage tells it if well, there is no smoke
without fire, it is for this reason that systems of detection
are in fact based on the detection of smokes. The principle
is simple, a radioactive source ionizes the two air bedrooms,
one open and the other closed The conductivity of the air is
controlled by means electrodes. When the smoke invades the air
of the open bedroom, the difference of conductivity between
the two bedrooms allows to trig the alarm. The most used Sources
are Americium 241, more rarely radium. The level of radioactivity
measured close to an ancient smoke detector has been superior
to 250 m Rem/h. Others more modern do not, apparent, present
radioactivity. The risk of contamination is analogous to that
lightning conductors in case of demolition of buildings (radio
toxicity notably).
