SEEIT TM-91N Manuel D'utilisation page 5

Interaction of radiation with matter:
The particles and photons from nuclear decay carry most of the energy released from the original unstable nucleus. The value of this
energy is expressed in electron volts or eV. The energy of Beta and Alpha ray is invested in the particles speed. A typical Beta particle
from Celsius – 137° has energy of about 500.000 eV, and a speed that approaches that of the light. Beta energy can cover a wide
range, and many radioisotopes are known to emit Betas at energies in excess of 10 million eV. The penetration range of typical Beta
particles is only a few millimetres in human skin. Alpha particles have even shorter penetration ranges than Beta particles. Typical
Alpha energies are on the order of 5 million eV, with ranges so short than they are extremely difficult to measure. Alphas are stopped
by a thin sheet of paper, and in air only travel a few inches at most before coming to stop. Therefore, Alpha particles cannot be
detected without being in close contact with the source, and even then the alphas coming from the surface of the source can be
detected. Alpha 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 substance also emits 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 thickness of material
without incident.
A free neutron driving through space, will decay in an average of 11,7 minutes, yielding a proton and 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 one. Detecting neutrons is specialized and beyond the scope of Geiger counters, but most
possible neutron sources also can emit Gamma and Beta radiation, affording detection of the source. The highly energetic X-rays lose
their energy as they penetrate matter. X-rays have 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 X-ray radiation are by the
most penetrating of all common types, and are only effectively absorbed by large amounts of heavy, dense material of high atomic
number as lead.