Sensors - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 24

causes microscopic damage to living tissue, resulting in skin burns and radiation
sickness at high doses and cancer, tumors, and genetic damage at low doses.
Therefore, monitoring radiation levels is imperative in many industrial applications
where human interaction with radioactive materials exists, as well as in guarding
against intentional or accidental exposure of wider population to radiation. Wireless
sensor networks provide ideal infrastructure for these kinds of systems.

2.8.2 Geiger-Müller Counter

Geiger counters are used to detect radiation usually gamma and beta radiation, but
certain models can also detect alpha radiation. The sensor is a Geiger-Müller tube,
an inert gas-filled tube (usually helium, neon, or argon with halogens added) that
briefly conducts electricity when a particle or photon of radiation temporarily makes
the gas conductive. The tube amplifies this conduction by a cascade effect and out-
puts a current pulse.

2.8.3 Quartz Fiber Dosimeter

A quartz fiber dosimeter is a pen-like device that measures the cumulative dose of
ionizing radiation received by the device. The device is mainly sensitive to gamma
and X-rays, but it also detects beta radiation above 1 MeV. Neutron-sensitive versions
have been made.
The quartz fiber dosimeter is a rugged form of a device called a Lauritsen elec-
troscope. It consists of a sealed air-filled cylinder called an ionization chamber.
Inside it is a metal electrode strip that is attached to a terminal on the end of the pen
for recharging. The other end of the electrode has a delicate gold-plated quartz fiber
attached to it, which at rest lies parallel to the electrode.
During recharging, the charger applies a high DC voltage, to the electrode,
charging it with electrostatic charge. The quartz fiber, having the same charge, is
repelled by the surface of the electrode due to the coulomb force and bends away
from the electrode. After charging, the charge remains on the electrode because it
is insulated.
When a particle of ionizing radiation passes through the chamber, it collides
with molecules of air, knocking electrons off them and creating positively and
negatively charged atoms (ions) in the air. The ions of opposite charge are attracted
to the electrode and neutralize some of the charge on it.
Since each radiation particle allows a certain amount of charge to leak off the
electrode, the position of the fiber at any time represents the cumulative radiation
that has passed through the chamber since the last recharge. Recharging restores the
charge that was lost and returns the fiber to its original deflected position.