Radiation detectors
are the Instruments that can identify the presence of radiation (in the
environment, on the surface of people, inside people, and Received by people
as exposure).
We use radiation detectors to know where radiation
energy came from and how many / how much it is.
There are two basic types of instruments
used for radiation detection:
1.
Particle counting instruments (Gas Filled Detectors, Solid and Liquid Scintillation
Detectors).
2.
Dose measuring instruments (Pocket dosimeters, film badges, and personal thermo
luminescent dosimeters).
The particle counting instruments are
measuring the number of particles (electrons, alphas, protons, neutrons, etc.)
or photons that give a signal in the detector, and give the result in counts
per minute (cpm) or counts per second (cps).
The dose measuring instruments are also
measuring the number of particles or photons, but the result is given in units
of dose (R, Gy, Sv, etc.), or dose rate (R/s, mSv/h, Gy/min, etc.).
Some types of commonly used detectors:
Geiger counter: The detector most common to the public
is the Geiger-Mueller counter, commonly called the Geiger counter. It uses a
gas-filled tube with a central wire at high voltage to collect the ionization
produced by incident radiation. It can detect alpha, beta, and gamma radiation
although it cannot distinguish between them. Because of this and other
limitations, it is best used for demonstrations or for radiation environments
where only a rough estimate of the amount of radioactivity is needed.
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| Geiger counter in use (Photo credit: Wikipedia) |
Scintillation detectors: Scintillators are usually solids
(although liquids or gases can be used) that give off light when radiation
interacts with them. The light is converted to electrical pulses that are
processed by electronics and computers. Examples are sodium iodide (NaI) and
bismuth germanate (BGO). These materials are used for radiation monitoring, in
research, and in medical imaging equipment.
Solid state X-ray and gamma-ray detectors: Silicon and germanium detectors, cooled
to temperatures slightly above that of liquid nitrogen (77 K), are used for
precise measurements of X-ray and gamma-ray energies and intensities. Silicon
detectors are good for X-rays up to about 20 keV in energy. Germanium detectors
can be used to measure energy over the range of >10 keV to a few MeV. Such
detectors have applications in environmental radiation and trace element
measurements. Germanium gamma ray detectors play the central role in nuclear
high-spin physics, where gamma rays are used to measure the rotation of nuclei
Personal Thermo luminescent dosimeter (TLD): A small radiation monitoring device worn by
persons entering environments
that may contain radiation. It uses lithium fluoride crystals to record
radiation exposure, not sensitive to heat and humidity and Available for use on
torso and finger.
Measuring radiation inside people:
The main paths for internal irradiation
of those working with radioactive materials are inhalation and ingestion.
There are two internal dosimetry programs have
been developed for measuring internal irradiation of personnel:
1.
Iodine measurement: I-131 is gamma emitters. Therefore, a gamma detector can be
used to measure the iodine content of the person's thyroid. Proper calibration
of the instrument is done using 'phantoms' that mimic human body composition.
After gathering information about thyroid activity (in Bq) and the moment of
iodine usage, we can estimate iodine uptake and intake. Since the level of
radioiodine in the thyroid decreases after 5 days, the measurement must be done
between 1 and 4 days after usage. The amount of radioiodine in the thyroid is
compared with the annual limit on intake (ALI) and the dose received by the
contaminated person can be estimated.
2.
Urinalysis:
most of the radionuclides tend to be eliminated in body fluids. By measuring
activity content in urine, we can estimate the uptake and the intake. The dose
is estimated by comparing the intake with the (ALI) for that particular
radionuclide.
