I Flashcards
Instruments
are classified into three categories relative to the function
they perform, namely
survey meters, laboratory counters
and personnel dosimeters
■ Geiger-Mueller (GM) instruments
■ Ionization chamber instruments
■ Scintilation instruments
Survey meters
■ Photographic film dosimeters
■ Thermoluminescent dosimeters
■ Pocket dosimeters
Personnel dosimeters
Level of radioactive
contamination
Radiation dose rate in area
Survey Meters
Identity and quantity of
radioactive material
Laboratory Counters
Accumulated dose to
individuals in area
Personal Dosimeters
Many radiation safety decisions - such as
the need for decontamination, shielding, personnel monitoring, change in work
procedures, etc. - are based on radiological survey results using
survey meters
The most common type of instrument is a
gas filled radiation detector
Two most common types of gas filled detectors
- Geiger-Muller or GM detector
- ion chamber
used to measure very small amounts of radiation
Geiger-Muller or GM detector
used for measuring large amounts of radiation
ion chamber
is a low range instrument for estimating gamma ray
exposure rates and detecting the presence of most beta radiation
GM survey meter
is used for determining background radiation levels, and for
detecting and measuring radionuclide contamination
GM survey meter
If the measurement is for contamination, the appropriate unit is
cpm (or
some multiple)
if the measurement is for dose rate, the appropriate unit is
mR/hr (mSv)
is
used for determination of
radioactivity, usually expressed
in dpm, from wipe test and leak
tests
sodium iodide well counter
may be
used to accurately quantify very
small amounts of radioactivity
well counter
is an
ionization chamber
that allows assay of
gamma emitters.
radionuclide dose
calibrator
are suitable for measuring
radiation exposure rate or cumulative radiation
exposure at high radiation intensities. They are
not especially useful at low radiation intensities
or for detecting small quantities of radioactive
material.
Ionization chambers
second most common type of radiation detecting
instrument is the
scintillation detector
most common type of material in scintillation detector
sodium iodide
The first part of the photomultiplier tube is made of another special
material called a
photocathode
is sensitive to ionizing radiation, and when it is used as a
monitor, the amount of film darkening is a measurement of radiation
exposure
Photographic film
The filmstrip and holder constitute the film monitor, called a
film
badge
• A small semiconductor material called a ________ may also be used to monitor radiation exposure. When radiation
interacts with a TLD, the energy is stored in the material. When heated, the
energy is released as light, and the amount of light is proportional to the
amount of energy stored
thermoluminescent dosimeter
(TLD)
The TLD most commonly used for monitoring is
_______, usually found as chips that are about 1/2 cm2
lithium fluoride
chambers are designed to measure the ionization
events within an air filled chamber
Pocket ionization
Determination of contamination level often most important
measurement in medical emergency setting Usually done with
GM probe called
pancake detector
Instruments to measure accumulated dose commonly
referred to as dosimeters, worn by person to measure
accumulated individual dose. Two types normally used: direct
read-out devices _____ and indirect _____
(pocket dosimeters) & TLDs & film
badges
