INSTRUMENTATION Flashcards
INSTRUMENTS ARE DESIGNED TO DETECT RADIATION OR TO MEASURE RADIATION, OR TO DO BOTH. THOSE DESIGNED FOR DETECTION USUALLY OPERATE IN THE _______ OR ____________ MODE AND ARE USED TO INDICATE THE PRESENCE OF RADIATION
Pulse, rate
THE PRESENCE OF RADIATION IS INDICATED BY A TICKING,
CHIRPING, OR BEEPING SOUND
pulse mode
THE INSTRUMENT RESPONE IS EXPRESSED IN
MILLIROENTGEN PER HOUR OR ROENTGEN PER HOUR
rate mode
USUALLY INSTRUMENTS ARE DESIGNED TO MEASURE THE INTENSITY OF RADIATION. THEY ACCUMULATE THE SIGNAL AND RESPOND WITH A TOTAL EXPOSURE. SUCH APPLICATION IS CALLED “DOSIMETRY”
integrate mode
are radiation measuring devices
dosimeters
3 types of gas-filled detectors:
- Ionization Chambers
- Proportional Counters
- Geiger-Muller Detectors
R in gas filled detectors is called as what
“Region of Recombination
It is the first stage when the voltage is very low, no electrons are attracted to the central cathode. The ion pairs produced in the chamber recombine
“Region of Recombination
I in gas-filled detectors is called as what?
“Ionization Region
- Most familiar type of ion chambers.
- This is used principally for area radiation surveys
PORTABLE ION CHAMBER SURVEY INSTRUMENT
the portable ion chamber survey instrument can measure a wide range of radiation intensities from __
10 µGy (1mR/hr) to several thousand Gy/hr (R/hr).
Used for accurate measurement of diagnostic x-ray beam
ION CHAMBER DOSIMETER
It is used in Nuclear Medicine to measure or assay accurately quantities of radioactive material
DOSE CALIBRATOR
unit used in the dose calibrator
MBq & mCi
P in gas-filled detectors is called as what?
Proportional Region
sensitive instruments that are used primarily as stationary laboratory instruments for the
assay of small quantities of radioactivity.
Proportional Counters
It is the ideal gas-filled chamber and this is the
region in which Geiger Counters operate
GM region
When did Geiger introduce the first successful detector of individual alpha particles
1908
What is CD in the gas-filled detectors?
Region of Continuous Discharge
It is the basis for the Gamma Camera in Nuclear Medicine , detector arrays of CT Imaging Systems, and Image Receptor of several types of Digital Imaging Systems
SCINTILLATION DETECTORS
Types of scintillation detectors
SOLID, LIQUID, and GAS
can be made to respond to radiation by
scintillation. This is rare because the detection efficiency is very low and the probability of interaction therefore is small.
noble gas
used frequently in the research laboratory to detect low-energy beta emissions from Carbon-14 (14C) and Tritium (3H). Nearly 100% detection efficiency for beta radiation
LIQUID SCINTILLATION
most widely used scintillation phosphors; have been incorporated into CT Imaging system detector arrays
INORGANIC CRYSTALS (Thallium-Activated Sodium Iodide (NaI:Tl) and Thallium-Activated
Cesium Iodide (CsI:Tl))
Is an electron vacuum tube that contains a number of elements. The tube consists of a glass envelope, which provides structural support for the internal elements and
maintains the vacuum inside the tube.
PHOTOMULTIPLIER TUBE (PMTUBE)
Through this application, unknown gamma
emitters can be identified and more sensitive
radioisotope imaging can be accomplished by
counting only those pulses with energy that
represents total gamma ray absorption
PULSE HEIGHT ANALYSIS
2 types of active dosimeters
pen & electronic personal dosimeters
It is required when there is any likelihood
that an individual will receive __________ of the recommended dose limit.
more than 1/10
Used in a hazardous environment, such as a nuclear reactor or other places with a high chance at higher radiation levels
active dosimeters
- Used when you are exposed to only low radiation levels, or only occasionally exposed to radiation.
- It records the amount of radiation over time but is not analyzed in real-time
passive dosimeters
- Generally used in Diagnostic radiology.
- It is similar to dental radiographic film and is sandwiched between metal filters inside a plastic holder.
film badge
what are the 2 metal filters of a film badge?
aluminum & copper
advantages of a film badge
Inexpensive
Easy to handle
easy to process
reasonably accurate
disadvantages of a film badge
can’t read exposures less than 10 mR
cannot be reused,
can’t be worn for longer than 1 month because of possible fogging caused by temperature and humidity
Uses LITHIUM FLUORIDE (LiF) with Z=8 in a crystalline form
THERMOLUMINISCENT DOSIMETER (TLD)
They experimented w/ the TLDs and were able
to show that exposure to ionizing radiation caused some materials to glow particulary brightly when subsequent heated
Cameron and coworkers at the University of Wisconsin
advantages of TLDs
more sensitive and accurate than Film Badge
can measure as low as 5 mR
can be worn for intervals up to 1year
disadvantages of TLDs
Expensive than Film Badge
This is worn and handled just as film badges and TLDs
and approx. same size.
* Light is emitted when an OSL crystal is illuminated
OPTICALLY STIMULATED LUMINESCENCE
(OSL)
who developed the OSLs
Landauer (1990s)
What material does the OSL use?
Aluminum Oxide
advantages of OSL
can measure as low as 1 mR
disadvantages of OSL
Expensive than TLDs and Film Badge
