Dosimetry Devices Flashcards
Basic Principle behind Thermoluminescence
6 Stages
- Radiation interacts, releasing valance band electrons to the conduction band
- Electrons remain in conduction band until they fall into one of the traps
- Electrons remain in traps until they gain enough energy to escape
- Electrons inside traps are stored information of the quantity of radiation that has entered crystal and measure a dose
- Crystal is heated, energy releases the electrons from trap. Electrons de-excite back down to the valence band emitting visible light. Light output is measure and graphed on a glow curve. Height and area under the curve are proportional to total dose
- After being read the electrons return to their original state in the valence band. TLD can be reused.
Two types of dosimeters used as whole-body dosimeter
DT-702/PD LiF (MCuP) as a primary dosimeter.
Detection Range <1mrem - 2,000 Rad. (NNPP sets a 1 mrem lower limit)
Electronic Personal Dosimeter (EPD). Secondary dosimeter in High Radiation Area
Detection Range 0-1,600 REM. Detects BETA, X-ray, Gamma
Position 1: 7LiF (0.38mm)
Detects: Low energy Photon
Filter: Clear Acrylic, ABS, Copper Filter (425mg/cm^2)
Dose Type: Eye Dose Equivalent
Position 2: LiF (O.38mm)
Detects: High Energy Photons
Filter: ABS and Teflon Filters (1006 mg/cm^2)
Dose Type: Deep Dose Equivalent - Photon
Position 3: 7LiF (0.25mm)
Detects: Beta, Photon
Filter: Mylar window (6.8 mg/cm^2) detects shallow gamma, x-ray, and beta
Dose Type: Shallow Dose Equivalent (skin)
Position 4: 6LiF (0.38mm)
Detects: Neutron, Photon
Filter: Clear Acrylic/ABS/Tin (1298mg/cm^2)
Dose Type: Deep Dose Equivalent - Neutron dose determine by subtracting position one from position four
fast neutrons are thermalized in the body (albedo affect) and interact with Li-6
Factors affecting the TLD
- Dirty TLD
- Damaged TLD
- Sunlight or intense fluorescent light
- static electricity or electrical discharge
- Neutron accuracy affected in not worn properly
- Exposure to temperature greater than 140 F
Purpose of the DT-518/PD
Contains Neutron accident dosimeter which consists of two sulfur pellets wrapped in indium foil. Five (5) Rads of Neutron exposure are required for activation
Submitted to Naval Dosimetry Center for exposure results: when conditions warrant neutron exposure determination
NNPP Requirements for wearing an electronic personal dosimeter
Whenever entering a High Radiation Area, secondary dosimeter is worn.
RASP Requirement for wearing an electronic personal dosimeter
RASP personnel shall use ion chamber pocket dosimeter (IPD) or electronic personal dosimeter (EPD) secondary dosimeters depending on the operation.
Dosimetry Requirements for Various categories of personnel
Personnel must be monitored for exposure to ionizing radiation if, in one year, they could receive a dose of 10% of annual limit
Program Requirements:
NNPP: Requires radiation workers to wear TLD while on watch in engineering spaces regardless of plant operational status.
Wearing Dosimetry
P-5055: DT-702/PD Front of the trunk of the body at the waist on the belt. Or lanyard front of trunk, front facing out.
RCFS: Waist oriented towards the front of the torso. Secondary shall be worn adjacent to primary
0288: Primary dosimeter shall be worn on chest or either a clip or lanyard. Secondary shall be worn adjacent
RASP: Gamma radiography or barrier monitors: Two low range IPD, LiF TLD as a primary whole-body dosimeter. RSO may grant written authority to temporarily use one IPD per person in the event of shortage.
Radiographers & Assistants- if no warning alarms are present, wear an alarming rate meter in addition to the 2 low-range SIPD and dosimeter.
Operation of an electronic personal dosimeter (EPD)
EPD is a silicon diode, solid state electronic technology. Ionizing radiation interacts with diode crystal producing a current then measured proportional dose.
