Dosimetry Devices Flashcards
State the basic principle behind thermoluminescence.
6 stages:
- Radiation interacts in material transferring energy to release valence electrons to the conduction band.
- Electrons stay in conduction band until they fall into traps.
- They are stuck there until they gain enough energy to escape.
- Electrons inside the traps represent stored info about the amount of radiation (dose).
- When the crystal is heated, electrons are released, de-excite, and emit visible light. The “glow curve” is measured to determine dose.
- After being read, the electrons return to their original state in the valence band and the TLD can be reused.
Name the two types of dosimeters used as whole body dosimeters.
- DT-702 PD LiF (MDA 1mRem)
2. Electronic Personnel Dosimeter (EPD).
The TLD has 4 chips labelled 1-4, how are they read/counteD?
Start in upper left and read counter clockwise with the “notch” down and to the left.
Name the TLD chip positions, the filters, and the dose type.
Position 1: 0.38mm LiF-7
Detects high/low energy photons, filtered by acrylic/ABS/copper, used for Eye Dose.
Position 2: 0.38mm LiF-7
Detects photons, filtered by ABS and Teflon Filters, used for Deep Dose Equivalent.
Position 3: 0.25mm LiF-7
Detects Beta and Photons, filtered by Mylar window, used for shallow dose.
Position 4: 0.38mm LiF-6
Detects Photon and Neutron filtered by Acrylic/ABS/Tin, used for Deep Dose Neutron (using position 1 to subtract).
List the factors affecting the TLD.
- Dirty TLDs
- Damaged TLDs
- Sunlight/Fluorescent Light
- Static Electricity or Electrical Discharge.
- Damaged TLD case
- Neutron accuracy affected in not worn properly.
- Exposure to temperature >140F.
State the Purpose of the DT-518/PD.
Contains a Neutron Accident Dosimeter, consisting of 2 sulfur pellets wrapped in indium foil. 5RADs of neutron exposure are required for activation and reading. These are submitted to NDC for exposure results when conditions warrant Neutron exposure determination.
State the Requirements for wearing an electronic personnel dosimeter (EPD).
NNPP: Whenever entering a High Radiation Area.
RASP: EPD - When working in high and very high radiation areas and when determined necessary by the responsible RSO.
- IPD x2 when performing operations requiring IPDs. Those using pulsed X-rays shall only use IPDs.
Who is required to wear a TLD?
- Personnel who could receive a dose of 10% of an ALI.
2. NNPP requires engineers to wear TLDs regardless of plant operational status.
Where is the TLD to be worn?
P-5055: Front of the trunk of the body at the waist on the belt. The front of the holder must be positioned so that it faces away from the body.
RCFS: Shall be worn on the waist oriented towards the front of the torso. Secondary shall be next two it.
RASP: Gamma Radiography/Barrier monitors. Two low range IPDs (secondary) on top of their LiF TLD Primary. If no alarms are present, must wear an alarming rate meter in addition.
What are the requirements of a pocket dosimeter.
Calibrated every 6 months. IM-235, IM-9, commercial equivalent. Worn adjacent to a primary dosimeter. Zeroed at start of every shift. Read often during every shift. Initial, Final, and net reading recorded in IPD log.
What if a pocket dosimeter is found to be off scale during radiography operations.
- Personnel immediately removed from RAD work
- Primary dosimeter sent to NDC.
- May return to work IF: 1/2 above were met AND RSO can establish that off-scale dosimeter is defective, the second IPD is functioning properly, and the RSO can determine that limits of P-5055 were not surpassed.
State the operation of the EPD.
- It is a silicon diode, solid state electronic technology. Radiation produces current which can be measured proportional to dose.
- Always worn next to primary TLD.
- Zero it at control point, alarm set to 150mrem, checked periodically while in HRA by personnel, and given back to the control-point watch after leaving area.
