Ch. 5 Flashcards
Personnel Dosimetry
Monitoring of equivalent dose to any person occupational exposed on a regular basis to ionizing radiation
When is personnel dosimetry required?
When radiation workers are likely to receive 10% or more of the annual occupational EfD limit of 50 mSv/ 5 Rem
Personnel Dosimeter
- Provides indication of radiation exposure working habits and working conditions (Am I shielding myself when needed? && Is the equipment I use working properly?)
- Determines occupational exposure
- Does NOT protect the wearer from exposure just measures the exposure to the wearer
Where should dosimeters be worn?
At the level of the collar, outside of the clothing
Personnel Dosimeters receive the dose to which of the following body parts?
- Thyroid
- Head
- Neck
When should a secondary dosimeter be worn?
During lengthy fluoroscopy procedures
If a second dosimeter is worn for a lengthy fluoroscopy procedure, where should it be worn and why?
- Underneath the lead, around the area of the waist
- This monitors the approximate equivalent dose to the body trunk
How much lead is in commercially available aprons?
0.5 or 0.25mm
Where should a pregnant woman were a second dosimeter
Beneath the protective apron, at the waist
What is a TLD Dosimeter made of?
Lithium Fluoride
How does a TLD work?
The Lithium Fluoride acts as the sensing material of the dosimeter
When irradiated, some of the electrons absorb energy are are “excited” to higher levels
This presence of impurities in the crystal causes the electrons to become trapped
When these crystals are passed through a special heating process for reading, the trapped electrons receive enough energy to rise above their present location into a region called the conduction band
From there, electrons return back into a normal state with the emission of energy in the form of visible light
The energy emitted in a TLD dosimeter is equal to the difference between what?
Binding energies of the two orbital levels
TLD Dosimeters should be worn as a second monitor when?
When performing fluoroscopic procedures that may require the hands to be near the primary x-ray beam
After the LiF crystals are heated to free the trapped, highly energized electrons, a TLD analyzer records the amount of light emitted by the crystals as the electrons return to their ground state, and a graphic plot is constructed to demonstrate the light output to temperature variation. This plot is called a
Glow Curve
ADVANTAGES of TLD Dosimeter
Small
Light-Weight
Can be worn for up to 3 months
Reusable after reading
DISADVANTAGES of TLD
Readings may be lost if not carefully recorded
The readout process destroys information afterward
Two types of personnel dosimeters that are used to measure individual whole body exposure to ionizing radiation
- OSL dosimeters
Direct Ion Storage (DIS) dosimeters
What dosimeter device is the most common?
OSL
What is the OSL Dosimeter made of?
Aluminum Oxide
How does an OSL work?
An exposed dosimeter is read by using a laser light
When this light is incident on the sensing material, the material become luminescent in proportion to the amount of radiation exposure received by the detector
What are the detectors components in the OSL?
Aluminum
Tin
Copper
Each detector of the OSL attenuates differently. Which component attenuates the MOST?
Copper
Each detector of the OSL attenuates differently. Which component attenuates the LEAST?
Aluminum
If the OSL Dosimeter has been subjected to only low energy radiation, the laser read out would be much more pronounced in the region covered by the __________?
Aluminum
Varied energy ranges are typically classified as what three different words?
Deep
Eye
Shallow
“Deep” penetration amount
1 centimeter
“Eye” penetration amount
.3 centimeter
“Shallow” penetration amount
.01 centimeter
The OSL Dosimeter provides an accurate reading as low as
1 mrem
The OSL detects energy ranges from 5 KeV to
40 MeV
ADVANTAGES of the OSL
Light-weight
Durable
Sensitive to radiation
Can be worn for up to one year
DISADVANTAGES of the OSL
Occupational exposure is only recorded in the area that the OSL is worn
If the facility does not have an in-house reader, exposure cannot be determined right away
Not accurate if not regularly used
Minimal reporting levels for x-ray & Gamma photons
Fetal
1mrem
Minimal reporting levels from Beta photons
10 mrem
Minimal reporting levels for fast neutrons
20 mrem
Minimal reporting levels for thermal neutrons
10 mrem
What is a DIS Dosimeter?
Developed in the 90’s, first applied in 2000’s
Basically a small ionization gas filled dosimeter connected to a “solid state” device with electrically erasable programmable read-only memory (EEPROM)
EEPROMS are used in
Voice activated greeting cards
Keyless entry systems (hotels)
When radiation ionizes the gas in the ionization chamber, the cumulative electrical charge is stored in the ___________ and will remain in the device
EEPROM
How is the DIS Dosimeter read?
read out through a USB and the data then can be stored electronically via a cellphone
ADVANTAGES of DIS
Instant access to read out
Durable
Lightweight
DISADVANTAGES of DIS
Exposure cannot be determined if device is not regularly used
Radiation survey instruments fall into three categories;
- Those with a readout scale
- Those without a readout scale
- Those who have a readout scale & are ionization chamber based
Most common radiation survey instrument
Geiger-Muller (GM)
Instruments without a readout scale
Possible allows adjustable sensitivity levels
Only a detector
Detector emits a repetitive sound, whose volume/ frequency is directly associated with the intensity of radiation
Instruments with a readout scale
Typically used either as area or room monitors or as portable survey instruments for the measurement of exposure rates at any area of interest
BUT they do not directly supply a radiation exposure reading
✨Cutie Pie✨
The most common type of survey meter that incorporates an ionization chamber
Why is the cutie pie called the cutie pie
Because it’s so little
Named in 1943 or 1944
When properly calibrated, what is the cutie pie capable of ?
Capable of measuring radiation exposure rates over a very wide range and also determines cumulative radiation exposure for the period of time the instrument is irradiated
Radiation instruments measure what two things?
- The total quantity of electrical charge reduction from the ionization of the air
- Rate at which the electrical charge was produced
3 types of gas-filled radiation detectors serving as field instruments
- Cutie Pie
- Proportional Counter
GM Survey Meter
The Cutie Pie & the Proportional Counter measure what two things
- Exposure
- Exposure Rate
The GM Meter measures what? (one thing)
Exposure rate
What type of radiation dose the Cutie Pie normally measure?
X- Radiation
Gamma Radiation
Proportional Counter VS. Diagnostic Imaginf
No useful purpose in diagnostic imaging because it is generally used to detect alpha and beta radiation in laboratory settings
Holding the Proportional Counter
The operator must hold this device close to the surface of the object being surgery because alpha radiation only travels a short distance in air, so must be held real close to get an accurate read
GM Survey Meter
Primary portable radiation survey instrument in Nuclear Medicine
Able to detect individual particles (electrons && photons)
Does the GM meter allow rapid or slower monitoring
Rapid
What can a GM Meter be used for?
Locate a lost radioactive source
Locate a low-level radioactive contamination
GM survey components
Audio amplifier and speaker that alerts the operator to the presence of ionizing radar ionization
Metal enclosed the counter’s gas filled tube or probe
GM readings are displayed in
milliroentgens per hour
