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Radiation Safety

Introduction
Background Information
X-Radiation
Gamma Radiation
Health Concerns

Radiation Theory
Nature of Radiation
Sources of High Energy
   Rad

Rad for Ind Radiography
Decay and Half-life
Energy, Activity, Intensity   and Exposure
Interaction with Matter
Ionization
Radiosensitivity
Measures Related to   Biological Effects

Biological Effects
Biological Factors
Stochastic (Delayed) Effects
  -Cancer
  -Leukemia
  -Genetic Effects
  -Cataracts

Nonstochastic (Acute) Effects
Symptoms

Safe Use of Radiation
NRC & Code of Federal
   Reg
s
Exposure Limits
Controlling Exposure
  -Time-Dose Calculation
  -Distance-Intensity Calc
HVL Shielding
Safety Controls
Responsibilities
Procedures

Survey Techniques

Radiation Safety Equipment
Radiation Detectors
Survey Meters
Pocket Dosimeter
Audible Alarm Rate Meters
Film Badges
Thermoluminescent
   Dosimeter

Video Clips

References

Quizzes

Thermoluminescent Dosimeter

Thermoluminescent dosimeters (TLD) are often used instead of the film badge. Like a film badge, it is worn for a period of time (usually 3 months or less) and then must be processed to determine the dose received, if any. Thermoluminescent dosimeters can measure doses as low as 1 millirem, but under routine conditions their low-dose capability is approximately the same as for film badges. TLDs have a precision of approximately 15% for low doses. This precision improves to approximately 3% for high doses. The advantages of a TLD over other personnel monitors is its linearity of response to dose, its relative energy independence, and its sensitivity to low doses. It is also reusable, which is an advantage over film badges. However, no permanent record or re-readability is provided and an immediate, on the job readout is not possible.

How it works
A TLD is a phosphor, such as lithium fluoride (LiF) or calcium fluoride (CaF), in a solid crystal structure. When a TLD is exposed to ionizing radiation at ambient temperatures, the radiation interacts with the phosphor crystal and deposits all or part of the incident energy in that material. Some of the atoms in the material that absorb that energy become ionized, producing free electrons and areas lacking one or more electrons, called holes. Imperfections in the crystal lattice structure act as sites where free electrons can become trapped and locked into place.

Heating the crystal causes the crystal lattice to vibrate, releasing the trapped electrons in the process. Released electrons return to the original ground state, releasing the captured energy from ionization as light, hence the name thermoluminescent. Released light is counted using photomultiplier tubes and the number of photons counted is proportional to the quantity of radiation striking the phosphor.

Instead of reading the optical density (blackness) of a film, as is done with film badges, the amount of light released versus the heating of the individual pieces of thermoluminescent material is measured. The "glow curve" produced by this process is then related to the radiation exposure. The process can be repeated many times.